Car charging boat battery

Hey All!

I was thinking about how to keep my batteries topped up in my boat while on the long drive to the lake with the fridge running. Both my boat and my towing vehicle are 12v, so was thinking I could connect the boat batteries to the cars 12v system while the car engine was running to keep the boat batteries at 100%.
Some things I thought of:

The connection between the two would only be made when the truck engine is running so that current wasnt drawn from the boat to the car to assist with starting?

Would the current need to be regulated so that the boat batteries dont draw too much current and over load the wiring? (How do you regulate this)

I had thought that I could utilise the ACC circuit in the car that is only active once the engine is started in the car to control when the connection is made.


Opinions?

Thanks!

Donald.

Hello Donald,

Interesting question. I think I would just isolate the fridge, flip the battery switch to 1 or 2, and save one for starting the engine when you get to the lake, maybe even increasing your house battery bank. Not the answer you are looking for, but I try to keep things simple, and self contained.

Reason this is not a good Idea.The cable you hook to the boat batteries including the ground has to be the same size or larger than the large cable off the alternator that charges your vehicles battery. If it is not, it is a fire hazard.

Right. A fire hazard I do not want.

Think I'll just scrap the idea!!

Actually Don, your idea is not new and has been common for a number of years. My old Dodge Charger came with a HD towing package that included a feed through the trailer connection to charge the boat's battery. The system included an isolater near the alternator, one lead of which ran to the trailer conection so that the boat battery would not draw down the car battery. Modern ACRs do that now in a much smaller package. I suspect 8 or 10 guage wiring would do the trick, but I am sure others will comment on the size of the wiring.

Gene

Go to your local RV service center for advise.----------------Very common with the camping crowd.-------Every day stuff for those folks.

Donald, I have a question for you: why is the refrigerator current draw (during your drive to your destination) any different than if the refrigerator was to run over-night while on the hook, for example?
Your HLBB (house load battery bank) should be large enough for this anyway.

If you feel the need to charge from your tow vehicle, a BlueSea ACR would work, and would do what you are asking of a system like this.
In fact, the ACR is not a bad addition to your boat's 2 bank charging system anyway.
The ACR allows the engine alternator to charge both battery banks independantly of the MBSS position.
(search Bluesea ACR and read up on what/how these work)



Your tow vehicle charging system could then connect into the ACR system.
All you'd need would be a heavy circuit running forward that the tow system could connect into.
There are connectors specifically designed for this very thing and are polarity fail-safe.


Fuse this new circuit, and you won't have any concerns.

.