Best inverter to use as a UPS

[SubnetMask]

I'm looking into setting up a fairly small setup with two inverters, not because I need 6000w of power but for inverter redundancy, and I'm thinking of starting out with two 12v 100Ah LiFePo4 packs in series, which would provide 2400Wh of energy at 24v - roughly 4x the capacity of one of my UPS's, or double that of the pair (APC SMX3000's). I'd like to have the possibility of adding solar, even if to start, it's just my two little 100W harbor freight panels that are set up in series and currently connected to a Renogy40A MPPT controller - A little less power bought from the grid is a little less bought from the grid. I have zero interest in outputting to the grid. I only want the inverters to connect to the grid to act as a charger/passthrough for the batteries and load. Ideally, I'd like for the inverter to take grid power (or generator power), convert it to DC, then convert it back to AC as a clean sine wave, and in the event of a grid failure, have the shortest transfer to battery time possible, if not a zero transfer time. For grid power, the conversion isn't all that important, but my generators output is 'dirty' (The APC units won't transfer off battery when connected to it), so if the inverter(s) could take in the 'dirty' generator power and output clean power, that would be ideal. The main thing is I'd like to replace my APC's with a setup that's a little more 'serviceable' and expandable as both of which have been giving me trouble.

I was thinking about the Growatt inverters, as the XH ones do appear to do an AC-DC-AC conversion, but it seems they require very high DC Battery voltage - 400V nominal, so that's really out and the SPF ones it seems only accept 48v battery input. I'd like to start off with 24v and go from there.

That all being said, I may be over thinking it for now thinking of the Growatts. Are there any good, recommended inverters that can act as a UPS, taking power from the grid/generator, with a small (for a start) battery running 24v, two solar panels that are supposedly 12v (but the boxes claim 24v max, and I've seen 40V+ out of the pair in series connected to the Renogy MPPT controller), and be able to be reconfigured down the road for 48v? They'd really need to have at least a 2000w continuous capacity so that either one alone could carry the continuous 1400w load in the event of an inverter failure (Most of the devices have dual power supplies, so the load would be mostly balanced). The packs I'm looking at to start with are rated for 120A continuous at 12V (1440W), so two of them in series should be capable of 120A@24v (2880W) and shouldn't be an issue at about 24V/60A. Some sort of grid/pv input/load output monitoring would be ideal, but I could live without it. The only thing I don't know is as most of the equipment has dual power supplies, and one inverter would be powering one in each device and the other inverter would be powering the other, would the inverters have to be in sync so they're phase is opposite each other like line voltage would be, or does that not matter since the power supplies convert to DC and output that?

Eventually, I'd love to have a full height rack full of EG4 batteries and a full solar array that can run the whole house as much as possible, which of course would be expensive and a big jump. Better to start small and grow with time.

Any thoughts?

 

[marbella]

there is a 3600VA 24V Battery hybrid Inverter from Voltronic that should be rather robust with AC from Generator

 

[ljwobker]

I'm in a very similar spot - I'm trying to build something that's bigger and more expandable than a "big UPS" but not ready to drop several grand on a full powerwall-type system. From my limited learning so far.... I don't think there are any (many?) inverters where you can easily change the voltage, or at least not without spending thousands of dollars on something much larger than what I think you're looking for. I think the internal construction of most inverters assumes a constrained voltage range and everything is built from there -- a 24v inverter probably has twice as many (or half as many) coil windings as its 12v cousin, and the rest of the system is probably the same.
I've been looking at the Sigineer all-in-ones, they advertise a 10ms max transfer time. Most computer/server/consumer electronics that I'm aware of have a hold-up time of one AC cycle, which would be 16.6ms in North America or 20ms if you're in a 50Hz geography.
Maybe this helps, maybe it'll just bump the thread where someone who knows more can add on

 

[marbella]

I use a cheap Must inverter and you can run it on free battery from bird scooter