Bafang BBSHD dies randomly, please help!

[rudivb]

Hello, thanks for reading and helping out, you can find the TLDR at the end.

Some background information:
- Delivery driver with Bafang BBSHD with pretty high mileage (30000+km, 2.5/3 years old)
- Current battery Chamrider 52v36ah about 15000km (1 year old)
- Have had minor issues in the past which I could all solve (broken displays, worn-o-ring, nylon gear, hailong battery contact worn/burned)

So I went on a long bicycle tour about 3000km, didn't have issues until near the end.

(I had been to the coast days/week before the fist problem occurred, it was very windy with lots of saltwater, could be related?)

First issues appeared, display/motor everything suddenly turning off.
As I remember correctly I could turn it back on but the same issue would occur minutes later.
The weather might have been wet/moist, but I'm not sure.


(after that I went with the train somewhere as my gf was visiting)
From the train I had to do a short ride (maybe 10km), but it was pouring rain, like really pouring.
Display/motor turned off again, this time not getting back on at all.
The next day at the hotel I was trying to get it back on, but it wouldn't turn on.
I started plugging in the USB programming cable, connecting my PC, connecting my phone and at some point miraculously it became alive.
And it kept working, tried multiple times turning on/off, rode around a bit, everything fine.

Gf left, my bicycle journey continued, without issues, even had some rain, but I had no problems.
On the end of my journey I took a train back home and the trouble started again.
I had to do about 40km from the train station back home, it was raining and I was close to halfway and a black display again.
Couldn't get it back on, tried everything including the USB cable, walked/cycled the heavy bicycle back for a couple hours.

Back home I could have a good look at everything, I thought maybe my lights weren't very well wired and caused the issue.
So I rewired stuff, checked connections, well it worked... but on my first day back at work the bike would turn off again, I can't turn it on until I re-plug the battery, but it kept turning off.

Checked everything again, but same issue, sometimes I can ride for an hour and it might just happen once, sometimes it constantly happens.

As a delivery rider I need to be able to fully trust my bike and being in traffic with suddenly no more power can lead to dangerous situations.

What I've done:
- I've checked most if not all the wiring and if it looked like it could cause an issue I would redo it
- I've put the speedo sensor closer to the magnet
- Pulled the controller and didn't physically see any problems, maybe a super super small amount of moisture?
- I heated up the controller in case moisture was the issue
- Left the bicycle ON without riding it and it doesn't seem to turn off this way
- Drawing high power does not make the issue appear
- Full throttle does not make the issue appear
- Pulling/moving wires does not make the issue appear
- Finally bought a voltmeter (should've done that long time ago)
- Checked the battery, checked the plugs/wiring for continuity but can't find the issue with a voltmeter.
(next up is measuring if the battery still has voltage at the moment the problem occurs)
Edit: So it just cut again and I had a voltmeter with me:
Started out riding with my battery voltage being 55.xxv
Power cut-out, left everything connected, measured the battery voltage: 5v (yes that is FIVE volt)
Disconnecting, measured battery voltage 55.xxv
Reconnected everything and powered on again

- I have not opened up the motor, as there are no strange noises and to me it doesn't seem to be a mechanical issue, but solely electrical


TLDR;
- BBSHD turns off (complete shutdown/black display/no power)
- Sometimes I can get it back on by re-plugging the battery
- During (heavy) rain it won't turn back on (until maybe the next day)
- Currently it turns off randomly, which makes it very hard to diagnose
- Issue seems to only occur when riding
- Drawing high power does not make the issue appear
- Full throttle does not make the issue appear
- Pulling/moving wires does not make the issue appear


I've read about every post and trouble shooting guide I could find, but haven't been able to resolve it.
What I currently think is water/moisture damage, I am leaning towards buying a new controller? but prefer not to waste time/money.

Your help is very much appreciated

 

[amberwolf]

Complete shutdowns with no power are almost always caused by the battery; the BMS turns off the output to protect the battery against whatever caused a limit to be exceeded.

The 5v that you see there is a ghost voltage from leakage current thru the FETs when they have shut off, so this is what is happening, though it doesn't tell you why it's happening. Disconnecting the battery makes the voltage go back to normal because it will detect the load has gone away and reset itself.

FWIW, batteries are rarely waterproof, often not even water resistant. So the problem could be water intrusion into the battery case, causing a problem at one of the cell groups, balance wires, or the BMS itself.

If there was saltwater intrusion into any of the elecrical systems it can cause rapid and severe corrosion of exposed conductors and metals that it contacts; even after the original water dries the salt remains and continues to corrode via moisture in the air.


Sometimes problems that cause batteries to shutdown are a low-resistance short causing overcurrent. This can be from the corrosion, or even just from the saltwater's presence since it is at least somewhat conductive on it's own. It could be anywhere in the battery bus wiring or interconnects, and if the BMS is a common-port type it could even be in the charger port (as that is then directly paralleled with the output port).

