Battery Drain - Fiberglass RV


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Old 08-01-2008, 11:08 AM   #1
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I have a dilemma.
When I drive with my refrigerator turned to 12V it drains the battery on the trailer. I have checked the power lug on the TV and it is live and checked that the trailers plug is connected to the 12V on the trailer end.
So I can't understand why the TV doesn't seem to support the operation of the refrigerator while driving. Does anyone have some clues?
Chris
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Old 08-01-2008, 11:40 AM   #2
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Quote:
I have a dilemma.
When I drive with my refrigerator turned to 12V it drains the battery on the trailer. I have checked the power lug on the TV and it is live and checked that the trailers plug is connected to the 12V on the trailer end.
So I can't understand why the TV doesn't seem to support the operation of the refrigerator while driving. Does anyone have some clues?
Chris

Does your tow vehicle have a large enough alternator to recharge your house battery as well as operate your fridge?

Does your 7-way plug have the alternator wire hooked up?

What size and type of battery are you using on your trailer.?

My fridge draws about 10 amps on 12 v. If I am travelling for 8 hours then it would draws approx. 8x10=80 amps. My house batteries are rated for 240 amp hours. However deep cycle batteries should not be depleted beyond 50% so I have about 110 amp hours to use (as long as I can plug in when I arrive at my destination).

You are probably exceding the capacity of the house battery.

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Old 08-01-2008, 01:26 PM   #3
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Quote:
I have a dilemma.
When I drive with my refrigerator turned to 12V it drains the battery on the trailer. I have checked the power lug on the TV and it is live and checked that the trailers plug is connected to the 12V on the trailer end.
So I can't understand why the TV doesn't seem to support the operation of the refrigerator while driving. Does anyone have some clues?
Chris
The problem is voltage drop. Your TV electrical system is set to about 13.6 to 14 volts but, when you draw 10+ amps through about 25 feet of wire from the front of your TV to the trailer you probably only have about 12 volts at the battery (even less at the refrigerator). The battery voltage is about 12.6 when it sits idle so it will discharge through the refrigerator and any other load you have on line until it gets down to 12 volts which is partially discharged. To charge the battery you have to have about 13.6 volts at the battery.

The best way to verify this in your system is to measure the voltage at the TV battery, coach battery and refrigerator with your TV running (set the engine rpm to about 1500 so you are getting a reasonable output from your alternator).

How to solve the problem:

A larger (lower gauge number) wire from the front to rear of your tow vehicle could help. Most factory wiring and many aftermarket installations use a fairly light wire, about 14 gauge, so a move to 12, 10 or even 8 if you have the bucks would be a big improvement. Also check your ground. Many campers and some TVs use a really wimpy ground lead. Remember that all the current flows in the ground lead; coach power, running lights, electric brake etc. I wouldn't use anything less than #10 for ground in my system.
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Old 08-01-2008, 01:55 PM   #4
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Make sure the TV voltage is getting to the camper. Disconnect the egg battery, plug up the TV and see if you have the voltage in the camper and at the camper battery connections.
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Old 08-01-2008, 02:27 PM   #5
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Wire gauge is critical. The attached url calculates the voltage loss for DC loads.

DC Voltage Drop

For a start, enter 13.5 as the input (I'm assuming 13.5 volts at the tow vehicle connection), 10 for the load, 32 feet (round trip from the tow vehicle plug back to the battery on a 16 footer), and 14 for the wire gauge and click the calculate button. It'll show you that only 12.7 vDC is actually getting to your battery. Change to gauge wire to 12 and then 10 and see how things improve.
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Old 08-01-2008, 02:57 PM   #6
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This problem haunted me for years until I looked at the issues more closely. Driving most of the day just left the battery quite depleted. Even if I turned the frig on to propane it would not charge worth beans.

Orlen is right: voltage drop. Think of voltage as pressure: If the battery has 12.6v in it and is being charged by a voltage from the tow vehicle at 12.4v the battery would actually slowly discharge because its "pressure" is more than can be gotten from the alternator.

A decent converter will charge the battery at something like 13.6 volts, enough pressure to force the electricity into the battery at a decent rate. What you need is something similar from you vehicle's charging system.

I eventually decided to put in a "battery minder" (Xantrex Link10). It told me everything I ever wanted to know about what was happening, so I was able to come to some conclusions.

Remedy: 6 gauge charge and ground wires all the way from the battery in the tow vehicle to the batteries in the trailer (through a switchable isolator relay). This is thick and stiff wire and not a pleasure to deal with. Incidentally, I changed the usual 7-pin into a 9-pin Pollak connector between the vehicles. I needed the extra pins for 3rd brakelight, backup light, etc. and it came with the bonus of 2 connectors which would actually accept the 6-gauge wires. Apparently truckers use this connector all the time. Other than the 9 pins, which are longer and make better connections, the housing and plug look just like the usual 7-pin.

Result: Let's say I leave the campground with a percentage battery charge somewhere in the low 70es. After an hour or two of driving the percentage charge in the batteries has gone up maybe a dozen percentage points. This is with the frig running on 120v through an inverter plus a towel warmer on (43 watts). The difference is huge from the non-functional earlier situation.

Conclusion: If you want to get the batteries charged while driving you have to deliver the extra voltage, and the only way to really do this is with hefty wiring. 6-gauge may be more than you need, but by the time you get to 10-gauge I suspect thing get marginal, especially with a long wire run.
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Old 08-01-2008, 08:54 PM   #7
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Wiring voltage drop is indeed the problem, both in the battery charge wire AND the ground or return battery wire and the typical 12-14 G wire is just not up to the task of running a heating element and replenishing all the other energy that may have been used from the egg battery.

I wired my truck with 6 gauge wire all the way to the truck battery on both the battery and return wires, plus connected the return wire to the truck chassis near the receiver hitch.

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Old 08-02-2008, 07:08 PM   #8
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I used to have that problem. Big time. Then I discovered the little red wire under the hood needed to be hooked up. Took about two minutes. No problem ever, since I did that.

I'm sure mine is an isolated case and I feel like everyone is giving you solid advice, but I still felt like it was worth mentioning. Since my vehicle came from the factory all ready to tow, I was surprised to learn that no one mentioned that it had to be connected. Thanks to these forums, I found out what I needed to do.
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Old 08-02-2008, 10:15 PM   #9
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Good point, Suz! I am so used to putting systems into older vehicles myself that I haven't adjusted to the concept of pre-wired stuf that just needs to be activated.
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