# Battery Charging Circuit



## hatcityhosehauler (Feb 13, 2004)

Ok everyone, the owners manual for my Ex says Fuse Position #115 is the Trailer Battery Charge circuit, and requires a 20A fuse.

The Pamphet the comes with the Ford supplied Brake control harness also identifiy's #115 as the trailer battery circuit, only it shows a 40A fuse.

I called the service department of my Ford dealer, and they had no idea what I was talking about, but they are looking into it, and are going to call me back. No where in either the manual, or the pamphet does it mention changing the fuse to the higher amperage when towing a trailer.

I know on my Chevy, it said right in the documentation for the harness that the fuse needed to be upgraded, and the harness even included the fuse.

Anybody have any info to share? Does your Ex or SuperDuty have a 20A or 40A in the trailer battery circuit? I figure I'll get a response quicker here, then from Ford.

Tim


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## Highlander96 (Mar 1, 2005)

Where is LateralG????

I am pretty sure he is a retired Ford Engineer.

Wish I could help, Tim!

Good Luck.

Tim (squared)


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## Y-Guy (Jan 30, 2004)

Tim on our last big trip I finally noticed it wasn't charging. From what I read I needed to add a 40A fuse. This was on my list to get this week, I'll report back what my dealer says. Since they are the Ford and RV dealer maybe they'll know better about this - thankfully I know the service tech guy in the RV dept. well enough that I can ask him and be assured too get the right answer.


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## chetlenox (Feb 3, 2004)

I had to replace mine once (I left the key turned in the "on" position, then plugged in the trailer, I think that's what blew it). I'll be darn if I can remember how many amps it was though.

I do know that I did replace it with what the owner's manual said though, so it was probably 20 amp.

Chet.


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## hurricaneplumber (Apr 12, 2004)

Tim #1, what does the owner's manual say??

kevin

My manual says this...

10AMP Trailer tow battery Charge relay

30AMP Trailer tow battery charge

30AMP Trailer tow electric brake

When I installed my Prodigy I also added a relay in the fuse box, did you have to do that??

Your 40 AMPS sounds about right.


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## hatcityhosehauler (Feb 13, 2004)

hurricaneplumber said:


> Tim #1, what does the owner's manual say??
> 
> I believe my fuse is more than a 20 amp.
> 
> ...


Kevin, the owners manual says 20A, and the other document, which is also a Ford document, titled_ "F Super Duty Series (F-250, F-350, F-450, F-550), Excursion Electrical Trailer Tow Installation Instructions" _ Ford Publication# is SK-2C3T-15A416-AE, says 40A. The dealer still hasn't called me back, and I've already gotten 3 replies here.....I guess I always knew where to get the answers.

Steve, thanks for letting me know when you get yours done. Unfortunately, I have to drive to the Spring Rally tomorrow, so I need to get this answer today. I will let you all know what I find out from Ford.

Tim


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## Y-Guy (Jan 30, 2004)

Tim I'll try to head over here after my AM meeting here in a few.


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## hatcityhosehauler (Feb 13, 2004)

Well, I just got off the phone with the Ford dealer, and after looking at the same documentation that I was, seems to feel the 40A would be the proper fuse. I'm off to the autoparts store, as I don't have happen to have one of those in the garage.

I'll let you guys know how things work out.

Tim


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## CamperAndy (Aug 26, 2004)

hatcityhosehauler said:


> Kevin, the owners manual says 20A, and the other document, which is also a Ford document, titled_ "F Super Duty Series (F-250, F-350, F-450, F-550), Excursion Electrical Trailer Tow Installation Instructions" _ Ford Publication# is SK-2C3T-15A416-AE, says 40A. The dealer still hasn't called me back, and I've already gotten 3 replies here.....I guess I always knew where to get the answers.
> 
> Tim
> [snapback]109577[/snapback]​


Sounds like the Trailer Tow installation instruction would supersede the manual. I would go with the Trailer tow instructions.


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## hatcityhosehauler (Feb 13, 2004)

That's kinda what I figured. I went and bought both a 20A and a 40A anyway. The first guy I talked to at Ford called back while I was out, and said, 20A, but he didn't realize I had called back and talked to someone else.

I also got a new battery, as that may have been an underlying cause...maybe creating to much of a draw for that poor little 20A.

