Trailer Battery not charging from F150???

[BuddyRay]

So, I wanted to add a 12v outlet to the bed of my 2016 F150. On past vehicles I've tapped the 12v charge line going to the 7way connector for power.

But on my 2016 F150 I immediately noticed 2 things:
1) the charge line is a TINY 18 gauge wire.
2) there was no 12v on the line - even when I started the truck.

Considerable homework later I discovered several things that readers of this forum that own an F150 might like to know:
On trucks PRIOR to 2016, Ford DOES NOT install the relay and fuse for the trailer battery charge line from the factory - EVEN IF the truck has a trailer tow package. The Relay and Fuse is usually in the glove box or seat pocket. Sometimes dealers install it - many times they don't.

On a 2016 F150 (can't confirm on F250 >) there isn't a relay. There is electronics to control the charge line. If it doesn't detect a battery that needs charging, it doesn't feed power to that line.

My concern is - with that tiny wire, will enough current get all the way back to the trailer to even replace what the trailers circuits (like the refrigerator control board) is using, much less charge batteries.

I'm seriously considering running at 10 gauge wire from the battery to the 7way connector and putting my own disconnect relay in like we used to do in the good 'ol days.

Has anyone else had experience with this stuff?

[Jhowemca]

I don't think it will charge a dead battery, but it will top it off if it's a little low and keep it there.
You can use the water pump if you need it, or lights or anything 12 volt and it will be fine.
I always keep plugged into the truck while running to extend the slide or awning too.

[klpoppe]

I read up on the 2015 F150 which should be the same as yours.

The following I found on another forum:

"Hooked my utility trailer up today, here's what I learned. Connect the trailer, then switch the ignition to accessory mode you will see a message that the trailer is connected. Name the trailer also enter the details about the trailer. If equipped, your blind spot and cross traffic alert will be disabled automatically.
when you start the truck it will power up the 12v terminal and charge the auxiliary battery. (Trailer battery voltage went from 12.4 to 13.6)
if you slide the brake controller you will see the gain setting and bar in the info panel. If you get a "Trailer disconnected" message the controller is not operating the trailer brakes. (Mine had a broken wire in the trailer harness).
Red lights come on in the info center to indicate running lights are working when you turn them on. Green marks indicate the other lights are functioning correctly.
In general the system works beautifully."

"
I see someone already beat me to it, but I can confirm the 7 pin plug back to the system center is an intelligent plug. It has to see a "load" before it will start the charging process.

If you see the "trailer connected" message on your display, charging will start.

I was not able to get a trailer connected message the first time, until I went into the display and gave the trailer a name, selected the brake type, then set it as the default trailer. Once I did that, trailer connected came on. Charge line went active. After that one setup, it gets it every time."

I can say that mine seemed to be charging yesterday when I towed my camper as I left to truck hooked up when I was done to help with the electric jack.

[Heady]

I had to install the relays on my 2013 F150. Truck tows great and keeps the battery topped off.

[Mustang65]

Originally Posted by Heady

I had to install the relays on my 2013 F150. Truck tows great and keeps the battery topped off.

2x on my 2012.

The relay was in the glove box for the factory installed towing package

Don

[Subaru297]

It has been a while but I think I get 4 amps while idling from our F250 2015. This would probably be a bit higher with a discharged battery but the battery was around 90%.

I'll have to run the battery down soon and note the amps and voltage when plugged into the truck for a data point.

With the small gauge wire and voltage losses I doubt you are getting enough to fully charge a trailer battery though.

With 20' of 14 gauge wire your losses are around 7% (assuming 10 amps) which just gives you float voltage (~13.4v) at the trailer. That is starting at 14.4v from the alternator. If you really had 18 gauge wire then you are around 17% losses (~11.9v).

I did not have to install a relay in my 2015 F250. Factory or dealer installed for me.

If you do install a larger gauge wire I would be interested in any comparisons before and after you can determine.

Cheers

[Subaru297]

I saw 12.9 volts at the battery while idling the truck this past weekend. No way that is going to charge a battery in any hurry or at all really.
It will help a little if your battery is very low to begin with but probably won't get your battery over 80% charge unless left running for days.

Cheers

[BuddyRay]

Hmm - I know voltage regulator used to kick altenator output as high as 14 volts.
When you add a discharged trailer battery to the mix it "Should" cause the voltage regulator to kick in. I guess it depends upon how low your battery was during your test.

However, if the line between the front and rear batteries is a 14 gauge thread then, you're right, the resistance is going to both inhibit the Voltage Regulators ability to read that battery AND charge it.

