[Mike N]

So here's my issue. I'm occasionally losing power when I exceed 60 amps on my electric motorcycle. My gauges stay on but I have to turn the key off and back on to regain power. I'm not sure if this is a battery issue, a controller issue, a solenoid issue, a motor issue, wiring, or something else entirely. Maybe heat?

I've got a homemade electric motorcycle that's running a 48 volt Mars Electric/Motenergy brushless motor, a Kelly KBL brushless motor controller KBL48201, and a YX YH DC ternary lithium battery pack running at 48 volts (54.7 charged) and 35 amp-hours. The controller is rated for 200 amps for 1 minute and 100 amps continuous. The battery can output 50 amps continuous and 100 amps for short bursts. This seems to happen when going downhill or very fast on a long, straight stretch. I'll be twisting the throttle to get the amp and speed up and then I'll let off. When I go to turn the throttle again, no power.

Any thoughts? Any help with be appreciated.

Mike N

 

[andrew*debbie]

I've got two guesses.

Heat related component failure.. The motor controller is the obvious one but anything that can turn off from overheating is suspect.

Heat related open circuit. When a connection gets hot it goes open. Did you use terminals for all connections? Check all the connections are tight and clean.

 

[Duncan23]

Here's another guess if it only happens when going fast (and it happens in circumstances like downhills that don't require constant high load):
The motor/controller thinks you are over-revving the motor and shuts down to protect itself (or because it is confused as to what the rpm sensor is saying). Maybe worth checking your gearing and how fast the motor is spinning at the point where it cuts out?

 

[Mike N]

I've got two guesses.

Heat related component failure.. The motor controller is the obvious one but anything that can turn off from overheating is suspect.

Heat related open circuit. When a connection gets hot it goes open. Did you use terminals for all connections? Check all the connections are tight and clean.

I thought about this actually! I did two things to try and remedy this. I installed a 12 volt case fan on the controller and one on the battery box; both powered with a 48 volt to 12 volt DC to DC converter. This is the same converter that I use for my lights and turn signals. I also have some aquarium thermometers, which are just LCDs with a wire and a metal sensor at the end, attached to the battery and the controller. These fans definitely lower the temps. However, it still seems to do this out of nowhere.

I'm increasingly thinking that it isn't temp related though. I'm in Kentucky and our temperatures fluctuate a lot. It was in the 80's the other day but it could also be in the 50's and even the 40's at night. I haven't put my jackets up yet, let say that. I was convinced for a while that it was all due to temperatures because I didn't see it for a while. I changed some wires recently and updated some things but I'm very careful to watch what I'm doing and make good connections.

I also neglected to mention that the controller has thrown up some error codes; mostly just one but occasionally two. It was late when I first posted and I forgot. This is how they are listed.

3,1 ¤¤¤ ¤ Frequent reset: May be caused by over-voltage, bad motor intermittent earthing problem, bad wiring, etc.

3,2 ¤¤¤ ¤¤ Internal reset: May be caused by some transient fault condition like a temporary over-current, momentarily high or low battery voltage. This can happen during normal operation.

The 3,2 error code, I've seen off and on for a while. Even back when I had some old deep cycle lead-acid batteries. It was rare though and I simply backed off the motor and battery current in the settings. I guess this one always confused me though. The controller can handle 100 or so amps continuous and is supposed to be able to run up to around 200 degrees F before shutting down (it never gets that high) and the motor can handle around the same 100 amps continuous. The controller is by no means the highest amp model (it was a money thing at the time) but it can still handle a lot of amps.

The 3,1 error code just confuses me. It doesn't happen as often as the 3,2. I only noticed this one recently. I don't think it's getting overvolted. It's a 48 volt controller that can handle up to 60 volts in the settings to allow for when the battery is fully charged (my lithium pack charges to around 54.6 volts when fully charged) and I've got the low voltage set to around 30 volts so that it has some wiggle room if it really needs to dip for a second but not low enough to damage the battery by over draining. The bad wiring? I don't think that's it but I'll check it again. The intermittent earthing problem!?!?! I mean, I don't even know. I tried to look it up as it related to EVs but I haven't seen much.

