I'm trying to repair an inverter for a friend. It is a 12v to 120v 400 watt continual.
My guess is that someone reversed the leads on the battery when they hooked it up.

I found one leaky electolytic capacitor, and changed it (it was a 200v 100mf, I replaced it with a200v 150mf)... that's the closest thing I had.

That didn't work.

My question. What would be the most likely components to fail if someone hooked it up backwards?
I've checked a few simple components, and found no problems, and I don't see any obvious damage to anything. Is there perhaps something that would act like a fuse, but it's not easy to find?

As usual, Thanks

 

Usually hooking them up backwards takes out the switching devices and or control circuits on the 12 volt input side of the DC/DC step up power supply.

Thats what I would start looking at first.

 

Electrolytic caps... reverse the polarity on those and they will blow up or leak bad. I would start with those, after that I would look for any zener diodes... possibly being used as voltage references. They are meant to operate reversed bias, typically systems aren't designed to for them to be forward bias... they may burn. Check normal diodes reverse and forward resistance using a ohmmeter... Do you have a make/model number?

 

Do you have make, model and any pictures of the inverter?

 

I had a 300 watt inverter someone gave me that stopped working. The problem turned out to be a broker wire on 1 of the capacitors. I guess being a portable unit it gets knocked round and broke the wire. The cap was soldered to the PC board the way I found it was by pushing on all the parts. When I pushed that cap it bent over about 20% angle in one direction because only 1 wire was holding it to the board. After replacing the cap it worked good.

Check for cracks in the PC board copper traces. Resolder all the connections.

Harbor Freight has inverters on sale this week I don't remember if I saw that on the online sales info or the sale paper. 400 watt unit was $27.

 

Reversed polarity hookup seems like something a decent design should anticipate. I could be wrong, but I'd keep looking for something that sacrificed itself when that happened. Maybe research to see if that is indeed a common feature in commercial inverters.

 

Reversed polarity hookup seems like something a decent design should anticipate. I could be wrong

No you're correct... designers should take the time to implement the hardware so in an event like this... so the components don't get destroyed... but it's not a perfect world

 

I have an old APC 650 laying here and it is fused. Also have an APC 450 and it is fused. They use automotive type fuses. Too bad you aren't around my area, I have a pile of the things which work and looking to dump. I have to wait till my suburb city has "Electronics Disposal" to get rid of a pile of old electronics. The APC 650 is open so I can see the fuses right on the battery plus side at the board. My experience with these things is without a schematic they are a pain to repair unless something obvious is toasted and then the smoke is frequently only a symptom leaving you to find the cause. Easier to just replace the things.

Ron

 

Sorry for the delay.
Thanks for the input.
I'll post back later with Model # and a picture or two.
I'm at work right now.
Thanks again,
Gary

 

It is a Tracker 300 Watt Continous, 600 Watt Peak. MN appears to be 326-300.
When I re-opened it this afternoon, I found a bulging cap that wasn't bulging the last time I had it open
I also found two wires spliced together that look like they go to something.

I'm going to start over. I may be able to find a schematic, if so, that will help.
I'll check the Zener diodes as well.

Here are a few photos.

See last photo. Home Depot sells one that looks identical, but it is 900 watt.

Thanks,
Gary

 

Does this have a reverse diode protection built into it at all? Hard to tell with these pics. Large caps look a little suspect but again, hard to tell. If you suspect one, change them all. Won't cost that much.

 

...smoke is frequently only a symptom leaving you to find the cause.

I was lucky. My inverter failed with a ppffffttt and a puff. I opened it up to find an electrolytic had spewed its guts. The smoke was long gone but I could see the spew, and I believe there was a visible fissure in the aluminum. With no other analysis of the board, I replaced the one cap and it was good to go again.

 

Unfortunately given its power rating the cost of repair, unless you have all the parts just laying around as good used take offs, once you do get it going will likely be higher than had you just went out and bought another new one.

 

Check to see if any of the switching Mosfets are shorted. Hopefully the parts numbers are conventional.