Forum Discussion

portscanner's avatar
portscanner
Explorer
Jun 15, 2015

Need confirmation on diagnosis of 12V electrical problem

(mods pls move if this is posted in the wrong location)

A friend has a trailer he just bought.

5 days ago when we picked it up everything worked - lights, A/C, fridge, stove, heat, water heater, etc. I towed it over to his house and dropped it off.

Yesterday he had some time to go out and check out the new toy he had bought, so he plugged in the 110V shore line to a 20a 110V plug in his garage (and yes, it was 110V outlet not 220). The the clock on the microwave came on, but no lights in the trailer. A quick check found the following - no 12V.

Pulled the 50A fuse that was in line w/ the battery and the battery only had 0.3 volts. 50A fuse was good. Checked all breakers and fuses and none were open/blown/tripped. Leaving the battery disconnected and connecting the 110V (so the converter would have power), still had 0V on the 12V line.

There is a Parallax Power inverter (http://www.spectrum-x.com/PPS/Products/Converters/PowerCenter/7100/7155/) model 7155 inverter in the trailer. This inverter is in a box that holds your breakers and fuses, along w/ the inverter. I disconnected the blue wire that supplies the 12v and goes from the inverter itself to the fuse panel and reconnected the 110V. At that time I was able to get 4 volts out of the inverter. Re-connecting the line and the output would go back to 0v

I suspect the inverter itself has failed. I can get a replacement for just the inverter from Amazon (http://www.amazon.com/Parallax-Power-081-7155-000-Replacement-Section/dp/B002SSEWD8) but before I blow $160, I would like to make sure I have not missed anything.

I know I will have to get a new battery. My best guess is the output transistor(s) on the inverter shorted/failed after we picked up the trailer (or maybe they were already toasted before we picked it up and the battery was supplying the 12v during out inspection - the prior owner did have the battery disconnected before we started our inspection) and leaving the battery connected for a few days to a failed inverter (with the loads from the CO and methane detector) killed the battery.

Has anyone experienced something like this and was able to fix it without spending $160?

Thx!!!

16 Replies

  • CONVERTER.........

    Needs 120V AC power going IN before 12V DC power can come out.
    Have you checked that it is getting 120V AC power? Could be a tripped GFCI outlet, could be a tripped AC circuit breaker.

    IF no 120V AC IN.........then NO 12V DC OUT

    IF you find 'converter' has 120V AC then converter has failed

    You also need a new battery.
    Mark batteries cables (or take pics) before disconnecting so that they don't get connected backwards. IF backwards then you will need to replace REVERSE POLARITY fuses on backside of converter---they blow when battery hooked up wrong
  • BarneyS wrote:
    I suspect a ground fault interrupter has tripped somewhere in the trailer. Look in the bathroom first. Same thing happened to me and after about an hour of trying various solutions I found the tripped breaker. Probably your fix is going to be as simple
    as pushing a button. I hope so. :)
    Barney


    GFCI is on the 110 outlets, not on the 12 V lighting system. OP states microwave comes on, so at least 1 of the 110 outlets has power.

    Don't think GFCI is the problem here.

    Sounds like a new battery is in order, and then possibly an upgraded converter.
  • I suspect a ground fault interrupter has tripped somewhere in the trailer. Look in the bathroom first. Same thing happened to me and after about an hour of trying various solutions I found the tripped breaker. Probably your fix is going to be as simple
    as pushing a button. I hope so. :)
    Barney
  • I would pull the inverter. Run it on the test bench. If you can get a schematic you may be able to find out what is wrong and repair it. Providing you have some equipment. To hire someone to repair it probably would cost as much as a new one.

    If initially a battery was bad in the RV like freezing, shorted plates etc. it could very well pull too much load on the inverter and destroy the output transistor. Transistors are cheap. That would be just a guess but if just an ouput transistor you could probably repair it for a couple of dollars.
  • First off, I believe you have confused yourself somewhat with terminology. You have a Converter, not an Inverter.

    If I'm not mistaken, some older Converters will not provide 12 volt unless there is a functioning battery connected. I believe your battery is dead.

    Most folks here on the Forum will recommend replacing the Converter with a Progressive Dynamics with Wizard, even if your current Converter is OK.
  • I,ve had that old outdated converter ,change it out easy to do, I ,ll go out to the shop and get the number for the one I put in, can,t remember the name.don,t know about the other problems but you need a good 12v battery to start ,the converter doesn,t do everything ny itself/

About RV Tips & Tricks

Looking for advice before your next adventure? Look no further.25,159 PostsLatest Activity: Aug 28, 2025