Direct Charge Circuit

[Kountryguy]

I would like to run a direct line from my truck alternator to the house batteries in my fifth wheel trailer. Has anyone done this project that could offer some suggestions on how to and what materials used? Any help will be appreciated.

[wa8yxm]

Salvo wrote:
The regulator also senses the chassis battery which may be full.
Sal

Though in this case you MIGHT be right, there is a bit more.

I have, recently, read about a "Smart alternator" (3-stage regulator) that can in fact sense battery voltage and switch to float when it's full up.. But it is new, and very expensive and it is **NOT** standard equipment on anything.

Most alternators put out the same voltage, 100% of the time, so long as you are not at full idle (They may drop at idle, epically if you have lights and HEVAC on (heating, ventelation, air conditioning).

Likewise the brakes on the trailer (if you are at full idle, you are either parked or have foot on brake normally).

So that does not really apply here.

And, when you have two batteries in parallel,, I often hear how the charging system will sense when the smaller one is full and shut down so the larger one won't fill... This is very simply IMPOSSIBLE with batteries side by side in a RV.

however in this case. the issue is not battery size, It's not "Sensing when one is full" it's the wire that connects the two. It is TOO SMALL in most cases so only a very slow charge gets pushed into the trailer.

I have problems with that on my motor home and the wire is shorter than his truck.. (Though in fairness I found the problem was a bad battery. The GC-2's finally gave up the ghose. They are "offline" just now awaiting repalcement and the G-29's are hauling the load quite nicely.. 8.5 years, not too bad 7-10 is average for this brand).

[Shadow_Catcher]

If you want to get serious http://www.balmar.net, they have the alternators and they have three stage regulators. I do have our trailer hooked up through the 7 pole plug and 10gs a wire but it is more to back feed the TV from the solar. Our Waeco refrigerator rides in the back of the TV and resides there in bear country.

[camperguy99]

I did just that. Ran #8 wire with a 40 amp fuse on both ends. I added another connector from this wire to the 5th wheel so it is totally in addition to the 7 pin wiring harness. It is paralleled with whatever FORD ran in the cable harness. Ran a second #8 to the ground wire that is screwed into the truck frame. Charging current went from 6-8 amps to more than 25 amps. Works great! With dual 6 Volt golf cart batteries (4 batteries) I've never blown a fuse.

[MEXICOWANDERER]

Diesel big rig plug and socket for electromechanical trailer lift gate

ONE GAUGE wire from the ALTERNATOR OUTPUT STUD to a fenderwell mounted 60 amp fuse, then out of the fuse, through a slitted garden or heater hose sheath all the way back to where it goes vertical and passes through your bed fender well and into the Cole Hersee or POLLACK one pin socket.

You MUST install a 2nd fuse coming off of your trailer batteries. Then run the line up to the plug. I borrowed something else from big rig technology: A suspension spring which prevents the cable from sagging and getting snared.

How much to expect? Around 30-45 amperes maximum. Even with 1 AWG wire.

Don't forget! You must as in, HAVE TO run a ground wire that is compatibly large. If you do not, you will lose the ground connection for your trailer brakes and quite possibly smoke the original TT umbilical wire and connectors.

It was worth the hassle IMHO. I would never consider towing a trailer without such a beefed-up charge lead wire.

[pianotuna]

Hi,

It may be possible to add a external regulator, to get around the chassis battery cutting down the flow of power.

external regulator

I do not use one, so I can't say if they are good, bad, or indifferent.

I do see up to 70 amps sometimes (the limit of my meter) on my dual charging paths. I try to limit it to no more than about 40 amps continuous as I have no desire to burn up an alternator.

[Salvo]

That may be a lot of work for little benefit. Alternators don't produce much current when idling. The regulator also senses the chassis battery which may be full.

Solar will give better results.

Sal

[Kountryguy]

There is one, but I want to increase the charging capability. I want to bypass the 7 pin connector. I will have to run new wires in the trailer also.

[K_Charles]

There should be one already that goes from your alt to the TV battery and then to the trailer battery through the 7 pin plug.

[Gdetrailer]

A 12V 40A "Bosch" style relay, a bunch of heavy ga wire and most important.. A BIG FUSE within 18" of the truck battery.

So, you have truck battery, then fuse, then fuse connects to the common terminal of the relay, the normally open (N.O.) terminal of the relay connects to your heavy ga wire which then goes to the trailer charging connection on the truck 7 pin connector.

One side of the relay coil is grounded and the other side of the coil goes to a KEY ON switched power (you will need to hunt this down since it is difficult to say where you will find that now days).

Wire ga size, well 8ga might be a good place to start..

Fuse size, size no larger than allowable current of the wire size or the lightest part (like the 7 pin connector).

10 ga wire 30A max fuse

8 ga wire 40A max fuse.

Any larger wire and I would say you are going to melt the 7 pin connector if you fuse larger than 40A..