Re: Lithium Batteries under Consideration


Scott SV Tengah
 

The hvd often occurs because one cell is over voltage. When that happens to me, if you look at the battery or bank level voltage, all looks fine. But that one cell is spiking. 

And if you don't cut off charging safely, and the cell goes above, i believe 4.2v, the entire battery is dead. Even if you can replace the cell, you now have a differentially aged battery. 

Point is that unless a charger is talking to the bms, it cannot detect cell level high voltage. 

If I understand right, seems the 24v parallel strings deal with individual battery hv and lv issues by disconnecting that one battery. For my system, the chargers were just shut off. 

I surmise as cells age they do it at different rates. Some develop higher resistance and therefore don't charge as fast. When I was drawing super high loads (150amps) and not fully charging often enough to trigger cell balancing, the imbalance reared it's ugly head. 

As you mention its unlikely that all batteries experience hv at the same time. What if you are leaving the boat in a very hot environment and the ambient temp spikes? High temp disconnect would affect all the batteries. How will your chargers and electronics deal with that? 

Also comparing longevity for cost comparisons implies that the only benefit of lithium is longer life. Consider that you will save 30% or more on generator runtime due to charging efficiency and high charge acceptance and the fact that you don't need to take it to 100% very often. And for us its nice to run all 230v without generator or even the 24v water maker all night but I understand you don't consider that a benefit. 

I'm full time for 2 years now and the batteries are as good as new. I know another a54 who has had it longer and they echo my experience. My experience with gel was that they declined linearly and then decayed exponentially until I got tired of charging every few hours. 

To me, the longevity is a nice benefit but definitely not the most important. 

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Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com

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