I'm a bit puzzled. I have a 20ah 48v with built in BMS (chinese sun-thing). And a cheap 1000w (allegedly) rear hub motor. The bike will happily pull full throttle up a hill and reach full speed etc. but will sometimes cut out straight away or mid ride and not turn on again without disconnecting/reconnecting the battery. This makes me believe it's the bms shutting the battery down. but for what reason? It happens most often when I throttle down and coast down hill going fast and then try to bring the throttle back in, which i would assume isn't a high load scenario. It also just happens randomly too. Dodgy bms?? dodgy throttle? dodgy anything else? how hard is it to replace a bms?? Any advice would be really appreciated as it's so much fun but i don't want to ride it until i know what's going on...
Deductive thinkers needed!! Confusing problem :)
- Thread starter Noonoos
- Start date
dnmun
1 PW
sounds like a loose wire, in the sense wire bundle/plug or where it is soldered to the pouches. can you measure the cell voltages at the BMS while the battery is charging, and measure when it is at full charge and the charger light is green.
Ok, do you mean a loose sense wire on the bms? I haven't actually taken the rapping off and had a look yet. And i need a new multimeter before i can test anything. But that's a really helpful place to start and a little hope is all I needed to stave of the no-ebike-blues!! Time to unwrap the beast then 
...
...dnmun
1 PW
if you can test the cell voltages at the BMS that will be enuff to learn something but you do need a decent meter for this stuff.
the loose wires are usually where they are soldered to the top of the cell in the pack. but first get a digital voltmeter.
the loose wires are usually where they are soldered to the top of the cell in the pack. but first get a digital voltmeter.
I'm not running regen charging. But does the motor send a current back anyway when it's coasting? Also the cut outs are not totally random they do seem related to throttle input/big variations in current. (but it does cut out anyway sometimes)
Multimeter is ordered and when it arrives i'll get up close and personal with my new battery.
Multimeter is ordered and when it arrives i'll get up close and personal with my new battery.
Oh another thing that might help is.. I only just installed this controller and throttle and motor. Before i had a new 1000w kit off ebay and I think I fried the controller pulling a friend on a skateboard up a hill (i was very sad ) It had no bms issue with this set up but now it does with a similar (second hand) replacement controller/throttle/motor. The bms is attached to the battery in an awkward place. Perhaps I was a bit too rough with it mounting it in the frame and have disrupted the wiring?? I'm going to have a look..
) It had no bms issue with this set up but now it does with a similar (second hand) replacement controller/throttle/motor. The bms is attached to the battery in an awkward place. Perhaps I was a bit too rough with it mounting it in the frame and have disrupted the wiring?? I'm going to have a look..
Lessss
1 MW
Chinese BMS = high chance the BMS is crap.
Other possibility is BMS is doing it's job and the battery is actually dipping below cut off voltage due to cheap(bad) batteries.
Other possibility is BMS is doing it's job and the battery is actually dipping below cut off voltage due to cheap(bad) batteries.
dnmun
1 PW
of course we have no idea how you mounted it on the frame since there are no pictures or other info but if the BMS was allowed to touch the frame you may have shorted out the BMS sense wires at the spot where the plug is soldered to the pcb. that would shut it off. but with no pictures there is no way to even guess. of course people will guess as you can see already, so you can chase all those wild geese until we know something useful.
meanunclebob
1 mW
I'm thinking along the lines of the controller (or some part of it) overheating or in some other way not being able to handle the christians generated by the motor in a long coast. I had a similar thing happen with my little scooter (no freewheel). Maybe just a circuit breaker thing? I've read that sometimes they "like" to pop after being popped a couple times.
cassschr1
10 kW
Possibly phase wires having a sporadic disconnect?
Martog
1 mW
The first thing I would try to determine is whether the fault is within the battery or the controller and the go from there.
So when it dies, check the output leads on the battery and see if they still have power. If so, the issue is likely in the controller or wiring on that side of the system. If when it dies you are not getting power from the battery, it's more likely to be an issue with a faulty BMS, or a good BMS shutting that battery down because it detected either an overcharged or undercharged cell.
Either way, a DMM is your friend. Good luck!
So when it dies, check the output leads on the battery and see if they still have power. If so, the issue is likely in the controller or wiring on that side of the system. If when it dies you are not getting power from the battery, it's more likely to be an issue with a faulty BMS, or a good BMS shutting that battery down because it detected either an overcharged or undercharged cell.
Either way, a DMM is your friend. Good luck!
agniusm
1 MW
I would suggest running a wire from controller to the battery avoiding BMS (negative wire). If that will help, problem is BMS.
dnmun
1 PW
agniusm said:
yep, this is a good test to isolate it to either the controller or the BMS. i would assume the BMS is hitting the LVC which is why it requires removing the load like he said but it could be caused by something in the controller or phase wires, but i don't really know how.
but when he made the comments about rough treatment of the BMS and putting it on the frame it seems like he is telling us more than he actually knows and has now disappeared too. so maybe it was just the sense wires shorting out on the frame.
dogman dan
1 PW
The cut out nearly has to be the bms. Question is why. Since 99% of problems on ebikes are a loose connector, or broken wire at the solder to the connector, do check that stuff. Anything loose can make the pattern of the cut out make no sense at all. You hunt a rabbit, but it's actually a fox wearing rabbit feet.
But it also sounds like it does relate to the coasting. Do you have regen enabled? Bms getting more current than it likes? I totally guessing on that, but.
Any restart is generally an amp spike, even when rolling. I just suspect amp spike pops the bms, due to some weak cell groups in the battery.
But it also sounds like it does relate to the coasting. Do you have regen enabled? Bms getting more current than it likes? I totally guessing on that, but.
Any restart is generally an amp spike, even when rolling. I just suspect amp spike pops the bms, due to some weak cell groups in the battery.
Lessss
1 MW
First test. borrow another battery pack. That way you can narrow the poroblem to the pack or the bike.
Put a real-time voltmeter on the battery terminals so that you can see the actual battery voltage when riding. It will show you if the BMS is cutting out or if the problem is elsewhere. There's so many possibilities. You have to e methodical to track down the cause, not just guess.
agniusm
1 MW
Borrowing battery is somewhat complicated. Voltmeter give no usefull info. It could sag 3V and per pack is OK but it might be a cell in which case BMS will cut out. Resolving a fault is more complicated than putting electronics together.
John in CR
100 TW
Check each cell's voltage with a multimeter. Since it was working before and now it's not, it could be that you've simply never allowed the charger to balance the pack and a cell is low. How long did the battery sit while waiting for the new controller? You can't leave batteries idle too long with a BMS connected, because they often draw a little power from one cell.
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