Originally Posted by Jeff Millar
How would you select a battery charger to charge a lithium - ion battery bank consisting of 2 - 12 volt - 300 ah batteries connected in parallel.
Would you buy a charger with a rated out put of 70 amps or 90 amps with adjustable input voltage levels.
Or what would one of you experienced experts care to recomment as the best.
We use a Sterling Pro-Charge Ultra and a "custom" setting. This charger allows you to build a custom program. With this charger I have it set to charge to 13.8V then drop to 13.4 which essentially turns it off unless a load kicks on. We very rarely use our battery charger though. Once the bank attains 13.8V it gets to a point where very little current will flow into the bank at that voltage. While it is not technically full
, as in upper knee full, it simply gets to a point where 13.8V can no longer push any more current into the bank... It tapers to this level, in fairly short order, once the current starts to drop...
When on the hard
I use a Mastech switch mode power supply with adjustable voltage and current settings and basically set it to run the "loads" but not really charge as I don't want the bank sitting at 100% SOC all the time. I prefer to leave the bank at about 50-70% SOC, if letting it sit.....
These batteries will work any charger very, very hard and this is why I prefer the power supply because I can turn it from its 50A rating down to 40A and it runs nice & cool and can do this nearly indefinitely. I had 30A unit but it proved too small for the cycle testing I was doing. I now run them in parallel and charge at 60A when needed. If I run the 50A at 50A and the 30A at 30A they begin to develop heat smell
...If I knock 10A off each they run nice and cool. I also have a 100A charger that I use in the shop and have stacked all of them together to pack two 80% DOD cycles into one day......
I charge to well below the upper knee so as to prevent any potential for cell damage... As near as I can tell, via capacity testing, we give up about 7-10Ah's by only charging
to 13.8V but that has been well accounted for. The cells have remained in perfect balance despite not pushing our BMS to shunting/balancing voltage level.... When I do push that high all the shunt lights come on at exactly the same time.....
As of Tuesday the bank has 164 cycles. A large number of those cycles to 80% DOD and many of those drawn down at a .25C load or greater (100A on a 400Ah bank)... 164 cycles to 80% DOD would leave many LA batts dead...
I am trying for 200 cycles before we pull the boat out of the water
in November. It takes WORK to get to 200 cycles!!!! The nice thing is that we have had a cold fridge all summer despite being on a mooring
.... The bad thing is my wife keeps complaining that we are freezing stuff because I have the fridge set so high in order to accelerate the cycling frequency.
I have been purposely deep cycling this bank because for me this is more of an experiment/product testing than for my own personal gain. I have been pushing this bank far harder than it would be on most cruising sailboats, just because I am curious.
Through hundreds of hours of testing and cycling this bank I have settled on 13.8V - 13.9V charging for my max voltage and it has been working flawlessly. Personally you would not see me pushing Winston cells higher, in daily practice, but that is where I have settled and I know others push higher...
I treat our BMS as a safety
net only... Essentially we are using/charging/discharging our bank without a BMS despite it being there as a safety
net. Others on here have ruined cells (Chris Witzgall & T1Terry that I know of) with no safety net to prevent it, so I do believe in having it to prevent my own HEF (human error factor) and save myself, from myself. So far we've never once come even close to utilizing it for LVD, HVC or for balancing....
In order to cycle deeply I had to install a manual alt cut switch and we often run the motor
with the alternator