Limited Electrical (12V) Power from Truck?

[Ramtough]

I have a power management computer in my RV. When the battery bank is down by around 50%, the onboard converter will charge at nearly 40 amps when hooked up to shore power. (Right at its rated capacity) I get slightly less running the external generator.



With the same level of discharge, when I hook the trailer to the truck, the computer never shows more than a 2. 5 amp charge. Is something in the truck limiting the flow of current to the trailer? Do you think that running a larger wire from the battery to the hitch pigtail female would make any difference?



Thanks in advance for your thoughts?

 

[Casey Balvert]

What is limiting your current is the voltage drop caused by a wire that runs from your vehicle charging system to the trailer battery and back to the vehicle ground. This wire is too long and too small a gauge to get any meaningful charging current to your battery. It is a bit more complicated than that but you get the picture. The best you can hope for is provide a maintenance charge for your trailer battery while running on the highway.



Casey

 

[Bill Stockard]

Yep, Casey is right! About the only thing the factory "hot wire" is good for is to run one dome light in a horse trailer.



To recharge the battery on my Lance camper and to operate the fridge on 12 volts, I ran a separate 8 gauge wire from the positive driver side battery post to the Lance furnished receptacle under the truck bed. Also I ran the 8 gauge ground wire directly to the battery post. The Lance camper has a built in battery separator so I didn't need a relay in the circuit, but you should have a heavy duty relay to keep from accidentally running down your truck batteries while the truck is connected to the trailer.



Bill

 

[klenger]

Wire size is part of the problem, but the other factor is that the truck alternator only puts out about 13. 75 volts. The deep cycle batteries in an RV need a charge voltage of over 14 volts (at the batteries) to charge completly. So, no matter how big of a wire you use in the truck, it will never charge as well as the converter in the camepr.



If you really want to charge the battery from the truck, you could install a 1000 watt inverter in the truck, run 115 vac back to the camper, and run the converter from that. I'm sure it would work, but too much work and expense IMHO for the results.

 

[y-knot]

I had the same problem As you, I have to red tops I keep in the trailer for power to run a large converter. The charging circuit on the trailering package is not big enough to handle the high current demand the batteries can have. I ran #2 welding cable from the truck batteries to a quick connect in the bed. And then #2 cable from the trailer batteries to a quick connect in the front of the trailer. Then I just hook the cables along with the normal trailer connection, and I have the problem solved.

 

[BillHicks]

My truck seems to put out enough power to run a 12 V refrigerator and charge the batteries. My Hi-Lo in the closed position will not work well on propane, so I have to use 12V going down the road. I just made 3000 Mi 14 day trip to Colorado and had no problems. I did not have to plug into electricity the whole trip. Previously I had a 2002 Chev Trailblazer and it would not run the fridg and keep the battery charged, so I was pleasantly surprised when the CTD did the job.

 

[slo-ryde]

Originally posted by BillHicks

My truck seems to put out enough power to run a 12 V refrigerator and charge the batteries. My Hi-Lo in the closed position will not work well on propane, so I have to use 12V going down the road. I just made 3000 Mi 14 day trip to Colorado and had no problems. I did not have to plug into electricity the whole trip. Previously I had a 2002 Chev Trailblazer and it would not run the fridg and keep the battery charged, so I was pleasantly surprised when the CTD did the job.

What kind of batteries are you using? I sure hope my truck can keep the batteries on my trailer charged. I'm trying to avoid going to a generator if possible.

 

[BillHicks]

slo-ryde,



I have two 12V Interstate marine-RV batteries. I would have preferred two 6V golf cart batteries, but they would not fit in the battery box. Running the furnace at night used about 20% of the battery capacity. If I towed a few hours the next day they would recharge. If I did not tow that day I would run my generator about an hour and be in good shape.

 

[Ramtough]

I'm using 6V Golf Cart batteries - I am very pleased with their performance.



Talked with the service guy @ the RV dealer. He said that Chrysler limits power (amperage) to the charge line in the factory trailer harnes.



Here's what I've done at his suggestion.



Run a 10 guage wire from the battery through a 30 amp breaker, then thorough an isolator (to prevent the trailer from drawing the truck batteries down) then to the female plug on the truck. The pigtail on my trailer has 10 guage hot & ground wires.



When I opened the taps the RV dealer had made on the factory harness for the 5th wheel receptacle, I was shocked at the size of the factory trailer wires - look to be around 20 guage, maybe smaller. I'm surprised that I can light up 12 or so running lights on the trailer.



I'll have the trailer out next week. Will report on results.



For most folks, a 2. 5 amp charge to the trailer is sufficent to maintain the batteries if they are charged but no where nearly enough to recharge a depleted battery.



I do considerably more dry camping than hooked up to shore power. On the road, I usually stay at Wall-Marts. With no ability to recharge the trailer batteries, evevy day the batteries get progressively weaker.



If I can get 25-30 amps to the trailer, I can recover around a 90% charge in 3-5 hours of running. Klenger is right - you would never expect to get 100% without the ability to charge at a higher voltage. I doubt that you could get to 100% at any volatage in less than 12 hours of charging.



I'm hoping that this will solve my problem.

 

[ronco]

Ramtough, you might consider a small 1000 watt generator to help keep up with your electrical needs in the event you don't move the camper for a few days. I will be the first one to say that listening to a generator for any length of time is a nuisance, although a necessary evil sometimes.





Ronco