Switched reluctance motors will save the planet? - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: July 27, 2020, 08:19:38 am
content: Someone sent this in for debunk as a "scam".Not putting this in the Dodgy Technology section, because it sounds more like over the top startup marketing wank than anything else?https://turntide.com/https://www.prnewswire.com/news-releases/software-motor-company-smc-has-rebranded-to-turntide-technologies-as-it-brings-the-smart-motor-system-to-market-to-solve-for-energy-inefficiencies-in-todays-motors-and-reduce-carbon-emissions-301097158.htmlI haven't done any more thought or investigation than skimming the video.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2020, 08:31:14 am
content: QuoteThe only motors less than 50% efficient are those really cheap and crappy ones found in toys and cost tens of pence.Most decent sized motors have much higher efficiencies, often above 95%.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 27, 2020, 08:48:14 am
content: The efficiency of motors depends a lot on size. Larger motor are quite efficient, like > 90%. 50% efficiency is more like a thing of very small cheap motors like 100 W range.I point where quite a bit can be saved is with speed control in things like fans and pumps, though with pumps there are limits to this as the pump part often also need a certain speed range. Here a switched reluctance motor can very well compete with a conventional induction motor with electronic drive / inverter. The 3rd competing technology with even slightly higher efficiency (especially in small size) are brush-less permanent magnet motors.Switched reluctance motors are already available for quite some time - I remember a shop vacuum cleaner that is available from before 2000, though relatively expensive. The control needs a little effort, but no AI or anything magic or new.

author: lsnair
author_rank: Newbie
timestamp: July 27, 2020, 08:52:41 am
content: https://new.abb.com/news/detail/1789/ABB-motor-sets-world-record-in-energy-efficiency-saves-half-a-million-dollars

author: wraper
author_rank: Unknown
timestamp: July 27, 2020, 09:00:51 am
content: Quote from: Zero999 on July 27, 2020, 08:31:14 amI can add shaded-pole induction motors with 15-30% efficiency. Consume about half of max power without any load at all. Run hot as hell. Used in almost every convection oven fan, axial AC fans and in most of 120/230V AC water pumps in washing machines and dishwashers.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2020, 10:13:49 am
content: Quote from: wraper on July 27, 2020, 09:00:51 amThat's true. I forgot, there are applications where efficiency isn't the most important design goal.

author: Ranayna
author_rank: Super Contributor
timestamp: July 27, 2020, 10:17:25 am
content: Hmm, would it even matter, in regards for efficiency, if a convection oven fan motor runs hot?It would mainly run when the oven is running anyway, and that has only one job: getting hot :pI am not all that familiar with the construction of washing machines and dishwashers. But both use warm water. Would motor heat not at least partially heat the water, and therefore reduce the load of the heating element accordingly?EDIT: Regarding the claims... Those generalized claims of amazing potential savings remind me of the BatterizerNot exactly *lies*, but waaaaaaay over exaggerated.

author: wraper
author_rank: Unknown
timestamp: July 27, 2020, 10:59:46 am
content: Quote from: Ranayna on July 27, 2020, 10:17:25 amMotor is located outside the oven and only it's shaft goes inside. The only thing it heats is surrounding air, so all of the heat is wasted. The other big downside is that because of running very hot, bearing lifetime is significantly reduced.QuoteAgain, motor itself is not water cooled. Heat goes into ambient air. Also in washing machine motor is used for draining only AFAIK.

author: wraper
author_rank: Unknown
timestamp: July 27, 2020, 11:06:16 am
content: Quote from: Zero999 on July 27, 2020, 10:13:49 amActually it is quite important in all applications I listed, maybe besides washing machine. Motor usually runs constantly during appliance operation, so quite a lot of power is wasted.

