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Batteries being charged while driving down the road


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I have owned an pull behind, Trailer and now a fifth wheeler and always thought that when your connected and driving down the road that you were also charging your house batteries...??? am I wrong or do I have a problem with my fifth wheel. I was boondocking and then moved 350 miles, thinking the batteries should be charged up on arrival, nope still low and needed serious charging. What went wrong, any solution? Do I need to run a different wire to charge the house batteries?

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am I wrong or do I have a problem with my fifth wheel.

 

That depends entirely on your tow vehicle. While most newer rigs are capable of delivering a moderate charge, they aren't always configured to do so "out of the box". Typically, the relays for your 7-pin connector may have not been installed at the factory. Generally it's no big deal.. a couple of $2 relays and you'll be in business, providing the 7-pin is also wired for 12v delivery (generally the #4 or center pin if you want to test for current using a multimeter.)

 

That being said... charge from your alternator is generally extremely poor. You can't expect much more than to "maintain" your batteries state of charge (SOC) with minimal power usage in your 5er while traveling (parasitic draw, fridge, detectors, etc.). That will largely depend on the size of your alternator and the gauge of wiring to your connector.

 

To get beyond "barely adequate" generally requires an alternator and wiring upgrade (or going to duals), but to me, it's hardly worth the expense since the charge will still be rather poor and may have some potential risks to the general "health" of your 5er's battery/ies. That would depend on the battery.

 

In any event, it's likely going to have nothing to do with a problem with your 5er.

 

If you do test your connector and you are getting current, then you might see if your 5er has a battery cut-off switch and ensure it is "ON" to allow current to reach your battery/ies.

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There is a wire from the tow vehicle to the 12V supply of all trailers that I am familiar with, but the wire size is such that it limits the amount of charging current available to the batteries. If you dry camp and plan to recharge while towing, you would probably be wise to increase the size of the supply lead. For best results, some folks use a lead large enough that it needs to be outside of the existing RV plug and to have its own connector. If you have a standard, 7 pin RV connector with proper wire codes, the 12V wire should be red and on pin #4.

 

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Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

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One thing to add to what has been said. Some manufacturers not only do not include the relay(s) and or fuse for the trailer battery charging, but the hot wire from trailer wire harness is also not connected. Look for a red wire taped to the trailer wire harness under the hood near the fuse/electrical box. The one on my Chevy 2500 was even labelled and the owner's manual had a section on what to do to connect it with a diagram of the location of the relay and fuse. That said, I don't plan on getting much if any charge to the batteries even on a long drive.

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Additionally the small size of the wire, which is usually 10 or sometimes 12 gauge wire is much to small for the long distance from the truck alternator to the trailer battery to get much charge power to the battery.

 

It would be much better if you ran 6 gauge or even 4 gauge wire (it needs to be both the ground and 12V wire run) from the alternator or truck battery to the trailer battery.

 

Get the extra flexible cable from an electric supply store, or Amazon.com.

Al & Sharon
2006 Winnebago Journey 36G 
2020 Chevy Colorado Toad
San Antonio, TX

http://downtheroadaroundthebend.blogspot.com/

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I've also used an inverter in the truck to run the trailer's converter to charge the batteries. Works well, just be sure to find a mounting place for the inverter where it isn't exposed to the heat generated by the engine.

 

Also make sure you disconnect the regular charging wire tying the vehicle battery to the trailer batteries. Otherwise you'll set up a perpetual motion loop where the converter is trying to charge the batteries while the inverter is drawing power out to run the converter.

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If your truck has the towing package it should have came prewired for installing the 7-pin trailer cord receptacle, including the 12V charging wire. #10 wire is the largest wire that fits fully into the 7-pin plug terminals. Have you looked this up in your truck owners manual?

We owned 2 different 5ers, and 2 different trucks, both of which fully-charged the 5er batteries while driving.

 

2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG retired;Good Sam Life member,FMCA ." And so, my fellow Americans: ask not what your country can do for you--ask what you can do for your country.  John F. Kennedy 20 Jan 1961

 

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wow, lots of info, thanks everyone. Currently I'm just going to run my little 900 watt generator in the bed of my truck and an extra extension cord into the battery compartment to a small battery charger hooked up to the batteries.. that might work.

That would work if you only very lightly drain the battery. Maybe 10% at the most. If you plan on doing much dry camping and want to use the generator to charge your battery, buy a good 3 stage battery charger. The small battery chargers only put in 2-5 amps. If you have used 50% of your 100AH battery it will take as LITTLE as 10 hours of running your generator to charge the battery. Much much longer is the charger only puts in 2-3 amps. The three stage charger will put in 20-30 amps to start and the taper down as the battery becomes charged.

Al & Sharon
2006 Winnebago Journey 36G 
2020 Chevy Colorado Toad
San Antonio, TX

http://downtheroadaroundthebend.blogspot.com/

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