rcxotic Posted November 17, 2021 Share Posted November 17, 2021 (edited) Hi team! 3 of my 4 batteries shows subvoltage of 0v. Back right is like 17v which is normal I believe. From what I was told, 0v subvoltage means there's a fault with the BMS. I suspect there was a Short in the old motherboard causing a fault with each batteries' BMS. None of the batteries would charge on its own when connected to the new motherboard. Anyone know how to reset the BMS after opening up the battery? Hopefully to avoid buying a new set of batteries. Thanks in advance! Edited November 17, 2021 by rcxotic Added clarity Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 17, 2021 Share Posted November 17, 2021 Hi! 24 minutes ago, rcxotic said: 3 of my 4 batteries shows subvoltage of 0v. Back right is like 17v which is normal I believe Between 84V/2=42V and ~76V/2=38V is normal - 17V is way too low. The back battery consits of two 42V (12s) packs in series with ?one common? BMS. But could be just a measuring artefact, because the activated output protection could have a comparable resistance as the voltmeter. Showing 0V is strange and worrying!? 27 minutes ago, rcxotic said: I suspect there was a Short in the motherboard causing a fault with each batteries' BMS KS BMS have overcurrent/short curcuit protection. Normally such a condition is reset by "curing the fault" (disconnecting battery from shortening mb). Maybe plugging in the charger once could be adfitionally needed? KS wheels should have fuses too which could/should burn once something shorts. 30 minutes ago, rcxotic said: None of the batteries would charge on its own when connected to the motherboard. Maybe the part of the motherboard responsible for charging is destroyed, too? Afaik the "new" KS motherboards could have some "charge control" - charging could be just shut off once the motherboard is dead... You have already a new motherboard? Could be not really recommendable to plug the batteries in the shorted one? The batteries afaik have a "sync" wire connecting all of them - so if one BMS has problems none will charge? So i'd try to charge each battery alone to check them. I assume that's what you tried? But with the motherboard - could/did you measure voltage arriving at the battery? Does the charging voltage arrive at the battery connectors on the motherboard? Do not reconnect batteries with different voltages! Be carefull messing around with the batteries - they can be dangerous! 2 Quote Link to comment Share on other sites More sharing options...
rcxotic Posted November 17, 2021 Author Share Posted November 17, 2021 @ChriullTy for the reply! Yes I have a brand new mainboard now. The main voltages of each battery is perfectly fine, below are their readings; FL 62.6v main /~0V subvoltage FR 62.6v main /~0v subvoltage BL 27.4v main /~0v subvoltage BR 36.6v main /~17v subvoltage I think the subvoltage is used as a way for each BMS to tell the motherboard the health of each of the 4 batteries. And the motherboard will only charge each battery if every battery that is plugged in has a proper subvoltage reading. Per ewheel, proper subvoltage is supposed to be like this: FL: 83.6V main/12.4V subvoltage FR: 83.6V main/12V subvoltage BL 42V main/11.9V subvoltage BR: 41.7V main/19.3V subvoltage Meaning of "subvoltage" is depicted below (courtesy of ewheels) I did purchase a new pair of back batteries which charged fine. So I know the motherboard & charger is all good. Hoping to reset the front pair's BMS instead of purchasing new ones. Thanks! 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 17, 2021 Share Posted November 17, 2021 3 hours ago, rcxotic said: @ChriullTy for the reply You're welcome! 3 hours ago, rcxotic said: The main voltages of each battery is perfectly fine, below are their I'd BL has a dead/some degraded cell group(s). BL and BR has to have the same voltage, (Bl+BR) has to be equal to FL and FR. 3 hours ago, rcxotic said: I think the subvoltage is used as a way for each BMS to tell the motherboard the health of each of the 4 batteries Presumably the "sync" wire - once one cell group has reach the overvoltage threshold (~4.25V) it signals with this wire that charging is stopped for all packs. This "condition" should reset itself within somerhing roughly around 1-2 hours, as this cell group gets discharged to ~4.19V by the balancing resistors. 3 hours ago, rcxotic said: I did purchase a new pair of back batteries which charged fine. So I know the motherboard & charger is all good. Hoping to reset the front pair's BMS instead of purchasing new ones. The front batteries have to be charged to the same voltage as the back batteries! Sounds as you just charged the back batteries? As written above - FL and FR have to be equal to (BL +BR)! Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 17, 2021 Share Posted November 17, 2021 11 hours ago, Chriull said: two 42V (12s) packs Ups, 10s of course... As the back packs are two half 20s 84V packs... Quote Link to comment Share on other sites More sharing options...
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