Community Forums

RichK · 07-08-2013, 01:30 PM

Hi Everyone - I'm setting up my Honda Fit to be towed behind my MH. My MH had a standard 7-way out spade plug, and I'm using a 7 to 6 cord with a 6-way round plug on the car. I noticed that one of the outlets (currently unused) is 12V power. I've seen some TOAD chargers that have to be wired all the way from the RV battery to the car to keep the TOAD charged, but figured it would make more sense to use the existing 12V that's already at the car to trickle charge the battery if possible. Can this be done? If so, what's the right way to do it?

I suspect the answer is 'no' and that the 12V is for accessory power, but figured I'd ask anyway. Thanks!

ebksafari · 07-08-2013, 03:52 PM

Twelve volts is twelve volts. But that is not the only consideration. Other things to consider are the size of the wire, whether the circuit is protected by fuses, and whether there is a method of regulating the charge so there is no overcharge. Also, some people would expect a diode to insure that the electricity only goes from RV to car and cannot go "backwards" to protect the RV battery.

BFlinn181 · 07-08-2013, 04:31 PM

I use a wire in my umbilical cord to keep the car battery up. I put a 30 amp auto reset circuit breaker near the tap from the chassis battery in the MH, then another in the wire from the plug on the front of the car to the car battery. You have just added the battery to the 12 v charge circuit of the MH. It can't overcharge the battery, just as the regulator protects the MH batteries, it will also keep the car from overcharging. Your connecting wires need only be the same gauge as the umbilical cord wires or one size larger. Unless you try to hook up a dead battery, there won't be that much difference in the two batteries to incur a large current flow. You are just maintaining the battery, not trying to jump start it. The maximum current flow is the sum of your lights and brake system, not the starter or other heavy electric draw.

RichK · 07-09-2013, 09:15 AM

Thanks EBK - @BFlinn - Why use 2 circuit breakers? Wouldn't one be enough? Also, does a circuit breaker prevent load feedback?

In my case I'd like to use the 12V that's already at the car - would one 30A auto reset circuit breaker work for that do you think? Thanks for your reply!

BFlinn181 · 07-09-2013, 09:29 AM

One CB will protect the circuit, but without the CB in the circuit between car battery and the front tow connector there is nothing to prevent a dead short if something happened to umbilical cord or plug on the front of the car.

The CB doesn't have a diode in it, but why would 12v car system create feedback to 12 v MH system? I don't try running the toad still hooked up to MH, so no power from my car alternator would compete with the charging system of the MH. If both engines are off and the umbilical is still hooked up, at worst the 2 battery systems equalize, not discharge. When I stop for the night I unhook umbilical cord, turn off Brake Buddy, remove key from ignition and lock car doors.

RichK · 07-10-2013, 11:48 AM

Quote:

Originally Posted by BFlinn181

but why would 12v car system create feedback to 12 v MH system? I don't try running the toad still hooked up to MH, so no power from my car alternator would compete with the charging system of the MH

I'm not worried about feedback from the car specifically - rather because the MH battery and car battery are very different sizes I wouldn't want one to overload or damage the other. The Honda Fit battery is tiny. I remember reading that you should never wire together different sized (capacity) batteries. Is this a non-issue?

BFlinn181 · 07-10-2013, 12:06 PM

12v is 12v. The potential amperage is different, but when connecting two almost charged batteries of the same voltage there will be little current flow. When starting the MH, a difference in voltage may result momentarily as the starter draws power from the chassis batteries and voltage might flow from the car battery, but that's why you have the auto reset circuit breakers in the circuit, to limit current flow.

**CountryFit** · 07-16-2013, 07:25 PM

don't mean to hijack... is there a device/component to regulate the current volume? i'd like to threshold the current to 5a. can it be done?

BFlinn181 · 07-16-2013, 07:52 PM

Quote:

Originally Posted by CountryFit

don't mean to hijack... is there a device/component to regulate the current volume? i'd like to threshold the current to 5a. can it be done?

You could buy one of these: Toad-Charge Towed Vehicle Battery Charger & Maintainer Kit - RV Power Supply

I'm curious, what would be drawing 5 amps of power when towing? If batteries in RV and car are both charged, very little current will flow from RV to car.

**CountryFit** · 07-17-2013, 05:39 PM

Quote:

Originally Posted by BFlinn181

You could buy one of these: Toad-Charge Towed Vehicle Battery Charger & Maintainer Kit - RV Power Supply

I'm curious, what would be drawing 5 amps of power when towing? If batteries in RV and car are both charged, very little current will flow from RV to car.

Thanks Bob. I agree with you - when both batteries are full, the current is only to compensate the loss of toad battery for (1) key a position II; (2) supplemental braking system; (3) braking lights driven by supplemental braking. I would guess 2-3a is ok but 5a in safe side.