48v bank wiring for MPPT / inverter

Excpta · Apr 15, 2024

hello everyone i have a off-grid house in the high country Victoria Australia.

i have 8x 150ah 12v batteries

i want to wire them to a 48v bank.

i want to series 4 together and then parallel the 2 banks together.

but where or is there a better place to wire in the MPPT controller to charge the bank, and then the inverter pulling out of it?

i hope that question makes sense.

Kind regards

sunshine_eggo · Apr 15, 2024

Two 4S strings in 4S2P config:

All (+) connections should be to the main (+) of one 4S string and all (-) connections should be to the main (-) of the other 4S string.

Ensure that you individually charge all 12V batteries to full before stringing them together. Once strung, confirm that they are VERY close in voltage when you are at peak 48V system voltage and that NONE are over their prescribed absorption voltage.

Excpta · Apr 16, 2024

sunshine_eggo said:
Two 4S strings in 4S2P config:

All (+) connections should be to the main (+) of one 4S string and all (-) connections should be to the main (-) of the other 4S string.

Ensure that you individually charge all 12V batteries to full before stringing them together. Once strung, confirm that they are VERY close in voltage when you are at peak 48V system voltage and that NONE are over their prescribed absorption voltage.

Thank you for your reply it makes complete sense to me.

A question tho, what happens if the battery cells are not exactly equal? Do they eventually balance out or does it cause bigger problems?

sunshine_eggo · Apr 16, 2024

Excpta said:
Thank you for your reply it makes complete sense to me.

A question tho, what happens if the battery cells are not exactly equal?

You haven't indicated type, but I'm assuming lead-acid.

Damage can occur either via over-volt or undercharge - usually both at the same time.

Excpta said:
Do they eventually balance out or does it cause bigger problems?

Lead acid will eventually balance out, but it's important that each 12V be checked at peak 48V to ensure they aren't out of balance/specification.

If balance can't be achieved, there are 48/12V balancers that that monitor each 12V and transfer charge from higher voltage batteries to lower voltage battery.

Excpta · Apr 16, 2024

sunshine_eggo said:
You haven't indicated type, but I'm assuming lead-acid.

Damage can occur either via over-volt or undercharge - usually both at the same time.

Lead acid will eventually balance out, but it's important that each 12V be checked at peak 48V to ensure they aren't out of balance/specification.

If balance can't be achieved, there are 48/12V balancers that that monitor each 12V and transfer charge from higher voltage batteries to lower voltage battery.

oh sorry they are Eaton 150ah AGM batteries.
do you have a specific balancer that you could recommend?

i actually will be replacing these batteries in the near future, but at this stage i'm bring it from a 12v bank up to the 48v bank seeing i have all the other hardware for it.

littleharbor2 · Apr 16, 2024

2 Parallel strings of batteries are doable with the diagonal+ of one battery/- of the other battery method but you could also go with a bus bar set up. Makes servicing batteries easier and adding 48 Volt loads easier.

sunshine_eggo · Apr 16, 2024

Example, not recommendation:

https://www.amazon.com/iSunergy-Battery-Equalizer-48V-Balancer/dp/B0BDF68PRJ

48v bank wiring for MPPT / inverter

Excpta

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sunshine_eggo

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Excpta

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Excpta

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sunshine_eggo

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