Second MP5 vector controller failure

[Andyl33]

My elation was short lived.

I took it out for a run of about 10km, did some shopping rode a bit more then on the way back it went dead again while braking, but this time on the flat. Regen worked many times during the trip but then just gave up. I'm not sure what else the problem could be - the motor won't generate any more voltage and current than it had been doing for the last 2.5 years quite successfully.
Luckily only had about 200m to cycle back, but I'm gutted and faced with either repairing it yet again or getting a new controller which will probably do exactly the same thing.
I want to be able to ride across Europe, but I just cannot trust it.
Perhaps the LM34923MM chip should have been an LM34923MMX?
Is there anyone at all a GM that can answer technical questions?
I've tried their support chat line, but there's never any response.
So, guess I'll have to try again and see how it goes using 12S. :-(

[Bikemad]

Did you end up changing the big 1000uF capacitor or is it the original "bloated" one still in there?

I was just wondering, if the "bloated" capacitor was no longer able to absorb high voltage spikes, could this have resulted in the failure of the new LM34923MM chip (assuming the same chip has failed). 

I'd be suspicious of an upper wiring harness/component problem taking out the lower harness main power and eventually the 5 volt dc regulated power which I would guess your mystery chip provides.


Have 5 volts at the board? If not perhaps a temporary external supply will help sort things out. AFTER you check for shorts...

If this chip does provide the +5V supply, it might be worth testing with an external 4.5~5v supply via the pedelec wires to see if the controller still works.

Alan
 

[Andyl33]

Did you end up changing the big 1000uF capacitor or is it the original "bloated" one still in there?

I was just wondering, if the "bloated" capacitor was no longer able to absorb high voltage spikes, could this have resulted in the failure of the new LM34923MM chip (assuming the same chip has failed). 

Good point - the bloated capacitor was in the first controller - the one in the current 2nd looks ok and gives a normal spark on power up. I suppose I could try to charge it through a resistor and observe the charge curve. Desoldering it is a nightmare as the bottom board is a huge heatsink and difficult to get at the legs.
Also, I cannot find any ZhiCheng capacitors on the net, or any of the required 18x25mm in size from anyone!
18mm radius is an immovable limit because of the upper circuit board, but I found some 18x30mm 1000uF 80V and ordered those from China just in case they may be useful one day.
Not impressed at all with this non-standardness!

If this chip does provide the +5V supply, it might be worth testing with an external 4.5~5v supply via the pedelec wires to see if the controller still works.

I haven't taken the controller out yet but I'm pretty sure it's the chip that's gone again - pumping 5V in through the pedelec sounds creative and I can easily do that with a buck board powered by the 58V->12V converter I use for the lights and usb chargers. If that works, then I'd be happy, but it sounds dodgy - the linear regulator would be seeing 5V without having a corresponding input and I don't know what other things might depend on the voltage from the LM34923 chip. It probably puts out more than 5V for the linear regulator to do its thing.
If I try again with another chip, I'll try to glue a heat sink to it but it's supposed to cope with 75V, and 58V is the max I use.
I don't think the motor would put out more voltage than its kv allows, and the high current flows through the fets not the buck chip, so am still a bit mystified why it would fail.

A circuit diagram would help a lot!

[Bikemad]

Hi Andy,

I have just been studying your photos of the controller, and there is a much larger 78M05 on the upper side of the top PCB that I think is far more likely to be the +5V regulator chip, so I'm puzzled as to what the SM5B chip is for.

I was actually looking for a shunt that controls the current (like all of the earlier square wave controllers had) but I could not see one.
I guess it must use a section of copper track on the PCB instead. 

As you've already stated, a circuit diagram for this controller would indeed be very useful.

Alan
 

[Andyl33]

I have just been studying your photos of the controller, and there is a much larger 78M05 on the upper side of the top PCB that I think is far more likely to be the +5V regulator chip, so I'm puzzled as to what the SM5B chip is for.

The SM5B chip is a 75V buck converter, so I think it's taking the high voltage from the battery or the regen and stepping it down to a voltage below 25V for the 78M05 chip to produce the 5V.  Seems a bit crazy given its tiny size.

I was actually looking for a shunt that controls the current (like all of the earlier square wave controllers had) but I could not see one.
I guess it must use a section of copper track on the PCB instead. 

As you've already stated, a circuit diagram for this controller would indeed be very useful.

High voltages carrying smaller currents can get away with smaller shunts so it may not be obvious - smd components make reverse engineering quite challenging!

I have a hypothesis that the BMS went into charge protection mode and cut the connection to the battery so the motor would be generating with no load to keep the voltage down - however based on what I think I've learned is that the MP5 is supposed to prevent this from happening. Maybe reducing the regen current down from 50A would help, though the BMS never seems to see this amount.

The BMS does provide logs but I'm not convinced of its accuracy. I've attached a couple of edited screenshots showing values for one cell over the duration of the ride, the whole pack, and a zoomed in area at the point of failure.

Resolution is only 1 min. However, if there is a 4V sag at 30A draw, then there's likely to be a 4V surge charging at 30A, and if that happens for longer than the BMS overvoltage duration threshold, then it could cut the BMS and leave the regen without a load, and possibly cause the voltage to exceed 75V.
The failure happened in this last case after slowing down from full speed in one braking action, so it could have caused the BMS to trigger. Pulsed braking or reducing regen current could perhaps avoid this too, but I would really miss it.

It gives me something to experiment with.

I could go back to my 12S lipo pack which doesn't have a BMS as I charge it at 12A with a balancing charger in two sessions.
I'd prefer to use the 14S with the BMS, as it's much higher capacity and I can charge it at 5A in one session and know the cells are protected even if the balancing current has no hope to balance 16 cells in parallel!

So, I think I'll replace the chip again, and use the 14S without the BMS and charge it in stages as I used to do.

If it fails again in a similar situation, then I'll know it wasn't the BMS!