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Old 09-21-2009, 09:35 AM
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Trailer battery charging

I just got a new/used hotrod trailer and it has a wire in the plug that is supposed to go directly to the battery positive. The guy said it is for charging the battery while traveling. I haven't had a chance to check my truck socket yet but I'm pretty sure there is a 12 volt hot wire in it. I'm assuming that this is the trailer "charging" wire that the plug has in it.

My question is; I would think that the trailer battery would go in to an overcharge with out some kind of regulater or cut off. Is this the way it works or do I need something else.

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Old 09-21-2009, 09:51 AM
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I have wondered the same thing. I have a pop-up camper that has a 12 volt battery mounted on the tongue. I knew it was for running 12 volt lights in the camper, but couldn't figure out how it got charged. I would check it with a meter before we would leave and it would be dead. When we got to where we were going I would check it again and it would be charged up . After some research I found out the camper is equipped with an inverter that operates an on board battery charger when you are plugged into 120 volt power, but it also operates off 12 volts when not plugged into a 120 volt source. So now when the camper is not in use I keep it plugged into 120 volt power. I have left it on for several days and it doesn't seem to be over charging.

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Old 09-21-2009, 10:12 AM
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That's the exact solution I came up while driving home this past week end. It seems like a hokey way to do it. 12v from the TV to the trailer inverter, converting to 110 then using that to drive a battery charger for the trailer. Looks like lots of energy is lost due to heat etc. Apparently it works pretty well especially if it is done for battery maintenance only. Now driving a refrigerator or other appliance might be a different story.

In further searching I found that indeed the direct battery charging from the TV is not a good idea. First there is very long run of relatively small gage wire causing a voltage drop. Second is the battery over charge possibility, Third and probably most important, The TV alternator is a maintance device and not really meant to charge a dead battery regularly. It will but the alt gets very hot and can over time kill itself. The commemt on an RV site was to ask the car dealer how many alternators they replace due to burn out. The number is very high and on todays cars and trucks very expensive.

The cleanest way seems to be what you have in the pop up. I have a nice 3500 watt generator and a good battery charger. With some good plug in connectors and cords I can simply start the generator a couple hours before arrival time and I'll have a charged battery. Not as nice as the inverter but similar in function.

I'll check some more on the RV forums and see if there is an aftermarket set up that you can simply bolt on.
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Old 09-21-2009, 02:31 PM
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Quote:
Originally Posted by bentwings
I just got a new/used hotrod trailer and it has a wire in the plug that is supposed to go directly to the battery positive. The guy said it is for charging the battery while traveling. I haven't had a chance to check my truck socket yet but I'm pretty sure there is a 12 volt hot wire in it. I'm assuming that this is the trailer "charging" wire that the plug has in it.

My question is; I would think that the trailer battery would go in to an overcharge with out some kind of regulater or cut off. Is this the way it works or do I need something else.
There's no "regulator" on your truck battery that turns off charging at a certain point. The voltage regulator on the alternator simply controls the voltage going into the system. It does not in any way control the state of charge of the battery.

There is no difference between charging the trailer battery and charging the truck battery. Simply connect the 12V wire to an ignition switched hot lead on the truck and you're done. One added enhancement would be to use a disconnect relay between the trailer battery and the truck battery. On Chevy pickups with the optional dual battery (for campers), there is a relay wired between the primary and secondary batteries. This relay is normally open and closes (connecting the two batteries) when the ignition is in the RUN position. This prevents the camper from discharging the primary battery when the truck is stopped. The relay doesn't care if the secondary battery is under the hood (as with the factory installation) or in the trailer, it works the same way.
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Old 09-22-2009, 07:53 AM
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I think I would go with the converter, NOT an inverter. That gives you two choices - either to charge the battery while enroute or to be able to plug the trailer in to either your "shore power" or a generator. That way you can use the 120VAC for some decent lights rather then some short run limited availability 12VDC lighting. Of course, the best way is both the converter and the inverter. My 5th wheel camper has 120V service, 2 big 12V batteries, the converter, an inverter plus a 160 watt solar battery charging array - a wiremans worst nightmare - but I'm set for any kind of camping - that is as long as the food, propane, water and TP last .

CONVERTERS: http://www.progressivedyn.com/about_...onverters.html

INVERTERS
: http://www.azsolar.com/page/page/1616360.htm

Dave W
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