I am setting up a new 48V battery bank but don't have access to the mains in the location (and I have already transported the new batteries over there). The voltages are a bit uneven so I want to recharge them fully before putting them into an array of 3-parallel x 4-series.
I don't have a powerful charger (and don't want to buy one for the purpose), but came to think of the MPPT controller itself that I am going to use, and I am wondering if I can use it to charge the new batteries from the existing 48V battery bank. The idea being to connect the "PV" input from the old battery bank (48V), and connect the "battery" terminals to the individual 12V batteries one at a time, and making sure there are no common grounds/connections between the 2.
The idea seemed great until I noticed a "maximum PV short circuit current" rating of 40A in the spec sheet. Which kind of ruins the idea because the batteries can deliver way more than that. But under what circumstances would it draw more than 40A if the controller is supposed to limit the input current? Can current "shoot through" the DC-DC step-down stage? Can it be protected by protecting the input side with a fuse?
