View Full Version : Power even after wire unhooked from battery?

06-11-2011, 05:19 PM
Trying to troubleshoot a fault on my inverter in the truck. It was working fine for months, but just recently on a trip home from the mtns, I tried to plug something in and charge it and I had no power in the plugs. After a bunch of different experiments, including swapping in another inverter, the inverter box is showing a "fault" and making a high-pitched whine whenever I power it on - and this happens in both inverters making me believe the problem is in the wiring. Here's what I've seen so far.

- 12.75 volts at the point where the 1 awg cable connects to the inverter (same as battery voltage).

- same 12.75 volts at the shut off junction near the inverter, and at the fuse near the battery.

But when I disconnect the wire from the battery to the fuse, I have 0 volts on the battery side, but the same 12.75 volts on the inverter side.

When I disconnect the cable from the inverter side of the fuse and check the cable (which is now touching air on one side, and the inverter on the other), it still reads 12.7 volts.

Does this mean anything about why the inverter isn't working? Does the inverter hold onto a charge at steady state? If I power on the inverter, it shows a fault and voltage in the wire drops below 2 volts.

Any thoughts?

06-11-2011, 05:31 PM
Put a 12v light bulb or some other resistive load across the mysterious 12v source and see if it goes to zero after a second or two. You might be measuring the 12V with a high impedence meter that does not allow enough current to bleed off a capacitor in the inverter.

Take both of the inverters and connect them directly to the battary to convince youself that the battery and the inverters are healthy. Then focus on the wiring.

06-11-2011, 10:01 PM
Thanks Bruce. The unit(s) were functional with a direct connection to the battery. Turns out the problem was in a junction block I installed in the back near the inverter itself as a safety/connection point. I'm not sure if the block shorted itself, or if it was shorting on some nearby metal, but when I removed it and ran the wire straight through from the fuse to the inverter it runs fine.

So bye bye junction block for now...