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Old 04-23-2019, 12:52 AM   #1
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Charging Batteries

So when my trailer is hooked up and Im driving down the road are my batteries getting charged from my trucks charging system???
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Old 04-23-2019, 04:08 AM   #2
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most tow vehicles only provide a trickle charge, at best.
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Old 04-23-2019, 05:49 AM   #3
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The short answer is "maybe".

It depends on the make and model of your truck, whether the truck came with the tow package factory installed, whether ( as in the case of chevy/gmc) the dealer prep included the fuse box fuse and connection, and the type of connector your trailer has.

If your truck has a 7 pin standard or 6 pin trailer plug, with the engine running, check for power at the connector as shown below. If it has a 4 pin connector, there is no battery charge circuit or electric brakes (unless you added them with a separate connector). The 7 way is most common,
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Old 04-23-2019, 05:53 AM   #4
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Originally Posted by bikendan View Post
most tow vehicles only provide a trickle charge, at best.
The reason for this "top off charger" is in the article below. Running the truck to charge up a depleted battery will most likely take more than a full tank of fuel.
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Old 04-23-2019, 06:02 AM   #5
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With my last trailer (not a Forest River), pulling it with a 2004 gas Silverado 2500HD with factory tow package, every time I took it to the dealer for service and it was there for more than a few days, the battery would be dead. I would always have to back my truck up close enough to connect the 7-pin to operate the electric tongue jack to get it hooked-up. I would then head home, which was about 30 miles. By the time I got home, there was always enough battery power to disconnect from my truck and use the tongue jack to get it level. I never measured anything to check the state of the battery — all I know is, it worked.

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Old 04-23-2019, 06:58 AM   #6
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Originally Posted by nomad297 View Post
With my last trailer (not a Forest River), pulling it with a 2004 gas Silverado 2500HD with factory tow package, every time I took it to the dealer for service and it was there for more than a few days, the battery would be dead. I would always have to back my truck up close enough to connect the 7-pin to operate the electric tongue jack to get it hooked-up. I would then head home, which was about 30 miles. By the time I got home, there was always enough battery power to disconnect from my truck and use the tongue jack to get it level. I never measured anything to check the state of the battery — all I know is, it worked.

Bruce
If you read the article, it will explain why it worked. "Worked" is not the same as "fully charged".

At the normal charge rate associated with the two battery "system" created when you plugged in your trailer, the alternator will see a start discharged starting battery and your depleted trailer battery. The alternator will start fast charging both batteries.

The start battery is designed to take (and deliver) high current quickly but has limited capacity so it is fully charged quickly. A starting battery is rated in "CCA" or Cold Cranking Amps. A starting battery rated at 660CCA will output 660 amps at Zero Degrees Centigrade (32 Degrees F) for 30 SECONDS till dead.

The trailer battery is designed to be take and deliver a lower current (typical deep cycle batteries are rated at 5 amps for a number of hours - a 100AH battery will last 20 hours with a 5 amp constant load) and can not take or deliver a high charge rate for very long without overheating. The more depleted they are the faster they can take a charge, but the voltage recovers much faster than the capacity.

Since the truck's alternator uses the combined voltage of the starting battery and the trailer battery "as a system", it will cut back the charge rate once the start battery has been topped off.

The trailer battery may only be 25% or so filled when that happens.
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Old 04-23-2019, 08:10 AM   #7
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The reason for this "top off charger" is in the article below. Running the truck to charge up a depleted battery will most likely take more than a full tank of fuel.
Interesting article, thanks for posting. I have read of others who have modified their vehicle's charging system to eliminate a camp generator. I don't recall the details. Maybe it was an unsubstantiated boast? Or maybe done by adding a second alternator and custom regulator?
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Old 04-23-2019, 08:44 AM   #8
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Has anyone installed a jumper battery terminal to their set up? I'm considering it. My thought is for situations like nomad297 mentioned. If the battery is dead, you can just use jumper cables from tow vehicle to battery for a few minutes and charge direct with the engine running. That would be significantly more efficient than trying to trickle charge through the tow system. Is my theory correct or would that not work? Attaching a link to the jumper terminal. I'd run that straight to the battery. Then there is a direct link from the jumper terminal to the battery without needing to open the battery compartment and everything else, just hook the jumper cables to the truck battery on one end, and the jumper terminals on the other end, and presto, charged RV battery.

https://www.amazon.com/dp/B07P6D5QSY...detail_1?psc=1
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Old 04-23-2019, 09:18 AM   #9
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Yes, but the process is slow. The alternator on your truck produces some power to bring up your batteries, but I agree that it is at a very slow rate. Don't rely on it.
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Old 04-23-2019, 10:45 AM   #10
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Originally Posted by DES-1 View Post
Interesting article, thanks for posting. I have read of others who have modified their vehicle's charging system to eliminate a camp generator. I don't recall the details. Maybe it was an unsubstantiated boast? Or maybe done by adding a second alternator and custom regulator?
The BEST way (IMO) to do this is to install a dedicated truck inverter connected to a dedicated deep discharge battery in the truck. Plug a dedicated Smart Charger into the inverter when you need to charge the camper battery.

That way you can run the engine to power the inverter when charging the trailer battery and can run AC power tools when not.

For this application I would use this charger:

https://www.amazon.com/NOCO-GB40-Ult...-1-spons&psc=1

Charger Reviews - https://mozaw.com/best-deep-cycle-battery-charger/

It pulls a maximum of 1200 Watts when charging (1000 amps peak times 12 volts) so a 1500 watt inverter would power it just fine.

https://www.amazon.com/Cobra-1575-Pr...s%2C128&sr=8-2

You would obviously need the engine running to supplement the Truck's deep discharge battery if the Camper's battery was less than 50% of capacity and to manage the initial peak load.
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