 

[Mike N]

Here's another guess if it only happens when going fast (and it happens in circumstances like downhills that don't require constant high load):
The motor/controller thinks you are over-revving the motor and shuts down to protect itself (or because it is confused as to what the rpm sensor is saying). Maybe worth checking your gearing and how fast the motor is spinning at the point where it cuts out?

I recently installed an electronic tachometer just to see what the motor was running at. According to the tac, the motor isn't spinning more than 2000 to 2500 RPMs. From what I've read, the Mars PMSM Brushless Motor ME0201013001 is capable of running up to 4000, maybe even 5000 RPM. I don't know how accurate the tac that I installed is though. I think it's accurate but I'm just not sure. It definitely cuts out only when I'm already going very fast (fast for this bike given the 48 volt pack, the 48 volt controller, the weight of the bike, which is heavy, and my fat behind, which is also heavy). I'll be pushing it to 65, 75, 85 amps and then let off the Magura throttle and when I go to hit the throttle again, there's nothing. I feel like it's got to be a controller issue. It doesn't like something I'm doing. Is it possible that I need a higher amp controller?

 

[metastable]

What’s your low volt cutoff setting?

 

[metastable]

I suspect your battery management system cuts off the battery briefly when you’re pulling a lot of battery amps, and that triggers the motor controller’s low volt cutoff. If you have a battery current limit setting in the motor controller settings I’d suggest reducing it to below 50 amps. You can leave the motor current setting around 100 amps. The controller does a voltage change between the battery and motor (lowering the voltage and increasing the amps like a buck converter) so your motor current limit setting can safely be higher than the battery current limit setting without endangering the battery — this gives better acceleration at low rpms.

 

[andrew*debbie]

3,1 ¤¤¤ ¤ Frequent reset: May be caused by over-voltage, bad motor intermittent earthing problem, bad wiring, etc.

A cooling fan isn't going to fix bad wiring.

You might have an iffy connection that heats up at high current. It doesn't take long for something to get hot at 60Amps.



It could also be the voltage drop gets too large and that causes the fault.



0.1 ohms at 60A is a 6 volt drop. Earth (ground) connections are the ones that often get overlooked. Earth is just as important as the positive wires. Are you using the frame of the bike for earth / ground?

What kind of connectors are you using? Do you have the tools for the connectors? The tools can sometimes be crazy expensive but they make a difference.

 

[metastable]

I ran a simulation of different motor/battery current limit settings assuming you have it geared for ~35mph top speed...

^With 100a motor limit / 100a battery limit controller you have the best acceleration performance (green line, bottom left chart), but above 15mph, full throttle pulls more than 50a from the battery (yellow line, bottom right chart)...

With 100a motor limit / 50a battery limit settings, you have the same acceleration as 100/100 up to 15mph, then the thrust & acceleration starts to decrease above about 15mph to keep the battery current under the 50a limit setting. Battery current at full throttle reaches 50a at about 15mph.

With 50a motor / 50a battery limit settings, acceleration at all speeds is reduced by half from 100/100. Battery current (yellow line, bottom right chart) does not approach 50a until you reach ~35mph.

 

[Mike N]

What’s your low volt cutoff setting?

I have the low voltage cutoff set to 30 volts.

 

[Mike N]

A cooling fan isn't going to fix bad wiring.

You might have an iffy connection that heats up at high current. It doesn't take long for something to get hot at 60Amps.



It could also be the voltage drop gets too large and that causes the fault.



0.1 ohms at 60A is a 6 volt drop. Earth (ground) connections are the ones that often get overlooked. Earth is just as important as the positive wires. Are you using the frame of the bike for earth / ground?

What kind of connectors are you using? Do you have the tools for the connectors? The tools can sometimes be crazy expensive but they make a difference.

Currently, I have the motor controller mounted to the frame and the motor, of course, mounted to a bracket that's mounted to the frame. The frame is painted though. This sounds stupid on my part but should I run a wire from the negative battery terminal or the negative on the controller and mount it directly to an unpainted part of the bike frame?

