Is 5HP really 5HP? - Page 1
Forum section: electronics / beginners

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 25, 2025, 03:33:41 am
content: Hello,There are many motors you can buy out there rated at 5HP, but some come in at exceptionally low prices. These are compressor motors with a typical description of "5HP SPL Air Compressor Motor 230V 17.6A 3450RPM 56 Frame"https://www.ebay.com/itm/317109013107I don't have one to examine in detail, nor the instrumentation to do so, but I hope that perhaps you know the answer.Is 5HPreally5HP?Thanks!

author: Analog Kid
author_rank: Super Contributor
timestamp: July 25, 2025, 03:42:00 am
content: Can't tell you for sure without knowing a lot more about that motor.However, based on the stated power consumption,230 X 17.6 / 746 = 5.4, so itcouldbe 5 HP (@ 92% efficiency).Maybe.

author: bdunham7
author_rank: Super Contributor
timestamp: July 25, 2025, 03:43:57 am
content: The differences between 5HP motors are explained by the term "Service Factor". You can google/wikipedia/Co-pilot that and read about it. Service Factor "SPL" is the designation for motors that just barely meet their HP specs and then perhaps only temporarily under the right conditions. I think SPL is roughly equivalent to SF 1.00.

author: brucehoult
author_rank: Super Contributor
timestamp: July 25, 2025, 03:57:17 am
content: Quote from: ballsystemlord on July 25, 2025, 03:33:41 amYes the SPL means it isreally5HP and not a 5.75 HP motor labelled as 5 HP.You'd probably want to use it in intermittent 5 HP use, not continuous.

author: picburner
author_rank: Frequent Contributor
timestamp: July 25, 2025, 06:04:48 am
content: The motor's nameplate also lists this: Output 2.98 kWwhich should be the power delivered to the axle.So the actual power at the axle is 3.99 HP

author: Analog Kid
author_rank: Super Contributor
timestamp: July 25, 2025, 06:45:06 am
content: Quote from: picburner on July 25, 2025, 06:04:48 amAh, so there's the fly in the ointment:Is this motor really 5 HP? or only 4?(If the above is true, then the nameplate has conflicting figures)

author: Kleinstein
author_rank: Super Contributor
timestamp: July 25, 2025, 09:34:11 am
content: With electric motors they usually give the power rating for the input side, not the ouput. The output is an extra information. 80% efficiency is somewhat OK for a cheap motor, though not great.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2025, 10:09:25 am
content: Yes, for electric motor the power rating is almost always input electrical power, so if you need to know mechanical output, multiply by efficiency.Small motors are less efficient.Single-phase (capacitor start/run) motors are less efficient than 3-phase.Cheap motors are less efficient.Intermittent duty motors are less efficient.Best, large, industrial grade motors can be nearly 98% efficient or so; tiny few-watt fan motors etc. can be just 20% efficient.For a 5HP intermittent duty motor, efficiency would be in the 70-85% ballpark.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 25, 2025, 02:01:13 pm
content: While the prices of 5HP motors can vary widely the actual power of a 5HP motor does not vary by a whole lot. The price reflects more about quality and reputation of the manufacturer than the actual/rated power factor.

author: calzap
author_rank: Frequent Contributor
timestamp: July 25, 2025, 04:42:19 pm
content: One problem I’ve encountered with cheaper single-phase motors of 5 HP or less is often the start capacitor is rated at less than 240 VAC even though the motor will be run at 240 VAC. This is done to save a little money. The manufacturer thinks they can get away with it because of the way the capacitor is wired to the motor coils, and it will be exposed for only a short time before the centrifugal switch cuts it out. They fail eventually.These motors are often part of a water pumping system, which is why I have to deal with them. I preemptively check the capacitors and replace any that aren’t rated for 240 VAC.Mike

author: u666sa
author_rank: Frequent Contributor
timestamp: July 25, 2025, 05:26:49 pm
content: Formula is Horsepower = (Torque x RPM) / 5252So HP is meaningless, you have to know torque at a given rpm.

author: TimFox
author_rank: Super Contributor
timestamp: July 25, 2025, 05:44:05 pm
content: A properly specified motor will show a curve of torque vs rpm.This is more obvious for a DC motor, where the no-load rpm is proportional to the applied voltage; induction AC motors show torque as a function of “slip” (difference between line frequency and rotation).If you multiply the two variables together, you will see a peak, which gives the maximum power available from the motor. With the other electrical parameters, you can compute the efficiency.Simple specs just give the max power at a spec value of rpm.Of course, not all motors are rated for continuous use.

author: alpher
author_rank: Frequent Contributor
timestamp: July 25, 2025, 07:20:08 pm
content: 5hp in 56 frame is really stretching it.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: July 25, 2025, 07:43:03 pm
content: Rule of thumb:never trust BLINDLY the product specifications provided on Ebay, Alibaba, heck even Amazon.A 5 HP rating may mean the motor can achieve that power only during a full moon which falls on a Tuesday, and as long as the motor is also LN2-cooled.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 25, 2025, 08:12:51 pm
content: Quote from: ballsystemlord on July 25, 2025, 03:33:41 amProbably, maybe, but sometimes it's only Holistic Power.Maybe you missed the memo, but horses have been obsolete for 70 years too.

author: TimFox
author_rank: Super Contributor
timestamp: July 25, 2025, 08:26:33 pm
content: Quote from: Doctorandus_P on July 25, 2025, 08:12:51 pmThat’s be because goading a horse to 1 hp (746 or 750 watts) useful output can be fatal to the poor animal.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 25, 2025, 09:26:59 pm
content: It seems nobody has yet addressed my question. Given this:Quote from: picburner on July 25, 2025, 06:04:48 amif that's true, then doesn't that directly contradict the "5 HP SPL" rating on the nameplate?Based on this info--basically, what's on the nameplate--what would you say is likely the actual HP rating of the motor?As I wrote earlier, given the power consumption rating (230 V @ 17.6 A), that means a total input power of 4,048 watts, which would theoretically yield 5.42 HP (at 100% efficiency).

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 25, 2025, 10:51:40 pm
content: Quote from: u666sa on July 25, 2025, 05:26:49 pm1HP == 746W is the formula I grew up with.

author: TimFox
author_rank: Super Contributor
timestamp: July 25, 2025, 10:58:22 pm
content: Quote from: ballsystemlord on July 25, 2025, 10:51:40 pmThat is the original value given by James Watt (550 ft-lb/sec), but I misquoted the metric value that is slightly lower. The original metric value used the bastard unit of kgf in its definition to get 736 W.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 25, 2025, 11:01:28 pm
content: No definitive answer yet:How many HP does this motor generate?(based on info on nameplate)

author: brucehoult
author_rank: Super Contributor
timestamp: July 26, 2025, 12:15:11 am
content: Quote from: TimFox on July 25, 2025, 08:26:33 pmIt is the opposite.Elite human athletes can produce 3 HP for a few seconds (e.g. sprint cyclists) while Tour de France competitors produce around 0.5 HP for hours on end.On the other hand a Clydesdale can do 1-2 HP all day every day, and 20-25 HP in bursts.

author: Circlotron
author_rank: Super Contributor
timestamp: July 26, 2025, 12:17:10 am
content: Quote from: TimFox on July 25, 2025, 08:26:33 pmA horse will be okay for that output for a limited time. Greatly temperature dependent. Same for this motor probably. So the "horsepower" rating seems entirely appropriate in this case.

author: brucehoult
author_rank: Super Contributor
timestamp: July 26, 2025, 12:42:54 am
content: Quote from: Circlotron on July 26, 2025, 12:17:10 amA light horse, yes, with a rider or a buggy. Canter or trot is around 1 HP, say 15-20 km/h for up to several hours.But Clydesdales are also horses, and are probably more what the people inventing early engines were comparing to, for ploughing, operating pumps at mines, pulling loaded wagons.

author: themadhippy
author_rank: Super Contributor
timestamp: July 26, 2025, 01:11:18 am
content: Quote17A is closer to 3 or 4hp depending on the power factor

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 01:55:00 am
content: Quote from: themadhippy on July 26, 2025, 01:11:18 amYes, but that's "FLA" or full load amperage. And apparently "full load" here is defined as ~3kW or ~4HP. LRA will be much higher and there may be some intermediate point where it can temporarily put out 5HP while drawing more than 17 amps. These SPL ratings show up in things like air compressors where the motor is most highly loaded during startup and then at the end of the pressure cycle. They may need to produce more than 4HP during 20-30% of their operating cycle and then they get to rest for a bit. The same or very simiilar motor might also be sold as a 3HP SF 1.15 motor for other applications.Like this one:https://www.inyopools.com/Products/00200017039440.htm

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 02:09:34 am
content: I'm gonna be a nag here:How many HP is that motor, really?

