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Old 07-29-2004, 08:43 AM   #1
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12 volt charge line...

Should the 12 volt charge line be a "switched" item from the tow vehicle? I just had a hitch place hook mine up, and if I put a tester on the plug on the back of my truck, it is always on, even with the truck key in my pocket. Is this normal? Wouldn't this drain the battery if I was parked and the trailer was still hooked up? Shouldn't turning off the key disable it?

Thanks in advance!
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Old 07-29-2004, 09:23 AM   #2
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Your charge line is wired hot, and it's OK to have it that way.

If you leave it plugged into the trailer, and you use some 12 volt power in the trailer, you will also use some of the tow vehicle battery power.

There are two ways to prevent that.

One, install a battery isolator.

Two, and the free one, is to simply unplug the trailer from the tow vehicle.

Andy
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Old 07-29-2004, 09:25 AM   #3
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Thanks Andy!
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Old 07-29-2004, 11:31 AM   #4
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The charge line from the tow vehicle should not be hot when the vehicle is off, let me say that again, the charge line from the tow vehicle should not be hot when the vehicle is off.
The charge line is intended to charge a battery on a connected trailer. It is not intended to provide power to the trailer. Charging can only occur when the vehicle is running.
It should only be hot when the ignition is turned on. One reason is what you have said, it would draw the battery down if you were parked, while it is true you could unplug the towing electrical cable, but this means that you could also forget to hook it up when you start moving again, and there is always the chance that you could forget to unplug it and wake up to a dead tow vehicle battery.
Another reason is the chance of a short occurring while the vehicle is parked. (not even hooked to a trailer) This can happen because a small animal crawls under your vehicle (a Cat or a Dog) and chew, pull on, rub against, and a variety of other reasons, they dislodge your wire and it has the possibility of shorting. (I had a cat do this on one of my tow vehicles a few years ago. Wires were all messed up, thank God they were not hot wires)

It is very easy to change the line over to a line that is hot only when the ignition is on, and I strongly suggest that you have this done to avoid problems down the road.
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Old 07-29-2004, 11:44 AM   #5
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Quote:
Originally Posted by JohnG
It is very easy to change the line over to a line that is hot only when the ignition is on, and I strongly suggest that you have this done to avoid problems down the road.
I strongly suggest you proceed with caution implementing this recommendation. The charge wire is rated for 25-30 amps. Moving the wire to a switched circuit will put additional load on that circuit which it might not be rated for. Thin curls of smoke are a good indicator of incompatibility.

If you are really keen on JohnG's recommendation, you will be better off having a relay powered by the switched circuit installed to handle switching the charge wire on & off.

Tom
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Old 07-29-2004, 12:24 PM   #6
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I would definitly have to agree with tcwilliams. A relay is ALWAYS the best and safest was to wire any high load circuit. Also make sure you are using a large enough gauge wire (10 gauge min.) running between the battery, relay and plug. I have a circiut breaker in line but it's probably not necessary. I've been in the car biz for over 30 years and can tell you from experiance that going cheap on wired accesories can cause nothing but trouble.
Good luck,
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Old 07-29-2004, 12:26 PM   #7
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Your right Tom, I should have said that you need to have the line capable of handling a 30 amp load without a problem. And they do sell a relay kit so you can hook directly into your battery for a charge line that works only when the key is on.
On my vehicle I hooked into a box on my firewall that powers up after ignition, and I also fused my charge line with a 20 amp fuse as suggested by a local hitch installer. I don't know if the 20 amp fuse is such a good idea since I thought a 30 amp would be more appropriate, but I haven't had a problem since it has been there. I also have my brake controller on a 20 amp fuse as suggested by the manufacturer. The brake controller will work with the key off if you press the pedal or the panic button.
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Old 07-29-2004, 06:30 PM   #8
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sneak


you can do it this way http://www.airforums.com/forum...ead.php?t=3770

all you need to add is the second battery and a relay. -or- just add a simple knife switch in the charge line.

remember, if you hook your trailer to shore power your univolt will charge the tow vehicle batteries also! that is, if you leave the umbilical cord hooked up.

john
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