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davidz71 05-15-2008 08:54 PM

Umbilical cord/battery draw
I've noticed something over the last 3-4 years regarding battery strength before towing and when I reach my destination. I usually am showing around 14.66 volts when the solar panels are turned on and I am boondocking. When I have turned the solar off and check the next day, the voltage is in the high 13 volt range. No problem there because the battery is settling. What I do find strange is that I have always noticed battery voltage is in the mid to low 12's after I have towed, say 110 miles or so. I plugged the trailer's umbilical cord in the other day with the solar panels on and noticed the voltage taking a consistent dive from mid 14 to mid 12's, a hundredth of a volt every second. Do you think one of my trailer plug wires may be wired wrong and drawing power from the trailer battery or is it because my trailer battery may be stronger than my Chevy 2500hd battery (2 years old and strong)? I have working turn signals, clearance lights, brake lights but no functional backup lights on the trailer when the truck is put in Reverse.

davidz71 06-16-2008 07:25 AM

While spending time on this, I found out why the reverse lights were not working on the trailer. One burned out bulb and one corroded base. Both bulbs replaced and it works fine. Now to find out if it had anything to do with battery draw once connected to the tow vehicle.

strmstr69 06-16-2008 09:53 AM

Does your coach battery voltage go back up when you disconnect to TV? If so, I would chalk it up to the draw from the many little things the TV has going while at rest. Things like the computer, radio sets and and other such things. This is normal and should not drain either battery under normal situations. Unless you leave it for an extended length of time..usually several weeks. Any draw at all will eventually take a battery down, but at the low current being used, it will take a while. Just a thought, hope this helps you.

Dan W.

overlander63 06-16-2008 12:35 PM

Your truck has an electronic regulator that turns off the charging when the battery is at or above a certain voltage (usually between 13-13.5 volts). If your trailer battery is above this voltage, the voltage regulator on the truck will see the increased voltage, and not apply more until the voltage drops below the lower limit. There is nothing wrong with it, that is just how Detroit has worked out not overcharging your tow vehicle's battery.

davidz71 06-16-2008 08:47 PM

Ahhh, that makes sense. I guess if the battery in the trailer is in tip top shape and the battery in the vehicle is several years older then it would also draw from the stronger battery even if there wasn't another draw from the vehicle electronic components. It hasn't been a problem but I was concerned that it could be.

Mexray 06-16-2008 11:33 PM

If wired properly, your TV has a relay or diode device that makes the connection from the TV's alternator to the tow harness when the engine (ignition on) is running. The connection should be 'open' (not connected) with the ignition OFF.

TV's that come equipped from the factory with 'Tow Packages' should have a relay/diode device Incorporated in the tow harness. If someone has 'added' the tow capability to your TV, perhaps the relay/diode was not added...a BIG no, no!

This prevents a trailer hooked to the TV from running down the TV's battery when parked if the power cord remains hooked up.

If you hooked up your power cord to the TV without the engine running, and the voltage 'drops' in the trailer, as you noted above...there is something wrong, or no relay, etc.

If you hook up, and the TV's engine is running, the trailer battery's voltage should be close to the voltage of the TV's battery, with a slight reduction due to DC voltage losses in the connections and length of wire, etc. You might check these two voltages at the respective batteries with a digital DC voltmeter - just touch the voltmeter leads to the TV battery, and then one of the batteries in the Trailer to could further check this out by doing it after dark when the solar panels won't effect the trailer's battery voltage.

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