12v AGM parallel wiring for balanced charging

[Justin B.]

I know I'm going to get roasted for this but...

Here is the scenario:

I have 6 120 AH 12V AGM Deep Cycle batteries connected in parallel in the off-grid cabin I am finishing. I have 7 Renogy 100 Watt mono panels, 60 amp MPPT charge controller, and a 3000 watt pure sine wave 12v inverter. Up until now I had them hooked up the "lazy mans" way and research has shown me this was/is a bad idea. My next trip to the mountains I will be re-wiring them for a more balanced setup. I bought an IOTA 45 amp charger and will also be hooking that up so I can charge the bank via my generator when sun is scarce.

I have found a lot of wiring diagrams to connect 4 batteries in parallel so they are "perfectly balanced" but I have not found any diagrams for 6 batteries. Will it be as easy as hooking all + to a copper buss-bar with equal length cables and same with the - side? I know everybody hates parallel battery banks but for the next several months I'm stuck with this arrangement.

I realize I should have did more research before doing this and have realized the errors I've made and plan on correcting them when finances allow. I will switch to a "name brand" 24V inverter/charger and reconfigure the batteries to series/parallel to run the inverter with. But, for now, I am going to have to get by with the 12v inverter. It's a Chinese inverter (Reliable Electric) but so far has worked nicely and hopefully will continue to do so until I can get a Magnum Energy or AIMS Power inverter.

Thanks in advance,

Justin B.

[Mike90250]

Bus bar is a OK method.
BUT
AGM's have a typical failure method at end of life, they start to short out. If you have 6, and one shorts, the other 5 will be happy to dump all their power into the dud. The end result is usually messy. So with parallel AGM's you should use a fuse on each battery, 200-300A or something like that.

[Justin B.]

Mike,

Thanks for the response. I have a fuse ordered to go between the battery bank and the inverter but nowhere did I see mention of each battery needing a fuse! I have ordered a length of 1/4" x 1 1/2" solid copper bar to make the + and - buss bars with now I will need to decide how to best implement the fuses...

Regards,

Justin B.

[littleharbor]

Blue sea fuses mounted right on the pos. terminal.

Blue Sea terminal fuse..jpg

[Justin B.]

Thanks for the info! Although I was initially a little shocked as to the price of these after adding up the prices of more ANL fuses and holders + more battery cables they were actually a bit cheaper so I bought some.


I'm really starting to be glad the solar tax credit got extended for another year! I think I will also try to buy my Magnum Energy inverter/charger this year as well. Right now I'm at about $2700 on this project but the cost of having grid power ran to the cabin was off the chart!