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Old 04-09-2016, 09:54 AM   #1
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TV charging camper batteries

Hello everyone,
We just became the proud owners of a 2016 2504S and I have a newbie question. So far I have upgraded from the single group 27 that came with the camper to three group 31 DP batteries that I got from work at a good price. Here is my question: if the camper battery(s) are way down after say a weekend without A/C hookups and you plug the camper int the TV and start the engine, what keeps the #12 gauge charge wire from the truck from burning up when there is a 140 amp alternator on the other end? What should happen is when the truck senses a big load like 3 batteries run down the alt should put out a lot of amps to try and bring the voltage up to 14. Because the load is the camper why doesn't the wire get hot and burn? The only other experience that I can think of is jump starting another car with cheap cables, they never got hot. Thoughts? Thanks in advance. Jay
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Old 04-09-2016, 10:05 AM   #2
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There is usually a resettable breaker ( on trailer) should the current get too high. There is also a fuse in the 12V TV fuse block for the Aux line.
You will get virtually no usable charge on the batteries by running the TV ( idle). You can get some minimal charge while driving, but due to parasitic loads in the RV and the wire size and length, the voltage delivered to the batteries will not be enough to make a significant impact on the charge. For that setup, you will need to plug into shore power, Plug into a generator, or add solar.
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Old 04-09-2016, 10:27 AM   #3
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You could run welding cables back to the batteries but that would be expensive. If I could afford it I would put solar in, that's the best way to go, again just expensive


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Old 04-09-2016, 10:42 AM   #4
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It seems unlikely to me that your truck would damage itself. You just don't hear about burned up charging circuits. You would have to drive at highway speeds for a couple of days to do anything to a battery bank like that.

The big banks are nice for additional capacity but the down side is that it takes a lot longer to recharge as well. No free lunch. Amp hrs out and Amp Hrs back in. And charging is less efficient than discharging. So, it will take more Amp Hrs in to replace a given amount of Amp Hrs out.

You should install a serious battery monitor, like a Victron, so you know what is going on with your battery bank.
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Old 04-09-2016, 10:55 AM   #5
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All I can go by is what we have as the factory charge circuit in our current TV. It would take a long time to charge a battery as it was only designed to maintain a charged battery and light electrical load. I haven't been able to find the factory spec for the pin 4 wire as it is missing from all of the connector pages but it looks be only 16 or 18 ga. Due to this I am adding my own higher current line to provide power to the TT while towing.
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Old 04-09-2016, 11:11 AM   #6
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Quote:
Originally Posted by keith_h View Post
All I can go by is what we have as the factory charge circuit in our current TV. It would take a long time to charge a battery as it was only designed to maintain a charged battery and light electrical load. I haven't been able to find the factory spec for the pin 4 wire as it is missing from all of the connector pages but it looks be only 16 or 18 ga. Due to this I am adding my own higher current line to provide power to the TT while towing.
Look at the size of the fuse for that pin in your tow vehicle's fuse box. That is the most your TV will EVER be able to deliver to your camper. My 2008 GMC Sierra is fused at 40 amps. That is a lot of amps possible, but in reality you will never see that much going to your camper's battery because the alternator's charge circuit will cut back on charging volts/amps when your truck's battery gets full (a lot earlier than your discharged camper battery bank).

See the attached about why vehicle alternators make lousy deep cycle battery chargers.
Attached Files
File Type: pdf Installing Auxiliary 12-Volt Feed to Trailer.pdf (457.4 KB, 50 views)
File Type: pdf Automobile Alternators as Chargers.pdf (805.9 KB, 43 views)
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Old 04-09-2016, 11:13 AM   #7
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Quote:
Originally Posted by keith_h View Post
All I can go by is what we have as the factory charge circuit in our current TV. It would take a long time to charge a battery as it was only designed to maintain a charged battery and light electrical load. I haven't been able to find the factory spec for the pin 4 wire as it is missing from all of the connector pages but it looks be only 16 or 18 ga. Due to this I am adding my own higher current line to provide power to the TT while towing.
Before you spend a lot of money doing this, please read my post.
You would need a dedicated alternator as well that did not connect to the truck's battery.
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Old 04-09-2016, 11:13 AM   #8
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Our batteries were at 3/4 after a day of boondocking, we unhooked the truck to go check out the area and left the trailer at camp. When we got back I connected the truck (w/2 group 78) to the TT and that brought the batteries back up for the next day. When we left the tt batteries were again down to 3/4. Once we got home, a 3 hr drive the tt (2- group 24) batteries were fully charged.

On my 5 ton dump trailer it uses a battery to lift the box. I have popped the 40 amp trailer fuse in the truck fuse box a couple times due to the battery getting old and weak. Otherwise with a good battery it recharges within 1-2 hours of driving ready for the next dump run.
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Old 04-09-2016, 11:40 AM   #9
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Originally Posted by Herk7769 View Post
Look at the size of the fuse for that pin in your tow vehicle's fuse box. That is the most your TV will EVER be able to deliver to your camper. My 2008 GMC Sierra is fused at 40 amps. That is a lot of amps possible, but in reality you will never see that much going to your camper's battery because the alternator's charge circuit will cut back on charging volts/amps when your truck's battery gets full (a lot earlier than your discharged camper battery bank).

See the attached about why vehicle alternators make lousy deep cycle battery chargers.
Already been through the schematics with the dealer and Ford. The dealer told me they have had to do a similar thing for another customer who needed more current for their trailer. Ford changed the circuit in 2015 F-150's to charge off the PCM which drives a few other thing too and is fused at 20A. Ford explicitly told me that pin 4 is only intended to maintain the battery and not charge it. I was able to get the gauges of the all the other wires going to the 7-pin connector. It is looking at this chart and comparing pin 7 to the other wires that I came up with 16 or 18 ga. Neither of which are good for much current over the roughly 30 ft of wire from the front to the back of the truck.

I'm not running the new line just to charge the battery but to be able to run the 12V heater on my fridge along with some other things we keep on. Since we run off shore power I have never bothered upgrading the group 24 battery as it does a good enough job keeping things going for gas stops or lunch breaks. This all worked fine in my previous TV that I wired for towing myself and should be just fine after I run a new 8 ga line to the back for the 12V line to the trailer.
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Old 04-09-2016, 11:53 AM   #10
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You might consider adding an ignition actuated relay to the circuit you are adding. This will prevent killing the TV battery if you park for a few hours with fridge etc running. Many of the large TVs have such a relay in the Fuse block.
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