Guru
Joined: 08/02/2015
Location: New ZealandPosts: 1252
| Posted: 09:47am 21 Jun 2025 |
We had a similar issue with a small 300AH 24v bank of lead carbon 6v batteries, not enough winter charge, so I added a temporary PV array with its own seperate mppt charge controller.
The batteries have a max continuous charge rate of 70 amps, this can now be exceeded by a large margin if suddenly we get a bright sunny day.
So I cobbled together a 24v bank 200AH bank of Lifepo4 cells (8 cells) wired in parallel to the lead carbon setup. As the end point voltages of both batteries are similar, it makes a great combination. The Lifepo4 cells can take 150 or so amps charge with no issues and absorbing any excessive charge from the additional PV.
Besides giving some extra capacity, the Lifepo4 bank really does all the heavy lifting, with the lead carbon bank taking over when the Lifepo4 cells start going flat, a high current vacuum relay switches them out of circuit when they get too low.
Cheers
Mike