Wiring problem - Page 2 - Fiberglass RV


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Old 06-07-2012, 11:33 AM   #15
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Name: Chantal
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Thank you everyone for your input and sorry for not being clear enough.
The battery we replaced was the one in the Boler. The car battery is always fine unless the car is connected to the Boler for more or less 15 minutes, then the car battery goes dead. When it happens the fridge is usually on 12V, which could explain the draw. I must point out though that even after the car battery dies, the Boler battery is not dead.
Yesterday I found a quote on etrailer.com that explained one of my problems:
On some vehicles, power to the 7-Way is terminated once the key is off and removed from the vehicle. On others, it will remain on. Since the ETBC7 has a direct connection to the vehicle battery via a 40 amp circuit breaker, the 12 volt pin will have power to it all the time. You would have to disconnect the trailer from the tow vehicle to avoid draining the vehicle battery. Or you could install Tow Ready Battery Isolation Solenoid to isolate the vehicle battery when the ignition is turned off.
So we might get one of those battery isolation solenoids.
Right now the trailer battery is being recharged (it was charged) and will do some of the step by step tests suggested above. Thanks again.
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Old 06-07-2012, 11:53 AM   #16
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Chantal, thanks for clarifying the situation. As mentioned the 12v fridge is a *BIG* draw especially on older fridges and I avoided it if possible - try using a frozen jug of water in it while traveling. Putting a terminator on your cars wiring would help but if you are driving with the fridge on the car battery is probable slowly being drained as it cant keep up to the amount being pulled from it by the fridge & running everything else you may have going in the car, even while driving - yup thats how big the draw of power may be.... so it may only take a few minutes once stopped to drain the car battery completely. Be aware anytime a battery is taken down to less than 50% it really shortens the life of the battery and it will not hold a charge well if that has happen more than 3 or 4 times ... so having the car battery checked before we get a real good cold snap next winter would be a real good idea as it may not be in as good of condition as you think it is.
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Old 06-07-2012, 12:19 PM   #17
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Ditto on what Carol said. I think you are on the right track with a relay.
We used a couple of blue ice packs in the freezer to keep it cool while traveling, re-freeze overnight.

I would add that the long run that the wire from power source in tow vehicle to trailer creates a lot of potential voltage drop. Unless the wire is at least 10 ga or better yet 8 ga it won't charge the trailer battery well and will add to the drain by things like the fridge on the tow source.

Best way I have heard it explained is it's like filling a tire the "pressure" in the source has to be greater than what already exists in the tire in order to add any air.

Battery voltage drops as it discharges so in order to "push" any charge into the battery the voltage from the source needs to be greater than the battery. Greater that difference faster it charges AND only if the wire can deliver voltage greater than fully charged will trailer battery get fully charged.

Can't take an air compressor delivering 25 lbs of air pressure and fill a tire to 35 lbs no matter how long it's hooked up.

Looking at my own wiring I would say my power feed to trailer is about good for having 12 volt lights at a rest area or getting a 3/4 charge on trailer battery.
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Old 06-07-2012, 12:36 PM   #18
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Very good suggestions: Will get the car battery checked at next maintenance appointment, which happens to be next Saturday, and will use ice instead of 12V when travelling. The air pressure comparison made the concept of trailer battery charging very clear too. Thank you!
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Old 06-07-2012, 03:21 PM   #19
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Originally Posted by Carol H View Post
..........Putting a terminator on your cars wiring would help but if you are driving with the fridge on the car battery is probable slowly being drained as it cant keep up to the amount being pulled from it by the fridge & running everything else you may have going in the car, even while driving - yup thats how big the draw of power may be.............
I'm not so sure that this is true. Car alternators are usually at least 100 amp capacity. A fridge draws about 10 amps. For sure, when the car is not running the fridge sucks the battery dry.

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...............I would add that the long run that the wire from power source in tow vehicle to trailer creates a lot of potential voltage drop. Unless the wire is at least 10 ga or better yet 8 ga it won't charge the trailer battery well and will add to the drain by things like the fridge on the tow source...............
I think that this is the crux of the issue.
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Old 06-07-2012, 04:27 PM   #20
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I'm not so sure that this is true. Car alternators are usually at least 100 amp capacity. A fridge draws about 10 amps. For sure, when the car is not running the fridge sucks the battery dry.
I think that this is the crux of the issue.
Thomas you may be correct re the crux. All I know is on my trailer it takes a number of hours of driving just for the tow to fully recharge the trailer battery that isnt close to being discharged to 50% to start with & even though I am not running the fridge while driving. Both my car and trailer have batteries less than a year old so they are in good shape. If the car battery is more than 4 years old and has been allowed to fall below 50% a few times it isnt going to be holding a whole lot of charge for long (same as the trailers) perhaps just enough to turn the car over so I would think the car is going to be working on recharging its own battery, as well as the trailers if its down and the 12V fridge on top of it all .... just dont think it is likely to do that very fast or well - for sure a drive of just an hour or two isnt going to be much help.
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Old 06-07-2012, 05:05 PM   #21
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....Thomas you may be correct re the crux. All I know is on my trailer it takes a number of hours of driving just for the tow to fully recharge the trailer battery that isnt close to being discharged to 50% to start with & even though I am not running the fridge while driving.....
Unless you have pretty heavy wire between TV charging and trailer the voltage that the trailer battery is getting won't be high enough to push charge in very fast. Your doing very well if you have enough to ever reach 100% battery charge.