 

[metastable]

I looked up your controller and it has an adjustable battery current limit setting. I'd make sure this setting is 50a or less since that's what your battery is rated for continuously.

Some people who do DIY EV's use the battery management system on the battery pack only during charging, and then while riding they bypass the battery management system to avoid cutouts, relying on a properly set battery current limit setting and low volt cutoff setting in the controller for battery safety / preservation.

If your battery management system is used during discharging it can cut off the battery if you pull too many amps, which then triggers the controller low volt cutoff (which is a good thing, to save your battery), but you can avoid this by making sure the battery current limit setting is low enough that it won't harm your cells.

 

[metastable]

This sounds stupid on my part but should I run a wire from the negative battery terminal or the negative on the controller and mount it directly to an unpainted part of the bike frame?

I doubt that's a good idea... might increase the inductance and/or capacitance on the battery cables which is generally a bad thing. You want your battery cables as short as possible to minimize inductance/capacitance & resistance.

 

[metastable]

In electric vehicles, why is the high voltage battery usually a floating voltage (i.e. not grounded to chassis)? - Quora

 

[Jeffrey Cooper]

Its not somehow related to regen ?

 

[Mike N]

I don't know. I don't have regen activated currently.

 

[Jeffrey Cooper]

I just noticed that in your description of the "where and when", throttle off was happening - just a thought, maybe you should check it really is off ?

 

[metastable]

when I exceed 60 amps on my electric motorcycle

The battery can output 50 amps continuous

^These are the two key points... the battery can put out 50a, and you are exceeding 60a, so the battery management system in the battery briefly cuts the power, and then the controller goes into fault mode because the voltage dropped below the low volt cutoff threshhold due to the battery management system cutoff.

the reason it happens at high speed is for the same thrust, it requires more amps from the battery when you are going at high speed than when you are going at low speed. that's because the motor puts out more back emf voltage at high speed and back emf voltage opposes the battery voltage so it takes more pulse-width-modulated effective voltage to put the same number of amps through the motor when the back-emf voltage is higher, which takes more battery amps at higher speeds.

 

[Mike N]

^These are the two key points... the battery can put out 50a, and you are exceeding 60a, so the battery management system in the battery briefly cuts the power, and then the controller goes into fault mode because the voltage dropped below the low volt cutoff threshhold due to the battery management system cutoff.

the reason it happens at high speed is for the same thrust, it requires more amps from the battery when you are going at high speed than when you are going at low speed. that's because the motor puts out more back emf voltage at high speed and back emf voltage opposes the battery voltage so it takes more pulse-width-modulated effective voltage to put the same number of amps through the motor when the back-emf voltage is higher, which takes more battery amps at higher speeds.

That actually makes a lot of sense. I've gone ahead and lowered the battery amps allowed using the controller software. I recently replaced the positive battery cables with something shorter as well. One wire was way too long. I'm going to do some testing tonight with all of this in mind and I'll report back. I really appreciate the feedback from everyone.

 

[andrew*debbie]

Currently, I have the motor controller mounted to the frame and the motor, of course, mounted to a bracket that's mounted to the frame.

It is important that all the negative connections are as good as the postitive ones. If you are using the bike frame for the negative, then yes it is important.


The capactance of the cables is pretty neglible. Keeping resistance and inductance low is important. Short heavy leads are a very good idea. At 60Amps the voltage drop across a low resistance is substantial. The battery has an internal resistance. At 60Amps the battery voltage will drop because of that internal resistance. If you are already dragging the battery down a few volts another few volts in the cables and connectors might be what is causing the error codes.

There will be voltage drop in both the + and - cables, so you need to calculate both of them.

At 60Amps:
6 feet of 20ga wire 7.3 volts !!
6 feet of 14ga wire 1.8 volts !
6 feet of 12ga wire 1.2 volts

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You never mentioned what type of termination you are using. At 60A that is important. A cheap connector smashed down with a vicegrip is not good enough.

You should be using high quality connectors with the proper tool.