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Old 09-22-2003, 09:08 AM   #1
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12v problem

discovered a 12v problem this weekend while dry-camping. Apparently, my battery didn't have much of a charge on it, even though the trailer has been plugged in at my house for the last couple of weeks. I did check the water level before I left, and it was low, so I added water. then I hooked it up to my truck and drove for 4 hours. When we set up camp, I noticed that the interior lights were rather dim. tried to use my tv w/ the 12v plug (first time I've ever tried this) and it wouldn't turn on.

So, I figured that my battery must be toast. I plugged the trailer back into the truck, and the lights brightened up considerably. Still couldn't turn on the tv. (not the end of the world, but made me curious). I tested the 12v receptacle...phone charger lit up, so I know the socket wasn't dead. So I took the tv out to the truck, and plugged it in there. worked fine. I'm figuring that there still isn't quite enough voltage availble to the trailers 12v system, even while plugged into the truck. Why would this be?

the battery is a 1 year old deep-cycle marine battery; trailer still has the original univolt. I haven't had a chance to put a meter on anything yet, but I'm wondering if you electrical gurus might have any insight as to the likely source of the problem.
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Old 09-22-2003, 09:17 AM   #2
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I will give you my best guess. I would say your trailer may have developed what can be called a dead cell. This would cause it be be low on power. As for attempting to run the tv from the truck over the distance, once again a low battery will draw from the trucks system and consider the distance the power has to run to get to where you plug in your tv. The power company uses High Voltage lines to transport electricity but when it comes from the generating station (power plant) it is high amp low volt. They convert it to high voltage in order to transmit it. Amperage dont carry well over distance and you may be loosing the amperage needed to run the tv in the trailer from your truck. Im still going to go with the dead cell theory.
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Old 09-22-2003, 09:19 AM   #3
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You should not discount corrosion on the umbilical plug to the truck. And a weak battery can cause a voltage drop in the circuit. But...

If you are trying to run your coach 12v off the tow vehicle, you have to consider that it is a rather long run from the battery, through the chassis, through the umbilical, and then through the coach. A very heavy current draw (and a tv probably qualifies) could easily drop the voltage down too low.

If the coach battery is weak, replace it and then see where you are.

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Old 09-22-2003, 09:45 AM   #4
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I re-built the umbilical last year, so it should not have any corosion, fwiw. There could be some elsewhere, though...like back at the univolt. haven't checked it yet, but I will.
I dealt with some corrosion problems in the 110 system earlier this year...had to replace the whole panel. But I didn't look at the univolt at that time, so there could be bad connections there from the same thing that caused the corrosion in the 110 panel. (I suspect just condensation and time; no sign of any bad leaks or anything back there).
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Old 09-22-2003, 09:54 AM   #5
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Chuck I have encountered this EXACT problem on both of my A/S's here is a link to my post on this subject http://www.airforums.com/forum...&threadid=5972 .But to be on the safe side I would still check the output of the Univolt right at the Univolt itself .But keep in mind that it may say 12 volts but when you put it under a load it will drop .Now that mine are both repaired I can turn every light on and still remain at 12 volts .I hope this helps ! Tom
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Old 09-22-2003, 01:50 PM   #6
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get the battery checked. before you start on the airstream wal mart, auto zone, advance auto parts and zillion orher part places will check it for free. if you put water in the battery plan on charging it for 8 hours before taking a trip. 12.65 volts is what you want to measure with a digital meter for a full charge.lol
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Old 09-22-2003, 04:47 PM   #7
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I agree with wb13798,whole heartedly and was assuming this was already done !
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Old 09-23-2003, 07:37 AM   #8
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Do those places do a "load test" on the battery?

I got out my meter thismorning, and did some checking...got some weird readings. (trailer has been un-plugged since driving it home sunday afternoon) At first, the battery read 12.5v, then the meter started climbing. it went slowly up to 14.5, which I thought was very strange. So I plugged in the trailer to see what the univolt would do, and the voltage jumped to 15.2. Ok...it should be higher...but doesn't that seem too high? is my meter f'd up? I unplugged the trailer, and checked the ac voltage on the 75 foot extension cord that goes to my house (12-guage wire in the extension). The voltage read 138, which again, seems high. wondering if I need a new meter. I'll check it with another meter when I get home tonight.....

Or perhaps the battery just needed another 4 hours of charge, which was provided by the return trip home. Before this trip, I probably had it plugged in for too long, too much water boiled off, and that affected the charge.
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Old 09-23-2003, 10:03 AM   #9
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Chuck I would first take the battery out of the trailer and take it to Wally Mart or Peppy Boys and have them do the load test .Then check the battery in your volt meter ,if you replace the battery in the volt meter and you still get weird readings I would try barrowing one from a friend . 15 volts off the Univolt with a load "ie. the battery " sounds a little high mine reads from the mid 12 volts to mid 13 volts.See the problem here can be a combination of bad Univolt and a bad Battery as a result of being hooked to a bad Univolt ,this was the case with mine after 2 batteries I decided to look at the Univolt ,the show stopper in my case was the Univolt appeared to be working .It even worked fine with a few lights on, this decieved me. Anyway one day I decided to take the Univolt out and found one lead goin to the caps was completely blown off......Not a GOOD Sign...too say the least.So the logical thing to do was to solder it back on ....which i did.This work great for .......6 hours....then the it blew the cap completely. So I replaced all 3 caps and have had no further problems.Till I bought my 2nd AirStream which is a 74 tradewind and guess what ........same exact problem. Ok well i just happened to have a spare Univolt in my garage and decided to power it up and You guessed it same thing. So now I have 3 perfectly workin Univolt at a cost of roughly $35 each and about an 1/2 hour work per Univolt.I hope this helps Tom
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Old 09-23-2003, 10:40 AM   #10
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couple of questions:

what is a good source for these capacitors?

what should the output of the univolt be without the battery connected?
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Old 09-23-2003, 10:40 AM   #11
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A quick word of caution on digital multi meters!
I own 4 of them. One from Radio Shack, another from Wavetek, a cheap yellow one from Harbor Freight, and an OTC with tach/dwell.
The Wave tek and the OTC seem to agree on the actual voltage, within ~0.1V. The Yellow one and the one from Radio Shack strongly disagree with actual voltages, both A/C and D/C, Meter batteries new.
So please make sure your meter has good batteries and is accurate enough for testing.
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Old 09-24-2003, 08:04 AM   #12
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yep, I think my meter was funky. I tried it this morning with another one, and got readings that make more sense:

AC from house: 122v
DC on battery: 12.2v

after plugging in the trailer, the voltage at the battery slowly started to climb up to 13.1 (may have gone higher if I waited long enough, but I had to get to work ). So, I'm leaving it plugged in and will check it when I get home. We'll see what 11 hours on the univolt does......
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Old 09-24-2003, 08:35 AM   #13
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12V problem

For lot's of information about voltages, charge rates, etc http://www.phrannie.org/battery.html
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Old 09-24-2003, 10:02 AM   #14
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You probably already know this but the univolt is a very simple charger and tends to overcharge a battery. Left pluged in to AC with out a batt cut off switch over time will ruin a batt.
If the batt is OK and the TV still dosn't work you will most likely have low voltage at the outlet under load and probably normal voltage at no or small load. This would be caused by a bad or corroaded connection somewhere between the outlet and univolt and it could be the at the fuse.

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