Saturday, November 27, 2021


Do-it-yourself inverter repair – Important to know

If you’re away from shore power, having a power inverter goes a long way to making life better. But if your inverter takes a vacation while you’re on vacation, life can get tough. Can you do your own inverter repair? In some cases, the diagnosis and treatment is easy for the competent do-it-yourselfer.

Hot weather invokes inverter croak

We had a recent inverter upset while dry-camping in a small town park in Nevada. We’d been in some extremely hot weather, and our air conditioner decided to act up. When we gained elevation – and shed temperature – we were overjoyed. But when we plugged our shore-power cable into our inverter, a weird chain of circumstances ensured we’d be enjoying a session of inverter repair.

Our inverter and battery bank is not hearty enough to run the air conditioner – and we weren’t even trying to. But little did we know, on our last shore-power-supplied air conditioning session, something went gunny bag with the air conditioner control system. Our a/c uses a remote control thermostat. When it failed to respond to the thermostat, we had to resort to using an emergency override system. What we didn’t know is that once that system is engaged, it’s ready to “rock and roll” the minute it senses 120-volt power.

When we plugged the shore power cable into our inverter, the a/c unit sensed 120-volt power. It immediately tried to fire off the compressor – an overpowering load for our 2,000-watt sine wave inverter. Not knowing what was happening, we were a bit puzzled that we got an indicator that the inverter was “ready,” but not delivering our desired shore-power alternative. We clicked the inverter off and tried again. This time we got a “power fault” trouble light. The display showed we had a 12.7-volt battery input, but zero volts a.c. output. Inverter repair was the new order of the day.

Two principal causes of inverter failure

Could you suffer the same kind of problem? There are two issues that can sideline a power inverter in a flash. Sometimes that flash is literal. Like us, you may put too much load on the inverter. Another common problem is easily seen by folks whose inverter is really portable and equipped with battery clamps, rather than “hard wiring” onto the battery bank. One fellow explained that he was just too lazy to get a flashlight out one night when hooking up his portable inverter. He figured he had a 50-50 chance of picking the right battery terminal connection. He picked the losing side of the chance. Reversing an inverter’s battery polarity connection is a guaranteed way of mandating an inverter repair.

After an email conversation with our inverter’s manufacturer, BELTTT, their technicians suggested checking out the inverter’s fuse. No, we’re not talking about the fuse that is installed between the battery bank and the inverter. We knew that one was OK, because we had power enough to the inverter to both light up the display and give us the trouble light. We’re talking about the inverter’s internal fuses. We’ve seen a few (rare) instances where some inverters have a fuse accessible from the outside of the device. Ours are all inside the unit.

Here’s our guide

Checking internal fuses isn’t difficult. The hard part is gaining access to the fuses. Here’s a guide.

First, DISCONNECT the battery supply to the inverter. We pulled power at the big fuse that ours has, right on the battery bank terminal block. If you’re dealing with a portable inverter, that’s a no-sweat. Simply disconnect the battery clamps.

The second step for bigger inverters is accessing the inverter itself. Ours was mounted to a wall inside a storage bay. While we could easily reach into the bay through an outside access door, actually getting “hands on” to make inverter repairs required taking out a false wall from the adjoining room and belly crawling up to the inverter. From there it was a matter of disconnecting both power cables from the battery bank, and a ground wire. We’d already disconnected the 120-volt power outlet cable.

In the surgery room

Once you have the inverter on your table or workbench, examine it closely. Are you “blessed” in having a simple cap over the fuses? Good for you! If not, cracking the case on the inverter can be tricky. Our inverter case is built like a long rectangular tube. On one end of the inverter are the controls and display and, at the other end, the fittings for the battery power connectors. It was quickly evident that yanking either of the ends off was one thing. If we had to get access to a part in the middle of the inverter’s printed circuit board, it would be a whole new issue.

Intuition suggested we take the end plate off the inverter, the one where the 12-volt cables connected. Good choice it was, because within finger reach of the open end was a set of two 40-amp blade-style automotive fuses. A quick eye-ball revealed the fuses had done their job and blown.

Typical inverter “innards” include blade-style automotive fuses. Photo supplied by

Since BELTTT had good foresight, they’d seen to it their fuses were mounted – not directly to the printed circuit board, but with the use of fuse holders. Changing out the two blown fuses made for a quick and easy inverter repair. We slipped in two new fuses, slid the end plate back in place, and replaced the screws. We reinstalled the inverter, hooked up the wiring and, sure enough, had a working inverter.

And if it’s a bit harder, here’s help

How’s this all apply to you? If you’ve accidentally (or stupidly – either way) reversed the battery wiring on your inverter, you’ll likely have a simple fix. If you suspect you’ve overloaded your inverter, the most likely suspects, again, are the fuses. What if your fuses need replacement but are soldered to the printed circuit board? If you’re not familiar with the fine art of desoldering, we recommend a review of a website Soldering Iron Guide’s tips on desoldering.

In any event, always use fuses of the same rating as those that come out of the damaged inverter. A smaller-rated fuse may require another inverter repair. A larger-rated fuse may require a replacement RV after burning up your existing rig!

One last point from our electricity guy, Mike Sokol: He always recommends you take a picture of ALL wiring before disconnecting anything. What if some of the wires are the same color? Then a roll of white or yellow electrical tape and a Sharpie is your best friend. Clearly mark large numbers on all connectors and their wires connected to them, then take close-up pictures.

When you go to reassemble the device, take a look at the pictorial diagrams as you reinstall the wires, and double-check everything BEFORE turning on the power and releasing the magic smoke.


RV Electricity – Don’t fix a blown fuse like this!



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jane shure
4 months ago

If only it was that simple. Fuses check good and it seem to power up but no output. Aims service department was a total joke. They consider a $1200 inverter a throw away when it fails.

Larry Lee
4 months ago

I agree with “West’s” remark regarding the real dangers inherent in accessing the innards of an inverter/charger combo (which many of them are). This article fails to state sufficient warning regarding the dangers contained inside inverters even after they have been disconnected from both 12 and 120 volt connections.
Plus what a disaster will befall the Magnum inverter owner who does the otherwise routine process of disconnecting the negative 12 volt line before the positive. Clearly states in the manual that the positive line must be disconnected first. You’ll have to ask Magnum why they did that.

Montgomery Bonner
4 months ago

Be aware, some inverters need the POSITIVE CONNECTION TAKEN OFF FIRST. And inverters can kill you. Please know ahead of time what you are doing, and if necessary call the manufacturer to make sure you get all the “gotchas” down before you attempt this.

Jesse Crouse
4 months ago

I would have to be completely comfortable with someone’s electrical knowledge and practical abilities in 12volt as well as 120 volt before advising them to work on an inverter.

4 months ago

My inverter decided “today” was the day it didn’t want to work. I was powering an item below the rated output but no go. I called the manufacturer and they suggested my output cables were too light. It was what came with the inverter but I upgraded to a thicker wire and everything worked fine.

4 months ago

Surprised you did not mention the energy stored in capacitors and the danger of shorting when the inverter case is open

4 months ago

Excellent points. Minor suggestion, get a label maker and label your cables at your leisure, or repent in your haste.