Car charging boat battery

[donaldboyer]

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.

 

[dwparker99]

Re: Car charging boat battery

Donald,

When I tow my dump trailer, I use the +12V pin of my 7 pin plug to charge my trailer battery. It is powered any time my ignition switch is in the ACC position. I put a 15 amp fuse between the trailer battery and the plug just to be safe.

 

[impatico]

Re: Car charging boat battery

if this REALLY is a car then you only have a 4 wire system, if so

either change it to a 6/7 wire system or add another connector just for charging, but all you would need to do is tap into your ACC circuit and run that to a relay kit and run that relay out to the connector, on the trailer side of the connector run it straight to the batt with a fuse

 

[joed]

Re: Car charging boat battery

I believe house trailers have this setup. It should not be hard to do. You will need a connection cable between the boat and the trailer. Make it something that will pull apart easy so when you forget to disconnect it it pulls apart instead of ripping the wire harness out.

 

[Silvertip]

Re: Car charging boat battery

The truck already has a voltage regulator to handle the battery in it. No need for another one since the two batteries are in parallel. Speaking of that -- remember that any connection that parallels the two batteries means that when you start the engine you are now drawing off BOTH batteries. That small gauge wire may not tolerate cranking amperage unless there is some sort of protection in that circuit in the form of an isolator or similar device that prevents pulling current from the boat battery.

 

[Boatist]

Re: Car charging boat battery

I did the same thing with my boat. In my case I took a 12 volt line under the hood that is only hot when the
Engine is running. It then goes to a 20 amp automatic reset circuit breaker.
I used 8 guage wire in the truck to the 7 wire trailer plug.
The wire to the trailer is 12 guage both 12 volts and Battery ground and frame ground.
Here I actually used a 12 guage Outdoor extention cord.
In the boat I used another extention cord from the bow plug to the my battery isolator so I can
charge both batteries. The plug from the trailer to the boat is a 3 wire trolling motor plug on the
front not on the deck. This plug I removed the locks so if I forget to unplug as the boat
slides into the water it will unplug itself and just hang down from the bow stop area on the trailer.

My Dad is the same except he went right from 12 volt battery line on the starter to a solenoid.
Then from the solenoid output to his camp trailer plug.
To activate the solenoid he came off the ACC line on his switch to a switch on his dash where he could turn the
solenoid on or off. His old truck has an amp guage so he can watch it charge and then turn it off.