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 02:35:59 am
content: Once upon a time, in a land not so far away called America, motor power ratings were what you get at the shaft, the mechanical output. This is the NEMA nameplate rating.But today, china has conquered induction motor manufacturing. I saw a new 5HP motor on an air compressor and did a double take at the rear vent holes: 1/2 the motor is empty! Somehow the stator/rotor is half the length for the good old day's enclosure. I mean really, why does it have to last 10 years when 2-3 years is good enough and you will buy from china twice.Of course the electrical power input is greater due to inefficiencies, and power factor causes a clamp ammeter to be misleading.

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 02:49:28 am
content: Quote from: Analog Kid on July 26, 2025, 02:09:34 amIt's a somewhat arbitrary rating and the nameplate just has numbers on it. If you connect it to 240VAC 60Hz and start loading it down, you can probably get anywere from 0 to 7-8HP before it breaks down and stops rotating. It will draw more than rated current and will get hot when you do that, but how many HP it produces depends on the load. If you connect 280VAC @ 80Hz perhaps you can get some more power out of it. Designing electric motors is somewhere between a black art and an arcane science. Apparently rating them is now a criminal conspiracy.

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 02:53:37 am
content: Quote from: floobydust on July 26, 2025, 02:35:59 amYou can get perfectly good motors made in China. Blame the low quality cheap crap on the people selling it to you, whoever they may be. That may be your local big box store that insisted on having the product thrifted to meet their cost of materials goals.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 02:57:21 am
content: Quote from: bdunham7 on July 26, 2025, 02:49:28 amAre you saying that those numbers are meaningless?Or that they're just made up?Can any of them be believed?I'm sure the OP must be scratching their head at this point ...

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 03:27:39 am
content: Quote from: Analog Kid on July 26, 2025, 02:57:21 amIf you get a spec sheet that tells you the type of duty (continuous, intermittent, ??), service factor (overload capability), maximum ambient temperature, slip factor, voltage, current, power factor and efficiency, then perhaps you'll know something. The rating and the absolute peak performance are two different things. This motor is rated for 5HP and will produce at least 115% of that continuously at up to 40C ambient provided the proper voltage is supplied. It will draw 11.2A @ 230VAC 3PH and run at 3490RPM when producing 5HP, that's 110RPM slip. I have no idea what the absolute maximum power is that it might produce if you supplied it with 460VAC 3PH and loaded it to breakdown. That's not really useful info in most cases anyway and it's not really an indicator of quality.Without those details the numbers don't mean much.https://www.abb.com/global/en/products/7bspm3212t

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 03:31:27 am
content: Quote from: bdunham7 on July 26, 2025, 02:53:37 amLet me know where to buy a decent 5HP chinese electric motor that isn't cheap shit. If you think about it, they are bypassing NEMA entirely (as the chinese do with other standards) and flooding the market. And it's our fault for allowing this.Plenty of fractional HP chinese motors burning up, catching fire, product recalls. Minimum copper, minimum steel is the communist way towards "efficiency".They are made cheap on purpose. Their efficiency is poor, so much so that the Dept. of Energy issued new minimum efficiencystandardsto prevent junk motors from being the norm.It's another example of where we think a product meets some standard but the manufacturer sneaks around it because there is no enforcement.I'll look at that 5HP popcan motor and see what brand, labels, certifications it has. If you think about it, 1/2 size means some serious flux density and airflow.An air compressor is only at max. load for a brief period at high tank pressure, and maybe the Cheapness Dept. has set it up this way.I know US industry is not buying them (bigger >25HP motors) because the work they do is worth so much more than any cost savings for an unreliable product.

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 04:40:59 am
content: Looking at some nameplates, "compressor duty" is a service factor 1.0Then you have efficiency which can be low. Made in Mexico, USA, Canada, china etc.Can you trust these nameplate numbers, they look dodgy.FLA rating from 15A to 21A (230V) for 5HP.Input 3.1-4.6kWOutput 2.98kW (ain't 5HP, 4HP is close enough lol).Power Tech L13605TInput 4.6kW, 208/230V 1PH. 3450 RPM 143TFLA: 22-21 SF: 1.15 AMB. 40CI'm surprised the Baldor is only 75% efficient, others are 84% for example.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 26, 2025, 05:11:09 am
content: Quote from: Analog Kid on July 26, 2025, 02:57:21 amIn addition to head scratching, I was also enjoying the technical discussion that has followed.Is there some rule of thumb that can be used to determineactualmotor capacity assuming you can see the nameplate?For example, you look at kw rating, SF, efficiency, or some other metrics?Thanks!

author: IanB
author_rank: Super Contributor
timestamp: July 26, 2025, 05:42:16 am
content: Quote from: Analog Kid on July 26, 2025, 02:57:21 amAsking, "How many HP is that motor, really?" is a question that is too vague and imprecise to have an answer. That's why nobody answered the question.Quote from: ballsystemlord on July 26, 2025, 05:11:09 amYou have to define what "motor capacity" means, before you can have an answer.For example, suppose you install the motor in a workshop to run a lathe or a bandsaw. In that case, you don't care so much about power, you care more about torque. You don't want the motor to slow down or stall under load.As far as power is concerned, it depends on how you load it. If you want the motor to run continuously, 24 h/day, for example to run a pump, then it needs survive that duty without overheating or burning out. If it is running in a hot environment inside an enclosure, it might have to be de-rated a bit.On the other hand, if you want the motor to run in short bursts, for example running an air compressor, then it might be able to produce more power and get hot doing so, if it has a chance to cool down between times.Case in point: I have a kitchen waste disposal unit under my sink which claims to have a 1/2 HP motor. But if I run it for more than short bursts it overheats and trips the thermal cutout. It does that even if it is just running and not doing much. So is it a 1/2 HP motor or a 0 HP motor?In general, if you want the motor to have a long service life and not be stressed, you might run it at less than its maximum output. The power of a motor is not a fixed thing, it is according to how much load you put on it. If I put a 1 HP load on a 2 HP motor, is it now a 1 HP motor or a 2 HP motor?Also, if you have a 5 HP motor, how often do you actually do the engineering calculations to find out if it will really have a 5 HP load?

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 26, 2025, 09:36:52 am
content: Quote from: IanB on July 26, 2025, 05:42:16 amMy apologies, but I ask this much like the question of, "Is a 5w resistor a 5w resistor?" (The answer is "yes" in that case.)Let me use your reply to elaborate:Quote from: IanB on July 26, 2025, 05:42:16 amIn like manner, if I'm pulsing current through a 5w resistor, I don't care so much about power in, as having the resistor not overheat nor changing resistance under load.Quote from: IanB on July 26, 2025, 05:42:16 amAs in the case of the motor, much like the resistor, it has an operating temp before de-rating, I think that's another topic. And, just as a 5w resistor can dissipate 5w all the time, so too am I asking more about continuous duty than intermittent, which can get much more involved rather quickly.Quote from: IanB on July 26, 2025, 05:42:16 amFor anything more practical, it isQuote from: IanB on July 26, 2025, 05:42:16 amJust because you don't put 5w into a 5w resistor doesn't mean that it can't handle 5w.Quote from: IanB on July 26, 2025, 05:42:16 amEver since I was a boy, I've tried to figure out why HP was so meaningless and how to make sense of it. I actually went through an industrial catalogue and mathematically proved that their HP ratings were incorrect/misleading. I compared gas engine HP, to electric HP, to hydraulic HP, each to each-other. Now inasmuch as I proved that, it follows that trying to calculate total load is meaningless -- because I don't/can't know what motor to stick on what load.I hope my question makes sense to you now.Thanks!

author: SteveThackery
author_rank: Super Contributor
timestamp: July 26, 2025, 10:06:21 am
content: Quote from: ballsystemlord on July 26, 2025, 09:36:52 amI think calling HP to be "meaningless" is a step too far. It is meaningful, provided the manufacturer states all the relevant information, including temperature derating, and the duty cycle at various loads.After all, electric motors are used extensively, especially in industrial applications, so the system works.

author: mikerj
author_rank: Super Contributor
timestamp: July 26, 2025, 12:01:06 pm
content: Quote from: Analog Kid on July 26, 2025, 02:57:21 amDid you not see the comment related the service factor? "SPL" on a motor is somewhat like the "Peak Mean Music Power" on an audio amp specification, may just about be possible, downhill with a following wind for a brief period. This motor absolutely cannot deliver 5hp continuously.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 26, 2025, 02:06:37 pm
content: Yes, I did. But IDK what difference service factors are. And, as false advertising is illegal in the USA, I was obviously asking the question to better understand what the motor could do if you actually ran it for continuous duty and expected X HP out of it at all times.

