Help with Motorcycle battery

Hoping someone has experienced something similar to the trouble I am having with a 72v / 60AH battery from Modi Battery. They use lithium Ion prismatic cells. I bought the battery NEW in August, connected it to the motorbike, and it worked. It charged, And worked after several plug in/unplugs repeatedly as I got the battery mounted over the course of a week - 10 days. The battery was fully working. Right when I was finally ready for a test ride, I hooked everything back up and the battery was unresponsive. It would not charge. I tried other fixes like discharging with a lightbulb, and hair dryer. No luck. I figured the BMS failed. I replaced the BMS and still nothing. While the new BMS is connected the Discharge and Charge connectors measure 77.5V. I measured the battery without the BMS attached and it read 78.6. I tested all 20 cells and all are reading 3.9/4volts (add up to 78.6) when tested off the series connections for the BMS (when NOT plugged in to the BMS). I didn't do anything to activate the new BMS and unsure if I need to. All i did was replace and plug all the wires in as they were. I feel as though i am missing something, or something stupid is happening. Any pointers. ideas, help would be greatly appreciated.

changeissimple said:

Right when I was finally ready for a test ride, I hooked everything back up and the battery was unresponsive. It would not charge. I tried other fixes like discharging with a lightbulb, and hair dryer. No luck. I figured the BMS failed. I replaced the BMS and still nothing.

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By "nothing" do you mean the bike won't operate, or only that it won't charge, or both?

While the new BMS is connected the Discharge and Charge connectors measure 77.5V.

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Is that while battery is connected to the bike, or only when not connected to anything?

I tested all 20 cells and all are reading 3.9/4volts (add up to 78.6) when tested off the series connections for the BMS (when NOT plugged in to the BMS).

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What do you measure *at* the BMS board itself, on the solder pads of the plug pins, for the same test?

If any of them is different, it probably means the connector itself has a problem with the contacts so they are not mating with the BMS pins for the one(s) that read incorrectly when plugged in.

This could be a bad crimp for a wire to a connector contact, or it could be a connector contact which is spread out just too much to make proper contact with the BMS pin, or that is not fully seated in the connector so it backs out when the connector is plugged into the BMS. You may be able to see any of these in good light with a magnifying glass, but sometimes you just can't visually see it very well.

I didn't do anything to activate the new BMS and unsure if I need to. All i did was replace and plug all the wires in as they were. I feel as though i am missing something, or something stupid is happening. Any pointers. ideas, help would be greatly appreciated.

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If the exact same problem is happening with the new BMS that was happenign with the old, then it is probably something other than the BMS causing the problem. Does the old BMS give the exact same symptoms and measurements that the new one does?

Thanks for the responses. I still have not figured it out yet. Both BMSs have the same measurements and the same unresponsiveness. I measured all the cells and they seem fine. I am wondering if it could be a temp sensor? I also found this link and wondered if anyone had experience resetting the BMS using this method. https://diysolarforum.com/threads/bms-wont-turn-on.17139/

Technically, you can measure every single line on the voltmeter, and there may be a hidden fuse someplace or a BMS wire that has come loose, I'd measure every wire from the BMS end twice using very precise multimeter tips if it's on the molex. If it's fine, and you have studied the BMS wiring diagram and hooked it up correctly, then you may well have to charge the battery a first time through a charger to activate the BMS, that's what was written on a Y.I.T. or something BMS that I had.