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Old 06-25-2011, 02:05 PM   #1
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Lost all 12V power

I've been going thru the AS for the last few days checking the systems to see what works and what don't. Been running a new battery and been plugged into shore power. I've been running the AC, frige, fans and lights. I ran out to the hardware today and when I got back I have no 12v anywhere. Can't find any blown fuses. Multimeter says theres 5.4v left in the battery. I have the charger on the bat. now to see if my lights etc. start working.

Any thoughts on where my problem is?
Thanks.
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Old 06-25-2011, 02:22 PM   #2
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5.4 volts is essentially a dead 12v battery. I would check to see if your converter is working at all. If it is the original Univolt, it will probably make a noticeable humming sound if it is working. Also, if it was working, you should be reading 13 volts or so even if the battery was dead. To check the battery level when the converter is working, you need to shut it off (disconnect from power). You want to make sure that there is 120 AC power to the outlet powering the converter. It could be something that simple.

It sounds like you have converter problems to me. There are lots of threads about replacing the original Univolts. Use the "Search" menu and choose "Google Search" for the best results.

Best of luck!
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Old 06-25-2011, 02:23 PM   #3
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Sounds like the battery has had it, but if you have a proper 120V to 12V converter, you should still have power in the coach.

There are two large fuses mounted right near the battery (not mounted in the fusebox). Did you see those when you were looking around?
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Old 06-25-2011, 02:35 PM   #4
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It sounds like the Univolt power converter is not working. It is located right behind the battery probably inside a cabinet or cupboard in the bathroom. Disconnect the battery cables from the battery and check for voltage coming from the converter in the cables. Ther will be a 50 amp fuse(large glass fuse) in the negative cable to the battery located right near the converter, check that to see if it is blown. If you have no voltage you will have to make sure the converter is getting 110VAC from the shore power. If you have 110 VAC to the converter and no 12VDC output the converter is dead and needs replacing.
Recharging the battery with a battery charger will not fix the problem as once you start using the 12VDC sysytems again they will drain the battery.
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Old 06-25-2011, 02:41 PM   #5
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On some trailers there is a 110 volt switch that switches off the converter. If the converter is switched off it acts just like you are describing. 12 volt things run until the battery dies dead. switch is usually behind the sofa and switches the outlet the converter is plugged into.
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Old 06-25-2011, 03:28 PM   #6
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Thanks for the quick replies. I pulled the shelf out from inside the back closet and the converter looks to be hard wired. The romex does run to a switch located about 4' up on the closet wall. It looks to me like they spliced the romex just outside the converter then up into the switch, and then back down into the converter. Without pulling all the tape off, I can't tell for sure. When I turned the switch on the converter started humming. Haven't heard that sound before. Same kind of hum as the battery charger makes. I took another look at all the fuses and they all "appear" to be good. I found one 50 amp fuse holder on the wall outside the converter box. It has a black cable running to it - appears to be the battery negative cable.

The multi meter that I have is a Harbor Freight special so I can only check 12V with it. I don't know if I have 110 VAC coming into the converter for sure, but my barn has a 100 amp feed so I think it is probably alright.

Right now I'm letting the converter recharge the battery. Still no 12V working. Is it safe to assume that the battery will have to come up some before I get 12V power again?

Should I let the converter recharge my battery? Or should I disconnet the battery and charge it with my charger?

Thanks again.
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Old 06-25-2011, 03:34 PM   #7
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flynavy well it sounds like the only problem you had is that the 110VAC feed to the converter was switched off. the humming you hear means it is getting 110VAC now. I would remove the extra battery charger and see what voltage you now have at the battery and let the converter recharge the battery.
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Old 06-25-2011, 03:38 PM   #8
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On my trailer, I'll have 12 volt power if shore power is plugged in and the converter is plugged in, even with the battery removed.
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Old 06-25-2011, 04:08 PM   #9
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Originally Posted by wasagachris View Post
flynavy well it sounds like the only problem you had is that the 110VAC feed to the converter was switched off. the humming you hear means it is getting 110VAC now. I would remove the extra battery charger and see what voltage you now have at the battery and let the converter recharge the battery.
Did that. Bat. reads 12.4VDC. Still no lights etc. Pulled the bat. Still no 12VDC. Converter continues to hum away. I put the bat on the charger to see if it will come up. Charger says it's dead.

