My first attempt battery backup


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Newbe

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Apr 5, 2024
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I am new to this game. I could use advice on just about everything.

I have eight 8s 33.6v max and 24v min 67 amp hour li-ion batteries. Want to run four “48”v packs (no solar) backup system for Florida hurricanes. Hopefully will not have much use.

It is difficult finding reasonably priced inverters with 48v to 67.2 v DC input. I found 24v hybrid inverters which will accept 33v input but 24v system would be more expensive (8 vs 4 BMS, larger cables etc.). WZRELB has a 60v inverter that will accept 50v to 75v input. I would like to use an inverter charger for the convenience but not necessary. Recommended charging at 22.3 amps. I will have to depend on gas generator for charging power.

I would appreciate any suggestions on inverters and chargers.
 
Most high performance and reliable inverters use 48VDC, ie 42 - 60VDC range, for the input. It's pretty standard.

And really, it's highly recommended to use 48V regardless of the size of the loads because the wiring management, fuses, etc is a lot easier/cheaper to work with.
 
Have you decided on anything since the original post?

One could use 16S lithium ion (NMC) with a 48V inverter with max input of 60V, but that is only 3.75V/cell, which is something like 60-70% SOC, so you'd lose a lot of capacity, but it would work.

Could also use these packs as "range extenders" for an off-the-shelf portable power station by hooking them up to the solar input. Or input to some other solar charge controller maintaining a separate 48V nominal pack (or even one of these packs you have). Maybe 24V battery would work better, you'd have to sketch out what happens and min/max voltages.
 
Could also use these packs as "range extenders" for an off-the-shelf portable power station by hooking them up to the solar input. Or input to some other solar charge controller maintaining a separate 48V nominal pack (or even one of these packs you have).
This strikes me as a potentially viable and very easy solution -- good thinking! It might be necessary to connect some of the batteries serially to get enough voltage to look like solar input, depending on the inverter/charger unit, but that isn't hard to overcome. You're right that it would require a separate 48v battery, but it could actually be one of fairly minimal capacity, with the idea that you're really running off the "solar" aka range-extender batteries. I like the simplicity of this idea, given that the batteries are already purchased.

I have also considered a "backup-in-a-box" type solution, with a 48v battery and an off-grid inverter, just to plug in rather than running a fuel-powered generator. (Or to bridge short outages, when it's just not worth firing up the big generator for only one or two hours.) Future projects...

Cheers, John
 
For me the answer is always Victron. The input voltage range for the 48v Multiplus II is 38-66V. That's a pretty fine match for your batteries.

There also ain't nothing wrong with the range-extender idea put forth above.
 
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