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Old 10-01-2012, 11:39 AM   #1
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Join Date: Aug 2011
Location: North East Nova Scotia
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Camper Battery not charging

I have a Forest River T12RB that I pull with my Toyota Tacoma. I have always noticed that my trailer battery is dead following towing with the fridge on 12V. The charge pin on my truck reads 13.5 at idle, however the + lead at the battery only reads 12.5 volts with the lead disconnected from the battery. (truck running) If I remove the 40AMP battery protection fuse in the converter(WFCO 8735P) then I read 13.5 volts in the + lead leading to the trailer battery. The 12.5 volts doesn't appear to be enough to keep the battery charged while on the road. The converter output voltage does correctly read 13.6 when connected to AC. The battery also charges fine on 110 AC
Any suggestions to get my battery to charge while trailering?
Robert and Paula Smith
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2008 Toyota Tacoma 4 cyl
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Old 10-01-2012, 12:22 PM   #2
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Its been while since we used a three-way fridge on 12 volt mode, but here's my take.

Its likely in your case that the voltage dropped across the charge wire while supplying the current to run your fridge on DC. A significant amount of current constantly going to the refrigerator would not allow the voltage to get high enough to charge the battery.

IIRC A refer on 12v draws quite a bit of power. Also, outside temps matter as, on a hot day, the refrigerator will run almost constantly and that will draw more from your battery. Also, the combination of distance, small wire size, and corroded hot or ground lines anywhere leads to voltage drop.

If you have a combination of these things happening - small line size with corroded wires plus a heavy draw from the fridge, for example, than the battery cannot charge. 13.2Vdc is considered a "float" charge and 14.4Vdc is a "bulk" charge so 12.5Vdc is way too low.

So basically, unless you have enough volts to push the amps into the battery, the amps just won’t go in and you will show a low state of charge or even a dead battery.

We used to run on propane with our old pup's three-way fridge as much as we could.
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Old 10-01-2012, 01:27 PM   #3
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Truck power most likely is NOT a viable option to charge batteries with fridge on 12v.
Run gas whilst traveling.

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Old 10-01-2012, 07:12 PM   #4
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your truck's alternator will provide only a trickle charge, at best.
you have to install a bigger charging wire to allow more juice to the battery.

many have done the mod but i haven't since i use the fridge on propane, since mine doesn't have a 12v option.
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Old 10-01-2012, 08:23 PM   #5
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Location: North East Nova Scotia
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Bikendan, is the larger, heavier gauge wire run direct from the battery to the charge pin on the trucks 7 way conecter?
In the mean time I was able to increase the charge voltage to 13.5 by cleaning up all the chassis grounds on the camper.(rust and oxidation) I won't know if this will do the job with the fridge on 12V until I make my next road trip in a week or so. Gas is also an option for the fridge while trailering. Thanks all.
Robert and Paula Smith
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2011 Flagstaff Hardside
2008 Toyota Tacoma 4 cyl
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Old 10-01-2012, 08:41 PM   #6
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There is a reset-able cicuit breaker on the trailer side that connects the battery to the tow vehicle. It is normally under the A-Frame of bumper trailers and under the pin box of 5th wheels. Its purpose is to prevent a battery dump if the 7 way cable is cut (pinched) and start a fire.

It can look like the pictures but will always be there.
It can be reset by pressing in the tab on the end.
Since it is exposed to the elements (though it is under a red cover in some installations) the terminals also get corroded and may need to be cleaned to make good contact.
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