Electrical Problem?

PineNut

New Member
I have a 2018 BH Rebel 27.5" PW-X bike. I'm posting here because my issue seems to be related to the Yamaha PW-X electrical system.

I got the bike in January this year and have 935 miles on it, mostly on dirt trails. The battery charging was working fine until today.

Yesterday I began my ride with 77% battery charge (per the Yamaha display unit). The battery showed three of four bars lit as it should (indicating >= 75% charge). After my ride, the display unit showed 52% charge and the battery showed two bars (>= 50%), again as expected.

Today I charged the battery for one hour which based on past experience should add 30 to the charge for a total charge of about 82% (I get about 10% more charge per 20 minutes of charging based on my experience). The battery once again showed three bars as it should.

However, when I attached the battery to the bike the display unit only showed 46% charge. The battery still showed three bars (>= 75%). Humm...

I took about an 8.5 mile ride and the display unit now shows 31%. The battery shows two bars (>= 50%). Something is way off. I've always gotten good correlation between the display unit and the battery bars in the past. I've tried removing the battery and reinserting it several times, but that didn't fix anything. I think the battery is giving the correct charge level, but the display unit is off by about 30-35% too low.

I tested the battery capacity per the Yamaha service manual, and it's fine at 75 to 100%. The number of charge cycles is also good at 0-100 cycles. My 500W, 36V Yamaha battery has three terminals on it to connect to the bike and I measured 35.50 volts on the two outer terminals. I'm not sure that is the correct way to measure the battery voltage, but I did not see any voltage on the center terminal.

I guess the next thing to try would be to charge the battery to 100% and see if that fixes anything. I'm reluctant to do that right now because the outside temperatures will be in the low 40s (deg F) for the next week or so and that's a bit cold for the long ride (about 25 miles) I'd need to do in order to get the battery back to 50% where I'd like to store it.

So, I thought I'd check here to see if there are any suggestions regarding what else to try before I get the cold weather gear out.
 

PineNut

New Member
Well, I charged the battery to 100% and it displayed the 4 lighted battery bars as it should.

I reinstalled the charged battery on the bike, turned on the Yamaha display and... the display showed 100%!

I was able to do a short 6 mile ride and all looks well so far.

I was worried I had some sort of a resistive short or bad power connector on the bike which might explain the low battery readings I saw on the display yesterday. I don't know what happened. I assume the battery/BMS has some sort of circuit breaker should a hard short occur.

Anyway, hopefully things continue to work well. Now I just need to get the battery charge back down to around 50% for the upcoming colder weather...