Tim


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## Y-Guy (Jan 30, 2004)

Tim mine doesn't use a fuse and the part it needed is installed. So I wasn't able to find out anything new. I know in my Av I had to buy a fuse - ran me like $25 as I recall.


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## snowtakampers (Apr 29, 2006)

The purpose of the fuse is to protect the wire. The proper fuse size depends on the length and size of the wire. Here's a web site that may be helpful.









http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html


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## hatcityhosehauler (Feb 13, 2004)

Steve, I finally got 2 different answers from Ford, one for each fuse, so I ended up getting both. I put the 20A back in, and connected, after getting a new battery. Viola, everything worked. I speculate that the battery died last night (I knew it was on it's last legs, but was holding out for as long as I could, since I never camp without electric). I had the camper plugged into shore power all week, making sure the systems all work, chilling the fridge, and what not. In prep for what was a test tow, I d/c'd the shore power before leaving for work yesterday afternoon. I forgot to shut off the turbo maxx fan, and I'm sure that accelerated the discharge of an already inadequet battery.

When I plugged the TT into the TV, the fan, the fridge, the propane detector, and the charging circuits on the converter all cried for power at once, and the little old 20A gave the supreme sacrifice. New battery installed, and NO problems.

snowtakampers, the issue wasn't that I didn't know,,,the issue was that I had two different Ford documents telling me to use different fuses. Since I have no idea of knowing what size wire Ford used to run the circuit, nor how long the run is, I couldn't guesstimate which fuse to use. I had one of the service techs tell me I should use the 40A, and another say to use whatever the manual called for.

I err'ed on the side of caution, and went with the 20A, and if that blows on the trip up to PA tomorrow, then I'll switch to the 40, and call someone in Dearborn a little higher up on the food chain.

Tim


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## NJMikeC (Mar 29, 2006)

Can't for the life of me see what is pulling 40 Amps. I'm not even so sure that any "high rate" battery charger pushes more then 6 or 10 amps and trickle chargers like the one I have for my batteries certainly don't.

Kind of like 40AMPS * 12 Volts= 480Watts, as in put your hand next to almost 5 100W light bulbs. Just don't add up unless the 40Watts are for the tail lights as well but that is even high.

In short (pardon the pun) seems like 20 Amps is fine for it. Correct?


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## hatcityhosehauler (Feb 13, 2004)

I'm pretty sure the '02 Chevy I had before this had a 40 amp fuse on the battery charge circuit, but don't quote me on that. The 20 is working, so we are going to keep it that way.

Don't forget, not all trailers are campers, and some may have other electrical accessories that work off that circuit, to power a hydralic pump or something of that order, and the vehicle manufacture's try to hit the whole market.

I'm confident that I have found the problem, but will post back if it is not the case. Thanks all for your input.

Tim


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## CamperAndy (Aug 26, 2004)

NJMikeC said:


> Can't for the life of me see what is pulling 40 Amps. I'm not even so sure that any "high rate" battery charger pushes more then 6 or 10 amps and trickle chargers like the one I have for my batteries certainly don't.
> 
> Kind of like 40AMPS * 12 Volts= 480Watts, as in put your hand next to almost 5 100W light bulbs. Just don't add up unless the 40Watts are for the tail lights as well but that is even high.
> 
> ...


The converter in the outback puts out up to 55 amps at 12 vdc. Most alternators installed with towing packages put out 130 to 150 amps at 12 vdc. So there is plenty of potential to put out more then 40 amps to a single circuit like the 12 vdc feed to the trailer.


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## chetlenox (Feb 3, 2004)

Hey, that's a good idea. I didn't know such a thing existed. I'll have to get on Google and check it out. The trailer charge circuit is ripe for that sorta thing, since I'm sure if it blows 90% of the time you find out about it when your batteries are dead at 3am in the morning...

Chet.


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## CamperAndy (Aug 26, 2004)

keeper18 said:


> CamperAndy said:
> 
> 
> > NJMikeC said:
> ...


The Outback converter made by WFCO puts out the following

14.2 vdc for the initial 4 hours as long as the current draw is over the set limit (not sure but think it is 15 amp)
13.6 vdc until the current draw drops to about 2 amps
13.2 vdc for maintenance at about 1 to 1.5 amp.

I over simplified the first answer when I said it puts out 55 amps at 12 vdc. That is more like the output when not connected to a battery but powering a high current item like the slide motor. I also over simplified the alternator output. Same situation.


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