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 03:18:30 pm
content: Quote from: ballsystemlord on July 26, 2025, 09:36:52 amActually the answer is "maybe", or if you buy from AliExpress then "no". This is the fundamental flaw in the reasoning that your question is based on--the assumption that there is a "correct" answer.With either 5W or 5HP as manufacturer ratings, those are simply designations that are applied to a product. How the manufacturer determines that rating and the actual characteristics of the product are two different things. With reliable manufacturers that follow industry standards and provide detailed data sheets those ratings have fairly a determinable correlation with the characteristics of the product. With the product you are looking at, IDK. Vevor stuff hasn't been terrible in my experience and I wouldn't just write it off as garbage. I had a 5HP air compressor with an "SPL" service factor motor and it worked for a number of years in commercial service even on 208VAC (the nameplate said 208-230VAC) and eventually the compressor section gave out, not the motor.The Chinese didn't invent all this, you can also get the Century B385 in a 56-size frame (which, IIRC, is what my compressor had) which lists the HP as "5 SPL" and the service factor as "SF=1.00" and has a rated current of 15A @ 208-230VAC. So instead of a less-than-1 SF, they have special horses. It's just a way to market a 3HP compressor as 5HP.https://www.surpluscenter.com/Electrical/AC-Single-Phase-Motors/Air-Compressor-Motors/5-HP-Special-Duty-208-230-Volt-AC-3450-RPM-Compressor-Motor-Century-B385-10-3327.axd

author: Siwastaja
author_rank: Super Contributor
timestamp: July 26, 2025, 04:54:05 pm
content: Quote from: bdunham7 on July 26, 2025, 03:18:30 pmThis. It takes some time to understand the idea that components even as simple as resistors, not to mention motors, cannot be described with a single "value" - or even a vector with two or three values.Eventually, the right thing to do is to specify everything topart numbers, based on which a full specification sheet can be acquired. Even a simple resistor can easily have 20 parameters and 3-4 2D datasets (plots)! And sometimes even that amount of data is insufficient and you need to ask the manufacturer (sometimes only possible if you buy a lot from them) or do your own testing.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: July 26, 2025, 05:24:13 pm
content: My late grandfather had a large distribution warehouse catering to the sale of electrical equipment. Basically, if it operated at 600 V or less, he had it or would procure it for you.He was the first to notice my interest for electrical stuff, so he would invite me over and show diverse electrical equipment and provide a brief explanation.Once, I was being shown some electric motors. A large, robust looking one made by Westinghouse, back then the gold standard for electric motors. Another, much smaller and lighter, made by perhaps a Taiwanese or Japanese company, don’t recall the exact name, only recall the characters.My grandfather asked me: “these two motors are rated 5HP, 230V 3 phase. Why do you think one is twice as large as the other, and also costs twice as much? If you had to buy one, which one would you choose?”Of course the cheapest one. Then he would proceed to school me on service factors, failure rates, and would point out the larger bearings, the improved cooling, the larger wire gauge, the heavier shaft, etc.He would conclude: “You purchase the cheapest, and I’ll see you back in two years or less. You purchase the Westinghouse, and I’ll only see you at church.”

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 07:18:08 pm
content: 90% of the time an air compressor is just sitting there doing nothing.Of the 10% of the time it's running, max. load is only for a few minutes, a tiny fraction of the cycle time.So why pay for a motor rated 24/7 when you can abuse a much cheaper one?Today's business model is importing cheap stuff from china. It's actually 1/10 the cost (at worst) of old school decent equipment. It's not 2x the cost for quality, it's a far bigger gap.There are no "electric motor police", there are no "compressor police" that check and measure the claimed ratings for consumers.I looked at Dewalt, Harbor Freight, Home Depot etc. offerings and you can see "5HP" is just a category. Many don't even list a power rating,The CFM rating is the bottom line it seems. Even worse is they've gone from piston to diaphragm heads which are pure garbage. All hail the race to the bottom.Indeed, the cheapness ends with the thin wall air tank. A few have ruptured. That seems to get people taking action lol.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 08:56:09 pm
content: I'm sure that @IanB's post above was made in good faith, and contains a lot of valid info.However, I find his conclusion dismissive in the extreme: basically that "HP ratings are totally meaningless".Well, that really doesn't help us here much, does it?Should we just totally give up on trying to rate motors by this metric? If so, how in the world are we supposed to choose a motor for our application?I have a table saw with a 1 HP motor; I have a pretty good feel for how much more power that motor has than my previous table saw with a 1/2 HP motor. So obviously having more HP makes a difference here.Can someone try to more directly answer the poor O.P.'s question here regarding that eBay motor that they posted? I'd be very curious to know what the assembled experts here think of that motor and what kind of performance one could expect of it, based on its stated nameplate ratings.

author: BillyO
author_rank: Super Contributor
timestamp: July 26, 2025, 09:20:59 pm
content: bdunham7 has given the correct answer.One thing I'd like to comment on though is this reoccurring BS rhetoric that "everything made in China is crap". Just stop. Whenever anyone starts spouting this nonsense they just sound like idiots.If it's your experience that Chinese products are crap, it's because you buy crap. Not because it was Chinese. Americans, Canadians, Australians, Europeans, are all capable of making and do make utter junk.By that reasoning, Siglent are crap, Fluke 107/17B/117 meters and most of what is inside any other Fluke meters is crap. Most Keysight products are crap. We can go on and on.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 09:49:25 pm
content: Quote from: BillyO on July 26, 2025, 09:20:59 pmAre you referring to this?QuoteSorry, I find that almost as vague and, frankly, unhelpful as @IanB's handwave-y answer."You can probably get anywhere from 0 to 7-8 HP from it"? How does that help us?And who would apply 280VAC @ 80Hz to this motor? (And where would they even get that 80Hz current from anyway?)C'mon; we can do better than this, can't we?OK: Let's just take what's on the nameplate of that motor:Rated HP: 5 (HP-5 SPL)Output: 2.98 KWVolts: 230Full-load amps: 17.6Phases: 1Service factor: 1.0Duty: continuousRPM: 3450Hz: 60So given these figures, what can we surmise about how many HP this motor actually produces?Which of these figures can be believed? Which would you question?What kind of service do you think this motor would be well-suited for?Surely we can do better here than just throw our hands in the air and say "wellll, it'll produce somewhere between 0 and 7-8 HP".

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 10:22:48 pm
content: The problem is the numbers can be fudged. Do some math on that nameplate.It's "Output" is 4HP, the FLA implies 4kW or 5.43HP but we don't know the power factor or efficiency. If you include PF and efficiency, the numbers don't add up, so one of them is fake.Induction motors will draw more current and produce more power, until either the slip limit or thermal limit. How long does this motor make 4HP before smoke happens?With an air compressor you just use a smaller pulley lol.It all reminds me of audio power amplifier specs, a 20W amp gets rated 200W peak effective music power or some other units.Quote from: BillyO on July 26, 2025, 09:20:59 pmAlthough the chinese are capable of making good quality- you have to pay for it, have everything specified in writing and in the language of their legal system, have inspections etc. or else you get scammed, as many OEM's discover the hard way. Their ethics and morals are below those of the West.china is synonymous with low quality, and no wumao propaganda will change people's experiences. They've earned it.china law bloghas some great examples.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 10:28:02 pm
content: Quote from: floobydust on July 26, 2025, 10:22:48 pmSo if you don't mind playing along for another round here:Which numbers do you think are fudged here, and which are believable?True, we don't know PF or eff%. But if you were forced to do so, what would be your guess as to those figures?Can this motor's HP be ballparked?

