Magnax Yokeless Axial Flux Motor Promises 98 Percent Efficiency - Page 1
Forum section: electronics / general

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 24, 2019, 09:43:34 am
content: This looks interesting, though I'm wondering how something with such an apparently massive power/weight improvement is coming from what appears to be a university startup when vehicle manufactureres are investing billions in EV tech.I'm a little suspicious of their comparison to the BMW i3 motor, which is maybe 8 years old, and achieves about 3 miles/kwH when modern EVs are at 4-5miles/kwHhttps://insideevs.com/news/361185/magnax-axial-flux-electric-motor/

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2019, 11:09:11 am
content: The BMW i3 motor they compare to is clearly not state-of-the-art in regards to power density.In any case, say, after about 3-4 kW/kg is exceeded, the motor energy density kinda stops being the bottleneck, everything else is.A 200kW, 250Nm motor could be used for propulsion of a 1500-kg car, out of which 200kg would be li-ion cells. Compared to these numbers, it is fairly insignificant whether the motor is:A) 93% efficient, weighing 30-40kg, orB) 98% efficient, weighing 16kg.Not saying it's meaningless; if they can deliver, it's going to be another great micro-optimization, but it doesn't solve any of the bigger problems, the current motors solve the motor problem well enough already. Just an optimization.Although, if we do see a massive breakthrough in battery energy density (unlikely in the very near future), something which would at least triple or quadruple the energy density in one go, then decreasing motor weight could become interesting again, for example in electric airplanes.

author: f4eru
author_rank: Super Contributor
timestamp: July 24, 2019, 11:56:25 am
content: Axial flux motors are interesting, they already were with commuting DC motors, but the useability for EVs in cars will be determined by the speed range where the maximum power is available, i.e. what is the ratio of field weakening.Without possibility to have field weakening on a 4:1 speed ratio, a motor is basically more or less useless (read too expensive, too much compromises) for EV cars.

author: Psi
author_rank: Super Contributor
timestamp: July 24, 2019, 12:59:18 pm
content: I don't see the gains over a normal motor being large enough for any company to choose to pay licensing for the technology.Maybe in super niche applications like a solar powered airplane where every 0.1% efficiency gain is useful.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 24, 2019, 01:27:36 pm
content: A significant increase in motor efficiency could be a fairly big deal, as it allows the same range on a smaller battery, giving more weight savings and should also improve regen efficiency.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2019, 01:46:50 pm
content: Quote from: mikeselectricstuff on July 24, 2019, 01:27:36 pmBut a significant increase in motor efficiency cannot be achieved, since usual COTS state-of-the-art is already somewhere around 93%. The theoretical maximum would be about 7% smaller battery, with a 100% efficient motor. Add extra gains for reduced motor and battery weight, and maybe the equilibrium is somewhere around 7.5-8% max.But from the viewpoint of removal of waste heat, the difference can be significant. 50kW at 92% produces 4kW of heat. 50kW at 96% produces 2kW of heat. The ratio of cooling reduction is 50%, completely different to the 4.3% battery size reduction for the same numbers. If you suddenly can afford dropping a water cooling loop from the design, it's going to be a significant micro-optimization for cost and reliability. And for a smaller form factor, less surface area is available for cooling, so increasing the efficiency at the same time is a must.98% is still very hard to believe. And over what operating range? Without a torque-speed-efficiency curve, the number is meaningless.

author: Psi
author_rank: Super Contributor
timestamp: July 24, 2019, 01:51:45 pm
content: Quote from: Siwastaja on July 24, 2019, 01:46:50 pmgood point

author: tszaboo
author_rank: Super Contributor
timestamp: July 24, 2019, 02:05:51 pm
content: Going from 93% to 98% means that the motor needs much less cooling, cause it has 3.5 times less losses.I see two possibilities:The company is there "for the grabs", so to be purchased by a big company, like VW, Toyota, Daimler, Tesla etc.. and there is no actual motor, only concept art with "just one engineering problem to be solved". Or they calculate efficiency differently. For sale. Only 1BEUR. For sale. Anyone?Or someone actually had a good idea. It looks nice, short (Like Toyota hybrid motors). Could yield almost a 100 KG saving on the entire car, including battery, cooling etc. Hopefully this is true.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2019, 04:45:46 pm
content: It can only save 100kg if arbitrarily compared to an excessively heavy and/or low efficiency motor.Tesla Model S motor, for example, weights 32kg and provides 270kW (source:https://chargedevs.com/newswire/elon-musk-cooling-not-power-to-weight-ratio-is-the-challenge-with-ac-induction-motors/), providing 8.4 kW/kg. Modern EV motors mostly show similar numbers, Tesla isn't super special.So suddenly the claimed 12.5 kW/kg isn't that much of a breakthrough, after all. It's indeed micro-optimization. Maybe it can shove 20-30kg off the total car weight, including cooling simplifications (maybe 2-3 kg) and battery savings (three percent of a typical 300kg battery would be 9kg off).