author: tom66
author_rank: Super Contributor
timestamp: July 27, 2020, 11:17:39 am
content: If the drain pump is anything like my washing machine it's only draining for about 20-30 seconds in the middle of the cycle and at the end of the cycle. The power consumption of the heating element and drive motor are far more significant. And those AC brushed universal motors can be quite efficient, well above 70% and only consume around 200W at the full speed spin.I know my Bosch dishwasher uses a more efficient water pump motor, it sounds by the description like a brushless type. It uses around 80W when the heating element isn't running. Which given the water pressure is decent, it also has to spin the arms via that pressure and still have enough to dislodge food etc from the plates. And it uses 900Wh for a full load on the economy setting and 1.4kWh on the intensive 70C setting. Surprisingly efficient.

author: coppice
author_rank: Super Contributor
timestamp: July 27, 2020, 11:23:52 am
content: Quote from: Zero999 on July 27, 2020, 10:13:49 amWith the temperature at which some small squirrel cage motors run, fire avoidance doesn't seem to be an important design goal, either.

author: coppice
author_rank: Super Contributor
timestamp: July 27, 2020, 11:27:45 am
content: The nicest thing about switched reluctance motors is how quiet they can make a lot of currently noisy home appliances. There were prototype kitchen appliances, like food mixers, with switched reluctance motors around in the 80s that were super quiet. Sadly the market preferred cheaper over quieter.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2020, 11:42:42 am
content: Quote from: wraper on July 27, 2020, 11:06:16 amNot really, fan oven motors only use a tiny amount of power, compared to the oven itself and the same is probably true for dishwashers. A quick Google found this one only consumes 22W. Cut that in half and we have a power saving of only 11W. The efficiency of the appliance could be improved more by better thermal insulation, than changing the motor.https://www.espares.co.uk/product/es1548541?utm_source=google+shopping&utm_medium=shopping&utm_campaign=google+shopping&gclid=EAIaIQobChMIxYSRpqnt6gIVb4BQBh2v6w9FEAQYAiABEgLU-_D_BwEQuote from: coppice on July 27, 2020, 11:23:52 amI don't think I've ever seen one catch fire. They're normally fitted with a thermal cut-out, which is usually one-shot. No doubt power could be saved by changing them for switched reluctance motors, but they tend to be the smaller, cheaper motors which only use tens of Watts, so it's not worth it. Using more copper in the windings and a copper rotor, rather than aluminium would probably give more bang for buck, than changing to switched reluctance.Anyway, this is off-topic. The manufacturer discussed in the original post is talking about motors which use 47% of the world's electrical energy i.e. large motors. The tiny motors used in fan ovens and dishwashers are a drop in the ocean. It's total BS that half of the energy used by the world's motors is wasted.

author: EEVblog
author_rank: Unknown
timestamp: July 27, 2020, 11:09:17 pm
content: Quote from: wraper on July 27, 2020, 09:00:51 amProbably means diddly squat in the global scheme of things though?

author: wraper
author_rank: Unknown
timestamp: July 27, 2020, 11:13:48 pm
content: Quote from: EEVblog on July 27, 2020, 11:09:17 pmConsidering they are in most of homes in somewhat developed countries, IMHO it matters. Say it makes 0.1% difference in overall home electricity consumption. Globally it means energy needed for powering a few small countries.They are also used in microwave oven fans BTW.

author: EEVblog
author_rank: Unknown
timestamp: July 28, 2020, 03:39:39 am
content: Quote from: wraper on July 27, 2020, 11:13:48 pmMicrowave oven fans would be the epitome of the cases where it doesn't matter. i.e. you have an already high load (1000W) working for only a few minutes a day.

author: james_s
author_rank: Super Contributor
timestamp: July 28, 2020, 04:02:30 am
content: Shaded pole motors are used everywhere, bathroom vent fans, desk fans, AC powered muffin fans, furnace and boiler draft inducers, medium sized fountain pumps, anywhere that requires a cheap low power AC motor. There are other types of induction motor such as PSC or even 3 phase motors that can easily be scaled down into these sizes, they just typically aren't because it costs so much more.My ~15 year old Maytag Neptune washing machine has a switched reluctance motor. It works fine although these days it seems like VFDs are cheap and good enough that ordinary 3 phase induction or BLCD motors probably make more sense. If they banned shaded pole motors I suspect PSC and BLCD would take over most applications where they are now used.

