Repairing smaller 400V HVAC flu motor with open wire - Page 1
Forum section: electronics / repair

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 13, 2024, 12:25:03 am
content: Picked up a dead 400V HVAC flu motor at a flea market. At 120V no current would flow so I took took it apart and found an open very fine copper wire. Soldered open wire, motor now passes current, and will move the shaft a fraction then quit,, at 120v. Also, tried manually spinning motor to give it jump start,, no go. I do not need the motor since I only have 120 and 230V. It has value and would like to sell,, but want to make sure it is working properly. Thought about connecting 220V but motor's power input only has 2 wires so I do not know how to hook up 220V(120V,, simple blue and red). The capacitor tests good. Attached is wiring diagram. Any advice how to test/wire motor for proper function greatly appreciated.

author: langwadt
author_rank: Super Contributor
timestamp: February 13, 2024, 12:50:02 am
content: a broken motor you found at a flea market, what value does it have?

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 13, 2024, 01:08:16 am
content: Here's clearer picture of wiring. Looks like wiring was backwards as found,, now I'm even more confused.Working,, has value of course. minimum, a spare when your heat or AC goes down. As long as the motor's windings are not burnt, motors can be quite robust lasting decades.Besides not knowing how to properly wire motor for test, also do not understand the stamping on motor "asynchronous single phase"...

author: Jwillis
author_rank: Super Contributor
timestamp: February 13, 2024, 08:01:20 am
content: That's a 460V motor. At 120V it probably doesn't have enough torque to turn over or keep running. Might at 220V.The connection of the blue and red wire to AC doesn't matter.

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2024, 08:41:51 am
content: It might turn at 240V, but will be weak and might even draw too much current and overheat. You need a step-up transformer to get it to work properly, which will cost more than the motor itself. My advice is to count your losses and junk it.

author: CaptDon
author_rank: Super Contributor
timestamp: February 13, 2024, 02:49:52 pm
content: Looks like that motor has had a rough life. If it is a bronze bushing motor I would junk it now as the bushings will probably be just about shot anyway. I have never encountered a 460VAC rated flue motor and can't imagine it has much use to anyone except those with industrial 3-phase wiring where this motor would sit across any 2 of the 3 phases, and if so, they would never pay for a questionable used motor. Here in the states I think the shift was from 440V.A.C. to nominal 480V.A.C. with that motor being 460 rated have I missed something? Surprised to see a 450vac rated capacitor on a 460vac rated motor?

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2024, 05:54:51 pm
content: Quote from: langwadt on February 13, 2024, 12:50:02 amI'm certainly not judging the original poster for buying junk. I've done it myself in the past and I'm sure many others here have. It's part of the learning curve. The best thing to do is dispose of it, hopefully getting some money back if possible and learning from the experience.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 13, 2024, 06:21:01 pm
content: Hope you all understand english:I have repaired the motor,,Motor/blade spins freely like new $500 motor,,My question is,, I don't understand how to wire motor to 220V for a QUICK test? As found, looks like leads are wrong,, per diagram appears capacitor leads should go to motor/vice versa?):I have a shiny new 220V bare extension cord on hand. Motor only has two power leads.Is it safe to join the 220V cord's 2 hot 120V wires then connect joined cords and neutral to motor's two AC wires?

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2024, 06:45:18 pm
content: The motor cannot be wired for 220V. The fact you've repaired it, does not change the fact that it is the wrong motor.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 13, 2024, 07:15:46 pm
content: Quote from: Zero999 on February 13, 2024, 08:41:51 amDo you think motor would withstand a 1 second test at 220V?UPDATE: I switched the leads per diagram. Flash on/off test,, motor has audible hum at 120V does not spin fan. As mentioned before,, as found wiring configuration had same motor hum, plus moved the fan blade 1 inch,, what colors do you think the power leads are? Maybe the diagram is wrong and as found wiring is correct (diagram could be for a single phase asynchronous motor per label), not for 3-phase wiring which this motor is? Just call me a confused knob