author: Domagoj T
author_rank: Frequent Contributor
timestamp: July 24, 2019, 05:31:43 pm
content: I am somewhat bothered by their comparison of peak power instead of continuous. I can't shake the feeling they're hiding something.

author: AndyC_772
author_rank: Super Contributor
timestamp: July 24, 2019, 07:25:54 pm
content: That's completely normal in an EV application, nobody needs or uses full power for long periods.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: July 24, 2019, 07:55:25 pm
content: It seems we are not understanding each other. They are using peak power in comparison. Why when information on continuous power would be more informative? Am I missing something?ELI5 if needed.

author: langwadt
author_rank: Super Contributor
timestamp: July 24, 2019, 08:04:24 pm
content: Quote from: AndyC_772 on July 24, 2019, 07:25:54 pmnot only EV, it only takes maybe 15hp to make a car go 90km/h on a flat road so an ICE is also at afraction of its full power most of the time

author: AndyC_772
author_rank: Super Contributor
timestamp: July 24, 2019, 08:28:11 pm
content: Quote from: Domagoj T on July 24, 2019, 07:55:25 pmIt wouldn't be more informative given the target application. The peak, short term power rating tells you how the vehicle will accelerate under normal road conditions, which dictates the published performance figures for the vehicle in which it's used. Provided the continuous rating is high enough to maintain a motorway cruising speed, it's largely irrelevant.

author: f4eru
author_rank: Super Contributor
timestamp: July 24, 2019, 08:33:05 pm
content: That's a problem for an ICe, because it needs to be dimensioned for the max power, and gets limited average efficiency as a result.As mentioned earlier, for electrics, the compromises are in another field, ratio of maximum speed, vs minimum speed @ max power(achieved with brutal field weakening), and cooling of stator and rotor, dimensioning for speed vs reduction ratio vs volume/weight, which often translate in cost.The axial technology is not new, so does not require licensing (but you can take the opportunity if you are a traditionnal auto OEM).It usually results in fast moving motors with a big diameter, which are not really nice attributes for EVs, so the complete packaging will decide the most efficient/cost effective form of the complete powertrain excluding battery (inverter-software-motor-fixed gearbox-diff-axles)A single component without meaningful integration in a full system will be economically worthless for huge quantities.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2019, 06:30:24 am
content: Quote from: Domagoj T on July 24, 2019, 07:55:25 pmIf we ignore the small sections of unlimited Autobahns in Central Europe where you can drive 200km/h, power required to move a typical passenger car at safe speeds at typical speed limits (<140-150km/h), is just some 30-40kW max. More typically (<130km/h), less than 20kW.Taking over someone driving at 110km/h, in a slight uphill, with a strong acceleration, may require 100kW for 3-4 seconds.The exact numbers are highly personal, but usually people would find an EV with peak motor power of around 100kW, and continuous power rating of around 30-40kW, nice to drive. Note the ratio of about 30-40%. Now, if you build a motor with a 100kW peak rating, the continuous rating is going to be higher than this 30-40kW, the difference between peak and continuous in motor ratings is smaller than the difference between peak and continuous needed on the field.For this reason, peak power tends to be more informative if ithasto be a single number. If you have enough of that, you have enough of the continuous rating as well.But of course, this isn't a proper spec. A proper spec includes a full torque-power curve for continuous operation, and another curve for peak operation, and the peak duration (is it just 10 seconds, or a minute?) must be specified as well.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: July 25, 2019, 07:00:40 am
content: Thanks guys. I never thought of it that way.Can a similar line of reasoning be applied to industrial applications as well?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2019, 07:03:57 am
content: Quote from: Domagoj T on July 25, 2019, 07:00:40 amOf course, but it's completely case-by-case depending on that application.

