adding batteries...do I need to upgrade wiring

[johnim]

After a while now evaluating how much energy I can get out of a single EG4 48v 100amp battery I've come to the conclusion that it's not enough especially with 2 minisplits. So I'm adding 2 more server rack batteries for a total of 15kw potential. Whenever they're back in stock I'll get another 3kw inverter. For now I'm focusing on hooking up 3 batteries vs just the one. I know I have to balance them out so there's that but in one of Will's video he's using 2/0 wire for inverter supply and 4/0 wire for the battery hook up (the one where he uses 6 batteries and two 6.5kw inverters).

If I only have 3 batteries do I need that big a gauge wire? With the one and one set up I have 4 gauge inverter and 6 gauge battery cable that came with the products. the wire gauge current chart I'm looking at only goes up to 200 amps. Is there a good online resource for bigger gauges.

Also, another thing I don't understand. With Will's system he uses 200amp T fuses for each inverter and battery cables are going through a 300 amp busbar. For so many amps are those hefty enough? In my Signature Solar manual they recommend using 600 amp bus bars.

 

[cs1234]

What is your current inverter? An EG4 3kw/48v? The number of batteries you have doesn't determine the gauge you need to use from the battery busbar to the inverter. It's the amperage you plan to be pulling from or pushing into the batteries to the inverter that determines that. If all you are trying to do is get more run time, then you don't need to change anything from battery busbar to inverter if they are currently sized correctly.

Not counting surge power on a 3kw/48v inverter, you would be fine with the 4 gauge to inverter and as you are pulling less than 100amps. The 6 gauge from the battery to bus bar is also ok assuming they are fairly short, but certainly not oversized.

If you were to run a second 3kw/48v inverter, each inverter still only pulls the same amount of DC current as a single one, so the cabling can stay the same there also. Your bus bar itself would be pulling twice as much amperage though (if you were running 6kw worth of load), so the busbar would need to be rated for 6kw/48v 125amps plus buffer, so say a 200amp bus bar to be safe. The batteries and inverters themselves are still pulling the same amount through their cables as if everything were like it is with your current config though.

tldr : each battery is still pulling/pushing the same amount of amps to the busbar regardless of how many of them you add, so the cabling can stay the same. The bus bar needs to be rated for enough amps to carry the combined total load of your inverters.

 

[johnim]

Well that explains a lot and saves me money on bigger cables and fittings and more crimping tools. Thanks!

 

[johnim]

oh and to answer your question yes I have the 3kw eg4 inverter. had I known what I know now I would've opted for the eg 4 6.5kw inverter and I'm a little bummed bc I will end up paying more for two 3kw inverters than if I had gotten the 6.5kw inverter in the first place but I think I would lose more if I tried to sell the 3kw and then wait on the 6.5kw inverter which is not due til mid September per website. but again thanks cs1234 ur clarifications really helped.