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2025, 11:04:42 pm
content: Quote from: Analog Kid on July 26, 2025, 09:49:25 pmAgain, the whole point is that there really isn't a neat, complete answer. The way my comments were intended to help was to demonstrate that both the specs and the questions give an incomplete story. But to some of your questions or points:You'd get 80Hz from some sort of VFD.Peak HP and starting torque are unstated but important factors so the fact that you might temporarily get 7-8HP out of it under the right loading is relevant.If the nameplate info is correct (and it might well be) then it quite explicitly lists the output as 2.98kW. Obviously that's mechanical output, the only kind there is for a motor. A kilowatt does not have to be an electrical spec, it applies to mechanical and thermal rates as well, so HP and BTU/hr all have kW equivalents. 2.98kW is about 4HP. So that along with the SF=1.0 and the word "continuous" would seem to indicate that the motor can put out about 4HP continuously, possibly right at the ragged edge of thermal survival. No ambient temp spec supplied. I think I said this earlier and also mentioned that the FLA of 17.6A and the specified 3450 RPM would also be at that 4HP load. I think the math actually works out OK on this, at least well enough so that it isn't obviously wrong.The motor is probably specifically intended for a single-stage or lower-grade two-stage air compressor.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 26, 2025, 11:14:02 pm
content: Quote from: bdunham7 on July 26, 2025, 11:04:42 pmOK. At about, let's call it anominal4 HP.Close enough for gov't. work?

author: IanB
author_rank: Super Contributor
timestamp: July 26, 2025, 11:55:06 pm
content: Look, it's really simple.If you connect a 1 HP load to the output shaft of the motor, it is a 1 HP motor.If you connect a 2 HP load, it is a 2 HP motor.Similarly with a 3 HP load.You can keep doing this, until eventually there will be a maximum load you can put on the motor before it slows down too much or stalls, or until the circuit breaker trips, or until it gets hot and makes a nasty smell, or until the thermal cutout operates (if there is one).This is your choice. You can choose the HP according to what load you apply.If the motor has a dubious rating plate like the one in this thread, you will probably take the stated output of 2.98 kW (4 HP) as a ballpark and not exceed that. The manufacturer has described it as a "5 HP class motor" with an actual output of 4 HP, which it can probably, maybe, do continuously, but you would do well to test it and find out, if reliability is important to you.But if you want a neat, simple answer, without reality intruding, it is a 4 HP motor.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 12:07:08 am
content: All well and good, except for the first part you wrote, which I find ... extremely odd, to say the least.You mean to tell us that if you're driving your souped up muscle car, with the 457 hemi you just dropped into it, but you're going downhill in idle, that you only have a, let's say, 30 HP engine?I don't think that's the way this works.

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 12:19:39 am
content: Quote from: Analog Kid on July 26, 2025, 11:14:02 pmYes.Put 5HP in get 4HP out under "nominal" conditions.The reason they rate it at 5HP is because when you design for it to be used under "nominal" conditions you better allow for a potential 5HP supply power. But as bdunham7 mentioned, you could use it off label and get very different results. It's done all the time.It's no different than any other kind of powerplant. Let's take for example my 2005 KTM 450 EXC. It's a dirt bike for those that are not in the sport. The engine in it is rated at 52HP. However, that is under very specific conditions. I doubt that in the 20 years I've been riding it that I have hit exactly that 52HP for more than a few minutes. Just because it can, under ideal conditions, pump out 52HP does not mean that it is doing that every time I start it up.Let's take the next step. The average ICE (Internal Combustion Engine) is about 30% efficient. My KTM is a pretty high spec race engine, so maybe 40% efficient? Meaning, the equivalent input "power" to get 52HP out would be 130HP. Meaning that I have to put enough fuel into it to make 130HP with 100% efficiency to reach that elusive 52HP ay 40% efficiency.Are you confused yet?Quite honestly, I probably demand less than 15HP on average from it since I'm primarily a woods rider. Explaining that goes beyond the scope of this lecture.So, you have an application to build a shop compressor. You figure you need a at least a 3.5HP compressor to deliver the air you need. Now you want to get a motor to drive that compressor. You see this one will deliver 4HP. Bingo. Now, what kind of circuit do I need to put it on. Okay, it will draw 5HP to deliver 4HP. Cool. I'll need 12 AWG wire (if the run is not too long, otherwise go 10 AWG) and a 25A breaker. I'm in business. Why a 25A breaker? Well, the startup current for that 5HP motor might blow your mind. And driving a compressor in a mechanics shop it will be starting a lot. My water here is supplied via a well. I have a 1HP rated pump motor. That sucker draws 40A on startup.Hope that helps...

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 12:21:12 am
content: Quote from: Analog Kid on July 27, 2025, 12:07:08 amYes, it is.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 27, 2025, 12:44:04 am
content: Quote from: Analog Kid on July 27, 2025, 12:07:08 amI think he means that the engine will only be producing 30 hp in those circumstances. I agree with you that saying it is a "30 hp motor" in those circumstances is a bit weird and somewhat misleading.My motorcycle has an 80 bhp motor. Obviously it doesn't produce 80 bhp all the time. 80 bhp is the maximum possible power output and only happens with a wide open throttle and the engine running at 6,500 rpm. At less than 6,500 rpm, and/or less than full throttle, it obviously develops less power. That does not mean it is "only a 40 bhp" motor! Everybody understands that "an 80 bhp motor" is a motor that will develop amaximumof 80 bhp.The same is true of a 5 hp electric motor. Assuming it's a truthful claim, it simply means that the motor can produce a maximum of 5 hp, and there will be criteria attached to that: supply voltage, armature rpm, duty cycle, temperature, etc.To say a 5 hp motor is actually a 1 hp motor because a 1 hp load is connected to it is a bit daft, if you ask me. It is a motorcapableof producing 5 hp (under the specified conditions) but is currently producing 1 hp. All perfectly simple and obvious.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 27, 2025, 12:45:18 am
content: Quote from: bdunham7 on July 26, 2025, 11:04:42 pmThat's kinda been the whole problem. I'm not asking for the unusual scenarios, but the normal type of operation you'd have your average motor under. Which, at least in my experience, is continuous, but not necessarily fully loaded down at all times, running.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 12:46:10 am
content: Quote from: BillyO on July 27, 2025, 12:21:12 amSorry, that makes no sense to me at all.Maybe it's a matter of semantics, but if I'm shopping for a XXX HP engine, for whatever reason, I want an engine that's capable of outputting XXX HP.Sure, when it's running with a lighter load it might only be producing YY HP. But in my book it's still a XXX HP engine, meaning that it's capable of producing that much power when called for.We don't say that our 250-watt computer power supply is a 50-watt supply because it may at times be only producing that much power.

author: brucehoult
author_rank: Super Contributor
timestamp: July 27, 2025, 12:51:05 am
content: Quote from: BillyO on July 27, 2025, 12:21:12 amThe funny thing is this is correct.A normal shaped car ... even a 60s one ... needs maybe 30 HP to cruise along the freeway and if you're driving calmly between cities that's what you'll average as a continuous power.Yeah, that souped up 457 hemi might be able to put out 800 HP on petrol or even 1100+ with methanol or nitro boost. Ok, you can run a 1/4 mile in the low 12s with a terminal speed of 130 mph.Congratulations -- you can produce 1100 HP for 12 seconds.Guess what happens if you put it on a dyno and run it at 1100 HP for an hour.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 12:57:15 am
content: Quote from: brucehoult on July 27, 2025, 12:51:05 amSorry, still not buying it. You're setting up odd, edge cases here to try to justify this concept.I think most reasonable people, when shopping for a XXX HP engine, would realize that there are different operating conditions possible, as you've described. But unless they're some kind of speed fanatic (and possibly also hopped up on speed as well), most reasonable people would accept that XXX HP means operating within certain restrictions, so as to not, you know, blow up their engine. Even if the engine is capable of producing XXX + YYY HP for some limited time before KA-BLAM.Hey, by your reasoning, why should we have HP ratings at all? Let's just give up on that altogether, so people will buy a motor/engine "that I think will work for my application without blowing up".

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 12:57:20 am
content: Quote from: ballsystemlord on July 27, 2025, 12:45:18 amIf you want a specific, consistent answer you need to list the specific, consistent conditions under which you test the motor. SAE lists specific ways in which auto engines are tested to determine maximum horsepower, NEMA has a manual for testing electric motors but I believe that set of conditions is more complex because motors are used in a lot of different ways. With electric motors the absolute maximum power it can put out is not directly relevant to the nameplate HP rating.

