Connecting the towed battery to the 12 v house system

[mikestock]

I made a fused jumper to connect along side of the regular tail light system. I ran + and - to the starter battery to be sure I had a good constant ground. I ran the same type fused jumper from my house panel to the back of the rv and have a 5 foot jumper to connect the two when towing. I added this because I added a Patriot electric braking system and wanted to be sure I didn't rune the towed battery down while towing.

My question is: should i install some sort of diode in the system to isolate the towed battery so that the current only can flow from the motor home to the towed and not vice versa? I always heard it was a bad idea to parallel different systems.

[mikestock]

Yes. See post prior to yours.

[enblethen]

Your profile shows a diesel pusher, it this is correct your starting batteries are in a compartment on the left rear portion of the rig.
Didn't the coach come with a seven conductor to the rear bumper fed from a fuse panel under the driver in an exterior compartment?

[mikestock]

I chose the house batteries because it was more convenient. Actually I was trying to kill two birds with the same stone. There was no lighting at the rear of the coach so I used the same pair of wires to power a string of LED's from the house system. If it doesn't work out or if the voltage is too low at the towed battery I will move the charging pair to the back of the 7 pin. I really never considered that the house voltage would be inadequate before reading all of your posts.

My tow cable was only 4 conductors provided by the guy I bought my Blue Ox tow hitch from. The 6 pin connector has two unused. I had a choice of changing it to 6 conductor or running an extra pair of wires for charging, which I am doing, for now.

[enblethen]

OP:
Just for conversation, why are you connecting to house battery system rather then to the chassis battery? Don't you have a fuse block near your chassis batteries? You could even connect to the chassis batteries.

[wolfe10]

mikestock wrote:
The point of the diode is to prevent the Honda from draining back to the house batteries in case there is a voltage differential in the wrong direction.

The point several of us have made is that connecting the house battery to the toad battery with a RELAY at the house battery end will do the same (isolate the two batteries) anytime the coach ignition is off WITHOUT THE VOLTAGE LOSS OF A DIODE.

[mikestock]

theoldwizard1 wrote:
Most "modern" vehicle charging systems are only putting out 13.2V-13.5V AT THE FRONT BATTERY. YOU ARE NEVER GOING TO GET ENOUGH VOLTAGE TO CHARGE YOUR HOUSE BATTERY !

I think you may be misunderstanding. I intend to tie my house battery system to my towed Honda CR-V to make sure the CR-V battery isn't drained by my Blue Ox Patriot brake, while towing. My house batteries are constantly being charged while on the move and I am tying them to the Honda battery so it doesn't drain. The point of the diode is to prevent the Honda from draining back to the house batteries in case there is a voltage differential in the wrong direction.

[doc_brown]

ets1996 wrote:
I bought a kit I think Roadmaster Camping world or ebay can't remember which anyway it has a voltage reg and everthing needed to connect the toad to the motorhome. I wired it through the seven pin connector as my toad only uses 4 wires for the lights. It keeps the battery charged while using the supplemental brake.

I used a similar system and the same wiring. Power is from the chassis battery.

[theoldwizard1]

wolfe10 wrote:
Amps is not the primary issue. Voltage drop, even if amps is rated way over actual could render the charge wire close to useless.
If voltage on the coach side of an isolator (wire run from batteries, fuse, etc is, say, 13.5 VDC and you loose .7 VDC across a diode-based isolator, you are NOT going to charge a toad battery with 12.8 VDC.


I agree, if you want/need it to be automatic, install a RELAY with an ignition-hot as the signal at the coach battery end. Fuse at coach chassis battery, fuse at toad battery and 8 gauge wire for hot and ground. DONE.

Most "modern" vehicle charging systems are only putting out 13.2V-13.5V AT THE FRONT BATTERY. YOU ARE NEVER GOING TO GET ENOUGH VOLTAGE TO CHARGE YOUR HOUSE BATTERY !

What you really want is a DC-DC battery charger in your trailer. They typically will work with as little as 10V in.

[mikestock]

I agree that it may have worked better to use the unused +/- ports on the 7 pin and 6 pin connectors but would have needed to change the cable anyway. That would be cleaner and may be what I will eventually do, but for now I have the other setup done.

[crasster]

enblethen wrote:
A standard diode like this would work.
Diode

Yes really an isolator is just a simple diode. You can get really cheap 12V diodes off ebay.

[wolfe10]

enblethen wrote:
Roadmaster diodes are rated at 30 amperes.

Amps is not the primary issue. Voltage drop, even if amps is rated way over actual could render the charge wire close to useless.

If voltage on the coach side of an isolator (wire run from batteries, fuse, etc is, say, 13.5 VDC and you loose .7 VDC across a diode-based isolator, you are NOT going to charge a toad battery with 12.8 VDC.

I agree, if you want/need it to be automatic, install a RELAY with an ignition-hot as the signal at the coach battery end. Fuse at coach chassis battery, fuse at toad battery and 8 gauge wire for hot and ground. DONE.

[ets1996]

I bought a kit I think Roadmaster Camping world or ebay can't remember which anyway it has a voltage reg and everthing needed to connect the toad to the motorhome. I wired it through the seven pin connector as my toad only uses 4 wires for the lights. It keeps the battery charged while using the supplemental brake.

[enblethen]

Roadmaster diodes are rated at 30 amperes.

[hanko]

wolfe10 wrote:
I see no reason for a diode-- that is unless you are dry camping and forget to unplug the charge wire.

And if you decide to use a diode, make sure it is not a standard one that "charges" around .7 VDC. That much of a drop will render the charge wire pretty well useless.

doent the 12 volt at the 7 wire plug run through and isolater. I know it does on my coach. the circuit goes dead when I shut the engine off on the motorhome