Enduro bike shuts off after a few miles on full battery

[supergadgetman]

Hello all,

Its been a while since I posted, but hoping I could pick your ebike brains. I have an 3000W enduro frame ebike with a 72v 70amp DC Moto Controller paired to SW900 screen. I have a 72V 26Ah battery and a GEL 3000W 72 volt hub motor

Here's the problem. The bike charges fine and reads about 83V after a full charge. I take the bike out and its good for about 4 miles of using 1/2 to 3/4 throttle. Then the power just shuts down. I go to turn the controller back on with the screen and it just flashes on then back off as if I had a dead battery. I only have 300 miles on this bike, but I just figured the battery was needing replacement or it was sagging and triggering the LVC. After charging the battery overnight I decided to connect a volt meter to the charge port on the bike frame then taped it to the bike and took it for another ride. Before my ride the battery measured 82.7 volts. During my ride under heavy load I saw no major sag in the battery voltage according to my volt meter. It went down maybe .5 to 1 volt under load. I was holding steady at 80 volts then the bike just powers off about 3 miles into my ride. I look at the volt meter and it is reading 20 volts. I peddle the bike a few hundred feet to my house and park it. I'm still looking at the volt meter and its steady rising about .10 volts every second. The reading finally rests at 43.5 volts after about 10 minutes. Of course the bike wont even power on with that voltage.

Now here's the kicker. I open the frame and unplug the battery from the controller and the voltage on the meter jumps back up to 80 volts! I connect the battery back to the controller and power the bike back up and it comes right on. Still measuring 80 volts so I pick up the back tire and give it full throttle. It stays powered on only dips to 79.8 full throttle no load.
I have the controller out and upon inspection I see no visible wire damage or signs of electrical failure. I do not know at this point if it is the battery, bms, or contoller causing this issue. I do not want to rip open this soft pack testing cells if it's not the problem cause the battery seems fine. It's almost as if the controller is shutting the battery off and limiting its voltage, but when it's unplugged from the controller it resets. Has anyone ever seen this behavior. Would love to get pointed in the right direction.

TIA

 

[latex]

Its bms. Give it a full charge, bypass bms and then go for a ride. It will be back to normal.

 

[supergadgetman]

Hello Thanks for your reply. Are you saying I should bypass the bms when I charge it? Like charge it through the output wires?
I've done that to "jumpstart" dead li-on cells in small battery packs that were too low to be recognized by the charger.

Or are you saying to charge it normally then bypass the bms before I go for a ride? How would I bypass the bms without opening the pack?

TIA

 

[dogman dan]

The bms is shutting down the bike during the ride. The suggested test is to ride without the bms a bit, to see if it runs more normal then.

If it does, then you likely have a bms problem, the most likely being a bad connection on a bms sensor wire. So the bms thinks a cell is empty, when its just poorly connected. So it shuts the battery off.

On that test, if you do have a bad cell group, you will be pretty likely to over discharge it, risking a fire. So be careful.

Since you see so little sag, not as likely its a bad cell group. But don't ruin a cell group going too far on that test.

 

[supergadgetman]

ok, makes sense. So I would need to open the pack and disconnect the bms, correct?

TIA