author: Zucca
author_rank: Unknown
timestamp: July 25, 2019, 07:43:01 am
content: ThanksSiwastajaI really appreciate your way of explaining things.It's a pleasure to read your comments.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2019, 04:31:06 pm
content: Another good comparison is audio amplifiers.  music has a fair dynamic range, especially on percussion, and especially in frequencies the ear is not so sensitive to (nor speakers), bass. Hence 100W is a typical capacity for loud listening (but nowhere near painful, even well into clipping), with adequate headroom for bass drum hits and such. The average power might be just a few watts.A note: commercial FM radio is terribly heavily compressed, partly for technical reasons but partly also for marketing reasons. I don't know offhand how satellite radio or streaming sources compare.Tim

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 25, 2019, 05:28:47 pm
content: Peak is probably the only meaningful figure as avarage is pretty much all down to cooling, and with liquid cooling, avarage isn't going to be far off peak - it's just a case of how much fluid you can pump through it

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2019, 06:10:14 pm
content: You still need quite a lot of cooling, for peaks on the order of seconds duration; especially for a motor that small. (I wonder how/if they deal with the rotor heating due to eddy currents, harmonics or PWM? Is it submerged in coolant?) Losses are quadratic with, well, let's see... copper losses with current, and core losses with voltage (or cubic even, because frequency too). Windage about quadratic with RPM. Output power is proportional to torque and RPM, which are proportional to current and voltage. So losses should always go up faster than power (efficiency decreases monotonically)?I'm guessing real curves are messier than that, though...Anyway, the important part is, if the efficiency is measured at peak (full) output power, the point again about losses is huge. At 90% efficiency, that's 10kW, enough to melt the thing into a puddle in some minutes. At 98%, that's 2kW, not much to worry about -- still enough to want water cooling, but a good strong fan can exhaust that, too. And if the average is much lower (and the temperature is monitored), you could get away with much less intense air cooling, no problem.Heh, it's easily to the point where losses due to copper tempco will be significant, and a good reason to keep temperature lower.Tim

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 25, 2019, 07:03:23 pm
content: Peak power is not really limited by cooling capacity in induction and PM AC machines*, rather, it is magnetic saturation: the stator can only induce so much field into the rotor of an induction machine regardless of how much current you cram through its windings, and, of course, the field strength is more obviously fixed in a PM machine.* - the time you can demand peak power does depend on cooling capacity, of course.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 31, 2019, 02:21:37 pm
content: Wow, can you really get over 8kW from a 1kg electric motor? Or is it 80kW from a 10kg motor?I know they are the same arithmetically, but a 1kg, or a 0.5kg, motor at that power level does sound interesting.Not in a car, but what about in a chainsaw? A big powerful chainsaw like the Stihl 661 drinks 2 stroke, and an electric motor replacement could be a really good idea.Yes, sometimes you are tramping around a wood to fell a tree, but once felled it then needs mechanical handling to extract. So, if you can get a forwarder etc to the tree, then putting a genset on to run the electric chainsaw is simple. The genset will be diesel, so 4-5 times more efficient than the chainsaw.Not mention the reduction in noise, that drives you crazy, vibration, so fingers stay a colour other than white.If using a chainsaw based sawmill then this really could make them so much more cost effective.Any thoughts please, like where to buy one of these motors. I have seen Lynch ones, but quite a long time ago, also quite large.

author: Nauris
author_rank: Regular Contributor
timestamp: July 31, 2019, 05:24:08 pm
content: Quote from: woodchips on July 31, 2019, 02:21:37 pmSure! Just go check specs for brushless rc-plane motors, that is very run of the mill power density there. Some actually claim well past 10 kW from motor that size (at 50000 rpm...)

author: Psi
author_rank: Super Contributor
timestamp: August 06, 2019, 05:21:50 am
content: Quote from: Nauris on July 31, 2019, 05:24:08 pmMy old RC delta wing plane had a motor the size of a D battery but not quite as long And that was rated for 1kW for 10 seconds.i think it was 500W continuous.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 11, 2019, 12:01:45 pm
content: Replacing internal combustion engines in things like chainsaws with modern electric motors is a no-brainer - they have a lot better power density and torque density, both volumetric and gravimetric, and they are probably cheaper to manufacture, too.The reason this still isn't done in full extent is not in the motors, but in energy storage, i.e., the still fairly low energy density of batteries compared to gasoline.

author: f4eru
author_rank: Super Contributor
timestamp: August 13, 2019, 10:35:37 am
content: Chainsaw is the example where the power density including the battery is still a problem because you have to carry the weight.For now, it looks like this :For other applications, the weight/energy ratio might be less of a problem