I have what is no doubt a simple question. I am looking to run some AC equipment with the following specifications using batteries:

Power consumption 1.1kW (Max power 1.25kW), Voltage 230VAC, Current 5A.

The device operates intermittently (switching on roughly every 9 minutes for periods of about 1.25 minutes at a time) such that over a 3 hour period the device is operating for ~23 minutes. Therefore, within each 3 hour period, the device requires ~0.3kWh of energy.

I would like to run this device away from regular power sources for periods of at least 12 hours. To do so, I have at my disposal ten 55Ah deep cycle 12V AGM batteries (see here for further detail: https://www.optimabatteries.com/en-us/yellowtop-deep-cycle-battery/d34).

My question is, what is the best way to estimate how many of the 12V batteries I will need to use to run the device for 12 hours? Obviously, I will need a suitable DC/AC Inverter to convert to 230VAC. As such, I was thinking of using this: https://www.elfa.se/en/dc-ac-inverter-1500-cee-hq-hq-inv1700-12/p/30060696?q=HQ-INV1700%2F12&page=1&origPos=1&origPageSize=25&simi=99.65&no-cache=true

However, maybe I will need an inverter capable of 24DC to 230VAC.

Any advice on this topic would be much appreciated.

Based on the advice given here a four parallel battery solution (12V) will work: 4 parallel battery solution (12V)

However, a 24V 2S2P solution would have less current and therefore less resistance increasing the efficiency of the system: 24V 2S2P solution

However, in order to keep the batteries balanced the following configuration may work better: enter image description here

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    \$\begingroup\$ Remember that you don't want to drain lead acid batteries deeply. Take what is "barely sufficient" and double it at least, I'd triple it. \$\endgroup\$ – Brian Drummond Jan 25 '18 at 12:28
  • \$\begingroup\$ Ok, thanks for the tip. That would suggest I should use at least 4 batteries. Based on my schematic have I understood "parallel" correctly? \$\endgroup\$ – user1912925 Jan 25 '18 at 13:33
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    \$\begingroup\$ Yes but you could connect pairs in parallel (2S2P) and make 24V which would be a bit more efficient (less current = less power lost in wire resistance). \$\endgroup\$ – Brian Drummond Jan 25 '18 at 13:36
  • \$\begingroup\$ OK, thanks again. Presumably, my second schematic is what you mean by a 2S2P 24V solution (using a 24VDC to 230VAC 1500W inverter)? \$\endgroup\$ – user1912925 Jan 25 '18 at 15:42
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    \$\begingroup\$ Ah OK. Maybe the third schematic is what you mean if we want to keep the batteries well balanced? \$\endgroup\$ – user1912925 Jan 25 '18 at 16:03

For each 12 hour period you need ~1.2kWh worth of energy. Each battery holds 0.66 kWh worth of energy. So 2 of those will be barely sufficient assuming the inverter is very efficient (>91%). If the inverter isn't that efficient then you will need a third battery.

If you put them in parallel you can use the inverter that you linked.


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