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sunnybeam asked

Which inverter for 48V 300Ah AGM batteries

I have 32 pieces of 12V 56Ah AGM batteries here. If I discharge the batteries to 70% I would have 48V 300Ah. I would like to connect this to a Victron multiplus-ii gx 48/5000 inverter. Apart from the installation, I have 6300Wp of solar panels. Every year I inject approx 3500 kWh on the grid. That's why I want a system to store my own energy. The question is would I use all the batteries? So 8 sets of 48V together 300Ah. Total 15 kWh or should I use a few batteries less because I only have 6300 Wp of solar panels? Which Victron multiplus-ii gx should I buy, a 3000 or a 5000? If the batteries have lost their capacity, it is the intention to replace them with LifeP04 cells.


Sunnybeam

Multiplus-IISolar PanelAGM Battery
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mvas answered ·

Do you actually plan to connect 4 AGM batteries in series, and then connect 8 Banks in parallel?
What is the plan to keep all 32 batteries equally changed / balanced?

14,400 Watt-Hour = 48 Volts x 300 Ah
4.8 Hours runtime at max power = 14,400 / 3,000 watts
2.9 Hours runtime at max power = 14,400 / 5,000 watts

Will you have enough Sun-Hours, in the winter, to recharge the AGM battery bank from 70% SOC?

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sunnybeam answered ·

Thank you mvas for your message. In theory, the plan is to connect 4 AGM batteries in series, and then connect 8 Banks in parallel. But I can also connect less. In winter I will not be able to charge the batteries if there is no sun, even on a sunny day in December I only have 8 kWh of solar panels. So not enough to fully charge the batteries with the solar panels.n.

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Alexandra avatar image Alexandra ♦ commented ·

Ypu cant leave agms just sitting they must be maintained.

It is better to have a big bank and not cycle only some of them to a low soc. (They will then mis match and be aged faster than the other batteries) the other batteries will self dicharge and be in bad condition.

What @mvas is saying is you will need a way to balance the different batteries in the bank and maintain them. You will also need to wire them in a way that they all current share well or some will work harder than others and also age faster.

Make sure you also have a 12v charger and good digital multimeter to keep checking them. Rotating batteries in the bank as well will be a good plan. And buy battery balancers.

You will have to be extra careful to fully charge the bank in winter as well. Maybe cycling (especially if you dont need to) is not such a good idea.

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