author: filssavi
author_rank: Frequent Contributor
timestamp: July 28, 2020, 04:24:45 am
content: Now I didn’t watch the video, but I can assure switched reluctance machines are absolutely a thing, the operating principle is the same as the BLDCs however instead of magnet the rotor is has a highly asymmetric radial reluctance profile.You also have synchronous reluctance (synrel) machines that work more like PMSMs but use the same principle. There are even hybrid machines where some torque is due to magnets and some torque is due to reluctance.Performance wise they are (for most Typical applications) strictly worse than permanent magnets machines, and typically(though not necessarily) have a terrible power factor (0.5-0.7 lagging) however they cost much less and you don’t rely on a single country for rare earths magnets. They are still better than induction machines though as there are no rotor copper lossesThat said these type of machines are extremely rugged, as the rotor is basically a hunk of solid steel, they don’t have brushes, rotor bars that can break, magnets that demagnetise etc just stamped steel laminations bonded together.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 28, 2020, 04:30:07 am
content: Hi,Switched reluctance motors have been around a long time, at least 40 years.The Dyson digital motor used the Dyson vacuum cleaners and hand driers are switched reluctance motors.They are very similar to stepper motors. They tend to by noisy and have pulsating torque, the rotor tends to 'snap' from one position to another.There is a Goodness Factor for electric motors:More here:https://en.wikipedia.org/wiki/Goodness_factor#:~:text=The%20goodness%20factor%20is%20a,efficient%20magnetic%20levitation%20induction%20motors.&text=From%20this%20he%20showed%20that,likely%20to%20be%20relatively%20large.This helps explain why switched reluctance motors are good.Ae is relatively large, short windings of thick wire.Le is the length of the electrical circuit, it can be short.W is large high RPMThey also need a driver.This goodness factor explains why large machines are better, more efficient than small ones. If you scale the linear dimensions, the areas, Ae and Am scale with the linear dimensions squared, Le and Lm increase proportional to the linear dimension. So goodness gets better.It also explains why switch mode power supply transformers are better than line frequency ones for a given size.The idea that the switch reluctance motor will save the planet seems like a lot of hype to me.Jay_Diddy_B

author: filssavi
author_rank: Frequent Contributor
timestamp: July 28, 2020, 04:33:27 am
content: Quote from: james_s on July 28, 2020, 04:02:30 amSwitched reluctance machines require a VFD just as much as a BLDC, the main reason they are not used in white goods and general consumer crap is not the drive requirements, but just the higher cost, that is not justified by any real advantage. Powe density is fine and good, however there is plenty of space inside the whashing machine. Efficiency wise the difference, at the low power levels we talk about is negligible (you will have maybe few watts difference if that)

author: WattsThat
author_rank: Frequent Contributor
timestamp: July 28, 2020, 04:46:11 am
content: What an absolute load of marketing wank.As someone on the front lines of VFD technology, all I can say is, thanks for the laugh.Switched reluctance motors have been around for years in appliances. Fine for low power, constant torque applications.On much larger, industrial scale, synchronous reluctance motors (synRM) and their drives have been built for years by ABB. Here’s a video that goes back to 2013, the drive has since been a replaced by the ACS880 which can control asynchronous, permanent magnet and synRM motors, all with the same firmware. 0.5 to several thousand kilowatts. Same drive. They’ve been building them for years. The only difference is that synRM is a variable torque, not constant torque machine. Power savings over standard induction machines is worthwhile, it does provide a quick payback.Yawn. Nothing to see here. Move along.

