F250 is not charging RV batteries on the road

[Scramjet]

I started this thread originally so I thought I'd follow up. Hooked up voltage monitor today and drove six hours. Didn't gain or lose and that's with the fridge on and the slide out being used several times, etc., so it's definitely charging just not getting ahead or falling behind. Thanks for all the helpful feedback here.

J,

I have a 2018 Ford F-250 gas with the factory installed 5th wheel plug in the bed. My Victron battery monitor says that I get about 7 amps from the truck best case. Not much considering the other parasitic draws as you have discovered!

Brian

[John303]

Thanks for sharing. To put that into work with my previous post, your are dropping 6 volts (14.2 - 8.2). Resistance = volts/current. Therefore, your circuit resistance is .24 ohms. Not bad. Probably most of it in your trailer plug. Interesting about your DC-DC charger. I wonder which fix is the least expensive, the DC charger or larger cables/connectors. ?? No experience with the DC Charger.

Even with larger cables you still need a higher than lead-acid voltage to effectively charge Lithium. Larger wires might lessen the voltage drop, but it will not take much to drop below lithium's needs. The DC/DC works well, and I did not have to putz around with crawling around underneath the truck.

[jjbbrewer]

A little more data here ..

I have an AiLi current meter/battery monitor between my 2 DC27 batteries and the RV ground. I left the power on for the last couple days while hooked to the truck.

The combination of the refrigerator, powered antenna, WiFi equipment, and whatever else is on with the main power switch was drawing about 2.2-2.6A. Predictably, this drew my batteries down to about 11.7V (30%)

My point in doing this was to find out how my F-450 charges the batteries. After getting the batteries to this low state, I started the truck and watched the ammeter.

Right after starting the truck, there was no current going in, so no charge. As others have mentioned, to enable power to the trailer, you need to push the brake pedal. That does start the charge, but creating a "door event" (opening or closing) will stop the charge. The driver's door will stop it immediately, the passenger (and other?) door will stop it when the "door ajar" alarm comes up on the dash.

So, to charge the battery from the truck ..

• I left the motor running & trans in park (of course)
• Rolled down the driver's window
• Got out and closed all of the doors
• Put the key on the driver's seat (so I didn't get a "key not detected" error)
• Pushed the brake pedal with a long stick

As long as the truck was running, the batteries were charging. I measured a peak of 12A which slowly decreased to 11A then 10A after a few minutes. I'm pretty confident that the batteries would eventually go to full charge after a couple of hours driving or so.

[Scramjet]

A little more data here ..

I have an AiLi current meter/battery monitor between my 2 DC27 batteries and the RV ground. I left the power on for the last couple days while hooked to the truck.

The combination of the refrigerator, powered antenna, WiFi equipment, and whatever else is on with the main power switch was drawing about 2.2-2.6A. Predictably, this drew my batteries down to about 11.7V (30%)

My point in doing this was to find out how my F-450 charges the batteries. After getting the batteries to this low state, I started the truck and watched the ammeter.

Right after starting the truck, there was no current going in, so no charge. As others have mentioned, to enable power to the trailer, you need to push the brake pedal. That does start the charge, but creating a "door event" (opening or closing) will stop the charge. The driver's door will stop it immediately, the passenger (and other?) door will stop it when the "door ajar" alarm comes up on the dash.

So, to charge the battery from the truck ..

• I left the motor running & trans in park (of course)
• Rolled down the driver's window
• Got out and closed all of the doors
• Put the key on the driver's seat (so I didn't get a "key not detected" error)
• Pushed the brake pedal with a long stick

As long as the truck was running, the batteries were charging. I measured a peak of 12A which slowly decreased to 11A then 10A after a few minutes. I'm pretty confident that the batteries would eventually go to full charge after a couple of hours driving or so.

J,

Thanks for the detailed update on the Ford charging system to the trailer. Unless I am mistaken those batteries are rated about 80 ah each for the 20 hour rating. If you are at 50% state of charge for 2 batteries you are down 80 amp hours that needs to be put back in the batteries. My guess is that will be quite a bit more than 8 hours of driving to recharge the batteries close to full as the charge current gradually reduces as the battery approaches 100% for lead acid batteries.

Brian

[jjbbrewer]

My guess is that will be quite a bit more than 8 hours of driving to recharge the batteries close to full as the charge current gradually reduces as the battery approaches 100% for lead acid batteries.

Yep, you're probably right. I have the RV plugged into the house right now and last I looked it was charging at 27A. I'll have to do another experiment with the batteries drained and just charging from the truck.