Towed Battery Charging

[rossboyer]

I am in the process of installing the wiring in my auto to be towed. Since I use an auxiliary braking system that operates off the towed’s battery, I would like to install a charge line from the motor home to the towed. I want to use a isolation diode to allow the current from the motorhome to pass through to the towed’s battery, but block the current from the towed back feeding to the motor home. I do have a charge line in the receptacle of the motorhome and have it routed to one of the pins of the receptacle on the towed. Near that point I want to install a diode and fuse (15 amp since wire is #14). Can you tell me the specifications for a diode for this purpose? Or do you have a part number or source for one that would work? I know how to wire it, I just need to get the correct diode.

[wolfe10]

While you can use a diode to isolate the batteries when the motorhome is not running, be aware that the diode-based isolators "charge" about .7 VDC penalty. Said another way, if your motorhome alternator is putting out 13.7 VDC, and you use a diode-based isolator, the most your towed battery will see is 13.0. Subtract from that the voltage loss due to resistance in the wiring and connectors, and keeping the towed battery fully charged is difficult.

A relay or solenoid can just as easily be used and has no voltage drop penalty.

Large gauge wire from battery to relay/solenoid. Ground from relay/solenoid to chassis ground. Any ignition controlled source to relay/solenoid signal terminal (to only activate the relay/solenoid when the motorhome's ignition is on) and large gauge wire from relay to towed vehicle plug.

Brett

[rpasetto]

Add a voltage drop of about another 0.1 volts through the #14 wire (# 12 may be a bit better). With any charge-wire setup your battery may not stay fully up-to-charge, nonetheless a charge wire should keep the car battery up enough so you can start it at the end of your trip. I regularly run the engine a few minutes every night as a matter of habit on long trips. I believe that action will help keep the battery up as well as circulate fluids.

PS: After reading your post, I looked up Schottkey diodes and found that they have less than half the forward voltage drop of silicon diodes. I'm going to look into getting for my own set up.

.. RP

[rossboyer]

Thank you for your comments. We have just traveled 1,800 miles in four days without problems with a new 2011 Cheverolet Equinox. The manual states that it may towed all wheels down. There is a specified procedure to follow before towing, and you are to run the engine for 5 minutes at every fuel fill up. Don't think they were thinking 600 miles between fill ups; therefore, I ran the engine when we stopped for lunch and at the end of day.

One item related to braking systems that draw power from and accessory port (use to be a cigarette lighter outlet) on the 2011 Equinox's, all ports are disabled when you pull fuse 32 as instructed. If you do not pull fuse 32, you will run the battery down in about 4 hours. I had to add a socket directly to the battery (with and inline fuse) to get around that problem.

[hermanmullins]

If you added the extra socket (cigarette lighter as most of knew as) why not run it to your lighting connection to your coach for 12v power? Of course you would need to put in a protective fuse on both ends. No worry of discharging your battery.

My 2003 Yukon does not have a locking pin in the steering column, does the Equinox?

I left the key on the first time we towed it and it pulled just fine but with the key on it recorded the miles.

[KenandSallyWarner]

Here is what I did and it works great: In the toad I used a 10 amp fuse at the battery and connected the anode side of 2 six amp diodes in parallel to the hot wire from the motor home. For more current and less voltage drop put more diodes in parallel. They come in packs of 4 at Radio Shack.

[wilbar]

Putting more diodes in parallel will not reduce the voltage drop. You will always have a 0.7 volt drop across them because diodes are a non-linear device. They will also probably not share the load equally. The one with the lowest voltage drop will carry most of the current. There are charging devices available that charge the battery and also provide some voltage and current limiting.

[desertdeals69]

Using a 30 amp Bosch type cube relay is the most efficient way to isolate the charge line. Use a toggle switch to activate the relay or trigger wire from mh ignition switch.