Whew! That sounds a little better......

 

I just hooked up a solar panel battery charger to my trailer battery. That charges my battery while it is parked. The solar panel was a cheap $40 amazon buy.

 

I am not going to go waste a bunch of time finding the posts about this when it came out in the '17 model trucks but the wire is small and charge current is very small as well- unless Ford changed it since it came out in '17

 

I think the truck looks for the resistance of the trailer bulbs. It then turns on the charge current but someone will have to confirm.

If it looks for a battery then how does the guy above claim he run his slides in and out with NO battery

 

I already have a 100w solar panel that keeps my (4) 6 volt batteries charged while it's in storage. I need to know that those batteries are being charged while driving south for the winter and having our residential fridge running in the 5er. solar won't keep up with the fridge/12v inverter.....

 

The best current I have been able to transfer is 10amps and I measured that with a meter. Gave up and ran 2/0 cables from the battery down the frame to a Anderson 350 connector. I can now use my dump trailer all day without it going dead. I also have added Anderson connectors to all my trailers so they all use the same charge connector as do my jumper cables.

 

Sorta off topic, but I had to help a guy at the storage yard one day, and the only way we could get his trailer any juice was to put his truck in Drive (with parking brake applied). Seemed crazy, and I don't remember the things we tried first, but that worked.
There's a lot of smarts in these trucks, so they don't always behave the way us dumb humans assume.

I assume the Amperage varies quite a bit.

 

I can't speak to the prior years but 2017+ won't ever see more than 30 amps as that's the limit of the fuse/relay on that circuit. Real world measurements indicate that the actual amps are closer to 20.

The OEM wire from the battery to the 7-pin plug would have to be 8 gauge at minimum. Assuming a 40' round trip distance, maximum of 30 amps at 12 volts, the voltage drop for 8 gauge wire would be 6.5%. If the assumption was that the source voltage would always be 13 volts, then the voltage drop is just below 6%.

 

The 12v going to the trailer is fused at 30A. You can use all 30 amps until the fuse blows. However, how much the battery draws while charging is dependent on the charge level of the battery, and voltage. Battery resistance changes based on the charge level. Examples: My trailer has a 30A converter/charger. I had 20A fuse going to the battery. The 20A fuse worked fine for years charging. Because I never ran the batteries below 50%, they never had a draw above 20A while charging. One time I accidentally ran the batteries dead. I fired up the generator so the converter would charge the batteries. 20A fuse kept blowing. I didn't have any 30A fuses, so I ended up using jumper cables from my truck to bring the batteries up to a point that the 20A fuse would hold.

The 12v from the truck will supply 30A all day if the load requires it. What happens with charging is, the batteries need more that 13.2 volts to effectively charge. 14.2+ volts ideally. When the batteries are low, they draw more current. That is when the resistance of the wire can affect things. If the truck is putting out 14.2volts at the engine bay, but the resistance drops that to less than 13 volts by the time it reaches the trailer. So you might be getting 30A at 12v let's say, but that is not going to charge batteries well. At that voltage, the batteries will only accept a small amount of current. But everything else in the trailer should still run fine.

By running a larger wire, you can reduce the voltage drop, and put the batteries at a voltage were they can accept more current.

 

A LiFePO4 battery directly connected to the 7-pin circuit can easily exceed that 30 amp draw limit. That battery chemistry has a much lower resistance than does lead acid. For that reason it is recommended that a DC-DC charger is installed between the 7-pin and the LiFePO4 battery. The DC-DC charger can be configured to limit the amp draw on the input side. What I don't know is if the truck CAN ever provide more than 30 amps. I don't plan to test this. At best, the fuse blows. At worst, the magic smoke starts to come out.

I have 560Ah of LiFePO4 in my RV trailer. A low state of charge on my batteries could easily suck up 100+ amps if allowed to. For that reason (and a couple others) I have separated my LiFePO4 battery bank from the truck's 7-pin circuit.

 

It definitely can. If you were to short the wire to frame, it would blow the fuse.

 

Does anyone know if there is a change in ForScan that can be made to charge as soon as the 7-pin plug is connected? I can't seem to find it.

 

I did some more testing today.
The trailer battery showed about 12.5 volts before I connected the truck, I connected the trailer to the truck and closed the door and hit the brakes. the voltage on the trailer battery stayed about the same. I then raise the dump trailer to start the trailers electric hydraulic pump.
The trailer battery went to about 11 volts when in use but started to climb back up after I stopped raising the bed and the pump stopped.
Slowly and steadily it climbed back to 13.2, so the truck is charging the battery, it just seemed that that the truck wouldn't start charging till is saw a voltage under the 12.5 that it was at when I connected to it.
I wanted to try a few things to verify some things that have been said about the trailer charging circuit.
first I opened the drivers door and for sure the voltage dropped off, then came back up when the door was closed, tried it a few times and I am confident that the door needs to be closed for the trucks trailer charge circuit to activate.
Next was if the key fob for the push button start needs to be in the truck for the charge circuit to activate.
Same type if tests as the door open test, verified multiple times that there was no charging with the key fob not in the truck and charging came back when the key fib was replaced.
My other trailer is burred behind other stuff right now so I cant test a different trailer.
So far it looks like that I need to get the trailer battery voltage down lower to get the trucks charge circuit to "wake up", then it seems to be ok. Also you have to have the door closed and key fob in the truck if you are testing, these are two things I was doing wrong when I was trouble shooting the charging circuit before.

 

bobv60, what year truck? If you use the "User CP" link at the top of the page, you can get to the "Edit Signature" page. That's the place to put your vehicle information so we don't have ask about it.

 

Anyone know if they changes in 2020 or 2021? I too would like to know if there is a Forscan parameter that we can set/adjust....