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Old 07-07-2018, 11:16 AM   #1
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1969 27' Overlander
Boise , Idaho
Join Date: Apr 2013
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New(ish) Powermax blown. What to do?

I bought and installed a Powermax PM3-35 several years ago. The trailer has done almost no camping since then, and has mostly sat in my driveway (powered and using the PM3), or at its storage site (completely unpowered).

I also have not had a battery installed. I wasn't camping in it, and so didn't figure I needed a battery as long as I was only using shore power.

While camping two weeks ago, plugged into 30 amps/110VAC, the PM3 quit working. I still had full 110VAC througout the trailer, but none of hte 12V worked. The 110VAC outlet that the PM3 was connected to tests out fine with a receptacle tester.

I've pulled the PM3, and have it on the bench. Using a neon tester and a receptacle tester, I can confirm I've got 110VAC going in, but there is no power across the 12V lugs. Fan does not run (of course, if it doesn't convert any power, it won't heat up and trip the fan).

I'd like to try to fix this, because I have zero recollection of where I bought it, and no idea if I can find the original paperwork, and don't even remember if I bought it new or used. So, what should I do next to troubleshoot and potentially fix this?
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Old 07-07-2018, 11:22 AM   #2
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1969 27' Overlander
Boise , Idaho
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Also, I've checked the 30A reverese polarity fuses, they both look good.
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Old 07-07-2018, 12:08 PM   #3
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1969 27' Overlander
Boise , Idaho
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Whoops!

Well, I jumped the gun blaming the Powermax. Multitester indicates 13.6VDC across the 12V lugs.

Problem is elsewhere.
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Old 07-07-2018, 12:13 PM   #4
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Corpus Christi , Texas
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Good that you updated your post. I'm sure some electrical wizards will be along shortly with suggestions on possible causes.


Good luck.
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Old 07-07-2018, 12:27 PM   #5
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2017 30' Classic
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Carlisle , Pennsylvania
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Hi

Ummm .... is there a battery in the trailer now? If so, does it read 13.6 when the converter reads 13.6? If it does not, is there a battery cutout switch on your RV?

What's on the 12V and in the category " did not work " ? On a 40 year old RV, guessing is probably not the best approach

Does the stuff that did not work before still not work? If so, are the breakers / fuses ok ? Is there 12V to the "input" side of the breakers / fuses?

Lots of possibilities and lots of directions this could go.

Bob
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Old 07-07-2018, 01:44 PM   #6
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1969 27' Overlander
Boise , Idaho
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I haven't reinstalled the PM3 yet, and still no battery. But what wasn't working was the lights, fans and water pump. The only things that worked were the 110V receptacles and the fridge. Until I hooked up my tow vehicle and turned on the ignition, at which point all the 12V stuff was working again.

I'm going to go work my way through all the fuses. I know there's a bank of fuses in the rear service area, but don't know whether there are others hidden elsewhere, perhaps in-line fuses I need to hunt down?
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Old 07-08-2018, 07:15 AM   #7
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2017 30' Classic
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Carlisle , Pennsylvania
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Hi

If we are talking about an RV from 1969, the most accurate answer to any systems question is going to be "who knows?". In ~50 years, a lot may have been changed by various owners. Even on a brand new unit, what yours got and what the next one got .... maybe not the same.

If nothing works until the TV is hooked up, then the battery *and* the converter are out of the circuit. If both are known to be ok then you have a wiring / switch issue. The only way to solve the issue is with some quality time running a multimeter. It's not crazy hard, it just takes time.

The first thing I would do is check the (likely thermal breaker) protection between the converter and the battery. Until the converter is linked to the battery, you will have a tough time. What you are looking for is going to be close to the batteries. Where that is depends a lot on the layout of your RV.

Bob
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Old 07-08-2018, 08:09 AM   #8
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A link to the Owners Manual for your trailer. There are electrical schematic drawings.
https://www.airstream.com/wp-content...-0004.085c.pdf

I would start looking at the fuses in the fuse block and the fuse block itself, first. There is also a main fuse that is in the wire between the battery and fuse block.

Good luck!
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Old 07-08-2018, 08:23 AM   #9
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1969 27' Overlander
Boise , Idaho
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I eventually found a blown fuse. Then I had the joy of learning, as apparently many on this forum before me have learned, that finding 40amp AGC fuses is not easy. Ordered a box of 25 so I probably will be set for life, and in the meantime I can get away with 30amps as long as I dont run the fans.
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