# How to count number of poles?

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Hello, I have a ATV BLDC motor and am adding a new controller (Kelly KLS6030N). The controller needs to know the number of poles in the motor but the motor has no useful information on it and the ATV vendor is not helpful.

I recall there is a way of counting the number of cogs a motor makes when it is rotated manually a single rotation and that number can be used to calculate the number of poles. If that is the case, could anyone kindly tell me what the conversion formula is? BTW, the number of cogs I count for my motor is = 60.

TIA for any help...
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#### 57Chevy

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can you see how many rotor magnets there are? Can you connect an oscilloscope and work out the number of voltage pulses per rotation? An analog voltmeter could work at a pinch if you turn it very slowly. You could also try shorting two phases (motor disconnected from inverter) and seeing how many 'stiff' sections per rotation there are. I've never tried that but it could work.

Some inverters want to know pole pairs which is half the rotor magnets.

#### ratchet6900

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can you see how many rotor magnets there are? Can you connect an oscilloscope and work out the number of voltage pulses per rotation? An analog voltmeter could work at a pinch if you turn it very slowly. You could also try shorting two phases (motor disconnected from inverter) and seeing how many 'stiff' sections per rotation there are. I've never tried that but it could work.

Some inverters want to know pole pairs which is half the rotor magnets.
I would have to remove an disassemble the motor to count the magnets as it is totally enclosed. But I understand from what you are saying that the number of poles = the number of magnets(?).

I could try the other two methods but how do you convert those results to number of poles? I'm just guessing but when I count 60 cogs with no phase wires connected, the number of poles might be 60 / 3 = 20 (since it is a 3 ph motor)?? And, with two phases shorted, the number of stiff sections = number of poles?

In my case, I think the controller wants number of poles (the documentation refers to it as "real motor poles"). The default is = 8 and the allowable range is 2 to 128.

Again, TIA!

#### brian_

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I would guess that you might feel one notch per combination of pole face and phase winding (or just one of the windings when that one is shorted) - just as you're expecting - so I agree that 60 of them in a 3-phase motor suggests 20 poles or 10 pole-pairs (and you would feel the 20 poles with one phase shorted) but that seems like a high pole count.

Although you haven't been able to get any information from the vehicle or its manufacturer, someone else might have... what ATV is this?

Even though there are no helpful labels, can you share an image of the motor, in case someone recognizes that, even from another application?

#### ratchet6900

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I would guess that you might feel one notch per combination of pole face and phase winding, so 60 of them in a 3-phase motor suggests 20 poles or 10 pole-pairs, but that seems like a high pole count.

Although you haven't been able to get any information from the vehicle or its manufacturer, someone else might have... what ATV is this?

Even though there are no helpful labels, can you share an image of the motor, in case someone recognizes that, even from another application?
Hey, that's my understanding of it too. Twenty poles seems high alright but I have no direct experience to base that on. Based on what the Kelly documentation says however (allowable config values from 2 to 128) maybe not. I'm going to have to verify from Kelly though if "real motor poles" means poles or pole pairs.

The ATV is sold by Venom Motor Sports (Canada), model E-Grizzly, 1500W. It has an 1500W controller but Venom says the motor is 3000W. Good idea on the motor image - I'll take one and post it later.

Thanks!

#### 57Chevy

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my blind guess is that it is a 10 pole, 12 slot motor. 60 cogging torque events per rotation would be about right (5 pairs x 12 slots)

#### remy_martian

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Tell the controller it has 4 poles. Command 100 rpm. Measure the speed of the motor with that setting.

#### brian_

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The ATV is sold by Venom Motor Sports (Canada), model E-Grizzly, 1500W. It has an 1500W controller but Venom says the motor is 3000W.
There's one image on the product web page which shows the motor:

Unfortunately the motor looks pretty generic, lacking distinctive appearance details, but maybe someone will recognize the motor or the ATV anyway. For instance, I have no personal experience with this or any similar motor, but it looks like it might be this "BM1424HQF-14BA" in Alibaba... but even that listing doesn't include the pole count. There are many similar-looking motors, and I just stumbled across one which has a rotor image and another for a similar motor with rotor and stator images, which show only 8 poles (and 24 stator slots). Two motors could be externally identical and have different pole counts.

The web site is really short on technical detail, but that makes sense, since Venom probably doesn't build these, but just gets them from a manufacturer in China. The axle-mounted motor is a simple and effective design.

I just realized that I've been finding 1500 W motors, but I wouldn't be surprised if, given the 1500 W controller, that the 3000 W value is a peak rating and it could also be listed as a 1500 W motor. Without something marked on the motor, it's never going to be clear.

#### ratchet6900

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Hey Brian, thanks for all the info and the image of the motor! I also looked around at AliExpress and found this one which looks v similar in Watt rating and dimensions.

Unfortunately no pole info given but based on 57chevy's comments, I guess I may just start with 10 poles, see how it works (hoping anything won't get screwed up if the pole # is incorrect) and experiment with a larger or smaller number.

