bbshd issues - works in bursts and shuts off

[AshBBSHD]

Hi all,
I had a BSSHD bike for a while and had no issues with it. It was in storage for a couple of months but I tried riding it recently and discovered a weird issue.
Basically when I pedal - the motor kicks in for a second and shuts off (I am way under the min speed limit set for it). Could anyone advice what I could do to fix it?
At first i noticed that the motor got a bit loose when I'd pedal so I thought it was that. I then suspected brakes (magura e bike brakes) were an issue but no. When I hold a button for uphill walk assist it works just fine and does stop when i engage brakes which confirms that the brakes arent a problem.
The battery pack is 48v13ah and is full of charge.
Any idea what could be an issue here?

 

[E-HP]

I don’t have one, but I believe the Bbshd won’t run on PAS if there’s an issue with the speed sensor, so I’d check that and the connectors.

 

[AshBBSHD]

I don’t have one, but I believe the Bbshd won’t run on PAS if there’s an issue with the speed sensor, so I’d check that and the connectors.

Speed sensor is working as it should, display shows the speed just fine. I also tried a different display but to no avail

 

[marvin78]

Describe

the motor kicks in for a second and shuts off

''shuts off"

Just the motor/assist, or the entire bike(including display)?

Either way, how old is the battery? How did you store it? Full of charge doesn't mean much if you've got an issue with it under load.

I would try a different battery if available.

 

[AshBBSHD]

Describe

''shuts off"

Just the motor/assist, or the entire bike(including display)?

Either way, how old is the battery? How did you store it? Full of charge doesn't mean much if you've got an issue with it under load.

I would try a different battery if available.

hiya, the motor is still on yeah. It feels like it thinks it reached the max speed and stops within 1 second (though that's not the case), battery is fairly new and I stored it at home. I dont think there's any issue with it.
Dont have another battery to test though sadly

 

[marvin78]

Welp, that's my imput done then

Someone with more experience with bbshd will probably guide you how to do further diagnostics ( voltage sag under load is still something I would look at first )

 

[neptronix]

What happens if you run it in a super slow gear ( whatever's the tallest on your casette ).. does it still cut out?

 

[AshBBSHD]

Actually no it doesnt, how strange!?

 

[amberwolf]

The most likely thing is the battery has a problem and is not actually full, some cells pretty low, so that the charger shuts off because the bms tells it to turn off, but it's not really full yet.

When you run the bike on it under load, the taller gears put more load on it and cause more voltage drop, so the controller reaches whatever it's programed for lvc so the motor stops but the system stays on.

A lower gear puts less stress on the battery, so less ovltage drop, so no cutout.

Measure voltage with a voltmeter while riding under each circumstance and post what you get, as well as what it is with no load.


Next most likely is the motor or controller overheating from overload, but that's not nearly as common without a mechanical problem causing the higher load

 

[neptronix]

Actually no it doesnt, how strange!?

yep.. battery is cutting off because it can't handle a load higher than that.

Cheap way to see what's going on then ( not on a per-cell level, but whole pack level ):
Turnigy 180A Watt Meter and Power Analyzer

Another thing to keep in mind.. lithium battery performance goes down a lot in cold temperatures.. this battery is either old, or there wasn't enough headroom in the output rating to handle that.

 

[AshBBSHD]

Right, thanks guys. I will try to test and see what happens.
Any advice on where you get your batteries in the UK? I currently have this shark-type battery. Ideally have 13ah or above with the following dimensions:
370mm L
90mm W
110mm H

 

[E-HP]

Right, thanks guys. I will try to test and see what happens.
Any advice on where you get your batteries in the UK? I currently have this shark-type battery. Ideally have 13ah or above with the following dimensions:
370mm L
90mm W
110mm H

Have you tried leaving it on the charger for a longer period or checking the individual cell group voltages? I seem to recall reading on this forum that some BMSs are powered off of a single cell group, so the parasitic load when being stored can drain one group. Probably unlikely since you are able to obtain a full charge, but if you’re replacing the battery anyway, you could do some forensic work.