Since the system operates normally when the power isn't shutting off, it's unlikely to be in the controller itself, or the display, as corrosion or intrusion in those severe enough to cause this kind of problem would probalby have caused damage to them, so it's more likley to be inside the wiring or connectors where you can't see it, the docking cradle the battery fits on if there is one, or inside the battery itself.


If you have access to another battery, I would test with that first, and if it works normally, then the problem is inside the first battery.

 

[rudivb]

@amberwolf

Thanks a lot for your in-depth response, I appreciate it a lot.

The battery itself is a triangle battery inside a frame bag. Taking the battery out of the bag, just looking at it, it seems well sealed off against the elements.

I've put my old battery (hailong) on the charger yesterday, as indeed the next step was trying out a different battery.

I will report back, with the results.

 

[caleb7]

Similar random cutoffs happened when my BMS was wet and had a burned resistor. It continued to happen in random times. It could have been worse (as it wouldn't balance cells properly with a burned resistor next to the balance connector) , thankfully i noticed and replaced it and also made sure it won't get any water again.

If it wouldn't look like a complete cutoff, I'd suspect the wiring harness cable. One time similar thing also happened to me when display cable connector's one pin was ripped off for some reason and it was just touching pins if it felt like it

 

[rudivb]

@amberwolf & @caleb7

It looks indeed that the issue is coming from the battery. Today I've been using my older battery without problems, tomorrow I will be using this battery again and after that return to the triangle battery to be sure that it is the battery.

So it looks like I will have to open up the battery, I am by no means an electrician, but I'm handy enough to follow basic tutorials and commands.

I will do my proper research, but if you have pointers/guides of what to look for, I will appreciate it.

Like will there be obvious physical damage or will I need to measure everything with a multimeter?


Changing the BMS is that a plug&play thing or will I need to be soldering stuff?

If it is out of my comfort zone, I guess a professional could look at the battery.

 

[caleb7]

It may be BMS or something else in the battery like one of balance wires disconnecting.

I'm not the most experienced one but if your BMS wires are soldered you may need to unsolder it first (to not make wires shorter by cutting them) . I connected mine via ring terminals, to avoid solder flux splashing into bms electronics. I don't know if that (not cleaned flux) cause a problem, but in some circuits it did.

Balance wires enter the bms via a multi-pin connector and can be measured via multimeter. I'd be very careful to not short any of them.

Balance wires may be ordered differently in different bms, but that's outside of my knowledge.

 

[rudivb]

@caleb7

Yeah I've been reading into it a bit already.
Was hoping that the multipin connector would be kind of a standard connector in all BMS, but looks like that's not the case, so all the wires would need to be done separately.

Did you get a standard BMS or a Bluetooth one? I'm kinda interested in the Bluetooth version.

Also if I understand correctly you want about 2x the max amp you're pulling, so in my case bbshd does a little over 30amps, so I would need a BMS rated for 60A continuous / 180A peak?

 

[caleb7]

My current battery has non-bluetooth one. When I build my next battery, I plan to use a Bluetooth one.

With stock BBSHD controller, I was using 40A Chinese Aliexpress BMS without problems (except the water damage). Now it is 60A version of same Chinese brand (they had same dimensions).

I don't know if 2x is a rule, I think it's rather just to be safe against cheap Chinese bms

I'd say 40A is ok but if space allows, go for 60A one. If you want over-current protection to work, you may need to check specs. as it may be too high in 60A version for your battery to kick in. I didn't consider it when i was building the battery honestly, but i use a fuse of course.

 

[rudivb]

@amberwolf & @caleb7

I've been riding with my old battery for 2 days without problems and the moment I wanted to try my triangle battery, I couldn't even get out of my street and it cut-off. So 99.9% sure the problem lays with this battery.

Today I've opened it up, again I am not an expert on batteries/electronics, so I am being very careful.
I didn't notice any physical damage, I did find a bit of black "powder", not sure what that could be.
I've measured all the 14 groups and they are all with 0.01v of each other, 3.99v / 3.98v, so I can assume that all the cells are good?

Not sure what to do next, should I just order a new BMS and see if that resolves the issue?

 

[fechter]

You could try unplugging the big connector with all the tap wires and plug it back in. A bad contact could cause your problem.
If any moisture got onto the BMS board, that could also cause problems. Make sure it looks dry. If this all fails, it could be a bad connection somewhere on the board, which would be hard to locate and probably easier to replace the board.

 

[amberwolf]

What do the cells measure under load?

If you have a space heater, or old non-electronic toaster oven, it might make enough of a load to cause voltage drop on anything that's got a problem in the battery.

