Not your typical 7-Way trailer connector question

[Yo Hoot]

I wanted to use the trailer connector on my truck to power up some 12v things I have. Not big power, just light duty.

I bought a loose connector at the auto store and wired in to the 12V (Black) and the ground (White) pins.

I measure 12v with a meter between those two... good to go.

Now I have this 12v battery charger I use for my Radio Control models. I connect it and it will not turn on. I check everything and there is 12v at the charger but it won't turn on. I connect that same charger to the battery under the hood and it works just fine. That's the way I always did it before but I thought it would be convenient to have a 12v power source at the back of the truck since we back in to our flying site. I made up this harness for a nice quick, convenient power source.

I then hooked up my cheapy 12v yellow revolving emergency light to it. It worked but it looked like it drew more current... the bulb lit for a short time brght and the motor ran faster than usual... eventually the light burnt out.

Now I'm wondering, Is this a direct 12v power source or is this a charging circuit for the trailer batteries that can't be used as a direct 12v source?

Also last season we took our camper on a three hour trip ... the batteries never charged.

Any ideas?

Thanks,

Mike

 

[Wiredawg]

I am not sure how many amps the factory plug has, but seems it has a 40 amp grass hopper fuse in the power dist panel. Might want to run a 10 or 12 gauge wire from that circuit to the recepticle plug and runa 10 or 12 ga wire for the ground all the way back to the battery. W/ this high a fuse, might want to make sure whatever you connect to has lower amp fuse as 40 amps can fry something rated a much lower than that. Even better, create a separate circuit w/ 40 amp auto reset breaker.



FYI I rewired my '02 w/ wiring this way so I could use batteries/charging for the RV from the truck for extended use. Paid off when I was living in my RV and power grid went out for three days.



Hope this helps.



Wiredawg

 

[Yo Hoot]

Yes I've been doing some research. For some reason I assumed and have read that the truck would charge the utility batteries (I have two) while driving.



I was wrong. What I discovered is that 12v in the 7-way connector is only there to keep the emergency brake battery charged.



So what I think I am seeing is that lead is a charging lead that does not give you pure 12v. I believe it's a variable charging circuit. That's why nothing hooked to it works right that needs straight 12v.



Not only that the wires to the 7-way are tiny. No way they could be used to charge a large 12v lead acid battery in any shorter amount of time.



So what you are saying is connect a larger fused wire directly to the trailer batteries with a quick disconnect at the hitch. The truck alternator will do the job?



Mike

 

[lebar]

Do you have the trailer towing package? Our Horse trailers have several 12 volt lights both inside and outside of the trailer and all work fine off of the 12 volt power in the 7 way plug. I have heard stories about trucks that the dealer installs a hitch and wiring with out the trailer package and they can cause major head aches.

 

[Yo Hoot]

Yes I do have the towing package.



Turns out these 7-way connectors aren't meant to charge big car batteries. It only provides enough to keep the little emergency brake battery charged. I would need to run a large fused wire if I want to use the truck to charge while driving.

 

[lebar]

We just bought a 4 horse trailer with living quarters (2- 12 volt batteries) We have only pulled the trailer a couple of times but the trailer batteries seem to be charging. I will have to put a meter on them the next time I plug it into the truck to check that I am charging the trailer batteries. I would think if you have a bad battery on the trailer it could over load the charging system.

 

[Road Dog]

The power at the trailer plug is simply truck power -- 12. 6 to 14 volts depending on the charging status of the truck's batteries. There's a small voltage drop because of the wire running to the back of the truck. (The voltage drop depends on the current draw. More draw, more voltage drop. ) It won't charge a trailer battery in a useful way.

I have a couple of ideas. The trailer power may run through the FCM (front control module) and might interact with the charger. Or the charger might consider the voltage too low and shutdown. Usually it's around 10 volts to avoid damaging the battery but who knows.

 

[Yo Hoot]

The power at the trailer plug is simply truck power -- 12. 6 to 14 volts depending on the charging status of the truck's batteries. There's a small voltage drop because of the wire running to the back of the truck. (The voltage drop depends on the current draw. More draw, more voltage drop. ) It won't charge a trailer battery in a useful way.

I have a couple of ideas. The trailer power may run through the FCM (front control module) and might interact with the charger. Or the charger might consider the voltage too low and shutdown. Usually it's around 10 volts to avoid damaging the battery but who knows.

That's exactly what I was thinking. Actually I think it's called the IPM (Integrated Power Module). The 12v at the plug is basically useless. No biggy. I know what I have to do if I want real power back there.

Does anybody know if charging the batts on the trailer from the truck with a big line will interact negatively with the trailer's power supply?

It's a PD9160A Power Convertor.
Intelli-Power PD9160A 60A Electronic RV Converter/Charger

 

[Wiredawg]

I repeat my orig recommendation. Disconnect the smaller wires to your 7-way and run heavy wiring from the battery, thru a 40 amp auto resetting breaker and use that as the 12V power lead. It won't jump start anything, but will charge your 12V batties while connected and driving and will add two more batteries in parallel for running 12V power in your RV.



Wiredawg

 

[Yo Hoot]

I repeat my orig recommendation. Disconnect the smaller wires to your 7-way and run heavy wiring from the battery, thru a 40 amp auto resetting breaker and use that as the 12V power lead. It won't jump start anything, but will charge your 12V batties while connected and driving and will add two more batteries in parallel for running 12V power in your RV.