 

[docw009]

I was going to ask if you had a throttle, and if you could run it at slower speeds or on PAS 1 w/o shuttng down. You want to rule out the low voltage cutoff problem.

 

[AshBBSHD]

Have you tried leaving it on the charger for a longer period or checking the individual cell group voltages? I seem to recall reading on this forum that some BMSs are powered off of a single cell group, so the parasitic load when being stored can drain one group. Probably unlikely since you are able to obtain a full charge, but if you’re replacing the battery anyway, you could do some forensic work.

I have, it does look fully charged (on display anyway). and I think it has a charge as the screen etc doesnt shut off when the motor cuts off. Do you have any instructions on how to measure cells and such?

I was going to ask if you had a throttle, and if you could run it at slower speeds or on PAS 1 w/o shuttng down. You want to rule out the low voltage cutoff problem.

ACTUALLY wanted to try this! will report asap

Any advice on where to get a reputable battery for bbshd would be appreciated

 

[E-HP]

I have, it does look fully charged (on display anyway). and I think it has a charge as the screen etc doesnt shut off when the motor cuts off. Do you have any instructions on how to measure cells and such?

If the display stays on while the motor cuts out, and battery appears full, then check the voltage while the problem occurs. The symptoms point to weak cell groups in the pack, that appear to be ok, but sag under load and cause a low voltage cutoff. The battery BMS doesn’t trip, but the controller cuts out.

 

[AshBBSHD]

Right tried with throttle. When I hold the throttle, the motor burst corresponding to the settings (ie 1-9) for about half a sec then goes into up-hill speed. So it still rotates just a tad. Doesnt matter which gear I use either, I probably noticed it working better on larger gears as they're easier to rotate.
I think you guys are right re battery. I bought the watt power meter and check tomorrow to see what exactly happens.
I don't know where to get a battery that wont die in a few months though I got this one in august

 

[2old]

The go to places here are Grin (ebikesca) and em3ev AFAIK.

 

[E-HP]

The go to places here are Grin (ebikesca) and em3ev AFAIK.

With both Grin and EM3EV, you know exactly what type of cells are being used, and for EM3EV, you choose which cells you want, plus what connectors the pack has. In general, if the seller provides information about the cells and BMS, and the cells are brand name cells, you're in a lot better shape than buying from one that says "grade A cells" or some other description, which essentially equates to cheap Chinese generic cells. I see Grin and EM3EV mentioned a lot, but have seen a few posts of folks buying from other vendors that provide those details.

 

[AshBBSHD]

Here's a vid of me testing the battery. I press and hold the throttle for the whole video, it's set to a max setting. Sorry its a bit shaky, bike wasnt stable on the stand, might need to download it for a better resolution.
Does this mean the battery/some of its cells are dead? Both screen and indicator on the battery itself shows full charge:

20250224_140440.mp4

drive.google.com

 

[E-HP]

Can you get it to run longer with partial throttle?

 

[AshBBSHD]

Can you get it to run longer with partial throttle?

Partial throttle?

 

[E-HP]

Never mind.

 

[neptronix]

It's a BBSHD.. so the equivalent should be turning the power setting down.

The 'power bars' on your display are very likely to not be accurate.. you need a proper numeric voltage and amperage readout

Measuring your pack to see if a cell is faulty will involve disassembling it and using a multimeter. Ideally this measurement is done at mid charge.. at mid charge, a weak cell will show itself.

You have a 13AH pack which may be a little weak to begin with. Cold weather makes that situation worse.

What brand is your battery and what cells are in it?

 

[AshBBSHD]

Here's a other vid. Going from 5/10 and down in increments of one.

20250227_103040.mp4

drive.google.com

The display seem to correspond to the watt power as it spikes and drops. I'll try getting a new battery and in the meantime disassemble this one and measure each cell

 

[AshBBSHD]

I actually got a 250w bafang motor on my other bike. I was wondering if I could test this 13ah 48v battery on it or is it too much you'd say? I wonder if my bbshd went tits up. I tried testing the battery charge by using a smart anger power bank and it charges it well, granted this is not a motor etc. I'd rather test it on another motor before disassembling and such