Power draw from tv battery when turned off - Fiberglass RV


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Old 06-02-2013, 11:02 AM   #1
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Power draw from tv battery when turned off

Is there a way to tell if my Scamp battery is pulling power from my tow vehicle battery when the Scamp is plugged to the tv and the tv is shut off? I do not want to stop for awhile and come back to a dead tv battery.
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Alice
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Old 06-02-2013, 11:27 AM   #2
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If you have a multimeter, check between pin 1 (Ground) and pin 4(Battery) on your 7 pin connector. If there is 12V with your ignition off, you don't have a relay that shuts off the connection when you tow vehicle ignition is off.

You can also purchase a 7 pin tester, however I don't recommend this one - very difficult to get a good connection with it.
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Old 06-02-2013, 11:31 AM   #3
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Originally Posted by Wallo View Post
Is there a way to tell if my Scamp battery is pulling power from my tow vehicle battery when the Scamp is plugged to the tv and the tv is shut off? I do not want to stop for awhile and come back to a dead tv battery.
Thanks,
Alice
Shouldn't there be a solenoid in the trailer to separate house battery and vehicle battery? By 2008, I would hope that Scamp considered doing this, if not you should add one. Perhaps someone with a scamp of this vintage could chime in here?

Derek

With regards to the solenoid, the following discussion may be helpful: 7 pin power question
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Old 06-02-2013, 11:37 AM   #4
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Originally Posted by glamourpets View Post
Shouldn't there be a solenoid in the trailer to separate house battery and vehicle battery? By 2008, I would hope that Scamp considered doing this, if not you should add one. Perhaps someone with a scamp of this vintage could chime in here?

Derek
Usually, the isolation relay is in the tow vehicle.
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Old 06-02-2013, 11:37 AM   #5
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You would have to have a simple 12 volt tester light that you can purchase cheep from any auto parts store, hardware, or Harbor Freight. Just place the clip on the end of the wire to a metal part of the tow vehicle, and touch the pointed metal tip of the tester to the rv plug connecter pin on the tow vehicle (there is a schematic of which post is used for this). If you have a "hot wire" to charge your trailer battery, it will light the tester up.
As long as you are plugged into your tow vehicle, you will also be using power from your tow vehicle battery also. I found this out the hard way the first time we went camping years ago, using the 12 volt setting on the refrigerator. Our tow vehicle & trailer battery were both dead in just 4 hours.
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Old 06-02-2013, 02:03 PM   #6
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Shouldn't there be a solenoid in the trailer to separate house battery and vehicle battery?]
How would that work? An isolation relay in the tow vehicle is controlled by a source of power which goes on only when the engine is running (or the ignition switch if on). If located in the trailer, what would be this controlling signal... the tail lights? This could work, but locating the isolation relay in the tow vehicle makes more sense to me.
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Old 06-02-2013, 05:36 PM   #7
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How would that work? An isolation relay in the tow vehicle is controlled by a source of power which goes on only when the engine is running (or the ignition switch if on). If located in the trailer, what would be this controlling signal... the tail lights? This could work, but locating the isolation relay in the tow vehicle makes more sense to me.
I guess you could have a more sophisticated relay that sensed the voltage on the vehicle side and only switched to the on position when voltage exceeded a threshold that would indicate the alternator was providing power. I'm with you, though, easier to install in the tow vehicle.
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Old 06-02-2013, 06:19 PM   #8
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In my humble opinion a isolation relay or solenoid, what ever you want to call it, is simply another failure point. I speak from experience. My first tow vehicle had one installed, it failed and my trailer battery didn't get charged. That before I got the solar panel. After a couple days the battery went dead, it should have lasted at least 4 days with a full charge from the tow. I couldn't just plug in the tow and charge the battery.

I did get the battery charged with a small inverter and a battery charger, but what a hassle.

A friend had a small motor home with a diode type isolator, it went bad and connected the cranking battery directly to the house battery. She had to run the motor every day to make sure she could get it started.