From what I understand I should have 12VDC even without the bat. in place, as long as the converter is working? Correct? Going to see if I can get current across those fuses that look ok. Be back.
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Old 06-25-2011, 06:41 PM   #10
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well, besides the converter there is also a 12 switch that cuts all the 12 volt off. usually a rotary switch behind the sofa near the converter. did that get turned off? I have seen them fail. contacts get dirty. you might try fipppint that on and off a few times to see if it makes contact. with the converter going and the the 12 volt switch on you should have power even with a dead battery. my converter puts out about 13.4 volts.
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Old 06-25-2011, 06:52 PM   #11
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If it is the original converter. It may have a large (30 or 50) amp fuse inside.
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Old 06-25-2011, 07:11 PM   #12
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So you had full off-line 12V before your errand?

My '73 when I got it home had no 12V w/ good battery... following the circuits I removed and reinstalled all the fuses and found the one of the main DC fuses off the battery had a thin layer of oxide built up in its holder and that had proved to be able to hold open the circuit - just a wisp of white corrosion lifted the metal contacts.

If you have an original converter DO NOT run it very long without any battery; it requires the load to balance the transformer circuit and will overheat after X hours running, killed my 73's that way - the louder humming is not a good sign...

Might be a good time to gently loosen and re-tighten every 12V terminal fastener in sight, and look at each crimped-on terminal for the mechanical bond of the wire, corrosion, or evidence of discoloration from a bad crimped connection from corrosion...
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Old 06-25-2011, 07:22 PM   #13
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Also look for the ground connection to the trailer from the battery.Probably a bare copper wire coming out of the converter going to the frame. It could be in the trunk area. Sometimes the connection gets corroded and cleaning it up will restore all the 12 volt.
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Old 06-26-2011, 09:23 AM   #14
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Thanks to everyone for their help.

Update: I pulled the batt. and put it on a 2amp charge overnite. Converter was off. Batt. came up to 13.2 . Cleaned fuse holders and replaced a 50amp on the closet wall and a 50 and a 40 amp inside the converter. These are the only large fuse I can see. Cleaned the plug in dissconnect inside the batt. case and installed the batt.

I now have all 12VDC power throughout the coach. Yippie!

From what I understand I now need to determine if the converter will keep the batt. charged. Correct?

Should I let the batt. run down a little before I turn the converter back on or just go ahead and turn it on now?

Would running the frige be the largest 12V. draw I could put on it?

In the meantime I will clean up ground connectors and anything else I find that looks questionable.

Thanks,
Paul
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Old 06-26-2011, 09:35 AM   #15
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Paul if you have the original fridge it uses no 12VDC power at all. The largest draw would be any of the fans, like the roof vent fans, the bathroom fan, the stove fan or the furnace fan. Anything with a motor will draw the most power from the system.
You can quickly check the operation of the converter by checking the voltage at the battery with nothing turned on and shore power disconnected, then plug in the shore power and the battery voltage should rise if the converter is working.
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Old 06-26-2011, 10:29 AM   #16
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OK, I will do that. I'll post what I find. ( I do have origional frige).
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Old 06-26-2011, 01:07 PM   #17
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Good news. Batt. came up from 12.4 to 13.1 over the last couple hours.

Thanks to all for walking me thru this.
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Old 06-26-2011, 01:33 PM   #18
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I'd think the converter would be putting out 12 volt on shore power, even with the battery removed. Maybe it's a different type converter than mine.
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Old 06-26-2011, 01:49 PM   #19
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Good news. Batt. came up from 12.4 to 13.1 over the last couple hours.

Thanks to all for walking me thru this.
Great! Sounds like you're set.

Enjoy.
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Old 06-26-2011, 02:26 PM   #20
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Paul if you have the original Univolt converter you will need to be vigilant in monitoring the water level in the battery. The univolts are famous for overcharging and boiling batteries dry. Make sure you use distilled water only, regular tap water will have minerals in it that will attach themselves to the lead plates and ruin the battery.
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