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 01:02:28 am
content: Quote from: Analog Kid on July 27, 2025, 12:46:10 amIf you're only using 10HP then it's a 10HP motor right then. It seems you have the answer, but for some reason are not willing to accept it.Your 457 hemi can have many different HP configurations. Normally aspirated it and it can be close to 800HP. Run it on alcohol with a blower and you can get 1,200 or more. If you are idling at a traffic light what would rate it at then? If you were selling it on eBay what would you rate it at?

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:02:56 am
content: Quote from: bdunham7 on July 27, 2025, 12:57:20 amCan you be any more specific if we limit the application to compressors, which seems to be what the OP is after here?(They didn't say this explicitly but it's implied.)

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 01:05:21 am
content: Quote from: Analog Kid on July 27, 2025, 12:57:15 amIt's been done before. Rolls Royce used to list their HP as "Sufficient".

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 01:07:07 am
content: I think Analog Kid is "punking" us.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 01:07:12 am
content: Quote from: Analog Kid on July 27, 2025, 12:57:15 amYou certainly shouldn't be selecting an engine based on one number alone. Ford used to make a 4.2L V6 that they used in certain trucks and vans, it was rated at 210HP. Dodge Ram pickups of about the same era had a Cummins ISB 5.9L L-6 turbodiesel that was also rated for 210HP. Neither rating was fake or understated, I'm sure they were both tested on a dyno to SAE standards. There would be no reason to assign a different HP rating to either one. Obviously they really performed quite differently in actual use.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:07:18 am
content: Quote from: BillyO on July 27, 2025, 01:02:28 amIt may befunctioningas a 10 HP motor just then, sure.But if I go to sell it on craigslist I sure as hell am not going to list it as a 10 HP engine.You do see that quite obvious point, don't you?Now regarding what I would list it as, well, I'm no automotive expert. But I'd rate it at the appropriate HP depending on, as you described, the type of fuel, carburetor type, etc. I'm sure there are figures for this. After all, if someone buys a 457 hemi, the HP rating is probably a figure of interest to them, wouldn't you say? Maybe not the only, or even the primary figure, but still a relevant one.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:09:41 am
content: Quote from: BillyO on July 27, 2025, 01:05:21 amHeh; file that under the same category as "if you have to ask how much it is, you can't afford it".

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 01:10:13 am
content: Quote from: Analog Kid on July 27, 2025, 01:02:56 amI think I did that. Go back a few responses.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 01:11:09 am
content: Quote from: Analog Kid on July 27, 2025, 01:02:56 amSure. If it weren't for the cheapo marketbabble "SPL" designation I'd call that a 3HP motor. But that would just be a rating consistent with how other high-quality motors are rated, not a definitive statement of all of its characteristics.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:12:29 am
content: Quote from: bdunham7 on July 27, 2025, 01:11:09 amOK, thanks. That's all I was asking for, an informed opinion. Nothing here for me to argue with.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 01:15:21 am
content: Quote from: calzap on July 25, 2025, 04:42:19 pmNo.Its done because the start winding is tied to the mid point of the 120 240v runwinding and as such allows the main run winding to be changed from 120 to 240 without requiring the start winding to be changed.The capacitor sees about 110vac in both cases.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 01:24:35 am
content: Quote from: ballsystemlord on July 25, 2025, 03:33:41 amIt will deliver 5hp for a few minutes every hour without burning up.The exact duty cycle will be debated endlessly by everyone on this forum who has never burned up such a motor before.My brother has my dads 1hp air compressor. It draws as many amps as does my 2hp air compressor which fills up the same size tank in a similar amount of time. Mine is a standard off the shelf 2hp 1750 rpm motor from tractor supply..My brothers, formerly my dads is a 1hp 56C frame motor, my dad bought 30 years ago, and it blows 20 amp breakers sometimes. Mine does not.Your mileage may vary.A 1hp 3600 rpm motor will weigh about 30 pounds and a 5hp will be about 90 pounds.If its less than that. It ain't continuous duty.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:39:58 am
content: Quote from: johansen on July 27, 2025, 01:24:35 amHmm; this one's listed as 34.5 lbs. (And nameplate claims continuous duty.)

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 01:55:01 am
content: Quote from: Analog Kid on July 27, 2025, 01:39:58 amThink like a triangle at 50% duty cycle.A 34 pound air compressor motor is about 2hp continuous.The lightest weight 5hp 3 phase 1760rpm motor ive ever found is the one i bought a dozen years ago at 76 pounds. It was also an aluminum case inverter rated motorQuote from: Analog Kid on July 27, 2025, 01:39:58 am

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 01:55:27 am
content: Quote from: johansen on July 27, 2025, 01:24:35 amHmmm, my 1HP pump motor weighs in about 18lbs (8kg) and is definitely rated at continuous duty and made by GE in the US of A. If a 5HP motor was made to the same spec I'd estimate it to run about 35lbs (((5^1/3)*8kg) lets call it 2x8kg to be safe) which matches the spec of the motor in question. Maybe things don't have to be built like Russian tanks anymore?The motor in my son's electric dirt bike is rated at 80HP and weighs only 20lbs. Being a brushless motor, it too is an induction motor. Let's not think like it's 1930.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 01:58:57 am
content: Quote from: BillyO on July 27, 2025, 01:55:27 amI had a couple good quality 2hp 3450 rpm 3 phase motors at 34 pounds each.You can sacrifice power density with efficiency. and cooling. you mention pump motor, lets make sure we're talking about the same thing.

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:07:19 am
content: Quote from: johansen on July 27, 2025, 01:58:57 amAre you saying the motor in the Stark Varg is inefficient? Well, it's actually not. 80hp from a 20lb induction motor is possible today. Your 34lb 2HP motors were probably based on a very old design philosophy. Probably one like "If it weighs more, they will pay more"Even my pump motor dates back to 1988. And it drives a jet pump, so it's not submerged. It's been in constant use since then. No signs of giving up, even though it only weighs 8kg.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 02:10:28 am
content: Quote from: BillyO on July 27, 2025, 02:07:19 amyeah no one has that power density in that small size. either you're confused or something.once you put a vfd on it and run it at 200hz, yeah you can get 50hp into a 5 gallon bucket sized volume. still weighs a lot.and yes i have a couple hot tub 2HP pool pumps. not only are they not loaded to 2hp actual shaft load, they can't produce it either. they are sized to produce 2hp for the maximum of about 10 minutes. and they weigh around 20 - 30 pounds.

author: IanB
author_rank: Super Contributor
timestamp: July 27, 2025, 02:12:56 am
content: Quote from: BillyO on July 27, 2025, 02:07:19 amYou've got to be sure you're talking about the same kind of motor. Namely, a three phase, 60 Hz, NEMA frame motor, running at a nominal 1800 (or 3600) rpm.

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:13:43 am
content: Quote from: johansen on July 27, 2025, 02:10:28 amNo need to be an ass.Have a look here and move into the 21st century:https://www.electricmotiontech.com/home/stark-varg

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 02:15:11 am
content: Quote from: BillyO on July 27, 2025, 02:13:43 amwell first off that's not going to be an induction motor, so fuck off.once you throw neodymium magnets at it, you double the practical air gap flux density which means the power density goes up by a factor of 4.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 02:16:35 am
content: Oooh, I just loves it when you Experts start getting all feisty and stuff.So sure of yourselves! Always stick to your guns! Never admit defeat!More popcorn!

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:17:17 am
content: Quote from: IanB on July 27, 2025, 02:12:56 amMy pump motor is of which you are talking (in fact, it's only single phase). The Stark Varg motor is not, but it represents what is possible. Even NEMA frame motors running on 60Hz need not be the pigs they used to be.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 02:20:32 am
content: Quote from: Analog Kid on July 27, 2025, 02:16:35 amI will pay the idiots here to call up motor manufacturers and ask them why they can't get a 1hp 1050 rpm induction motor into a 4" long 56C frame size.10$ an hour. i want to hear the phone calls.you will have to consent to be recorded, because,, well, what would be the pointif it was possible to get that torque density from copper alumium and steel alone, why wouldn'\t everyon edue ot?

