unit still won't fire up when offline although it charges the battery OK
Is it designed to provide AC power as a standalone unit? An old UPS I worked on only provided power either:
(a) when it lost its existing connection to mains AC, or...
(b) when I pressed a relay inside the enclosure so it closed.
In other words it did not operate as a standalone unit.
Did your UPS previously work as a standalone unit?
Or else can you locate a similar relay inside?
Another question: Does the inverter need to have a load attached in order to turn on?
Or does it stay off if it senses no load?
The accidental reverse polarity must have damaged devices before the fuse blew. This might include body diodes inside mosfets if they're used.
Or electrolytic capacitors. Etc.
There could be a controller somewhere detecting something isn't right, therefore the unit doesn't turn on. Does it flash a code, or beep a certain number of times?
I can't see a Fuse 3 anywhere!
BradFinding it is probably key to fixing the unit. Although labels often say 'No user serviceable parts inside', fuses really are there for someone to service.
My personal stories:
I once hooked up my 800W power inverter to a battery in reverse polarity. My mistake blew more than one fuse. Blade type as used in automobiles. I had to test all of them. Replacing the bad ones finally made the unit work. I was lucky that the fuses were easy to locate.
My 2500W power inverter stopped working after I allowed it to make a freak connection through a metal table, to a copper pipe carrying fuel oil, to house wiring somewhere. I had to replace one of the MOV's inside before it would work. It looked like a large blue ceramic capacitor.
Fuse #3 might be glass tube type, or solid cylinder, or fusible wire, or blade type, or circuit breaker.
There are also thermal fuses which open up at high temperature. I replaced one among coils of wire in a fan. It resembled a silver-colored resistor.
Such fuses might be labelled with abbreviations instead of 'fuse' or 10A or 20A. Such as CB or FW or FL or TF, etc.
Circuit breakers reset via push button.
A fusible link might have insulation with a spiral color pattern, which may or may not reveal that it's blown. A good one should show low resistance with an ohmmeter.
MOV2 is 4.2 ohms both ways, both tested in-circuit. I could maybe de-solder those if I have to though I am struggling to get the pcb out
Hi BradMOV= metal-oxide varistor. Common form of circuit protection. It's designed to have high resistance in normal operation. It conducts when exposed to overmuch voltage.
So your MOV2 sounds like it's blown.
Ordinarily it survives many brief voltage spikes that come through house voltage every so often. But one severe jolt destroys it.
I chose a replacement from a catalog listing. I had to look over part designations containing a lot of characters. AC voltage is there (120 or 130V in USA). I think also power rating, or speed rating, or joule rating. Maybe size too. I wasn't certain I chose the right one and I was just happy it made my inverter work again.
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Is it easier for you to clip one of its leads? Your unit may then work with it gone, since an MOV is not supposed to conduct normally.
Possibly then solder a replacement to the other side of the board, if that's more accessible?
Now that's certainly cause for congratulations!
Often we fix something without knowing just how we did it.
Do you by any chance have an attic so you could climb up from the living area and climb down into the garage?
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