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Old 05-10-2021, 07:53 PM   #1
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12V system not working, but battery power good

Shaking down a 2010 Coachmen Clipper pop-up that we bought a couple of months ago, and having trouble with the 12V electrical system when shore power is disconnected. Just replaced the battery with a new marine deep-cycle number, which is reading a healthy 12.8 volts on my multimeter when disconnected from shore power. But when I unplug the AC current, none of the 12V equipment runs: no lights, no water pump, no ceiling vent blower. The odd thing is that I'm getting good voltage at the junctions (wire nuts) behind the converter: 12.8V on the lighting circuit, furnace circuit, water pump circuit, refrigerator circuit. And everything runs fine when AC power is plugged in. One clue: the lighting circuit runs in one of the curtains up to the ceiling, has a junction right at the bottom of the curtain. I'm getting only a fraction of the proper voltage there -- 4 to 6 volts -- but the reading is good where that same circuit is tied in to the converter output. With shore power on, that same connection (at the curtain) shows 13-plus volts. So there's nothing wrong with the wiring, evidently. Anybody have any insights into what might be causing this maddening glitch?
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Old 05-10-2021, 08:10 PM   #2
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Bad ground between battery and trailer frame?
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Old 05-11-2021, 07:05 AM   #3
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Ground connection looks good, though I suppose it can't hurt to clean it up. I'll take a closer look. Voltage is good (12.8v) between ground (white wires) and positive (red wires) behind the controller.
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Old 05-11-2021, 07:32 AM   #4
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Two items.
Check the reverse polarity fuse(s) in the distribution panel ( large 30-40A fuse). These blow occasionally when battery replaced.
Check that the polarity of the new battery is correct. The wire colors are not standard.
FYI The new battery is likely a dual purpose battery and not a true deep cycle battery.
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Old 05-11-2021, 08:29 AM   #5
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All fuses look intact. The puzzling thing is that I'm getting good voltage readings on all the circuits where I can access them, immediately behind the controller. Next step, probably, will be testing the hot side of each circuit directly against the ground/frame.
Yes, that "marine" deep cycle battery was something of a compromise -- best I could find on relatively short notice without going all over town. But it still ought to power a few LED lights when fully charged!
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Old 05-11-2021, 08:34 AM   #6
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check the fuse to the battery... usually found in a 4x4 electrical box under the tongue of the camper near the battery. push the little black button
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Old 05-11-2021, 09:47 AM   #7
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Behind the converter there is likely a bus bar where all of the negative wires are connected together. Make sure all the wires are fully inserted into the bus bar and all the screws are tight. Especially the main negative cable coming from the converter.
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Old 05-11-2021, 11:52 AM   #8
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check the fuse to the battery... usually found in a 4x4 electrical box under the tongue of the camper near the battery. push the little black button
This! ^^^^^^
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Old 05-11-2021, 12:31 PM   #9
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Quote:
Originally Posted by NavyLCDR View Post
Bad ground between battery and trailer frame?
Quote:
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check the fuse to the battery... usually found in a 4x4 electrical box under the tongue of the camper near the battery. push the little black button

X2 & 3 on the above
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Old 05-11-2021, 12:59 PM   #10
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Alas, there is no such resettable breaker anywhere in the lines from the battery to the camper body. Closest thing to it is an inline fuse on the positive cable a few inches from the battery. (It's fine.) Underneath the chassis I did find a bus -- with a single set-screw, no bar -- where the white negative wires are all grounded to the frame. All clean and tight, no corrosion.
I have found some new clues: When testing voltage on the individual circuits (where they're tied in to the controller wiring) I found that while it was a healthy 12.68v between the incoming positive cable and the individual circuits, I got little to no voltage between the circuits and the negative cables (chassis ground.) So that helps me focus. I'll try to rig a way to test those circuits directly against bare metal on the frame, then try to back up through the white negative cables. One other clue: there's a light fixture in the forward "trunk," which works fine. So I'll be comparing its wiring with all the other circuits. Thanks for all the suggestions!
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Old 05-11-2021, 01:45 PM   #11
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(where they're tied in to the controller wiring)!
Are you referring to the distribution panel with the fuses and breakers?
Did you actually measure the conductivity of the fuses or are you using a visual inspection or the led indicators?
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Old 05-11-2021, 03:55 PM   #12
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I've been testing the circuits immediately behind the distribution panel, where the output from the AC-to-DC converter is tied with wire nuts to the individual 12V circuits. Have not attempted to open the controller box.
I did a continuity test with my multi-meter on the 30-amp reverse-battery fuse. It checked out OK. Have not done that with the individual 15-amp fuses, though they look OK and none of the LED warning lights are showing. I suppose it can't hurt to do a continuity test on those fuses, too. Easier than crawling around underneath trying to test voltage on various wires!
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Old 05-11-2021, 03:58 PM   #13
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Bingo! FlyBob wins the prize on this one. And I learned an important lesson: Sometimes a bad fuse looks perfectly good. But it failed the continuity test, and that was the answer to the whole problem. Plug in a new one and we're good to go. Many thanks to all for many useful suggestions; I now understand my camper's electrical system a lot better than I did before.
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Old 05-11-2021, 04:07 PM   #14
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Maybe u need to change the battery cables maybe corroded
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Old 05-11-2021, 04:13 PM   #15
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Originally Posted by Carolina Clipper View Post
Bingo! FlyBob wins the prize on this one. And I learned an important lesson: Sometimes a bad fuse looks perfectly good. But it failed the continuity test, and that was the answer to the whole problem. Plug in a new one and we're good to go. Many thanks to all for many useful suggestions; I now understand my camper's electrical system a lot better than I did before.

FIXED!!
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Old 05-11-2021, 04:13 PM   #16
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Maybe u need to change the battery cables maybe corroded
Please read the post before yours.
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