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:38:53 am
content: Quote from: johansen on July 27, 2025, 02:15:11 amNice. Do you kiss your kids with that mouth?Strictly, you are right. But it shares a lot of the operating principles with poly phase induction motors, such as the rotating fields in the stator and a unpowered rotor.Quote from: johansen on July 27, 2025, 02:15:11 amMore than that, I think. And why is this a bad approach?Look, none of this means anything, your colorful language aside.Despite what your "experience" says, and I don't discount experience, modern motors have improved WRT size and weight vs power. My stupid pump motor is evidence of that 1988 evidence. The 35lb motor in question could indeed be a 5HP input 4HP output motor. I'm not sayin it is, but pointing to it's weighing less than 90lbs and calling it a fake for that reason is, well, unreasonable.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 02:43:20 am
content: Quote from: BillyO on July 27, 2025, 02:38:53 amis there a reason you had to hijack OP's questions about an air compressor duty induction motor?

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:44:39 am
content: Quote from: johansen on July 27, 2025, 02:43:20 amTalk about projection!!!I answered this:QuoteYou went on about how it had to be fake because it did not weigh 90lbs.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 02:45:42 am
content: Quote from: BillyO on July 27, 2025, 02:44:39 am5HP SPL Air Compressor Motor 230V 17.6A 3450RPM56 Framei will be tempted to buy this 134$ motor from the OP's ebay link. just to prove to you it will not survive 5hp for any significant length of time.

author: BillyO
author_rank: Super Contributor
timestamp: July 27, 2025, 02:57:58 am
content: Quote from: johansen on July 27, 2025, 02:45:42 amOFFS!A 56 frame motor can be of any length. Why could you not have a NEMA 56 frame 5HP motor? There are many 5HP 56 frame motors for you to enjoy. Just google it. Have fun and the last word.

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 03:00:25 am
content: Quote from: BillyO on July 27, 2025, 02:57:58 ami have never found a nema 56C frame longer than about 10 inches.care to provide a counter example? and no.. no one has ever made a 5hp version.Edit: i have to add the qualifiers: 60hz. 2 pole single phase motornow.. do small diameter high hp 60hz induction motor exist?yes they do.https://www.amazon.com/Goulds-25GS50412CL-Submersible-without-control/dp/B00IZI9BN6the cost a lot.... and are about 5 feet long.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 03:17:47 am
content: Quote from: johansen on July 27, 2025, 03:00:25 amThe Century B813 is a 5HP (not SPL) SF 1.00 compressor duty motor specified for 40C ambient, 3450RPM @ 22A FLA, 230VAC only (no 208) and the case is 14.5" long.QuoteIt really doesn't claim to survive 5HP continuous, however it might last a lot longer than you think even if it quite warm.As much as I enjoy a good pissing match, let's not all start throwing feces...

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 03:27:49 am
content: Quote from: bdunham7 on July 27, 2025, 03:17:47 amsure. feel free to buy it and defend the folks in this thread who say such things are theoretically possible.in my experience, a 1 hp air compressor SPL motor will consume around 22 amps at shut off on a 120vac circuit. so thats 11 amps at 220.a 5hp motor that costs 134$ that pulls 22FLA at 230vac? i have room temperature superconductors to sell you...

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 03:43:23 am
content: Quote from: johansen on July 27, 2025, 03:27:49 amWhat are you replying to? The Century B813 is certainly a real product from a reputable manufacturer. 22 amps at 230VAC is 5060 VA, use 84% efficiency and a PF of 0.9 and you get 3825W, divide by 736 and you have 5.19HP. So, reputable brand and the math pencils out. It costs a lot more than $134 and weighs 45 lbs.IDK about the motor in the OP's link, but I certainly can't rule out that it basically is what it says and performs more or less as specified.As for your 1HP compressor drawing 22A, either it is really overacheiving or is really, really inefficient.

author: eugene
author_rank: Frequent Contributor
timestamp: July 27, 2025, 02:07:37 pm
content: Quote from: BillyO on July 27, 2025, 02:07:19 amSomewhat apropos to this thread (at least the parts that aren't just pissing in the pool) is the fact that the motor in the Stark Varg has configurable power. There's a touch screen on the handlebars that allows the rider to set themaximum outputof the motor to anything between 10 and 80 hp. I understand that it's marketing, but according to the language in the Stark Varg literature, when you set the output to 10 hp, you have a 10 hp motor. Do I expect that to satisfy Analog Kid? Of course not. But that's not a goal of mine.

author: floobydust
author_rank: Super Contributor
timestamp: July 27, 2025, 05:25:56 pm
content: I think I found the exploit confusing us.Leeson Electric116523motor "5HP" that has only FLA 15A 230V (38lbs size 56):"Motor is rated for a breakdown torque of 5 HP and a continuous compressor duty at 3 HP."Compare to CenturyB813FLA 22A 230V (45lbs size Y56HZ) but 45% higher cost.NEMA ratings are different for the 5 different electric motor design categories, or letters. Seems to be gaming Type E with Type B or something like that maybe.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 06:09:40 pm
content: Leeson seems to give additional specs that help understand the real motor characteristics. Compare to this one that appears to be a "real" 5HP motor with a service factor of 1.15 and that can manage a more than 250% overload. The breakdown torque is twice that of the 5HP SPL-rated motor. 55lbs and yes, 56-size frame.https://www.regalrexnord.com/products/electric-motors/ac-motors-nema/definite-purpose-motors/air-compressor-motors/air-compressor-motor-5-hp-1-ph-60-hz-230-v-3600-rpm-56h-frame-dp-056b34d5302

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2025, 06:45:08 pm
content: Quote from: Analog Kid on July 26, 2025, 09:49:25 pmThat's going to be a simple one! It has even output (= mechanical) rating - just convert to HP e.g. using Google.So if you put this motor into a dynamometer and instruct it to extract 4HP of mechanical power, it will run at 3450 RPM, consume 5 HP of electricity, and will keep doing that continuously without getting damaged.Things are sometimes complex, but we also don't need to make them needlessly complex. It is however worth understanding that some mechanical loads behave badly - maybe they consume more torque than the motor can supply and it keeps operating at much lower RPM, much worse efficiency and can't deliver much power at all, or overheats. To takethatinto account, you need the torque - RPM charts, and know the characteristics of your load. Driving with VFD simplifies this game - pretty much all that remains is to not exceed the current, and possibly, if running at close to max current (torque) at low RPM, replace the on-shaft fan with separate fan, because the internal one doesn't move much air with low RPM.Generally, ignoring floobydust's incoherent rants is a good idea. For him, all Chinese stuff is always crap, all old stuff have automagically significant margins and not engineered to cost, and all specsheets and datasheets of modern days are lies and conspiracies; his personal favorite is trolling on every thread discussing resistor power ratings, no matter how many times he is proved to be wrong with actual measurements. Just ignore, really, he's one of those who never admits their mistakes.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 07:02:49 pm
content: Quote from: eugene on July 27, 2025, 02:07:37 pmWell, I think I can actually accept that.It's a weird case to be sure, but if the motor is somehow configured (through software/firmware: how do they do that?) to only deliver a maximum of 10 HP then it's essentially a 10 HP motor.Not the same thing at all as the esoteric argument above that if the motor is only delivering X HP that it's then a X-HP motor. Same reason we don't say a 250-watt power supply is suddenly a 10-watt power supply because that's all the power that's being drawn from it. (At least I don't, and don't believe that most reasonable people would either.)But whatever.

author: floobydust
author_rank: Super Contributor
timestamp: July 27, 2025, 07:30:12 pm
content: Quote from: Siwastaja on July 27, 2025, 06:45:08 pmAn EEVblog beginner's thread can never discuss a motor's fake ratings, or resistor power ratings without siwastaka floating up and going for personal attack.Ignoring your infantile valueless answers are a good idea.Did you want to find out what party changed from being honest and rating a motor by 24/7 power, or the "breakdown torque" it's good for, for a few seconds?Are you capable of that discussion here, or do you need a diaper change?

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 08:06:26 pm
content: Quote from: floobydust on July 27, 2025, 07:30:12 pmThis was going on well before the Chinese arrived on the scene. I think the corporate greed and moving manufacturing to Mexico started in the 1970's. Snake oil and marketing BS have been around for a long time as well as USA-made shoddy products. My 1978 Ford F250 had a cardboard glovebox.

author: Simon
author_rank: Unknown
timestamp: July 27, 2025, 08:18:39 pm
content: Quote from: floobydust on July 27, 2025, 07:30:12 pmTip: Don't report a post and then go on to commit the exact same "crime"! So what do you want mw to do now? clean up your mess, or shall we say 2 wrongs do make a right and call it quits!?