I also was able to come up with the ATV manufacturer (Yongkang Eagle Motor, Model E-A07). I just emailed them so they might prove to be helpful.

And yeah, I'm a bit puzzled too on why a 1500W controller would be mated with a 3000W motor - maybe they just used what they had available at the time(?). Anyhow, the new controller I bought is rated for 3000W motors so I hope it doesn't turn out to be way too big.

Dang it though, I saw a YouTube about a year ago on figuring out the number of poles by cog counting but am unable to find it now.

#### 57Chevy

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put your max amps to 50 or some small amount for testing. It will either run or not and if the amps are limited then there is little chance of damaging things. A Hall sensor motor won't run if the pole count is wrong. Sensorless will just run at the wrong speed

#### brian_

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And yeah, I'm a bit puzzled too on why a 1500W controller would be mated with a 3000W motor - maybe they just used what they had available at the time(?). Anyhow, the new controller I bought is rated for 3000W motors so I hope it doesn't turn out to be way too big.
There are a few possible reasons for the mismatch, including ratings which apply under different conditions so they're not directly comparable. One possibility is that they chose the the motor to deliver the required torque (with the gear ratio of the transmission), and are not using high enough battery voltage to reach the full rated power of the motor.

#### ratchet6900

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put your max amps to 50 or some small amount for testing. It will either run or not and if the amps are limited then there is little chance of damaging things.

OK, I will do that.

A Hall sensor motor won't run if the pole count is wrong. Sensorless will just run at the wrong speed
Ah, I was wondering what would happen. What to do, start with best guess and ramp pole number up or down until it runs?

I also wonder what happens when the Identification Angle procedure is run (if the pole count is wrong)? What does that procedure do anyhow? The Kelly docs say how to do it but no explanation of what it does.

BTW, the vendor (Venom Motor Sports) insists the number of poles = 3. I've tried to tell them that can't be correct and will talk to their tech in person on Monday. I think they are confusing poles and phases.

#### ratchet6900

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There are a few possible reasons for the mismatch, including ratings which apply under different conditions so they're not directly comparable.
Yeah, that would not surprise me. One thing that annoys me about the Kelly controllers is that they specify continuous and peak amps for each controller but not wattage so it's not evident what motor wattage is compatible. The amp figures apparently apply to the phase side of the controller so one cannot simply multiply amps by battery voltage to get watts. Since my existing controller is rated at 1,500W and I get more than adequate acceleration & speed from it, I thought a smaller controller would work fine but Kelly said no to it without offering an explanation as to why.

I also checked out a reseller in Lithuania - they recommend a smaller Kelly controller:

Note that the recommended motor size is 3 to 5 KWs. I asked Kelly about it however and they said it is too small so go figure...

One possibility is that they chose the the motor to deliver the required torque (with the gear ratio of the transmission), and are not using high enough battery voltage to reach the full rated power of the motor.
Yes, that sounds plausible alright.

#### 57Chevy

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the vendor (Venom Motor Sports) insists the number of poles = 3.
It could be three pole pairs, i.e. 6 poles, but I'd guess that you are right, poles and phases are confused in translation.

The angle setting routine will fail of the pole count is wrong and you won't be able to run it without doing the angle. You might just have to shotgun it using the angle setting function on low amps

#### ratchet6900

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It could be three pole pairs, i.e. 6 poles, but I'd guess that you are right, poles and phases are confused in translation.

The angle setting routine will fail of the pole count is wrong and you won't be able to run it without doing the angle. You might just have to shotgun it using the angle setting function on low amps
Yes, they may be talking about pole pairs. I will talk to their tech this PM and try to get clarification.

Fany says the same about the angle procedure - start with the default pole value of 8, try it and adjust if necessary. He also says if I use a fairly low current value, no harm will result.

Still haven't heard from the manufacturer but not expecting much as I tried to contact them a few months ago with another question but received no reply.

I'm still a bit mystified as to how others have dealt with this situation. The number of poles seems not to be readily available at least as far as I can tell by looking at advertising for other BLDC motors. Is it a value typically included on the motor faceplate or available from some other source??

#### cricketo

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Is the number of poles the only thing strictly necessary for motor characterization ? On the serious controllers they want to know stuff like inductace, back emf... without automatic characterization it becomes an impossible task to have a mystery motor setup. Otherwise just open the thing and inspect the magnets

#### ratchet6900

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Is the number of poles the only thing strictly necessary for motor characterization ? On the serious controllers they want to know stuff like inductace, back emf... without automatic characterization it becomes an impossible task to have a mystery motor setup. Otherwise just open the thing and inspect the magnets
AFAIK the things you strictly need to know (at least for the Kelly software) are voltage, watts, sensor type and number of poles. The first three are easy - it's the number of poles that seems to be a mystery in my case and it is necessary for the angle ID procedure to work.

Yes, opening the motor is an option - trying to avoid that though as it would have to be dismounted from the differential/axle as well and I've never done any of that (probably easy to take apart but hard to get back together properly?). I think for now I'll go try it with the default number and see if it works method.

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