How much battaery do I need to start my system

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How much battaery do I need to start my system

Postby DThorp on Mon Oct 23, 2017 2:11 pm

Hello Forum. I am new here and have just finished installing my Outback system Flexnet with 2 controllers. Off Grid 48V system. I have a delay in delivery of batteries (up to 4 weeks) and would like to power up the system to make sure all is well, not big loads, primarily just want to know that everything is working prior to winter arriving. I have access to 4 automotive size 12 volt batteries which will get me the required voltage, but am wondering if this will put anything in danger. My PV array is 24 290 watt panels. Can anyone comment? Thank you
DThorp
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Re: How much battaery do I need to start my system

Postby Mike Curran on Mon Oct 23, 2017 3:49 pm

This site http://www.chem.hawaii.edu/uham/bat.html says:

"A standard small car battery is about 45 amp/hours. That means that it will supply over two amps for 20 hours. A battery should not be discharged at a higher current draw, or asked to deliver more amps than its amp/hour rating divided by 10 in order to get maximum capacity out of it. In the case of a 45 amp/hour battery that would mean it should not be asked to deliver more than about 4 amps for best service."

This means you'll have to set up your FlexnetDC to limit charging and discharging current appropriately. This is important considering the size of your array could easily overpower these batteries' capacity. And at a maximum 4 amp current draw, the largest load you could put on this battery would be around 4A × 48V = 200 watts - pretty small. Should be doable, though.
Mike Curran
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My RE system: Outback: 8 (2x4) Evergreen 180's into one MX60, 6 (2×3) ALEO S79-300's into one FM80, 2 grid-tied GVFX3524's classic stacked for 120/240VAC, 12 Surrette/Rolls 2V x 1766Ah, Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar: 30 (2x15) 235W panels with Enphase M215 microinverters. 6,450 nameplate watts AC, grid-tied.


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