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Old 10-25-2003, 01:07 AM   #1
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How do batts re-charge?

I'm leaving this week to pick up our trailer and drive it back. My question is; does the 7 wire hook up recharge the battery on the TT as I drive, or is it constantly draining? Can I hook up a charger off of the 110 panel at RV site, or does the plug in of the trailer to this automatically recharge?
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Old 10-25-2003, 07:34 AM   #2
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frozen,

yes it does charge your trailer.

assuming that your vehicle's socket is wired properly. also it can work in reverse. you can recharge your vehicle battery with the univolt when plugged into shore power.

handy option not many folks know about.

john
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Old 10-25-2003, 11:30 AM   #3
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Re: How do batts re-charge?

Quote:
Originally posted by frozen chosen
I'm leaving this week to pick up our trailer and drive it back. My question is; does the 7 wire hook up recharge the battery on the TT as I drive, or is it constantly draining? Can I hook up a charger off of the 110 panel at RV site, or does the plug in of the trailer to this automatically recharge?
If properly wired your tow vehicle will charge your battery as you drive. You will also be charging as you are plugged in to 110. A couple of words of caution, dependent upon your tow vehicle wiring and the load on your alternator the amount of amperage delivered to your battery can be minimal. Many tow vehicle manufacturers provide larger alternators on those models that have the factory tow package option.

The final word of caution is again dependent upon your tow vehicle. Battery power from your tow vehicle could flow back to your trailer when your vehicle is not running thus depleating your tow vehicle battery. As a practice whenever I stay hitched up overnight I pull the trailer hitch plug from the receptical as a safety.

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Old 10-25-2003, 03:39 PM   #4
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If wired properly, the tow vehicle to trailer charge line does not work both ways. There should be either a relay to shut it down when the truck isn't running or isolation diodes to prevent reverse current. The idea is to keep a dead trailer battery from creating a dead tow vehicle battery.

Also, the charge current from a tow vehicle to a trailer is likely to be rather small due to wiring resistance and the fact that the tow vehicle charging system is set by the truck battery and needs.

A day's worth of driving will usually charge a night's worth of RV battery use but I wouldn't depend upon it.

If you want to charge your truck battery, follow the instructions in the driver's manual for the vehicle and don't depend upon an RV converter doing it.
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Old 10-25-2003, 04:00 PM   #5
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Quote:
Originally posted by Leipper
If wired properly, the tow vehicle to trailer charge line does not work both ways. There should be either a relay to shut it down when the truck isn't running or isolation diodes to prevent reverse current. The idea is to keep a dead trailer battery from creating a dead tow vehicle battery.

Also, the charge current from a tow vehicle to a trailer is likely to be rather small due to wiring resistance and the fact that the tow vehicle charging system is set by the truck battery and needs.

A day's worth of driving will usually charge a night's worth of RV battery use but I wouldn't depend upon it.

If you want to charge your truck battery, follow the instructions in the driver's manual for the vehicle and don't depend upon an RV converter doing it.
leipper

all of the tow vehicles i've had have just had a direct fused lead from the battery to the charge line, except my current silverado.

this is how i set it up to not drain the starting battery when overnighting. http://www.airforums.com/forum...&threadid=3770

my truck does a fine job charging the trailer batteries through the ten gauge wire feeding it. then again, my truck has a 160 amp alternator.

as for the reverse flow issue, i once had my rig hooked up a couple of days before a trip, left a interior light on and killed the starting battery on my tow vehicle. plugged it in overnight and started right up the next morning.

how long it would have actually took the univolt to recharge my truck is unknown.

but as i stated above a handy option to have!

john
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Old 10-25-2003, 05:06 PM   #6
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ten guage drops a millivolt per foot per amp. Figure at least 25 feet from engine to RV battery for a roundtrip of maybe 50 feet. knock off maybe 10 feet as a bit of optimism that the ground return path is much better (usually isn't). Forget about connection resistance (which can be significant) and figure that a drop of half a volt from the engine battery reference voltage pretty well puts you into the useless charge current category.

So how much current for a half volt drop at 40' of ten guage? If I figure right, that's about ten amps of charging uder optimum conditions (totally dead RV battery and so on). Actuality is probably quite a bit less than this. That's why it takes a lot of driving to charge most RV batteries. And most have 12 or 14 guage wire, too, which doubles or quadruples the resistance.

I know about the improperly wired charge lines, too. But relays and isolation diodes cost money and most folks don't worry about it if indeed they even know what to worry about - so they often get skipped for a fuse link.

Most factory or dealer installed RV wiring is just barely adequate. How may do you see with 4 and 6 gauge brake and charge lines?
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Old 10-25-2003, 05:16 PM   #7
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Old 10-27-2003, 08:42 AM   #8
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If you want to go "hog wild" on a project like this, just run copper welding cable to the rear of the tow vehicle, and put a quick disconnect at the existing trailer connector. Do the same on the A/S, make up a jumper between the two QD's and your good to go.
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Old 10-27-2003, 04:59 PM   #9
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sounds like a good idea pick!

ya think 1/0 awg would be big enough?

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