Re: Lithium Batteries under Consideration

Scott SV Tengah


At least with my batteries, they are passively balanced. Most are. That means they don't balance between cells (even if I had a 12v system because recall that a 12v battery is 4 lifepo4 cells in series) unless you get them to 95% SOC or more. Only then do the "voltage knees" start showing up - before that, there is very little difference in voltage. Even when I had imbalanced batteries, the cells were perfectly matched up to 90%. At 95%, that's when the voltage spike became apparent and the balancing starts kicking in. I can't see how you would notice imbalance otherwise due to the voltage vs SOC curve of lithium. 

As you apply current, which will be reduced as SOC approaches 100%, that's when balancing occurs. This is all per my lengthy conversations with the Victron techs. That's how "automatic recovery" happens. Now in my 24v system with pairs of 12v in series, if you start with an imbalance between the two 12v batteries in series, the imbalance can get worse and may not be corrected. Same problem as in lead batteries. I just connect via bluetooth to my batteries whenever I'm approaching 100% SOC to verify that series pairs are balanced. FWIW - Victron advises against using battery balancers in systems such as mine where 12v are put in series to make 24v and then paralleled. I'm not sure why?

With regards to temp, my system doesn't have a "bank temp sensor" nor does Victron recommend one. High temp disconnect means that the BMS tells the chargers to stop charging when even one of the 24 total cells gets too hot per each cell's internal temp sensor. Note that charging is simply stopped - the battery is still connected.

The Mastervolt Alpha Pro 1,2,3 is controlled by a "reg-on" wire. That's how I have it safely stop charging if the BMS senses something awry. It required two Hella relays and a solid state relay - I wrote it about it in another post. I also installed a switch inline to turn off the alternator during long motoring sessions when I don't want to keep the batteries at 90%+. Very easy to do.

I honestly think if you're not living full time liveaboard, often away from shore power and you're willing to use the generator a lot, lithium does NOT make sense. It's a lot of brain damage and cost to get it right. It works for people with my use case and people like Garulfo (A54 with Mastervolt lifepo4 system for much longer than my 2 years) who when I asked him if his lazarette 230v breaker is working, he shrugged his shoulders and said, "I can't remember the last time I plugged in, so not sure." Not to put words in his mouth, but I'm pretty sure for him, he would never go back to lead.

2007 A54 #69
SV Tengah

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