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2025, 08:25:56 pm
content: Quote from: Analog Kid on July 27, 2025, 07:02:49 pmA motor, engine or power supply that is actively controlled is one thing, but a regular induction motor is better compared to a regular iron-core mains transformer. We can all understand that a transformer may have a specific VA rating and that it can supply more than that for some time if you overload it. The transformer feeding my house also feeds three others and is rated at 50kVA. The houses have 200A service so 48kVA each which seems too much. However, these types of transformers are typically rated for something like 400% overload for one hour and 175% continuous overload at standard temperatures. So why the 50kVA rating when it can put out more than 200kVA? It's just a sort of sizing thing that correlates to it characteristics but does not precisely describe them. I think that one spec is that the transformer should have no more than 2% voltage drop at rated power, but IDK where I got that.In the above discussion there are two Leeson motors, one rated 5HP and the other 5HP with the "SPL" designation. The first can apparently put out 7.5HP for some time and over 10HP at breakdown. The second can put out 5HP at the very most for a short time under ideal conditions. But they also have different torque curves and they're really two very different motors. But I'd have a hard time giving you a single number that correctly and completely describes either of them. If you want to see peak marketing wankery, look at vacuum cleaner HP ratings.https://www.homedepot.com/p/RIDGID-4-Gal-5-0-Peak-HP-Portable-Shop-Vacuum-WD4070C-Wet-Dry-Vac-with-Fine-Dust-Filter-Accessories-and-Car-Cleaning-Kit-WD4070C/308058433

author: TimFox
author_rank: Super Contributor
timestamp: July 27, 2025, 09:14:14 pm
content: The discussion of nameplate hp ratings and possibly misleading values reminds me of the late 1960s, when hi-fi power ratings went seriously fictional (remember “+/- 1%” fraudulent values?), and it was criticized as “a horsepower race”.At that time, SAE horsepower tests for ICE engines were a bit fictional, done in a lab with belt-driven accessories disconnected (that has improved since).There were theoretical values for horsepower and tractive effort for steam locomotives, but the railroads would use their own dynamometer cars to measure drawbar force vs velocity to do their planning.

author: Simon
author_rank: Unknown
timestamp: July 28, 2025, 06:25:37 am
content: https://www.drivesandautomation.co.uk/useful-information/electric-motor-duty-cycles/Typically S1 is 60 minutes and S2 30 minutes. Whatever you want to call them I generally looks for graphs on motors.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 28, 2025, 02:30:40 pm
content: Does anyone have a link to where SPL and other such terms are defined?

author: Simon
author_rank: Unknown
timestamp: July 28, 2025, 03:43:25 pm
content: Basically get the datasheet, it should tell you albeit maybe at the bottom on some graph what the limits are. If it does not, find a motor that does tell you.

author: bdunham7
author_rank: Super Contributor
timestamp: July 28, 2025, 06:34:59 pm
content: Quote from: ballsystemlord on July 28, 2025, 02:30:40 pmHere are some general links about motor ratings and nameplates. I can't find anything that spells out what SPL means, probably because it simply means that the rating is not consistent with any NEMA standard. NEMA states that it is not necessary to list the service factor unless it is greater than 1.00 and until this discussion I always thought that the SPL was an indication of a less-than-unity service factor--which I still believe to be more or less true in reality as these motors cannot put out their stated HP continuously. However, these motors--even the non-Chinese Leeson and Century--appear to use SPL and SF=1.00 together. Datasheets are often either nonexistent or brief enough to be useless, even with known name brands. When I was setting up my custom made (by me) pool pumps I had to dig a lot to get on ancient Pentair document that showed me the relevant data for the various impellers and motors. That is pretty much all a lost art now as the new way to do it is to use the 3HP TEFC ECM motors with the largest impeller and just program it for what you want.https://www.nema.org/docs/default-source/motor-and-generator-guides-and-resources-library/6-electric-motor-terminology-and-performance-characteristics-v2.pdf?sfvrsn=62ad61a9_2https://new.abb.com/news/detail/80778/how-to-read-a-nema-motor-nameplate

author: IanB
author_rank: Super Contributor
timestamp: July 28, 2025, 06:42:43 pm
content: From what I can gather, SPL means "special", and it broadly equates to "stated without any warranty or guarantees".If performance matters, you would source a motor with a comprehensive data sheet giving much more information than you would find in the nameplate alone.If your motor does not have a manufacturer data sheet that you can trust, then the actual performance to be expected is anybody's guess.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2025, 06:59:38 pm
content: OK so now that our "experts" here claiming that this kind of motor is impossible to have and a therefore a scam, let's reference to industrial fully enclosed (non-weigh-optimized, non-cost-optimized) motors, is ABB good enough brand? See, e.g.https://www.siemens-abb-drive.com/Uploads/file/20210329/20210329143354_16699.pdf, page 105. The motor "M3AA 90LE 4 3GAA092550-••E", has exact same weight (16kg) as our Ebay specimen, and is rated for 1.85kW output, while the Ebay specimen is, again for same weight, rated for 2.98kW output --- 61% more.What are the differences, then? Even though IEC motors do not specify service factors, the ABB motor is expected to survive the typical 15% NEMA overload pretty much forever, while the Ebay specimen openly admits to have service factor of just 1.0. So let's compare 1.15*1.85 vs 2.98 --- 40% difference.Secondly, the ABB motor is "fully enclosed" type so only cooled from the outside; industrial motors often are for obvious reasons. The downside is that the weight and size must increase compared to blow-through type, because with worse cooling, more surface area is needed, and also better efficiency is needed, meaning more copper and more iron.Is this difference in cooling type 40%? I don't know, it probably is - it can be even more.I call the claimed power density completely plausible and see no red flags in the specifications at all. If OP buys it and puts it on a dyno to run against 4HP mechanical load all day long, I expect it to survive for pretty long, probably years. But designed for a price point, things change if you overload it, take it to high altitude, or block the cooling with dust. And dust is probably the biggest enemy of these open motor types.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 07:25:45 pm
content: Quote from: Simon on July 27, 2025, 08:18:39 pmNo other electronics forum has this problem as EEVblog does and it's getting tiresome with beginner threads getting derailed by personal attack. You can't have basic discussions and figure things out without shit flying around and threads going into the toilet.I have an expectation of mods to notice, hence the post reported, so that perhaps this forum can evolve and (policy) deal with this ongoing problem instead of allowing the Wild West.It seems better to ask this in the Supporter's Lounge or what would you suggest as a place to discuss?

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 07:35:07 pm
content: Quote from: ballsystemlord on July 28, 2025, 02:30:40 pmLooking at "5HP league" air compressor and motor offerings at the local hardware store.I love the "high quality" label that omits HP rating, I mean why include such a number? They put "SPL" thereIt's NEMA terminology that is being exploited.Interestingly, when you dig in, the cheaper panda bear motors are made by the same one company.These motors have nothing to do with NEMA aside from the enclosure- frame size, shaft size etc.How the measurements are performed is unknown. Hence a little fraud.Their only certificate is for electrical safety for hi-pot and thermal overload operation, and some motors include the efficiency spec. test.