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 13, 2024, 10:24:40 pm
content: Quote from: DAVEISGREAT on February 13, 2024, 06:21:01 pmNot in my case!!So in as found motor wiring configuration, I shorted both 120V hot wires at the bare end of a 240V plug together and connected both live wires to one motor winding, then connected plug's neutral wire to other motor wire. Then I plugged plug into 240 outlet ---> LOUD POP THAT THANKFULLFULLY TRIPPED THE 240v BREAKER AND ALSO TRIPPED THE150A100A HOUSE BREAKER !! Now I know how ElectroBOOM must feel. Can someone explain what just happened (please refrain from lecturing lucky to be alive)?

author: langwadt
author_rank: Super Contributor
timestamp: February 13, 2024, 11:30:24 pm
content: Quote from: DAVEISGREAT on February 13, 2024, 10:24:40 pmput down the wires and do some reading before you kill yourself or someone else, you seem to be missing the most fundamental understanding of how 120V/240V mains works

author: Gregg
author_rank: Super Contributor
timestamp: February 14, 2024, 12:37:36 am
content: I fully agree with Langwadt.First thing you need to do is figure out what is wrong here: "I shorted both 120V hot wires at the bare end of a 240V plug together"

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 02:32:49 am
content: For the 250V test, should have wired the two hot 120V leads to the two motor leads. Double Doh.What should I do with the plugs ground wire? If ignored does current have a path? If no path, ground it to motor -help?

author: vk6zgo
author_rank: Super Contributor
timestamp: February 14, 2024, 03:23:22 am
content: Quote from: DAVEISGREAT on February 13, 2024, 06:21:01 pmNO! in the NA system those two "hot" 120v wires are at 240v potential with respect to each other.Connect them together & you will see a big flash & your Mains circuit breaker will trip.If you plug the extension lead into your 240v power outlet you should be able to measure 240v across the two "hots".If I was testing your motor with the single phase 230v (nominal) Australian system, I would probably "take the chance" & connect its two AC wires between Active (hot) & Neutral, as the latter is connected to ground at the entry point into the building, & in any case, even with a wrong selection of connections there is probably little chance that any of the accessible metal parts are connected to either side of the mains connection.It would probably be OK with a motor designed for 400v, but I have zero experience of that system.

author: Jwillis
author_rank: Super Contributor
timestamp: February 14, 2024, 04:59:21 am
content: North America has split phase. Connecting two 120V to make 240v off of one phase will blow the breaker. Think of split phase as a centre tapped transformer with 3 terminals. 120V-0-120V.To get 240V the 2 120V live from each phase without the common from either makes 240V. Just like a centre tapped transformer. that has 12V (first tap) 0V(centre tap) 12V (last tap) the centre tap is Common. When you connect the to out taps it makes 24V.If you don't understand this. STOP NOW! Before you hurt yourself or burn your house down.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 05:04:02 am
content: Quote from: vk6zgo on February 14, 2024, 03:23:22 amDo you think if two motor leads are connected to two hot 120V leads and plug's ground is left open motor will draw proper current?

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 05:22:59 am
content: Quote from: Jwillis on February 14, 2024, 04:59:21 amPlug and outlet are 240V so connecting the two hot leads separately to the two motor leads, leaving plug's ground open should send 240V to motor without popping breaker this time, if I understand correctly?

author: Jwillis
author_rank: Super Contributor
timestamp: February 14, 2024, 07:19:57 am
content: Please be careful. I had a colleague that was highly experience with high voltage equipment and wiring. One slip up and he died hours later after severely burning himself. Not a nice way to go or to have to remember.A 240V outlet can have 120V 0Vcommon 120V plus a ground for a total of 4 terminals (for a dryer is an example) Or it can have 3 terminals 2 120V one ground but no common (electric stove or welder).Before you start make sure that the coil of the motor is not shorted to the body or rotor, A simple continuity check would work. I also suggest a switch between the motor and power. Secure the motor so you don't have to hold it. If the motor trips the breaker, This would indicate that a short is in the coil. Then it'd best to dispose of it.Again. Please be careful.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 07:54:07 am
content: Thank you. Motor has no shorts and I will add a switch as you suggest, along with a resettable fuse, and try in the morning in case of a black-out.

author: soldar
author_rank: Super Contributor
timestamp: February 14, 2024, 10:43:50 am
content: Quote from: DAVEISGREAT on February 13, 2024, 01:08:16 amDo you understand "460 V"?

