diy solar

diy solar

External charger vs new inverter

trig2

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Feb 25, 2022
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I have an as yet uninstalled growatt 12k low frequency inverter. I was planning on using the grid bypass function but after reading half a dozen threads on how to handle the neutral I'm having my doubts.

So I'm wondering if I can just run "off grid" but use an external battery charger running off grid power to keep my batteries from getting too low. I'm thinking of controlling it with a smart plug and home/solar assistant to turn on and off at certain states of charge or possibly when the loads are high relative to pv input.

Will this just unnecessary stress my batteries (30kwh lithium) and should I just get a different inverter instead?
 
That's exactly what I have lined up for my 4 MPP Solar LV6548 inverter setup. I purchased 2 AIMS 120v to 48v LFP battery chargers, to have one charger per generator leg, to be able to provide charging without requiring to go into inverter bypass.

There isn't anything bad about charging this way. I'm still going to run little single breaker box from generator to the inverter AC input (just so in some emergency I could charge with the MPP Solar charging if ever needed, but don't speculate that I'd ever need to use those onboard chargers ever.
 
That's exactly what I have lined up for my 4 MPP Solar LV6548 inverter setup. I purchased 2 AIMS 120v to 48v LFP battery chargers, to have one charger per generator leg, to be able to provide charging without requiring to go into inverter bypass.

There isn't anything bad about charging this way. I'm still going to run little single breaker box from generator to the inverter AC input (just so in some emergency I could charge with the MPP Solar charging if ever needed, but don't speculate that I'd ever need to use those onboard chargers ever.
Aside from the battery health concerns it's not going to be very efficient, I should only have to do it in winter though so the waste is just going to heat the shed anyway.
 
Aside from the battery health concerns it's not going to be very efficient, I should only have to do it in winter though so the waste is just going to heat the shed anyway.

I don't think it's inefficient. Probably worse if the generator is over-sized and not being loaded down all the way (with the exception of an inverter-based generator). If the generator was hardly loaded down, I might use 4 battery chargers instead of two, say... Try to get the charging amperage up as high as I can for the fuel spent burning. Then I'd be getting maximum fuel burn for the time spent to charge.

But in your case, you didn't indicate if you're using grid power for charging or generator like I have to (we have no grid out at my place)...
 
Currently (on my temporary RV system), I use 4 IOTA 12v RV chargers wired up to my Prius APC UPS to charge my motorhome off of my car, and it is super efficient (in my opinion). I get 200a of battery charging at 12v (it'll burn maybe a gallon of gas in 8 hours), for when solar output is low. The Prius plays the role more like an inverter generator, as its RPM can vary, and it shuts the engine off each time when the car battery gets full, so it manages low fuel burn for the power it generates pretty well. Usually takes about 2 or so hours to get the batteries charged to 100% when I'm at about 60% SoC...
 
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