author: bdunham7
author_rank: Super Contributor
timestamp: July 28, 2020, 04:48:28 am
content: Quote from: Jay_Diddy_B on July 28, 2020, 04:30:07 amMy car has a version of the switched reluctance motor. They don't say much about it, and it is sometimes referred to as a 'synchronous motor' but it has that characteristic little quiver if you creep very slowly up a steep incline like my driveway. Other than that it is very smooth and efficient, which I assume is due to the tweaking of the very large liquid-cooled electronic motor drive module.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 28, 2020, 05:00:02 am
content: Quote from: bdunham7 on July 28, 2020, 04:48:28 amThere are some techniques in the motor design that can reduce the torque pulsation. There are also some techniques that can be applied to the driver, similar to micro-stepping in a stepper motor to reduce the pulsations.In the conditions you describe, high torque, low speed, the output power is low, since power = torque x angular velocity. The efficiency is low under these conditions.Jay_Diddy_B

author: tom66
author_rank: Super Contributor
timestamp: July 28, 2020, 06:43:26 am
content: I've noticed an interesting phenomenon with my Golf GTE (plugin hybrid.) In electric mode, if you creep up a hill at very low speed, it will eventually stop. In this mode it seems to use about 5kW. It seems as if the electric drive does not like you using creep for long periods of time. You can press the pedal again and it will creep once more but stop after 10 seconds. Whereas it will creep endlessly on flat surfaces. If you actively use the accelerator it will always go faster than this creep setting, so I wonder if it is microstepping and that is inefficient and there is a thermal/time limit here for a reason.

author: tszaboo
author_rank: Super Contributor
timestamp: July 28, 2020, 07:24:57 am
content: Different appliances have different design goals for the motors. For example I have a blender, that is probably used a few hours over it's entire lifetime. So, you can design in a very powerful, efficient motor, with diagnostic, variable drive, controller etc. Or find the cheapest rotating thing, and attach a blade for it. The first one would be acceptable for a blender for an ice cream factory I guess, but I'm using mine maybe once a week.Actually the EU commission recently have been spending a lot of time optimizing the efficiency of white goods. They had new lays for vacuum cleaners and the controversial kettle law. So there is a push to reduce wasted energy.These guys probably found out that many 20-30 year old building appliances, HVAC could be more efficient with these motors. (I've studied about them in university BTW) Good for you, start replacing old motors, make money. It's actually very nice, that they correctly identified the market niche for their product.

author: filssavi
author_rank: Frequent Contributor
timestamp: July 28, 2020, 07:52:32 am
content: I see there is a lot of confusion about different kinds of machines and how they are driven, so I will try and clarify a bit...First and foremost we are talking about synchronous machines where the mechanical and field rotation frequency are the same, there is thus no slip, such as in induction machines.These machines can then be classified in:Wound rotor:These are the big turboalternators that are used in power plants, the rotor field is generated through an electromagnet, energized with either a set of brushes (exceedingly rare nowadays) or an exciter machine (basically a rotating transformer) with a rectifier on the shaft[/ li]Permanent magnet machines: these use permanent magnets (usually but not necessarily rare earths based) to generate the rotor fieldReluctance machines: these machines don't use a rotor field at all to generate torque but instead they rely on a radially asymmetric reluctance profileThe first class of machines will be ignored as it is competitive only at the MVA scale.Both other classes can be then further split into two sub-groups based on what is the back-emf waveform shaped (this is determined by how the rotor is physically designed).Trapezoidal:These are BLDCs and switched reluctance machines, they are typically driven by turning on only the phase that is aligned with the rotor quadrature axisSinusoidal:These are PMSMs and synchronous reluctance (or synRel or synRM). they need to be driven with a sinusoidal current profile at the correct angle for each phaseNow that the theory is clear, the real world is much messier than that a bldc can be driven with a sinusoidal waveform, and it will have less torque ripple (though not as low as a properly designed and driven PMSM), and a PMSM will spin if run like a BLDC (though with lowish torque).Reluctance machines have few advantages over magnet ones:Much wider speed range due to better flux weakening supportThey are a lot more rugged, both thermally and mechanically since the rotor is basically a solid hunk of steelDisadvantages arelower power density as reluctance is much worse at generating torque than magnets (basically you need to throw more current at it, thus more copper in the stator)They have typically (though not necessarily) a somewhat worse power factor (down to 0.5-0.6 lagging) requiring larger drivesThey have typically (though not necessarily) have a worse torque rippleThey are typically harder to drive since the d and q axis inductances change widely with the rotor angular positionFor all machines listed above the control NEEDS to know the rotor angular position, either through a sensor or with some sort of observer (sensorless control) in order to work at all they CAN'T be run as stepper machines, they do not use microstepping, they can't be run open loop and they most certainly can't be run without a drive by just sticking them in a mains socket.Now stepper motors are the red headed bastard step-child of the synchronous machine family. they are fundamentally either BLDCs or Switched reluctance machines (or a mix of both) that have been specifically designed by maximising cogging torque (which is usually very undesirable). They sell efficiency, torque ripple, torque capability and maximum speed to the devil in exchange for the possibility of being run open loop as they now step consistenty with each current pulse at the winding and hold position if energised.They are great for low performance low power and low complexity tasks, where the lack of a proper drive can be made up by just overspeccing them. however as soon as you need reliable actuation under load they must be run in a closed loop configuration, and by that poin you are more than half way towards implementing a true machine drive and might as well toss that piece of trash where it belong and buy a proper electrical machine that will have higher performance in basically every metric you can think ofAs for the EVs at creep, my guess is that it is a thermal limit probably on the machine drive rather than the machine itself (their thermal time constants are measured in minutes not seconds)

