Thank you for hat makes sense. I was wondering if there could be any damage done if the BMS was bypassed completely?It's been a while since I looked at one of these batteries, so I have to go from memory. In principle, the BMS works the same as any other, but it has its own software and comms.
Like any battery, the output is switched by a some mosfets. They switch on when they get 14v on the gate (left leg). Somewhere on the PCB, I found the 14v supply, which is switched on to the mosfets by a transistor that's controlled by the CPU. I tested that when I bridged across the transistor, the battery switched on, which is logical. I didn't have the bike when I was looking at this, so I couldn't test whether the comms was working. That's as far as I got to.
If it works on the bike like that, you can leave it permanently bridged, or you can put a switch on it in the case to switch it on and off as you wish. The only downside is that you lose the low voltage cut-off, so you have to keep an eye on your display and make sure that you don't over-discharge the battery.
If you go ahead with this test/modification, please let us know the outcome.
Without the specific diagnostics for the battery and access to the software, you've got no chance of figuring out why the battery won't switch on unless it's something visual and obvious.
The left output mosfet legs will be connected directly to the transistor that switches the 14v, and you'll find the 14v on the other side of that transistor, though my memory says that it wasn't quite as straight-forward as that, so you might have to probe around a bit to find the 14v. The 14v could be 12v or something in that general range, though 14v is ringing strongly in my head.
It most likely can't be done because the BMS does some hand-shaking with the other modules. When you bypass the output switching transistor, the BMS will have all functions except low voltage control. I think the comms must still be working if you can charge the battery because that also does some hand-shaking.I was wondering if there could be any damage done if the BMS was bypassed completely?
Ahh thanks for that. Will try find him. My husband has an electronic s background and repairs electronic circuits for machinery manufactured in the 80's and 90s...however the new PC board s are mounted differently so many of the chips are "computed" in newer ways which is not his area of expertise. He can manufacture boards with the circuit diagrams. I think he needs to up his game as spending the fortunes on these batteries is not funny. There is going to be plenty of work repairing the BMS systems going forward.Hi,
I have not used him but at the end of this thread I started about my own battery/charger connector issues there is a member called Cosas who has said he can fix Yamaha battery problems either with the connectors or the BMS by fitting his own designed BMS.
https://www.pedelecs.co.uk/forum/threads/yamaha-battery-charger-problem.31092/
Thank you
you could try email them and see if they can get hold of one prob a long shot tho
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