Power cutting out on BBSHD

[vfr400]

There's no temperature sensor that I can see. After over-current switch-off, the BMS normally switches back on by itself. That leaves low cell detected. I think my next step would be to spray some contact cleaner on the multi-pin connector and work it a few times, then put it all back together and pray.

While it's apart, you could check which way the switch works. I think off is on. If so, pull the plug off the BMS and run it without the switch to eliminate it as a possible cause. If everything is OK afterwards, reconnect it and try again. that will show whether it's the switch or the connector.

If the cut-outs continue after cleaning the connector and eliminating the switch, the problem is going to be something deeper and more difficult to solve. It could be a faulty BMS or a bad cell weld. For testing, you can bridge the negative wires to bypass the BMS completely, then run your bike for a bit and check the cells again. If there's a faulty weld, you should see a difference in the voltages. I would expect to see at least some difference now if a weld were faulty, so I would gamble on the fault being elsewhere .

It could also be an intermittent short or bad joint on a sense wire. Have a good look at them while you have access.

 

[trevor brooker]

many thanks for everyone's helpful replies - I am going beyond my comfort zone/ability to remain safe when investigating a potentially dangerous battery.
I have learnt a lot, but do not wish to make an error & short something whilst my eyes and hands are trying to check things out.
So, assuming that I have the good quality cells as described when I purchased it & they have only had a relatively few cycles I think its worthwhile getting it checked/repaired professionally, so I have contacted Jimmy at ebikebatteries.co.uk

 

[Nealh]

You could rule out the controller mosfets being at fault first by simply carrying out the phase wire checks, a faulty controller will cut all power and switch off the display until fets cool down then act as normal until heat raises it head again.
I have had this twice with 6 fet controllers and using a 9 fet controller has solved it.

Shorting out a battery using a dvm isn't easy unless you lay a probe end a cross two opposing points, you did the hardest part by measuring the 14 cell group voltages.

 

[trevor brooker]

I have had a discussion with Jimmy at eBikebatteries.co.uk and decided that as the cells remain balanced its unlikely they are the problem. The cost of investigating the BMS & welds is about half the cost of a new battery, let alone any new parts.

I have found some helpful posts

https://electricbike.com/forum/forum/main-forum/trouble-shooting/38870-diagnosing-intermittent-voltage-drops-bbs02-52v

https://electricbike.com/forum/forum/knowledge-base/motors-and-kits/bbshd/39217-troubleshooting-the-bbshd-bbs02

I have reconnected all of the plugs on the wiring harness, moved the speed sensor closer & changed the position of the battery leads to the controller (just in case they had broken on a bend) all without luck. I'm only drawing 15 amps & its cutting out between 100 to 1000 watts, so not based upon high load, but only cutting out under some load ( I went our early this morning & left the display on & its still working).

So I feel its time to bite the bullet & buy a new battery. If that does not work I will have a spare good battery, but even less hair.

 

[trevor brooker]

It could also be an intermittent short or bad joint on a sense wire. Have a good look at them while you have access.

Well I purchased the cheapest ebay battery I could find (48v 10a) so I could substitute my battery to test the system.

Did a 10 mile ride with the new battery no problems. Switched back to original battery - managed 1 mile before power cut off as before.
Then repeated switch to 48v then back to 52v batteries, with the same result.
So I feel confident that its the battery.

I tried to purchase a replacement BMS, but can not find a close enough match, so as a first step will look to replace those sections of the sense wires that were bent around the battery cells & compressed by the battery case.

Any tips, i'm thinking of just using but joints using Solder Seal Wire Connector Heat Shrink Butt Connectors to splice in new wire.

I assume that the BMS just measures voltage from the sense wires not timing, so if the new wires are longer that the original it should not matter.

If that does not work then I will have to move onto the next part of the battery system.

 

[Nealh]

Wire length not importatnt as only 4.2v and milliamps are carried along them they don't physically carry any charge, as for monitoring only.
Splicing wire I find solder and shrink pretty simple and cheap.

 

[trevor brooker]

While it's apart, you could check which way the switch works. I think off is on. If so, pull the plug off the BMS and run it without the switch to eliminate it as a possible cause. If everything is OK afterwards, reconnect it and try again. that will show whether it's the switch or the connector.

There are two plugs on the BMS.
Mutlipin with the sense wires
Double pin to the on/off switch.

Can I just clarify, before I do anything, that your suggestions is to pull the double pin plug off the BMS, stick a volt meter on the battery case connectors to check voltage & then take a test ride to see if fault reappears?

 

[vfr400]

The switch makes a simple bridge between the white wires. Unplug it and test the connector with a meter to see if it is open or closed with the switch in the on position. If open when on, you can leave it off for testing. If closed, you have to make a bridge between the white wires to bipass the switch.

 

[trevor brooker]

The switch makes a simple bridge between the white wires. Unplug it and test the connector with a meter to see if it is open or closed with the switch in the on position. If open when on, you can leave it off for testing. If closed, you have to make a bridge between the white wires to bipass the switch.

many thanks

 

[trevor brooker]

The switch makes a simple bridge between the white wires. Unplug it and test the connector with a meter to see if it is open or closed with the switch in the on position. If open when on, you can leave it off for testing. If closed, you have to make a bridge between the white wires to bipass the switch.

Ok - pulled switch connector off BMS - no power showing on battery outputs.

So the easiest way to make a bridge with the connector back on the BMS is to unplug the switch & use two connectors with a short bit of wire in-between.

I should then get voltage on battery outputs & can give a test ride.

If that cures the intermittent fault it shows that the on/off switch is faulty - can you buy replacements or do you have to purchase any entire battery case?

 

[vfr400]

It needs to be eliminated as a cause, but i'd be surprised if this is your problem. If it turns out to be a faulty switch, I'd be inclined to join the wires and leave it on all the time. If you want to leave your bike unused for a long time, you can always remove the battery. When the battery is on the bike and the controller is switched off, the battery is isolated just the same as it would be by the switch on the BMS, so the switch isn't really necessary.

Having said that, there was a case of a BBS** that smoked badly when water got past the rubber potting and shorted out the mosfets when the bike was switched off and parked up, but the chance of that happening again isn't very high.

 

[trevor brooker]

It needs to be eliminated as a cause, but i'd be surprised if this is your problem. If it turns out to be a faulty switch, I'd be inclined to join the wires and leave it on all the time. If you want to leave your bike unused for a long time, you can always remove the battery. When the battery is on the bike and the controller is switched off, the battery is isolated just the same as it would be by the switch on the BMS, so the switch isn't really necessary

Made the switch wires from the BMS into a loop, to turn the battery on.
Went for test ride - 100 yards max 100 watts = power loss.
So switch also now ruled out as the problem.

Ordered a new BMS. Started to read up about how to replace a BMS.

I must say I am really learning a lot from all of this, i'm just glad the replacement battery has made me mobile again.