We did one time flatten an RV battery in good condition by running fridge, stereo (plus two power booster amps) and lights while doing a straight through run from Mi. to Colorado in a motor home. So I know it is possible to drain battery while hooked to running alternator as Carol suggests.

That was a short heavy wire run from 150 amp alternator to battery. Bigger wire and shorter run than typical for RV trailer. It took about 16 hrs and things started dying, thank goodness for battery isolator. Oh and other bank of RV batteries. Still not happy to get below that 50% charge on the one that was drained.

Between myself and the kids had three CDL's plus two that could handle a stick and air brakes, easiest long trip I ever made, except for the part where driver gets to pick the music. Knew more about what kids were listening to than I wanted by the time we arrived <_<
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Old 06-07-2012, 05:13 PM   #22
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Thomas you may be correct re the crux. All I know is on my trailer it takes a number of hours of driving just for the tow to fully recharge the trailer battery that isnt close to being discharged to 50% to start with & even though I am not running the fridge while driving. Both my car and trailer have batteries less than a year old so they are in good shape. If the car battery is more than 4 years old and has been allowed to fall below 50% a few times it isnt going to be holding a whole lot of charge for long (same as the trailers) perhaps just enough to turn the car over so I would think the car is going to be working on recharging its own battery, as well as the trailers if its down and the 12V fridge on top of it all .... just dont think it is likely to do that very fast or well - for sure a drive of just an hour or two isnt going to be much help.
Just call me Tom.



Roger explained it well with his analogy to pumping up a tire. It comes down to the voltage available at the trailer battery during charging. The voltage starts out at about 14.5 volts at the TV's alternator and is reduced by every millimeter of wire and connection. Add a load like a refrigerator and the voltage drop is even greater - in fact a guy named Ohm had a great theory about all this.

Unless and until you measure the voltage at your battery while charging, you really don't know what is going on. You may be trying to inflate a tire to 35 PSI with a 35.1 PSI hose. Thus the heavy gage wire requirement.
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Old 06-07-2012, 06:12 PM   #23
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First is the battery good or bad? Have you had it tested. Until you do that nothing else matters.
Battery ok, then how many amp draw on battery?
Is there a amp draw with tv unhooked and everything turned off?
Keep it simple
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Old 06-07-2012, 07:03 PM   #24
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First is the battery good or bad? Have you had it tested. Until you do that nothing else matters.
Battery ok, then how many amp draw on battery?
Is there a amp draw with tv unhooked and everything turned off?
Keep it simple
Works if you have a meter and can use it to measure amp draw. The process of elimination steps or suggestions on what might be the cause are a "no meter" approach that depend on nothing but logic steps or things anyone can check that can take you pretty close to the source.

Would be worth a stop at one of those auto parts stores that test batteries for free but clearly something was hammering the TV battery, only a question of where located. Trailer or TV, if trailer then what appliance.

Think it's been tracked down to fridge on 12 volt, with plans to have TV battery tested to make sure being run down has not hurt it too much.
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Old 06-07-2012, 07:15 PM   #25
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...........Think it's been tracked down to fridge on 12 volt, with plans to have TV battery tested to make sure being run down has not hurt it too much.

Yes, I think the OP nailed it in post #15. You need a relay between the TV and the trailer battery and a heavy gauge wire, especially if you want to run an absorption type refrigerator while towing.

And even with that, you need to disconnect the fridge from the trailer battery when the TV is not running.
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Old 06-07-2012, 08:21 PM   #26
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Key to a cold fridge when traveling: Run the Fridge on shore power 2 days B 4 departure and Freeze some bottled drinking water in the home fridge and move them to the camper fridge just prior to departure. You will be putting frozen water bottles in a cold fridge and that will get you through the first day and hopefully shore power during the camping night will help extend the frozen water bottles for another day.
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