author: CaptDon
author_rank: Super Contributor
timestamp: February 14, 2024, 02:11:22 pm
content: Question, the motor carries a 460 volt rating. Was that a typical rating for the old U.S. 440 V.A.C.? Since the U.S. has now chosen standards of 120, 208, 240, 277, 480. The 460 would seem a bit odd today. At G.E. in Erie Pa. we also had some 550vac and 600vac circuits. An engineer had to be very careful about connecting to the mains. We had equipment destroyed by the oddball 120 / 120 / 208 orange wire 'wild leg' 240vac tapped delta where one side of the delta is center tapped to get 120-0-120 or 240 as single phase. Sadly an electrician mistake put 208 on our lab 120vac receptacles. I worked around a really stupid implementation at a central Pennsylvania factory, 13.2KV 3 phase ran across the parking lot on poles and when it reached the roof of a particular building it was supported 2 feet above the roof for about 20 feet of distance and you could walk right into it!!! I have no idea how it functioned when the snow covered it?? Amazing no one was ever killed, even by coming into contact with the snow!!

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2024, 06:23:10 pm
content: Use a small control transformer run in reverse. There appear to be plenty of units available with a 460V primary and 110V secondary. Running on 120V is no problem because it'll have extra turns to account for the volt drop, under load.Here's one I found on eBay, but 50VA is a bit small for continuos operation.https://www.ebay.co.uk/itm/184160007031Here's a brand new one, which would be my recommendation.https://us.rs-online.com/product/mgm-transformer-company/m22427/73662402/

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 06:43:42 pm
content: Placed both hot leads across two motor leads,, with protective inline fuse and inline microwave switch(always off. as a kill switch). With motor secured,, used a broom handle to momentarily depress switch for two or three seconds. Unfortunately, similar motor hum, little if any rotation. Mercifully, no million amp short!Plan B: I do have a 120V to 240V transformer rated at 500W . Would it be possible to wire 220V into T's 120V side to briefly get 440V output, then test motor start-up?UPDATE: Zero999 just noticed your post. Like your similar, better idea but don't want to spend that much. You think plan B is useable option?

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 14, 2024, 07:02:04 pm
content: Plan B is not a good idea. Seehttps://www.eevblog.com/forum/chat/hv-transformer-dude-almost-terminating-himself-and-the-house-cat!/It probably won't explode like what he used, but better safe then sorry. You will melt your transformer when you input double the nominal voltage.Edit: The motor most likely has two windings. The main winding that is fed directly from the mains and an auxiliary winding that is fed via the capacitor to get a phase shift between the two windings. Make sure the capacitor is connected when you apply the voltage. Internally the mains wires will be connected to both windings and the capacitor will be in series with one of them.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 07:30:47 pm
content: Quote from: pcprogrammer on February 14, 2024, 07:02:04 pmRemember, purpose is for a 2 second test,, would it still melt,, any other major concerns?

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 14, 2024, 07:33:28 pm
content: I would not risk my transformer even for only a couple seconds.

author: Gregg
author_rank: Super Contributor
timestamp: February 14, 2024, 07:39:22 pm
content: Check the capacitor and its winding; the motor won't want to rotate without a proper capacitor.

author: Jwillis
author_rank: Super Contributor
timestamp: February 14, 2024, 07:54:42 pm
content: I should have looked at the wiring more closely. I wonder if the starting cap is toast or not connected properly. Can we get a closer look at the connection of that?

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 08:20:24 pm
content: Capacitor measures spot on using my old reliable battery sucking UNI-T multimeter.Earlier I questioned wiring using 120V so reversed them,, very similar results using 120V. Will reverse leads again using 220V,, this time wiring will be as per diagram,, and report back.UPDATE: Can confirm cap holds charge for a long time. For safety, shorted it with an insulated set of pliers and got a big spark. Note to self,, make a proper cap discharger.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2024, 08:31:45 pm
content: Quote from: DAVEISGREAT on February 14, 2024, 07:30:47 pmI don't think it's much of a risk. Transformers take a long time to overheat. A 100VA transformer can happily be short circuited for a few seconds, without smoking.Heck, I would wire the 120V:220V transformer, as an autotransformer to give 340V, which will stand more of a chance of getting it to turn. To this, the 220V secondary needs to go in series with the 120V primary, which is connected to the mains as usual. Some experimentation with the phase might be necessary: if you get it the wrong way round, it'll drop the voltage by 220V, so give close to 100V; if that happens, just reverse it and try a gain.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 09:43:54 pm
content: Quote from: DAVEISGREAT on February 14, 2024, 08:20:24 pmDouble checked wiring diagram only to note above tests with 240V test was made correctly, as per diagram. So I did not test with reverse cap/motor wiring since error noted, and because I don't really understand this assemblies wiringStill trying to comprehend getting 340V from 120V--240V step up T in USA?

