Dinghy charging from MH

theoldwizard1 wrote:
The only way you will ever be able to maintain/charge a "toad" battery is with a DC-DC charger. Have it permanently mounted in the toad, close to the battery. You can pick up B+ from the tow vehicle via the standard 7 pin connector.

You need to be ABSOLUTELY CERTAIN that B+ from the tow vehicle does NOT connect to B+ of the toad ! Thus way require some relays to keep these two systems isolated ! Using separate brake/turn signal lamps is a good first step !!

Have to respectfully disagree with this, based on what I've experienced and learned over the years.

I've flat towed a total of 4 different vehicles over course of last 10 years. Two of which (Ford Fusion Hybrid and Ford Taurus) were such that battery would be dead after just a few hours towing.

I installed a charge line several years ago. Basically, just a wire going from + of Motorhome battery to + terminal of towed vehicle battery with a 20 amp inline fuse (what you are saying should not be done).

To be clear, I did not physically run a new wire from the Motorhome battery to the towed vehicle. The wiring on the Motorhome side was already there somewhat, by using the auxiliary power line in the standard 7 pin connector at back of the Motorhome. After verifying that 12V power is always on that line when Motorhome is running, I just used that and wired it to the + terminal of towed vehicle battery.

And, it has worked great all these years, on all the vehicles I've towed. Kept the battery well charged up, on vehicles where the battery would die in just a few hours of towing without the charge line.

Wiring in a DC charger definitely isn't a bad idea, especially if you have something that will put a huge load on the towed vehicle's battery (like maybe an auxiliary braking system that needs a lot of 12V power). However, I don't think its fair to say that is the only way you will keep the battery charged, as my experience over the years proves otherwise.

I have a charge line in my toad. In my case I do need a diode in the line. This is because I have my motorhome backup camera powered by the trailer charge line (it's an on with ignition source, right were I wanted it, made sense at the time).

If I simply used a charge line with a fuse, then the backup camera would be powered by the TOAD battery anytime the ignition of the motorhome was off. A diode prevents this.

Fwiw, you can buy a simple charge line with a fuse and diode for $25 on etrailer. (I instead used an RVI Toad Battery Charger, but that's another story and not something I would recommend or do again).

Most folks use a 7pin to 6pin cable to connect between the motorhome and the toad, so power is already there. In your case, since you're using only the 4 pin connector, you'll need to figure out how to get power from your motorhome over to the toad.

My motorhome already had power at the 7 pin, and I use a 7-6 pin cable to the toad with a standard 6pin round connector on the front of the toad, so power was already right there. All I had to do was wire from the new 6pin connector up to the toad battery.

camperdave wrote:
I have a charge line in my toad. In my case I do need a diode in the line. This is because I have my motorhome backup camera powered by the trailer charge line (it's an on with ignition source, right were I wanted it, made sense at the time).

If I simply used a charge line with a fuse, then the backup camera would be powered by the TOAD battery anytime the ignition of the motorhome was off. A diode prevents this.

Agreed, a diode is a great idea, also, to prevent current from back flowing into the Motorhome. And, in your case where the camera at the back of the Motorhome is powered by the trailer charge line, a diode is most definitely in order.

I remember when we set up the charge line, I wanted to wire in a diode, and planned to initially. However, it turned into one of those things I found was not needed, so kept putting it off and it never got done, haha.

Here is what I used for my 2012 CRV to keep the battery charged.

Hopkins 39332 Brake Buddy Towed Vehicle Battery Maintainer
https://smile.amazon.com/gp/product/B004RCXB8A/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Thanks for all the replies. We use a 4 Pin because we've had the car about 10 years and towed it behind a former MH that only had the 4 pin connector, so that's how we wired it. My short term until I pick a method is to just start it and run it for about 10 minutes every 2 hours when we stop.

theoldwizard1 wrote:
The only way you will ever be able to maintain/charge a "toad" battery is with a DC-DC charger. Have it permanently mounted in the toad, close to the battery. You can pick up B+ from the tow vehicle via the standard 7 pin connector.

You need to be ABSOLUTELY CERTAIN that B+ from the tow vehicle does NOT connect to B+ of the toad ! Thus way require some relays to keep these two systems isolated ! Using separate brake/turn signal lamps is a good first step !!

disagree in the OPs case….if the brake lights are the only draw. And assuming it’s not for days on end in city traffic.

OP, you’ll need to have a larger connector on the RV that has 12v constant wired into it. Like most all truck receptacles.
Do yourself a favor and skip the round 6 pin. Nothing wrong per se except they are basically not used in hardly any applications anymore.
You don’t need the other 2 pins in the 7 way (backup lights and trailer brakes) but run your 4 pin wires to the 7 pin for lighting and add the one for 12v+. Scrap the 4pin or whatever makes sense.
Know that like theoldwizard said you’re not going to power much from that but you’ll get more current in than just brake lights remove.
But like most things, the diagnosis is vague. And not having context, you could just have an old battery. Or ??

Grit dog wrote:
...Do yourself a favor and skip the round 6 pin. Nothing wrong per se except they are basically not used in hardly any applications anymore....

Have to respectfully disagree with this. 6 round connection is used quite frequently for vehicles towed behind Motorhomes. Its not used for trailers, no, but it is the preferred approach for towing a vehicle behind an RV.

And, I think one 6 pin wire would be much better than having two separate wires and connectors to connect between the Motorhome and the car (one for the 4 flat, one for the charge line). A single 6 round wire would look much better and be much more organized, too, than having to run two separate wires. Not to mention, would be less parts to wear out, develop shorts, and have to be maintained.

willald wrote:

Grit dog wrote:
...Do yourself a favor and skip the round 6 pin. Nothing wrong per se except they are basically not used in hardly any applications anymore....

Have to respectfully disagree with this. 6 round connection is used quite frequently for vehicles towed behind Motorhomes. Its not used for trailers, no, but it is the preferred approach for towing a vehicle behind an RV.

And, I think one 6 pin wire would be much better than having two separate wires and connectors to connect between the Motorhome and the car (one for the 4 flat, one for the charge line). A single 6 round wire would look much better and be much more organized, too, than having to run two separate wires. Not to mention, would be less parts to wear out, develop shorts, and have to be maintained.

I would tend to agree, however - the 4 wire for the tail lights is sort of hard wired in. I ran it under the sill plate, through the frame and into the tail light housing. While I could remove all that, it's really neat and tidy the way it is and I can hide the harness in a nice spot in the lower grill. What's the issue with adding one wire with a bullet to the appropriate spot in the 6 round adapter and just tie it to the 4wire harness? Aesthetically it will be the same. It's just one extra wire that can be tied and hidden with the 4.

For my CRV, I have a wire from the motorhome batteries through an inline fuse to a relay that is activated only when Moho is running. Through a 6 pin to the Honda and another inline fuse to the battery.
I originally had the wire direct ( with a fuse ) but added the simple relay to keep the two different batteries separated when parked with the two vehicles together.

Another option could be swapping your CRV taillights to LED. Then you wouldn't have to worry about them draining the battery.