author: bdunham7
author_rank: Super Contributor
timestamp: July 28, 2025, 07:43:35 pm
content: Quote from: Siwastaja on July 28, 2025, 06:59:38 pmIDK why you chose that motor to compare to--was it just the weight?The one you cite is 4-pole, 50Hz, low-efficiency, high slip/torque and TEFC. It's also 3-phase 400V but that matters less.I'll agree with your point though that theres no particular reason that the OP's Vevor motor is somehow impossible. I think there was only one person claiming that the power density was impractical, perhaps I missed someone.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 08:12:12 pm
content: Taizhou Zhengli Electric Motor Co., Ltd./ Taizhou Power Industry & Trade Co., Ltd. - same manufacturer for "MAT Industries" andVevortheir "5HP SPL" is only FLA 15A 230V which we know is a ripoff.Vevor is not a great product.More than 90 recalls and safety alerts.Vevor UK recallssome products are blocked at Customs.I looked at the size 56 electric motors which went from 1/2HP (well over half empty space), to the highest power Century 6HP. Its windings the copper wire look twice as thick as the panda bear competitor.My sense is what we are seeing is the same product out of china, build to different performance requirements. Some misleading/fraudulent nameplates of course because there is no oversight, no formal testing or evaluation of these motors to any standard aside from safety. So you have no idea what you are truly getting, in North America for these consumer-grade motors.Building air compressors, you chose a head with input power rating... HP/CFM/PSI/sheave RPM as the spec'd maximum and mate it with a suitable electric motor.But to cut corners, use a smaller pulley and motor yet claim the "HP" as what the head's maximum capability is. So the overall air compressor product gets a HP number that's inflated.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 28, 2025, 08:21:04 pm
content: Let me attempt to bring this whole shit-show discussion somewhat back down to earth.Many agitated posts here throw doubt on the whole idea of even rating motors by HP at all, and seem to favor completely disregarding this measure of power output.While I do understand that this is not a simple matter at all, with lots of nuances and gotchas and the influence of other factors, the fact remains that sometimes a guy needs to find a motor of a certain horsepower-age.Take my table saw, which currently has a 1 HP rated motor on it (I think it can believed, as it's a reliable name brand, Rockwell). If I needed to replace that motor I would naturally be looking for other 1 HP motors, because I do need that much (my previous, smaller table saw had a 1/2 HP motor, and I know the difference by feel) but not more (anything more would be somewhat overkill, and might not work well with the current power setup, which is that the motor gets plugged directly into a 20A 120 volt outlet with no problems tripping breakers).Current saw is capable of easily ripping a 2-1/2" thick piece of hard wood (with a good sharp carbide blade). A 1/2 HP motor would definitely get bogged down here.So the poor OP is probably still sitting here scratching his head, wondering WTF all theSturm und Drangis about. But at the end of the day, we still need to deal with HP ratings and be able to evaluate them rationally, especially now that the market has expanded to include a lot more products from overseas, some of which are good, others not so much.So maybe we could limit the focus of this discussion just a wee bit so that this issue can be addressed ...

author: bdunham7
author_rank: Super Contributor
timestamp: July 28, 2025, 08:55:37 pm
content: Quote from: Analog Kid on July 28, 2025, 08:21:04 pmHow simple do you want it? The OP's motor, unless it really is junk and the nameplate is fiction, will likely work OK in applications like shop machines, dust collectors, fans, pumps, etc that require 3HP.Not saying HP should be disregarded entirely, rather that in some cases you absolutely must consider other factors. For your table saw, you can probably use almost any class of 1HP motor and it will be fine. Compressor duty won't be a problem, but one with an SPL might be disappointing. However, the main spec you'd want to consider for your application here--after the obvious shaft size, speed, voltage, RPM, rotation and mounting--would be breakdown torque. And since a table saw is a pretty mild use, you'd probably find it difficult actually come up with a 1HP motor from a reputable manufacturer that would NOT work. You can just shop for 1.0 HP (avoiding SPL) and maybe SF=1.15 and not worry too much.Now if you had a different application, one with extremely high starting torque requirement like an overhead crane, manure auger, conveyor belt, etc, then most of your regular 1HP motors simply won't work.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 28, 2025, 09:10:22 pm
content: Quote from: bdunham7 on July 28, 2025, 08:55:37 pmOK, we've heard 5 HP, 4 HP, 3 HP. How about 2.5 HP? 2 HP?Going once, going twice ... SOLD to the gent in the 3rd row.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 09:58:30 pm
content: Keeping it simple, I use the FLA number and math to give me a ballpark full load power. We don't know the motor's efficiency or power factor but can use an estimate:Vevor FLA 15A 230V = 3.45kVAR and then 85% efficiency and power factor PF=0.85 gives 3.14HPCentury B813 FLA 22A 230V = 5.06kVAR and then 85% efficiency and power factor PF=0.85 gives 4.90HP, close enough to the rated 5HP.Problem is we don't know how hot the puppy is getting at full load. This is yet another place to fudge numbers. It could be roasting the windings to achieve that.For a panda bear air compressor, under intermittent duty, seems ok.Another way is apply Einstein's equation and compare the mass. A heavier motor uses more copper and steel, the nemesis of cheap manufacturing.I'm not sure if these fake motors can be imported/sold in Europe?

author: Analog Kid
author_rank: Super Contributor
timestamp: July 28, 2025, 10:09:32 pm
content: Quote from: floobydust on July 28, 2025, 09:58:30 pmFake?You're the only one here who's making that accusation.I see now what@Siwastaja meant in his reply here:Quote

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 10:34:07 pm
content: The motor label makes fake, misleading claims to the consumer.Isn't that why this thread exists? Or is it done according to you, 5HP=5HP?The power is of course much less than claimed. Pics example:claimed 5HP, weighs in at 32.84 lbs and 15 mega amps. Do the math.

author: bdunham7
author_rank: Super Contributor
timestamp: July 28, 2025, 11:24:38 pm
content: Quote from: floobydust on July 28, 2025, 10:34:07 pmBut printing SPL is the same as having your fingers crossed behind your back, it means the rest of the specs that follow don't mean anything specific or traceable to a standard. The motor you linked is different than the OP's. The SF=1.15 is a nice touch. They should print CAT IV on it as well.I have a Vevor electric demo hammer, it's about the same size as one you'd rent from Home Depot. I bought it because it was cheaper than renting even for a weekend by the time they got done with chisel fees and what not--and I need it for multiple uses. It really works well and seems to be solidly built. But look at the description and note that it plugs into a standard NEMA 15-5 outlet. Is that fake?https://www.ebay.com/itm/286435484979?_skw=vevor+jackhammer&epid=3063269263

author: floobydust
author_rank: Super Contributor
timestamp: July 29, 2025, 12:38:48 am
content: The jackhammer is rated like a few power mosfets lol - "theoretical/calculated peak instantaneous power" kind of numbers.But I do like the chinese tools that pay for themselves after one use, compared to the Bosch.edit: is the jackhammer's CPU really smooth operation like the pic? They wouldn't lie about it."SPL" I thought is a NEMA acronym- on a label/product with no NEMA anything aside from the frame size.For me the "ISO 9001" sealed it as a legit company and product, like others are telling me is the real maga truth. They can surely provide the quality report to back up the photo-shopped "3.1kW" number on the label

author: bdunham7
author_rank: Super Contributor
timestamp: July 29, 2025, 04:12:13 am
content: Quote from: floobydust on July 29, 2025, 12:38:48 amI thought so too until I looked and didn't find any reference to it. IDK.Although ad copy for many Chinese products is hilarious, it often has nothing to do with the product. The thing is a beast (for a demo hammer) and they included a spare set of brushes. The same thing is sold through US distributors who get them branded and selll them for much more, including barebones but realistic documentation and some minimal support. Probably not a UL listing or meaningful product liability coverage though.

author: floobydust
author_rank: Super Contributor
timestamp: July 29, 2025, 05:45:23 am
content: What do you think is the limiting factor to this motor ratings scam?Yes they will run hot... and then what? Rock bottom way back in 2011/2012:"DeVilbiss Air Power/Craftsman/Porter-Cable/Husky Recalls Air Compressors Due to Fire Hazard"Units: About 460,000 "motors overheating" with the thermal protector also failing to trip, which leads to a fire.It's sad because I'd guess 90% of the motor's BoM cost is there for the housing, bearings etc., a few more dollars of copper wire, a thermal protector - they would not add.Well, now the UL/CSA cert is for the thermal OL.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 29, 2025, 08:52:48 am
content: Quote from: bdunham7 on July 28, 2025, 07:43:35 pmJust weight to show that claimed power density is not that different from heavy-duty industrial motors, so nothing shady going on there.No one questions that these motors are the result of extreme cost cutting - it is obvious from looking at the price - but it is well possible, even probable that the motors conform to their specifications and last years doing so - but probably just barely so.Typical failure mode for cheap power tool motors are the brushes, but induction motors do not have this problem.For the OP, most important takeaway is that the motor specifications show both input (electrical) and output (mechanical) power, and first assumption should be they are approximately correct.

author: u666sa
author_rank: Frequent Contributor
timestamp: July 30, 2025, 03:50:30 pm
content: Quote from: ballsystemlord on July 25, 2025, 10:51:40 pm

author: themadhippy
author_rank: Super Contributor
timestamp: July 30, 2025, 03:56:23 pm
content: wonder how long before it start leaking