EV Motor Not Powerful Enough? Make Your Own.

Many of us have tried our hand at the ol’ electric car conversion hack. Yank the engine, throw in an industrial DC or AC motor, and bob’s your uncle. Simple stuff. But if you can’t find just the right motor for your application… why not design and build your own brushless DC motor?

This mind-blowing build is by an electrical engineer who decided to design a 45kW motor (that’s 60HP). That’s not a typo. Design and build a 45kW motor! He has a video series on the design process which includes the CAD and all the calculations he did to make this thing work. Once he had the design complete and ordered the custom parts, he started building it.

In his living room.

We’ve seen lots of cool conversions before, but this project takes the cake. We’ll have to update you guys once he throws it into his EV Opel Agila. And if you can’t wait — check out his YouTube channel, there’s tons of amazing electric motor based projects there.

[via Reddit]

25 thoughts on “EV Motor Not Powerful Enough? Make Your Own.

    1. Looks at the specs for the engines used in the Agila. I don’t know what year the Agila he’s doing the conversion on is, but this *could* be a higher powered engine than what he’s got. He also may be constrained by space. Or it could be a matter of cost vs size, and cost of a DIY 45kW engine is what he can afford to risk.

    2. Well, it’s pretty damn easy to just do another one and double up.

      20 kW is enough to cruise a regular size sedan. 12-15 kW in nice weather on a smooth road. You don’t need the extra power except for accelerations, and a nominally 45 kW motor can be overdriven to 60-70 kW easily for short periods of time because the limit is in overheating it.

  1. Why is this a surprise? Motorcycle guys have been doing the reverse of this for decades. Most motorcycles are sold with a garbage stator and rewinding it with more turns and heavier gauge wire can double the electrical power output. This is pretty close to the same thing. he took an existing motor and re-wound it and made modifications. Now if he cast those metal parts in his living room with a home forge, I’d be far more impressed.

    Motors are simple devices, what he is doing is a normal thing that many people before him have done. It’s a custom rebuild that is very interesting. Anyone here can do this kind of stuff with a little reading and a LOT of patients.

    1. It’s not a “rebuild”, since he designed and laser-cut all the stator/rotor laminations himself.

      Other than that – yes – it’s not actually very difficult to make a BLDC motor. The difficulties come in optimizing the geometry and materials for the particular purpose.

      Many of those re-wound motors are also completely misunderstanding the point. Electric motors are inefficient at producing high torque at low speed – they’re efficient at producing high power at high speed. If you wanted to get more torque/acceleration/power at low speeds, you should use a reduction gear and sacrifice your top speed, because then your batteries would last about 30% longer than by simply re-winding the stator for higher magnetic flux.

      1. Also, rewinding the stator with more turns per coil increases the inductance of the stator, so your top speed drops anyways; impedance is frequency dependent, so as the drive frequency increases the motor starts to draw less current and puts out less power. You essentially shift the peak power to a lower RPM.

        So while you gain torque and power output at low speeds, you lose power/torque at high speeds. You could do the same simply by changing the final gear ratio of the bike without adding the extra weight of all that copper wire, which would let the motor run faster and more efficiently as it is.

          1. It’s not very different for PMDCs. The main point is that below some frequency the impedance of the motor is not sufficient to keep the stator current from saturating – typically by hitting the output current limits of the controller – and once that happens you start to waste power.

            As long as the current keeps growing, energy is being stored in the magnetic field, and that energy gets transmitted to the rotor. When the current stops growing – when it hits coil resistance or controller limits – then you’re simply heating the copper without adding any energy to the field, and the longer you keep doing that during the cycle the lower your efficiency is going to be. At the ultimate low frequency, trying to maintain static torque is going to have zero efficiency because the rotor does not turn, therefore it’s not doing any work and there’s power input but no power output.

            As a rule of thumb, VFDs become useless below about 25% of a motor’s design speed, and if you need to run the motor that slow, you should either double the number of poles or add a reduction gear. That however doesn’t mean that people won’t try, and most commercial electric cars for example basically sacrifice efficiency for not having to include a simple two-speed gearbox.

      2. He did not laser cut them himself, he got a local shop in Romania which only had M330-50 grade steel, with higher losses. If he was cutting it himself I’m sure he would have used M250-50, M235-35 or something else along those lines.

        1. That’s because, for small orders like Iulian’s, they didn’t had another materials on stock. He accepted to use what they had on stock. I know him and he is not “bullshitting”. Cheers!

      3. For a little shameless promotion. https://youtu.be/DpdHRiAKkAI

        That’s a 3 speed transmission with no hydraulics for the shifting elements. Ratios were 2.71, 1.56 and 1:1. It’s powered by a Remy HVH250 motor on a 320VDC bus with a Rinehart Motion Systems PM100 inverter. Using simulations that took the EPA drive cycle the transmission could improve battery to wheel efficiency by about 10%.

    2. In the 1960s, slot car racing was a craze, and rewinding motors was done by almost everyone to get more power out of them. Usually, we rewound with fewer turns of heavier gauge wire – fewer turns means less magnetic lines of force (well, not actually, but you know what I mean) but the lessened resistance of fewer turns allowed a lot more current, which made up for it.

  2. From the article:

    “Delta connection will give you higher power per cooper amount, higher RPM, higher current, lower phase voltage.”

    A delta connected winding will be resonant to the third harmonic of the drive frequency because three phases in a delta will be 1/3 cycle apart in phase, and the third harmonic is a full cycle apart, meaning the nodes of the frequency happen at the connection points and the voltages cancel – and the third harmonic current is basically short-circuited around all the coils.

    This is basically a good thing and a bad thing, because third harmonics (and 6th, 12th…) caused by transient loads and non-sinusoidal input waveforms don’t get out of the motor – the controller gets loaded at the fundamental frequency only.

    It’s a bad thing because these harmonic currents dissapate as heat and may cause the stator to go into saturation. When that happens, when the motor starts to dissapate the third harmonics in a non-linear fashion, the distortion causes the power to reflect back to the source in odd harmonics, or 5,7,9… times the fundamental frequency.

  3. This is an excellent build! Such attention to detail.

    I own a VW fox of 2008 vintage with the 1.2 three pot. This motor has 5 more hp and probably scads load more torque than my car does. 55hp and 80 ft/lb of torque or 41kW and 108Nm respectively.

    I would look at converting mine to electric if it wasn’t for battery tech not being in the right place and price point for me.
    That and I think a 20-60kW inboard motor on each wheel could make for some serious poops and giggles once there is a power source available that can provide that kind of power in a small car cheaply and safely without adding more weight than the original petrol engine. As well as providing the same range as a tank of petrol currently does.

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