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Dec 11, 2019, 06:16 PM
Drew RT
Thread OP
Discussion

Rewinding Hoverboard motor questions


Hello all,

I'm looking at repurposing a used hoverboard motor as an alternator. It has 27 coils and 30 magnets and is rated at 350W. I bought a batch of 4 the same to experiment with. I'm looking to maximize low voltage output, ideally aiming to get 12V at around 60-100 rpm.

On opening, it appears to be wound 5 in hand, and star configuration AaABbBCcC AaABbBCcC AaABbBCcC with about 0.5mm wire. I haven't unwrapped a coil, but it looks to be between 3 and 5 turns per tooth, but it may be more.

There are some things I find a bit surprising. The 5 in hand bundles of 0.5mm magnet wire terminate into a single soldered 16 or 18 G stranded copper wire. These 3 16 or 18 G wires are what is lead out of the motor.

This seems weird and very light, but maybe because they are trying to get it all out through the hollow axle? Along with the hall sensor wires, it's pretty tight, but I might go to a larger axle.


Right now at about 400 rpm I get about 10 -11V and 3A (measured after rectifier), with a 1-4 ohm load, and with a 10 ohm load 13-14V at 1.25A

If I were to rewind this, instead of 5 in hand, 2 in hand, and double the number of wraps, I should get roughly double the volts per rpm?
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Dec 11, 2019, 07:21 PM
Registered User
funny you say alternator instead of generator have me searching the definition. word nerds be warned you can call a generator an alternator it seems.

why would they use 30 magnets instead of the closer to 27...28 or cheaper 26. maybe you miscounted?

I bet they went small on the leads cause of esthetics and simplicity with the design in the axle. maybe even pegging the leads down with glue would transfer heat of them better, with the something.


what you do to put power in and what you do with it at other end?
Dec 11, 2019, 09:45 PM
Drew RT
Thread OP
Quote:
Originally Posted by Hummina
funny you say alternator instead of generator have me searching the definition. word nerds be warned you can call a generator an alternator it seems.
I'm using this in a wind turbine project. Since it produces alternating current, it's an alternator? Or I guess PMA. I thought generators produce DC?


Quote:
Originally Posted by Hummina
would they use 30 magnets instead of the closer to 27...28 or cheaper 26. maybe you miscounted? .
I have trouble with dyslexia, so I write numbers on things to minimize miscounting. In this case I definitely counted a 27 pole stator, and 30 magnetic poles.

It's beyond my knowledge as to why they would use a 27coil to 30 magnetic pole ratio. I had thought that it was important to stick to the 4 magnets 3 coils ratio, or at least factors of 4 and 3, but clearly these motors work, so....


Quote:
Originally Posted by Hummina
bet they went small on the leads cause of esthetics and simplicity with the design in the axle. maybe even pegging the leads down with glue would transfer heat of them better, with the something.
Could be, also the whole system is maybe designed more for short intermittent heavy loads, with current limiting, so they don't need more?

Quote:
Originally Posted by Hummina
you do to put power in and what you do with it at other end?
I'm hoping with heavier wire and a winding with more turns of less in hand, to get more volts at lower speed.
Dec 11, 2019, 11:04 PM
Registered User
Quote:
Originally Posted by drewrt
I'm using this in a wind turbine project. Since it produces alternating current, it's an alternator? Or I guess PMA. I thought generators produce DC?


Yes was confused

I have trouble with dyslexia, so I write numbers on things to minimize miscounting. In this case I definitely counted a 27 pole stator, and 30 magnetic poles.

I always see the magnet number as close as possible to the teeth number

It's beyond my knowledge as to why they would use a 27coil to 30 magnetic pole ratio. I had thought that it was important to stick to the 4 magnets 3 coils ratio, or at least factors of 4 and 3, but clearly these motors work, so....




Could be, also the whole system is maybe designed more for short intermittent heavy loads, with current limiting, so they don't need more?

I know nothing about it just guessing u could maybe make the motor a bit better thermally that way.



I'm hoping with heavier wire and a winding with more turns of less in hand, to get more volts at lower speed.
I think more turns and less in parallel to produce higher voltage. I think this because higher kv motors produce less backvoltage for a given rpm.
Last edited by Hummina; Dec 12, 2019 at 06:34 PM.
Dec 12, 2019, 06:31 PM
Registered User
http://www.bavaria-direct.co.za/scheme/calculator/

Plugging in the 27 w 30 v 28....the 28 shows slightly better winding factor and also many more cogging steps equating to less cogging torque ( which I believe will be there unpowered as a drag and also to some degree also a drag when powered and called something else I forget.) I wonder why they chose that combo.
Dec 14, 2019, 12:09 PM
Drew RT
Thread OP
This has worked better than I expected. I imagined that by joining the wraps in series in such a small space I’d for sure missconnect something, but apparently my eye strain headache is worth it. It generates high voltages at very low speeds, much higher than before. I’ll do a longer write up about it and post it, after I try it with some known loads to see what sort of efficiency I’m getting. Right now, having reconnected the 5 in hand winding, (5 parallel strands) to 5 in series, I’m getting 12-15V at about 60 rpm. Previously it was 12-15V at 400rpm. It seems to me that I’ve also increased the resistance by 5x, so the efficiency might drop. This is actually more V/rpm than I needed. I might reconnect it in Delta, to lower voltage, increase current capacity. Right now with only 3 ends of 20G wire, I figure that 6 amps is all it can take. What I had been thinking is that I should rewind this motor with 2 in hand 22G 10 turns.
Dec 14, 2019, 01:07 PM
Registered User
Wonder if u could get more copper in w a single strand.
What do u do to turn the generator and what do u do with the power out the other end?


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