So here I sit on board the boat
, on the mooring
, with the Honda generator
chugging away in my work
skiff, which is tied behind the boat. No matter where I placed the Honda generator
on the boat, both of my CO alarms go off.
IMHO things are a Darwin Award
creator for sure..P
So why am I running a portable generator? Why, because one of the BMS cell boards decided, all on its own, that it need to shunt energy from cell#2 100% of the time
By the time I noticed it, had not been on-board in a few days, cell #2 had become way out of balance with the others. The cell board failure happened when we were not on-board and with the bank sitting at approx 62% SOC...
Here we have a case where a BMS failure actually caused cells to go out of balance, not to stay in balance. Lucky for me I had a spare cell board and I am now sitting here rebalancing a pack that has not needed any balancing in 862 cycles...
So much for trying to get to 1000 cycles without any balancing. The old cell board is being sent out for repair and hopefully I can get an answer as to why it went tits up on me?
On the good side the BMS saved the BMS from itself and also saved my cell.. If I had not yet fully convinced myself that balancing is unnecessary, at the charge voltages I use, I am now... I plan to talk to the designer
and see if the BMS's other parameters will be impacted if the resistors are physically removed from the cell boards. I personally have zero need for automated balancing as evidenced by the previous 861 cycles.
To test some theories, I discovered this last Thursday before we were leaving on a four day weekend sail, I decided to simply lower peak charge voltage to 13.7V and set an alarm
for the low cell. It worked like a charm, though with less capacity, and we continued to use the out of balance bank without the high cells pushing over 3.55V and triggering HVC due to the imbalance.
If I had to take the LFP off-line the Firefly AGM
was sitting on the bench waiting for the coach to play him. Despite the injury, the star player pulled through.
All in all the cell board replacement, and quick regulator
re-program of the alt reg, took about 25 minutes. The hard part is now to re-balance the pack on the boat on a mooring
. More just tedious than difficult though...
My B&K 60A bench top power supply has been running flat out for 2:10 and the low cell is still only at 3.41V once it gets to 3.55V and 10A the pack will be wired in parallel and charged to 3.6V and 0.0A to 0.1A. Before I leave tonight I will parallel wire it and tomorrow will push it to 3.6V..
I suppose it never hurts to do a manual rebalance it just kills me that it was caused by the very thing we install to try and protect our banks... I am not really surprised by this and accept that it is just one of the prices you pay to be on the bleeding edge...
A new feature on my dream BMS is a manual lock-out for cell balancing so this type of failure mode can't occur..