Larger Charge Line

Tools Josep Ma. Rosell

October 5, 2012
Filed under Resources, Trailer How To, Trailer Q&A

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Q: While traveling to Florida we sometimes stop and use only our 12-volt house battery for powering interior lights and other appliances. This drains a lot of the battery, and the normal plug-in from truck to trailer does not do much to recharge the battery. 

My plan is to run an 8 gauge wire directly from the truck charging system to the house battery. Will trying to recharge a deep-cycle battery in this manner work?

David Sumner, Grand Haven, Mich.

A: Running a new, larger-diameter charge line would indeed help your trailer battery-charging situation, David, but it’s better to start by troubleshooting the system you have. It sounds like you may have a bad connection or two, or perhaps a damaged charge line, which is preventing your tow vehicle from adequately charging the batteries.

With the trailer hitched up and plugged in, start by checking the alternator voltage output on the tow vehicle. Next, check the voltage indicated at the trailer battery. I’ll wager it will be significantly less than the alternator voltage, which means somewhere along the lines, there’s a bad connection. Work your way back toward the alternator, checking each junction point — the battery charge line, the trailer’s junction box, the trailer plug wire junction, the tow vehicle socket and so on. Somewhere along that line you’ll probably find the voltage increases, which means you’ve narrowed down where the bad part of the circuit is. Then you’ll need to clean the terminals or circuit connections, clean and tighten wire terminals and so on.

Be sure to inspect the trailer and tow vehicle’s ground connections as well. The ground is just as important to completing the circuit, and if it’s bad, the charge voltage still can’t get through.
- Jeff Johnston 


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