Or if you can setup the bike with the powered wheel offground, and connect the battery to the bike, and use the motor to create the load, and then the mechanicla brakes to load the wheel / motor to draw more current (until the system shuts down or you see enough voltage sag somewhere to be a problem).

In either case, you'll measure the cells (groups) the same way you did so far, while teh load is present, to see if any of the cells show more drop than others, or if they all drop a lot, etc.

 

[rudivb]

@fechter

Thanks, I've reconnected that main connector, it looked perfectly fine and clean, but just in case.

@amberwolf

I can see voltage on my display and I usually keep an eye on it and never saw any abnormal voltage sag. And the problem occurs even under very low load (100/200watt).

I could still measure the groups under load, but I don't expect to find anything unusual.

 

[amberwolf]

I can see voltage on my display and I usually keep an eye on it and never saw any abnormal voltage sag. And the problem occurs even under very low load (100/200watt).

I could still measure the groups under load, but I don't expect to find anything unusual.

The voltage on the display is usually very low sample rate, so dips can take time to show up, and may not show up at all before a system turns off.

But the big thing about it is that you could have just one cell that is sagging far enough to trigger the BMS without the displayed voltage changing that much (highly unlikely since they're all the same voltage without a load).

It's not a test you have to do unless you don't find any other problems with the battery. Was just suggested as a way to verify the cells are actually all ok.

It could even be something as simple as a fuseholder with insufficient contact on the fuse (lots of crappy fuseholders out there), or a discharge connector with a bad contact (spread pins, etc) or a bad solder joint or crimp in the discharge positive or negative from cells to connector.

 

[rudivb]

The voltage on the display is usually very low sample rate, so dips can take time to show up, and may not show up at all before a system turns off.

But the big thing about it is that you could have just one cell that is sagging far enough to trigger the BMS without the displayed voltage changing that much (highly unlikely since they're all the same voltage without a load).

It's not a test you have to do unless you don't find any other problems with the battery. Was just suggested as a way to verify the cells are actually all ok.

It could even be something as simple as a fuseholder with insufficient contact on the fuse (lots of crappy fuseholders out there), or a discharge connector with a bad contact (spread pins, etc) or a bad solder joint or crimp in the discharge positive or negative from cells to connector.

Alright thanks.

Should there be a fuse located somewhere that I can check?

I Also read that you can "reset" the BMS, which might fix things, by simply disconnecting the large plug with all the balance wires and connecting it back again?

 

[amberwolf]

Alright thanks.

Should there be a fuse located somewhere that I can check?

Many batteries have one on the positive discharge line between the battery cell block and the controller-side connector. If it's a blade type fuse

it's common for the holder it fits in to have loose-fitting contacts that the fuse fits into. That can cause excess voltage drop across the fuse, causing system problems like shutdowns. (but not usually power-offs).

Same thing with glass fuses

I Also read that you can "reset" the BMS, which might fix things, by simply disconnecting the large plug with all the balance wires and connecting it back again?

Maybe, but some BMS are sensitive to connection order and can be damaged by having the cell wires connected in the wrong order, so if the plug isn't reconnected the right way, it might cause problems rather than solve them.

However--a reset is for if the BMS is stuck off (crashed). If it works but just cuts off under load or early, then a reset is unlikely to help.

EDIT: I note that you said that you have already reconnected this connector anyway, in response to Fechter's post, so if this BMS resets this way, it's already done.

 

[KEC]

It may be BMS or something else in the battery like one of balance wires disconnecting.

I'm not the most experienced one but if your BMS wires are soldered you may need to unsolder it first (to not make wires shorter by cutting them) . I connected mine via ring terminals, to avoid solder flux splashing into bms electronics. I don't know if that (not cleaned flux) cause a problem, but in some circuits it did.

Balance wires enter the bms via a multi-pin connector and can be measured via multimeter. I'd be very careful to not short any of them.

Balance wires may be ordered differently in different bms, but that's outside of my knowledge.

Yes I'm going to check that right now.

 

[emeauraux]

i've had the exact same issue. i occured on a rainy day for the first time. everything the same, sometimes was turning back on sometimes not. ar the end i disassembled the entire battery and found a couple of failed spotwelds and a dead cell.

after completely redoing the battery the issue bever occured again. so i guess the dead cell in combination with loose welds triggered the bms shut down.

 

[rudivb]

i've had the exact same issue. i occured on a rainy day for the first time. everything the same, sometimes was turning back on sometimes not. ar the end i disassembled the entire battery and found a couple of failed spotwelds and a dead cell.

after completely redoing the battery the issue bever occured again. so i guess the dead cell in combination with loose welds triggered the bms shut down.

Sorry for not updating the post, but finally I bought a new (bluetooth) BMS which has completely resolved the issue!
Been riding for months now without any problems.