36V Amp Challenge

[2old]

I rebuilt a dilapidated, yard find cruiser with 36V Amp DD motor, 22 amp controller and on/off/throttle. The bike and motor were refurbished, and the system runs great on a bike stand, but won't accept full power when I'm on it unless I accelerate very slowly. Also, occasionally when the throttle is released, the motor still provides some power and I need to use the "off" switch (the 36V battery had been used effectively in a mid-drive). Any ideas?

 

[glennb]

Doesn’t sound like you’d be tripping the BMS current limit, because you’d hit that at full throttle regardless of quickly you accelerated.

Have you tested it up hill?

 

[2old]

No hills yet, just flat areas; I can hit full throttle on a bike stand and it accelerates fine. Normally it would seem (to me) like a battery problem except sometimes when the throttle is released, the bike still has power so I'm wondering whether the switch/throttle could be faulty..

 

[glennb]

Doesn’t sound like throttle issue either.

On the stand you’re pulling very little current.

Can you describe “won’t accept full power” in more detail?

 

[E-HP]

The bike and motor were refurbished, and the system runs great on a bike stand, but won't accept full power when I'm on it unless I accelerate very slowly.

How many watts is it drawing when on the stand running full speed?

 

[amberwolf]

I rebuilt a dilapidated, yard find cruiser with 36V Amp DD motor, 22 amp controller and on/off/throttle. The bike and motor were refurbished, and the system runs great on a bike stand, but won't accept full power when I'm on it unless I accelerate very slowly.

What specifically does "won't accept full power" mean? What exactly does it do when you apply full throttle (assuming that's what you mean by full power).

If it isn't shutting completely off (no power at all) then it's not a battery problem, at least not one where the BMS trips.

If it's noises, incorrect motor behavior, etc., then it's probably a phase/hall wiring combination problem; easiest to use the self-learn function fo the controller if it has one to fix this.

Also, occasionally when the throttle is released, the motor still provides some power and I need to use the "off" switch (the 36V battery had been used effectively in a mid-drive). Any ideas?

That usually means the throttle is not going to zero output (normally around 0.8v). That most often happens from mechanically stuck throttles, and second most often from a bad ground wire / connection from throttle to controller.

 

[2old]

Doesn’t sound like throttle issue either.

On the stand you’re pulling very little current.

Can you describe “won’t accept full power” in more detail?

When I depress the thumb throttle fully on the stand, no problem; on the bike the motor cuts out. I need to feather the throttle slowly, and (usually) it will eventually achieve full power.

 

[2old]

How many watts is it drawing when on the stand running full speed?

It has the simplest on/off switch with throttle only; no display.

 

[2old]

What specifically does "won't accept full power" mean? What exactly does it do when you apply full throttle (assuming that's what you mean by full power).

If it isn't shutting completely off (no power at all) then it's not a battery problem, at least not one where the BMS trips.

If it's noises, incorrect motor behavior, etc., then it's probably a phase/hall wiring combination problem; easiest to use the self-learn function fo the controller if it has one to fix this.



That usually means the throttle is not going to zero output (normally around 0.8v). That most often happens from mechanically stuck throttles, and second most often from a bad ground wire / connection from throttle to controller.

When I depress the throttle fully, the motor cuts out. As above, I need to "feather" it When I'm on the bike). On the stand, no problem.

 

[amberwolf]

Is it just the motor cutting out, or does the system power off?

For the former, there are several possible issues. It could be the battery sagging so far it drops below the controller LVC. Could be the phase/hall combo is wrong so the controller current limit is vastly exceeded and it stops trying to run the motor to protect itself. Etc. If it only cuts out, is there any other symptom at all other than the motor ceasing to provide forward motion?

For the latter it's usually the battery BMS shutting off due to an internal pack limit being exceeded.

 

[2old]

Thanks everyone; AW, the motor cuts out, but doesn't shut the system down. I guess the battery is at fault (as suspected initially). It worked well with a mid-drive a couple of years ago and has been maintained at 30% - 80% SOC during the interval, but I guess it's toast.

 

[Chalo]

If the BMS were getting tripped, the bike would shut down entirely. So it's not that.

My best guess is that you are getting enough voltage sag under load to trip the controller's LVC. And that's not a good sign for the battery's health. Does it cut off the same way, under the same load, with a full battery as with a partially discharged one? Do you have a way to measure system voltage in real time?

If you have any way to try it with a different, known good battery, that would be a really valuable comparison. If another battery cures it, then you know your old battery is bunk. And if the problem persists anyway, then you can divert your investigation to the other parts of the system.

Closely inspect the battery and phase plugs for signs of arcing, heating, or looseness. Any such problems could result in the symptoms you report. And if that's it, it would be a very cheap and easy fix.

Another possibility is that you have a false positive phase/Hall combination and the thing is drawing excessive current until it cuts out. An ammeter or watt meter would be the best tool to assess this, but if the unloaded wheel speed is unusually fast or the plugs and wires quickly become hot, those would be other indicators.

 

[amberwolf]

Thanks everyone; AW, the motor cuts out, but doesn't shut the system down. I guess the battery is at fault (as suspected initially). It worked well with a mid-drive a couple of years ago and has been maintained at 30% - 80% SOC during the interval, but I guess it's toast.

If you haven't tested the battery voltage during the fault, to see how much it drops, to then compare to the LVC marked on the controller, you don't know that the battery is the problem--it could still be one of the other issues. Chalo covers the ones I can think of off the top of my head.

 

[2old]

It turned out that the battery was the offending parameter, and the bike runs perfectly with a new one. While I was waiting for it, I removed two and a half feet from the throttle/switch and motor wires. Thanks again for all the help.

 

[999zip999]

The biggest deals of wire are the length of your phase wires and the length of your battery plus and minus those are what you want to keep as short as possible.
As the phase wires can heat up. Also if you have those cheap bullet connectors those can heat up put your hand on it.