author: Jwillis
author_rank: Super Contributor
timestamp: February 14, 2024, 10:25:30 pm
content: As Zero999 says, the only way to step up single phase 120V or 240V to a higher voltage is with a transformer.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 14, 2024, 11:36:08 pm
content: Working on this motor has been my introduction to 220V. Always have respected 120V and haven't been zapped since I was a kid. After yesterdays escapades jumping to 480V scares the crap out of me. All my safety fuses and switches only have 220V ratings. Still, want to briefly pump 480V in this sucker with my 120V to 240V transformer,, come hell or high water,, any tips wiring for safety, etc. would be greatly appreciated.UPDATE: Another question. How to add a bleeder resistor to circuit. Last 240V test, I measured 240V across motor several minutes after I thought power was off? Lastly, I do not understand 3 phase very much,, is it important for this test?

author: Jwillis
author_rank: Super Contributor
timestamp: February 15, 2024, 12:34:05 am
content: Depends on the size of the cap will determine the power of the resistor in watts. A 15K to 56K resistor 1W should be about right for that cap. That just goes across the capacitor terminals to discharge cap when not in use. Won't effect the motor performance as long as the resistor isn't to low in value. You don't need to worry about 3 Phase with that motor since its single phase.Imagine a sine wave as single wave or single phase . Then imagine 3 sign waves equally spaced 1/3 apart from each other as 3 phase.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 15, 2024, 04:20:53 am
content: Dug up the step-up/step-down transformer. The T is contained in a metal box and intended for travel, though quite heavy spec'd at 1000VA and 20+lbs.The million dollar question: How to wire 240V into this 120V to 240V step up transformer, and get 440V out to briefly run motor. Here's pictures of transformer and wiring. Thinking the two 120V bare hot wires on the big 240V plug should clip into the smaller hot and neutral of 120V plug?? Not sure if it matters,, the small 120V plug is non-polarized? Also, current wiring scheme leaves both grounds open? Should this set-up work? any advice greatly appreciated!

author: Jwillis
author_rank: Super Contributor
timestamp: February 15, 2024, 07:31:12 am
content: Yikes. I'm going to say you can't or shouldn't. Simply because the impedance of the 120V will be twice as low as it should be for 240V input. You could very well fry the transformer but at the very least trip the breaker. Keep in mind that tripping breakers repeatedly weakens them. I'm not that experimental or brave enough to try.If you could find a second transformer like that then you can wire the primary in series and secondary in series. I can't advise plugging the 120V side into 240V source.I'm not afraid of high voltages, but I do respect them.

author: Gregg
author_rank: Super Contributor
timestamp: February 15, 2024, 07:13:35 pm
content: Most of those type of step up/down transformers are auto transformers meaning that the primary and secondary are NOT ISOLATED from each other. Since you earlier indicated a desire to learn, I suggest you read up on transformers and learn before doing something you may regret.

