Battery charged, but no power to bike.

[gmatht]

My battery is charged (it is sitting at 28V and is a 24V battery), but there is no power the the bike electronics, except when the charger is plugged in. What can cause this? In what situations is the Signalab BMSs designed to cut power to the load?

Some context:

There is 28V going into my Signalab SH-S E321748 but essentially nothing coming out. Most of the cells are at 3.4V, but one is at 3.5V.

The bike has worked before. It had a problem with the anderson connectors leading to the motor. This meant that the throttle did nothing. I fixed the anderson connectors, and then it worked for a while. The bike was rained on a little, it still worked, but I disconnected the electronics and let it dry for a couple of days before I charged it. It seemed to charge fine. Most of the electronics worked (e.g. the cycle computer at the front), however again the throttle didn't work. I fiddled around with reconnecting various connections to the motor. During the fiddling the bike fell over. I don't know when exactly this happened, but the bike computer stopped showing anything. I don't see any obvious corrosion anywhere.

The battery seems to be fine. It is sitting at 28V, which is pretty high, usually it sat around 26.6V when the motor was off. I would suspect that if the battery was simple dead, the voltage would drop, perhaps below 24V on load. However, the battery stays at 28V and only the "load" voltage coming out of the BMS drops. Also the battery was fine a couple of days ago, so I would have though the battery would die.
The Signalab BMS doesn't seem to be drawing any power from the battery.

If I attach the charger the electronics comes on, and throttle moves the wheel somewhat.

It sounds to me like the BMS is dead, but I don't have a manual so I am not sure if it might be cutting power because of a fault elsewhere.

 

[dnmun]

can you measure the gate to source voltage on the output mosfets of the BMS? do you have a voltmeter or did you rely on the bike computer which is now broken? but if you can measure the voltage between the left most leg on the mosfet and the right leg on the mosfet, it would help.

 

[gmatht]

Thanks. I measured the voltage using a Mooshimeter. IIRC the voltage was about 28V on the bike computer as well. I have just measured the battery voltage, it has dropped to 27.4V, as I'd expect since it has been a few hours since it was charged.

There is no voltage between the left and right legs of the mosfets. There *is* 25.3V between the legs and the heatsink. There is also about 25V between the legs of the four main mosfets and the fifth mosfet.

The four mosfets are soldered together, as shown in:

 

[gmatht]

Since the BMS still seems to be working as a charger, would it be safe or sensible to bypass the BMS and connect the bike straight to the battery? Perhaps via a fuse?

 

[d8veh]

I would check the cell voltages before bypassing the BMS. You should only bypass the discharge controls if you know that the cells are healthy and behaving properly. Your battery should be 29v fully charged, so it looks like you've got a dodgy cell. Is it a LiFePo4, in which case it's not so bad? Put your black probe on the B- pad and your red one on each of the pins on the multipin connector to get 8 incremental results. Post them here.

 

[gmatht]

The first half the cells are 3.6v, the next half are 3.4v. If draw a test load of a 3 amps directly off the battery, the total voltage drops by about 0.2v

 

[d8veh]

Sorry, I just re-read your first post, which implies that your BMS is working correctly. If the motor twitches when you open the throttle, the power is geting to your controller. Why do you think the BMS is faulty?

Have a look at your motor wire. Did it get damaged in the fall, especially where it comes out of the axle? What about the motor connectors?

With everything switched on, check whether you have 5v between your red and black throttle wires. If you do, it's your motor or controller that needs fixing, not the battery.

 

[gmatht]

Because there is only power to the electronics, including throttle, when attached to the charger. At the moment:
(1) Bike draws power from charger: everything works
(2) Bike draws power directly from battery: everything works.
but
(3) Bike draws power from battery via BMS: nothing works
(4) Nothing draws power from battery via BMS: BMS "load" voltage only rises to 3v even though no load, without enough current to fully light a small LED.

So everything seems to work except the BMS, which never provides any real voltage or current to it's load connector. Replacing the BMS is perhaps ce

When I charge the battery red light come on at the 3.6v cells. They flash random, then the 4 red lights go solid, go back to flashing randomly and so on. I don't have a manual but I guess the red lights mean the 3.6v cells are fully charged, and the lack of red lights mean the 3.4v cells aren't.

 

[d8veh]

The red LEDs switch on when the cell voltage is above the balancing voltage, which means the gate is open to the bleed resistor that will bleed the voltage down to the final voltage. The idea is that the charger gives enough voltage to charge all cells to 3.65. The bleed resistors open when the cell voltage is a bit below that, so the high cells bleed down to allow the lower ones to catch up.

LiFePO4 cells are more or less fully charged at 3.3v, so anything above that means that the cell is OK. If all your cells are above 3.3v, and the BMS won't allow power, it's faulty.

One last thing: The BMS is pretty well protected from water ingress. You didn't say exactly, but I guess that the water you mentioned didn't get in. The rest is very robust. The only thing that can be affected in a fall, other than a wire ripped off, is the multipin connector. Looking at your photo, it doesn't look like it's fully in. Where did you measure the cell voltages? Check them on the back side of the pcb to verify the connection all the way through.