On 3/13/21 1:57 PM, Lee Hart via EV wrote:
John Titman via EV wrote:
Hello: Nobody answered my question The whole reason I need to balance my
batteries is that a number of batteries reach 3.6 volts before the
others,
who only reach only about 3.3 volts The Orion BMS shuts of the
charger and
balances the batteries but, the same problem occurs after the next
recharge . I've discharged the batteries a number of times but, they
still
bounce back to about 2.51-2.53 volts . Do they need to ALL be exactly 2.5
volts before recharging?
Hi John,
When the batteries reach anything close to 2.5v, they are effectively
dead -- no useful capacity remains. It doesn't matter whether they're at
2.5v or 2.6v -- they're still DEAD!
I don't recall what current the Orion uses to balance, but I think it is
pretty small (milliamps). It may be that your batteries have aged to the
point where the differences between them are too large to balance with a
small current.
I see several possibilities here:
The pack may have some bad cells as you speculate.
It may be that the pack has never been properly balanced and the BMS is
stopping charging when a cell or two reaches max voltage and John has
not recognized that some cells have never been brought up to near
charged voltage.
As Lee mentions, the first thing to do is examine the voltage on each
cell immediately after the BMS has turned off the charger. Also, see if
total pack voltage is reasonable.
Should the pack need initial balancing (top, not bottom) and does not
have bad cells, several options:
1) fool proof is putting all cells in parallel and charge to ~3.4v
(assuming LFP cells) with a single cell charger (could take weeks with a
typical ~5 amp charger)
2) repeatedly run pack charger and allow the BMS to slowly bring up the
low cells (could take many hours). Each BMS/charger cycle improves
balance only slightly.
3) Identify low cells and charge them with a single cell charger to
about 3.4v (could take hours per cell with a ~5 amp charger). If you
have several single cell chargers, you can do several cells at a time.
John has given us insufficient information. Does the car have an
EVAlbum page?
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