author: Zero999
author_rank: Super Contributor
timestamp: February 15, 2024, 08:25:52 pm
content: Quote from: DAVEISGREAT on February 14, 2024, 06:43:42 pmThe one you already have appears to be an autotransformer, so my idea of configuring it for 340V won't work.The transformers I've posted links to are not expensive.Are you really that strapped for cash? If so, then look around for second hand control transformers, similar to the one I posted the eBay link to.Trying to save money too much appears to be a common beginners mistake. It invariably results in it costing more in the long-term. Heck I would just junk it and shell out for a brand new motor of the correct voltage, from a reputable supplier. That way it'll be covered under warranty and I don't have to worry about it burning my house down. Peace of mind is well worth a few hundred quid.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 15, 2024, 11:09:00 pm
content: Had never used this T before so needed to test it. Meter showed 250V output unloaded.Only 240V load I had was a discarded stove element<--(BLEW UP THE FUSE). Worked for a second, lukewarm, then blew a fuse. What happened was the T is missing its AC indicator bulb(don't know what kind?),and its exposed wire shorted to the transformer while testing.<-- WRONG(read Greg's correct analysis below)Yea, I would like to avoid blowing this thing up and not trip the main 100A main house breaker ever again. Not smart enough to know if pumping 240V across this T's 120V input plug through this "transformer" and 440V out to motor will pop/weaken main house breaker again, but sure do appreciate all the advice from everyone. :'(That quick 2 second 480V test may never happen,, at least with this T. With a normal isolated T, I would definitely risk it but the wiring here is over my head. For completeness I added more pictures ofautotransformer, not Tif anyone is interested.

author: Gregg
author_rank: Super Contributor
timestamp: February 15, 2024, 11:43:32 pm
content: Dave,You need to start at the very beginning and get a working knowledge of ohm’s law. You tried to power a stove element of at least 1500 watts from your 500 watt transformer. What could go wrong evidently went wrong as you should have expected.The low resistance of the stove element was about the same as a dead short to the transformer you used.In one of your earliest posts you mentioned using incandescent light bulbs to limit current; ohm’s law tells you why this works. Also you could put two 120 volt lamps of the same wattage (basically the same resistance) in series to test your 240 volt transformer output. If you use two 100 watt 120 volt lamps in series and power them with 240 volts they will draw 200 watts of power.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 16, 2024, 04:54:18 am
content: When I was about five I stuck my finger in a light bulb socket,, once a knob always a knob.T is rated 1KW and knobs assume things like small stove element is only 750W, not 2400W(as latter measured 10 ohms). Thanks for correcting, and for the bulb tip. Still enjoy learning though and these lessons have been valuable yet painfullyembarrassing,, I'm old and dying,, only wish I had the time to start from the beginning again.BTW, its Jim,,username is in honor of our host's fabulous forum--> DAVE JONES.

author: Jwillis
author_rank: Super Contributor
timestamp: February 16, 2024, 05:30:27 am
content: Nothing to be embarrassed about. Making mistakes is half the learning process. I'm not getting any younger either. Not as steady any more and can't see a darn thing without coke bottle bottom glasses.But I always enjoy learning and figuring out new things, Many times with disastrous results. Even when I don't figure out how something works after destroying it, at least I know not to do that procedure again. As Victor Hugo say's "We're all fools most of our lives, it's unavoidable"

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 23, 2024, 10:44:56 am
content: Words of wisdom and encouragement-- Thank You Again!:Motor rating per tag shows that at 460V, motor consumes only 47 watts. Typical MOTs output 2.2kV, but if 80% of the secondary winding is removed then voltage out should be very close to 460V. Seems pretty simple. Motor needs1.7 amps(oops, .17 amps)at 460V per tag. Do you all think this simple modification to a MOT would have enough juice to briefly run this motor just as a test,, possibly even continuously maybe somehow?

author: CaptDon
author_rank: Super Contributor
timestamp: February 23, 2024, 02:31:18 pm
content: It says OUTPUT 47W. And the amps are .17!! You realize at 460vac 1.7 amps would be 782 watts which is about 1 horsepower. If you can't get that motor to turn over slowly after giving it a bit of a spin by hand at 240vac then its junk. How many different wiring schemes have you tried. B.T.W., yes, you may get 460vac from the partially unwound secondary of a M.O.T. but NONE of them are designed for continuous use. They run in partly saturated mode and you MUST knock out the magnetic shunts. I highly doubt you will ever see this completely useless motor spin.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: February 23, 2024, 08:09:33 pm
content: Quote from: CaptDon on February 23, 2024, 02:31:18 pmUPDATE: Will source a MOT and try this.

author: johansen
author_rank: Super Contributor
timestamp: February 24, 2024, 02:49:11 am
content: The motor can be re wired for 240.Find the mid point between the two coils and snip it, wire in parallel.The capacitor winding will need to be snipped as well and the capacitor value doubled