Hub motor stops and go under high load

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Jérôme.BDX   100 µW

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Hub motor stops and go under high load

Post by Jérôme.BDX » Jul 25 2021 5:39pm

Hello ! I've got a problem with my motor that I can't solve by myself.

It's a 350W motor that I run sensor less with a 48V 26 amps rated current controller with SW900 display.
The battery is 48v and able to output 1000W

My problem is that at around half speed and under high load, the motor completely stops and is free to spin for less than a second and then goes back to work until it meets high load again (usually a second later if the throttle is kept as it was)

It is not caused by the battery LVC as I tried with no BMS,
I think it is not caused by the controller LVC as I set it to the minimum via the SW900 display
I set the current limit to the maximum via the SW900

For sure the the motor is limited in power and torque but should stop accelerating or decelerate instead of going to an instantaneous complete stop.

Have you hot an uh suggestion to improve the behavior of the motor?

Keep in mind that I don't mind overpowering the motor as my use would be for really short period of time with no overheating problem.

Thank you!
Last edited by Jérôme.BDX on Jul 26 2021 2:43am, edited 1 time in total.

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Chalo   100 GW

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Re: Hub motor stops and go under high load

Post by Chalo » Jul 25 2021 7:02pm

What is your controller's amp rating?

I recommend adding a voltmeter to your setup so you can see what the instantaneous system voltage is.
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Jérôme.BDX   100 µW

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Re: Hub motor stops and go under high load

Post by Jérôme.BDX » Jul 26 2021 2:42am

My controller amp rating is 26amps, and max amp is 45 amps.

Ok, I'll test with a voltmeter :) I guess you suggest it could be because of a voltage drop of the battery?

Thanks!

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Chalo   100 GW

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Re: Hub motor stops and go under high load

Post by Chalo » Jul 26 2021 2:03pm

Jérôme.BDX wrote:
Jul 26 2021 2:42am
My controller amp rating is 26amps, and max amp is 45 amps.

Ok, I'll test with a voltmeter :) I guess you suggest it could be because of a voltage drop of the battery?
That's my guess. But a trustworthy measurement is better than anybody's guess.

1000W for a 48V nominal battery is about 20A. Aging or previous damage can reduce a battery's current capacity, and battery vendors aren't always honest about what they're selling anyway.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Jérôme.BDX   100 µW

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Re: Hub motor stops and go under high load

Post by Jérôme.BDX » Jul 26 2021 3:11pm

I just checked the battery voltage of my 48V 1000W battery with the same setup and it only dropped from 52V to 50.5V. As it is still above the nominal voltage, chances are the battery is not the problem here.
Plus I set the controller LVC to 30V(way below)

I also tested my setup lowering the PAS level(It only lowers the maximum speed) and it worked fine but I can't reach the speed intended. Going on low pass level full throttle and slowly increasing it to the highest PAS level seemed to work. But is not convenient..

Thank you for your answer!

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E-HP   100 MW

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Re: Hub motor stops and go under high load

Post by E-HP » Jul 26 2021 6:53pm

I'd check your phase wire connectors to make sure none are loose.

Jérôme.BDX   100 µW

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Re: Hub motor stops and go under high load

Post by Jérôme.BDX » Jul 27 2021 4:50am

I just checked every connection from phase wires to throttle and none seems faulty.
I can't make them any stronger.

The problem could come from the controller itself that is made to run slightly higher power motor.
Could it be that the controller detects too much resistance on the windings(because of small motor) at some point and goes in an error mode? Or fail to measure back EMF, then fails to time the powering of the phases?
Do you think this could be the reason? And if yes, have you got any clue to reduce the problem? (Changing the motor for a more powerful one will be the last solution)

Thank you!

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neptronix   100 GW

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Re: Hub motor stops and go under high load

Post by neptronix » Jul 27 2021 7:02pm

Jérôme.BDX wrote:
Jul 26 2021 3:11pm
I just checked the battery voltage of my 48V 1000W battery with the same setup and it only dropped from 52V to 50.5V. As it is still above the nominal voltage, chances are the battery is not the problem here.
Was that 1.5v drop while you were under a heavy load.. IE actively watching the meter while you start the bike from a stall, climb a hill, etc, where load peaks?

What battery do you have?
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Jérôme.BDX   100 µW

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Re: Hub motor stops and go under high load

Post by Jérôme.BDX » Jul 28 2021 4:39am

Hello neptronix
The 1.5V drop is an instantaneous drop on pretty heavy load yes, actively watching the voltmeter.
The motor already had some speed.

So your reply made me think I could test it on a bench to apply even bigger load. I just tested It (braking the motor to a complete stop on full throttle) and I measured a slightly bigger instantaneous maximum voltage drop of 3.4V from 53V to 49.6V. But as it is still higher than nominal voltage, I guess it is still perfectly fine.

Plus the problematic behavior doesn't happen at the lowest voltage but instead at around 1 or 2v of voltage drop when it reaches about half speed. And there no cut off on the battery side when the problem occurs.

And a quick precision on the problem : It's different from a step slip as it takes some time to go back to full throttle (it follows again the throttle ramp up that takes about a second)
To sum up, it looks almost exactly like a low voltage cut off, but it doesn't happen when I pull the max amps nor when the voltage is the lowest.

And for my battery, it is a Li ion 1000W 48V 10Ah with a 60A BMS (It will hopefully never reach 60A 😅)

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