Back in the 60's when I was pulling a Rolite (extra points for anyone who knows what that was!) I had a 10 gauge wire running all the way, front to back, with a large isolation relay in between and appropriate connectors. My Ford E150 Van had a 60 amp "police" alternator on it that could charge a completely dead RV battery in a couple of hours. I know, I did it more than once while boondocking and using my vehicle as a very inefficient generator.

Nobody seems to do this anymore. Perhaps it's because modern Voltage Regulators, and trailer wiring setups are just too "smart" to do this efficiently.

[Mustang65]

Here is what I have noticed about the charging of the TT battery by the F150 (280Amp Alternator). When the F150 starts up the charging voltage jumps to 14+ volts and as the trucks battery charges it levels off at 13 Volts and then down to 12.6VDC. When I add the TT's batteries that are 12.4VDC (minus the SOLAR charging) the trucks charging circuit does not jump to 14+ volts that would be expected. It only goes up to 12.6 or 12.7VDC. The trucks battery is a couple weeks old, decided to get a new one before we left for GA.

Based on what I see, there is a controller in the trucks wiring that doesn't care what the TT's battery voltage level is. I am thinking that there is a blocking diode in the trucks circuit, that isolates the TT's battery from the trucks circuit for protection, and it only sees the trucks battery. So, the TT's battery only gets the trucks output based on what the charging circuit is doing to the trucks battery. When I return from Chicago, I will do some testing to see what I find.


Don

[ALJO]

On a RAM the alternator charges the TV battery through electronic regulator. The Batt+ to the 7 prong plug comes off the Battery+ Circuit. So whatever voltage is available at the time is also going to the TT battery with some loss through wiring.

[DanNJanice]

Originally Posted by Mustang65

Here is what I have noticed about the charging of the TT battery by the F150 (280Amp Alternator). When the F150 starts up the charging voltage jumps to 14+ volts and as the trucks battery charges it levels off at 13 Volts and then down to 12.6VDC. When I add the TT's batteries that are 12.4VDC (minus the SOLAR charging) the trucks charging circuit does not jump to 14+ volts that would be expected. It only goes up to 12.6 or 12.7VDC. The trucks battery is a couple weeks old, decided to get a new one before we left for GA.

Based on what I see, there is a controller in the trucks wiring that doesn't care what the TT's battery voltage level is. I am thinking that there is a blocking diode in the trucks circuit, that isolates the TT's battery from the trucks circuit for protection, and it only sees the trucks battery. So, the TT's battery only gets the trucks output based on what the charging circuit is doing to the trucks battery. When I return from Chicago, I will do some testing to see what I find.


Don

Interesting findings. I built my own wireless battery monitor for the trailer, so I can watch it, inside the truck, while driving down the road. I will have to deliberately discharge my trailer batteries a bit and then check it. BTW, I have a 2015 F250.

[Subaru297]

Originally Posted by DanNJanice

Interesting findings. I built my own wireless battery monitor for the trailer, so I can watch it, inside the truck, while driving down the road. I will have to deliberately discharge my trailer batteries a bit and then check it. BTW, I have a 2015 F250.

That would be cool to see!

As I typed my earlier response I was thinking I should have checked the voltage at the truck battery as well to see what the alternator was putting out. The truck just started though so it should have been around 14+ volts.

[Mustang65]

Originally Posted by DanNJanice

Interesting findings. I built my own wireless battery monitor for the trailer, so I can watch it, inside the truck, while driving down the road. I will have to deliberately discharge my trailer batteries a bit and then check it. BTW, I have a 2015 F250.

Our TT's MPPT SOLAR charge controller is plugged into the TT's wireless Wi-Fi router (on 24/78) and we can see the battery voltage on our Windows tablet that is in the truck. We switch between the Wi-Fi rear view camera (on back of the TT) and the MPPT controller while driving. The battery is usually around 12.6VDC while driving and drops to 12.4 when under the canopy at the gas station. I should have unplugged from the truck to see what the voltage was with SOLAR only. The fridge which runs on electric pulls the battery voltage down when it kicks on.

Don

[DanNJanice]

Originally Posted by Subaru297

That would be cool to see!

As I typed my earlier response I was thinking I should have checked the voltage at the truck battery as well to see what the alternator was putting out. The truck just started though so it should have been around 14+ volts.

I watched the charging on the trailer as I came home from camping this weekend.
When I left my campsite, the batteries were at 75% SOC. When the truck was running and connected to the trailer, I saw about 12.9V on the trailer batteries, with a charge current of about 7 Amps. After about an hour of driving the I was getting about 6 Amps and just over 13V at the trailer batteries. I think the most I have ever seen when driving is about 9 Amps charging the trailer batteries.