author: Zero999
author_rank: Super Contributor
timestamp: March 20, 2021, 07:28:27 pm
content: Switched reluctance motors saving the planet? No, die cast copper rotor motors will. They're much more efficient than aluminium rotor motors and work with ordinary variable frequency drives, or directly off the mains, if speed control isn't required.https://www.copper.org/environment/sustainable-energy/electric-motors/education/motor-rotor/pdf/Three-Phase_Induction.pdfhttps://www.aceee.org/files/proceedings/2007/data/papers/11a_2_069.pdf

author: tszaboo
author_rank: Super Contributor
timestamp: March 20, 2021, 11:13:34 pm
content: Quote from: Zero999 on March 20, 2021, 07:28:27 pmSo they concluded that copper conducts electricity more than aluminium?I am more interested in Figure 2, the power vs efficiency curve. So the motors are most efficient at 50% their rated power. All cars today have grossly oversized engines, and spend 99% of their time at less than 25% of their rated power. You need maybe 15 HP to go on the highway.So having a secondary 30 HP motor would make the car more efficient by at least 5%. And would you look at that: The Toyota Prius has a 27 hp electric engine.

author: Zero999
author_rank: Super Contributor
timestamp: March 21, 2021, 11:49:35 am
content: Of course it's been known for a long time that copper is a better conductor than aluminium. What's new is improvements in copper die casting, which makes motors with copper rotors easier and cheaper to make.https://www.machinedesign.com/news/article/21829687/industry-could-take-a-shine-to-copperrotor-motors

author: tszaboo
author_rank: Super Contributor
timestamp: March 21, 2021, 12:00:10 pm
content: Quote from: Zero999 on March 21, 2021, 11:49:35 amYes, that was my point. If it would be cheaper to make, they would've switched to it, so something tells me that it is not cheaper. We are talking about companies that try to shave pennies off the BOM cost of ECUs.Copper is getting stupidly expensive in general, and machining it is harder.The other issue is the typical upfront cost of things. If switching to copper would add 500 EUR to the sales price of a car, and it would add 3% range improvement, who would buy that? That 500 EUR is very visible, while that 3% would be a range of 360Km instead of 350Km.If people would think about long term running cost of cars, most people would drive a hybrid.

author: Zero999
author_rank: Super Contributor
timestamp: March 24, 2021, 08:43:18 am
content: Quote from: tszaboo on March 21, 2021, 12:00:10 pmI'm not talking about for use in cars, but industry in general. If the motor needs replacing anyway, it might make sense to spend a little extra to save more in the long run. Changing to a switched reluctance motor would require new drive electronics, whilst a copper rotor motor would be a drop in replacement.