Wiredawg

That does sound like the simple, effective way to go. I already have two deep cycle batteries on board the trailer.


Thanks Wiredawg

 

[Yo Hoot]

What about the ground? Maybe I should add a large wire to the ground pin too?

 

[Yo Hoot]

OK I just did an assessment.

The Dodge bumper receptacle is custom type that cannot be opened up to replace wires. Basically the truck has a rectangular connecter that plugs into rear of the custom bumper receptacle.

That means I would need to purchase a new bumper receptacle and cut off the Dodge plug.

I have decided against this method due to the final result. I also thought about the wire in the trailer end. It's probably a bit small too. Doing the dedicated wire is less work and provides more power.

Based on this I'm just going to run a dedicated fused power line from the battery with a separate connector at the bumper. I'll then make up a pigtail for the trailer that directly connects to the batteries.

 

[Road Dog]

That's exactly what I was thinking. Actually I think it's called the IPM (Integrated Power Module).

Maybe. I don't have a factory manual handy. Depending on the the year there's an FCM, IPM or TIPM (totally integrated power module).

 

[Yo Hoot]

I just picked up 40 ft of #8 stranded automotive wire. Getting to work now.

 

[Yo Hoot]

I just finished running the 8 gauge wire tonight. I put an inline 30 amp circuit breaker up close to the battery. All I have left to do is install the disconnects at the end and make up the trailer pigtail.

I talked to the RV center. They said they do something. . not sure what. They charge $120 to do it. I didn't get specifics. I asked what size wire they use. He didn't say he just said it would be ample enough to do what I wanted. With that I decided to do it myself.

I'm using these SMH 50 AMP connectors. I picked them up at my local truck outfitter company.

#ad


8 AWG Breakaway Power Connector 50A

 

[Kirwin]

Trailer battery charging

I have a large battery bank on my TT to supply my inverter with a Link 1000 installed to monitor battery state of charge. If the batteries are discharged the truck charges them at about an 8 amp rate. So if you have any significant amount of discharge you can see that it takes a long time to restore their charge. They will recharge if you pull the trailer all day but even 8 hours at 8 amps is only 64 amp-hours of recharge. This is not a significant amount of energy. The 7 pin connector is not designed to provide a large charge current, its more of a maintainer circuit. K Irwin

 

[Yo Hoot]

I just did some research in the wiring diagrams.

Looking at the pinouts at the connector (Trailer Tow Connector Add-On) Pg 8W-80-99

Cavity 4, Circuit A100 14 RD/VT Function Fused B(+)

I accounted for all other functions including Electric Brake, Cavity 7, B40, 14DG

A100 Cavity 4 is the charging circuit 12v(+).

A in A100 stands for battery feed. This is a straight run with it's only connector on the way being C217. From there it goes directly to the IPM (fuse Box) under the hood. It's connected to Fuse 19. 20 Amp. It's a 14 gauge wire.

Looking at power loss on a 14g wire supplied with 20a... . at 20+ feet you end up with 10a so Kirwin what you described makes sense.

I would like to know why my circuit acts up when I put a load on it. I have another fellow on another site who is having the exact same symptoms as me. He made a trailer connector up to power a mini 12v compressor. He measures 12v there. He says his camper battery doesn't charge either.

I hooked up a cheap revolving yellow beacon to the trailer connector. It worked but it seemed like it was getting too much voltage as it was spinning faster than normal and the bulb was super bright then burnt out. I have a feeling something is up either with the ground or the connection. It's supposed to be a straight run without any "modules" in the circuit to confuse us so it's got to be a bad wire/connection/ground. Only other thing it could be is some strange backfeeding through ground from another circuit?

 

[Yo Hoot]

Here's the finished product...



#ad




#ad




#ad




At the trailer



#ad




#ad

 

[lebar]

The RV dealers probably put a constant duty solenoid in line and trigger it from a 12 volt source that is hot when the ignition is on so you don't have to worry about running your truck batteries down. If you run the wire direct from truck batteries and the trailer is plugged in and not running all your batteries will go down. There are more sophisticated ways to do this but the 12 volt constant duty solenoid works. Don't use a ford solenoid as they are not constant duty.

 

[Yo Hoot]

The RV dealers probably put a constant duty solenoid in line and trigger it from a 12 volt source that is hot when the ignition is on so you don't have to worry about running your truck batteries down. If you run the wire direct from truck batteries and the trailer is plugged in and not running all your batteries will go down. There are more sophisticated ways to do this but the 12 volt constant duty solenoid works. Don't use a ford solenoid as they are not constant duty.

I don't expect to be hooked up once I get to my destination. Even if we had to spend the night in a hotel for some reason it would not be an issue as the two batteries in the trailer alone can last a weekend. My truck is diesel with two batteries. That's four batteries. I don't think I'll have an issue.



I also want to use that 12v power for when I go flying my radio control helicopters. I have a few electric ones that need real juice to charge plus I can power anything else at the field off the truck. Normally I open the hood to attach my charger to the battery. This is much more convenient. I don't want to have to have the keys in the truck all day. Yes I could do a switched solenoid. I'll see how it goes. If I need it I'll add it later.

Thanks.



This isn't mine but this model, believe it or not is electric. You can imagine what it takes to charge the batteries. They use twin lithium polymer batteries in the 5 ah range. They dump all of it in about 6-8 minutes of flight.

We can charge them at 20-30 amps.



#ad




#ad




#ad




#ad