Like I said, to me any type of isolation is just another failure point that will fail.
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Old 06-02-2013, 06:24 PM   #9
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I guess you could have a more sophisticated relay that sensed the voltage on the vehicle side and only switched to the on position when voltage exceeded a threshold that would indicate the alternator was providing power.
Yes, that's a good point - this would work. It would also be more hassle to design and build than a simple ignition-switched relay, and one would be needed per trailer (instead of one per tow vehicle, which needs wiring anyway)... but it certainly would work.

I suspect that no trailer manufacturer would want to pay for this, since tugs that supply charge power are typically properly wired and don't need it anyway.

If someone wants to take this approach, and doesn't want to build it, they could buy an isolation system of this type intended for mounting in the tow vehicle, and just put it in the trailer: these are usually called Automatic Charging Relays.
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Old 06-02-2013, 06:51 PM   #10
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I was looking for vehicle specific wiring for my car and the only place I found them is in the UK, where they use A LOT more wires to connect a camper to tug (2x12 pins instead of 1x7 pins). When looking at them trying to figure out how to make them work I stumbled upon an interesting feature. One harness has a relay that switches on when the voltage reaches 13.5V and switches off when voltage drops to 12.6v (approximate, I'd have to look it up again) on the refrigerator power wire. BTW they have separate power wires for brakes, camper 12v battery, and refrigerator.

Cliff notes; I found a trailer wiring kit with a relay that switches on when voltage goes high enough and back off when voltage drops enough. It is sold as a universal kit and appears to adaptable to 7 pin RV plug.

Jason
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Old 06-02-2013, 07:21 PM   #11
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...........
Cliff notes; I found a trailer wiring kit with a relay that switches on when voltage goes high enough and back off when voltage drops enough. It is sold as a universal kit and appears to adaptable to 7 pin RV plug.

Jason
Who knew? There seem to be a number of these sold.

Amazon.com: voltage sensitive relay
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Old 06-02-2013, 09:24 PM   #12
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I found a trailer wiring kit with a relay that switches on when voltage goes high enough and back off when voltage drops enough. It is sold as a universal kit and appears to adaptable to 7 pin RV plug.
Good find!

Quote:
Originally Posted by SilverGhost View Post
I was looking for vehicle specific wiring for my car and the only place I found them is in the UK, where they use A LOT more wires to connect a camper to tug (2x12 pins instead of 1x7 pins). When looking at them trying to figure out how to make them work I stumbled upon an interesting feature. One harness has a relay that switches on when the voltage reaches 13.5V and switches off when voltage drops to 12.6v (approximate, I'd have to look it up again) on the refrigerator power wire. BTW they have separate power wires for brakes, camper 12v battery, and refrigerator.
They use more pins, but not that many. The old system uses two 7-pin connectors (the "12N" and "12S", not named for the number of pins), and the new scheme uses one 13-pin. There are more pins, but mostly for trailer lighting: turn signals are separate from the stop lamps (as cars are required to have), there is a fog light circuit, and even the tail/marker circuit is split left/right so you can leave the parking lights lit on one side (the one facing traffic) only. With all those pins, there is still not one for electric brakes, because they don't use them.

There are those two power circuits in the Euro system instead of our one: one that's always on and one that is on only with the engine running (which they could accomplish with that voltage-based switching).
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Old 06-02-2013, 09:29 PM   #13
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In my humble opinion a isolation relay or solenoid, what ever you want to call it, is simply another failure point.
I think that's a valid point, but I think I'm less reliable than a simple relay, so personally I would rather run the small risk of the relay failing (which I can bypass on the roadside with a pair of pliers) than the large risk that I park the rig for something like a meal stop with the refrigerator on and forget to unplug... or worse, unplug and forget to plug back in when I pull away.
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Old 06-02-2013, 09:37 PM   #14
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If your tow vehicle is a GM product with factory trailer plug, yes your trailer will drain your TV battery unless you unplug the trailer when stopped. I had a 2006 Chevy pickup that would anyway. More than once I forgot to plug it back in when I started out the next day. Late model Ford pickups with factory trailer wiring disconnect the "hot post" in the trailer plug when you shut the key off so no problem.
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