On Wednesday, May 13, 2020 at 8:00:09 PM UTC-7, kinsell wrote:
On 5/10/20 12:10 PM, wrote:
On Sunday, May 10, 2020 at 10:50:22 AM UTC-7, wrote:
On Sunday, May 10, 2020 at 1:40:44 PM UTC-4, wrote:
On Sunday, May 10, 2020 at 10:06:53 AM UTC-7, wrote:
On Friday, May 8, 2020 at 4:55:35 PM UTC-4, wrote:
There was a thread about this, K2's mentioned, a rew years ago that Steve Keorner replied too. He asked the K2 engineers about reduced capacity he was getting, IIRC, their answer was to leave them on the charger for weeks at a time so they can balancecout the cells with the BMS on board.

CH

Question: I don't know about K2 batteries and chargers specifically, but generally I thought the BMS in LiFePO4 batteries disconnects completely from the charger once some maximum battery voltage is reached. How, then, does leaving them wired together for "weeks" going to do anything?

Perhaps over time the battery voltage drops back somewhat and the BMS re-engages with the charger?

The internal BMS itself has a top balancer. It will detect when one or more of the cells are undercharged and very slowly discharge the others to first equalize them, then top them all off together. This may happen multiple times over a fairly long time until all cells are equalized since the undercharged cells themselves are unequally so. This can happen by passive balancing (resistive) or active (energy transfer from one cell to another).


I have seen my charger cycle when charging my LFP batteries (it's not K2 though).

There is no hard disconnect. Monitoring by the BMS is continuous.

David

So you concur with the BMS-reconnects-over-time hypothesis.

I usually charge my battery with my iMax B6 charger because it shows me what's going on, voltage and mAH. But when the battery reaches about 14.6V my battery's BMS disconnects - a bit before that charger would have stopped the charge anyway. And that charger then complains loudly about the connection being lost, and won't restart automatically.

If I want to give the battery BMS time to balance the cells further, I'd need to put it on a different charger. Would connecting the battery at that point to a "dumb" fixed-voltage source of about 14V be a good idea? Would using an SLA charger that aims for a "float" at 13.6V or so be a good idea?

With my battery (Stark Power) and charger (see below) this is not just a hypothesis.

The BMS in all LFPs may not have the same functionality regarding balancing but at the very least they should start/stop accepting charge appropriately.


It matters not what you think should happen, the truth is not all LFP
batteries have a BMS, and of those that do, not all of them protect from
over and under voltage.

Which LFP batteries don't have a BMS?

Tom