Battery charging wire

[Joseph Domingos]

LOVE that this thread was started, I've wondered many times about adding a charging wire to my tow vehicle for my trailer. I'm a little puzzled though, I thought that one added the charging wire to the alternator, and then ran back to the trailer. Is that an option, or should you only go to the tow vehicle's battery, or what?

[Herb P]

LOVE that this thread was started, I've wondered many times about adding a charging wire to my tow vehicle for my trailer. I'm a little puzzled though, I thought that one added the charging wire to the alternator, and then ran back to the trailer. Is that an option, or should you only go to the tow vehicle's battery, or what?

On my vehicles, the wire from the alternator goes right to the battery. So it's probably easier to wire to the battery posts than the alternator connector.

[Pete Dumbleton]

On my trucks, what I did was make a sort of bus connection off the battery posts, one for the grounds and one for mounting the autoreset breakers. Since I am coming up the driver's side of the truck with all the wiring, and the battery has large connectors, it was much easier to put the connections there.

BTW, in the case where the truck's voltage regulator is separate from the alternator, one would NOT want to connect to the alternator. That's why the battery connection is best, from electrical, installation and troubleshooting perspectives.

Tekonsha specifies an autoreset circuit breaker in their installation instructions.

Here's a link to a personal site by a poster on another RV group about installing a battery isolation relay

http://www.neon-john.com/RV/Electrical/rv_...tion_relays.htm

[Brian B-P]

Actually I meant the one on the trailer, which has the long run. On the Casita the battery is way back in the boondocks!

That's what I meant, too. That cable ran to just inside my Boler, with wire from there forward again to the battery. Now it runs to a termination box on the tongue, with more direct connections to the brakes and battery.

With a battery near the back, I don't know that I would run the seven-conductor cable all the way there, because brake wiring would then need to return all the way to the front to connect the breakaway switch... maybe that's okay. Anyway, with that much length, I might want bigger wire than even good 7-conductor cable has, because it normally is expected to only run about the length of the tongue.

...I just bought some 7 conductor cable from the local hitch place. The white/black were 10ga, the blue was 12ga, and the rest were 14.

That combination sounds quite well suited to the function of each conductor.

[Roy in TO]

Here's a link to a personal site by a poster on another RV group about installing a battery isolation relay

http://www.neon-john.com/RV/Electrical/rv_...tion_relays.htm

Thanks for the link Pete,
It answered my question of using a solenoid or diode isolator.
Neon-John said:

"One method is to use a diode isolator that consists of two heavy duty diodes mounted to a heat sink. The anodes are connected together and connected to the alternator output terminal. One cathode goes to the chassis battery and the other goes to the house battery.

While the diode isolator works when the OEM electrical system is designed for it, for a variety of reasons it isn't the best solution. A simple heavy duty relay or "solenoid" is the much better and simpler solution."

Roy

[Roy in TO]

While the diode isolator works when the OEM electrical system is designed for it, for a variety of reasons it isn't the best solution. A simple heavy duty relay or "solenoid" is the much better and simpler solution.

OK, so I am going to contradict myself. Elsewhere I read that we should avoid solenoids because the contacts can foul by arcing making the solenoid ineffective. Right now, I am leaning towards the Isolator. Any thoughts or discussion?

I thought it best to provide a link in this thread to the thread I started on the wiring diagram to make sure I was wiring things up right since they are related to each other.

[Brian B-P]

Elsewhere I read that we should avoid solenoids because the contacts can foul by arcing making the solenoid ineffective. Right now, I am leaning towards the Isolator. Any thoughts or discussion?

A properly selected relay (a.k.a. contactor, a.k.a. solenoid) is one rated for continuous duty (on all the time), not just intermittent use; there are lots available, cheaply. The right one won't have a problem, but the simple diode setup is inherently a problem for charging control. The diode isolator is also a much more invasive modification of the tow vehicle's electrical system. I considered both and my choice was clearly the relay... but everyone has their own reasons, and makes their own decision.

[Pete Dumbleton]

One reason a diode isolator isn't good is because there may be a 0.5VDC voltage drop across the diode. That may not seem like much, but look at a Percent Charge vs Voltage Table, subtract half a volt from the full charge and see what your road charge will be limited to even if all your other connections and wiring result in no voltage drop...