charging marine battery off car?

[William R. Watt]

Wondering if it would be feasible while driving on the highway to charge a
battery for an electic trolling motor off the car's chargin system. Seems
you could charge for free that way using the unused output from the
alternator.

[Mike Romain]

Yes, that works very well with a proper isolator. They make them to
handle mis matched batteries so you end up with both batteries fully
charged.

You should check with RV shops for the setup and it is easy enough to
put some quick connects for welding cables at the marine battery end so
you don't need tools to plug in the battery. The trolling motor's
cables can also have the quick connects.

I know places like Warn (just because I have a winch) sell the cable
kits with the quick connects for putting a winch at the back of the
vehicle or plugging in booster cables. Something like that with an
isolator instead of a switch would be perfect for having the battery in
the back charging up.

http://www.warn.com/truck/accessories/quick_connect_all.shtml

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

[M.M.]

That would work OK but nothing is free and there's no 'unused output
from the alternator'. It might be small but there's still a cost (in
fuel, in this case).

[Dan_Thom...@yahoo.com]

>That would is free and there's no 'unused output

>from the alternator'. It might be small but there's still a cost (in
>fuel, in this case).

Right, but very, very small. A 10-amp draw, for instance, equals
about 140 watts at the battery's charging voltage, and since 746 watts
equals one horsepower, that 140 watts requires another 0.19 hp from the
engine. The engine will burn no more than 1/10 of a gallon of fuel per
horsepower per hour, and prtobably a lot less, so that 140 watts will
require at most an extra .019 gallons per hour. Your mileage will go
from, say, 25 mpg to 25.019 mpg or a tiny bit more than that if we
factor in the efficiency loss of the alternator.

Dan

[Dan_Thom...@yahoo.com]

>Your mileage will go
>from, say, 25 mpg to 25.019 mpg or a tiny bit more than that if we
>factor in the efficiency loss of the alternator.

See that! I made an error. The mileage drops from 25 mpg to
24.981 mpg.

Dan

[ed]

just charge the damn thing
<Dan_Thom...@yahoo.com> wrote in message
news:1138472715.2...@g14g2000cwa.googlegroups.com...

[Al Bundy]

But the poster wants to charge it while he's driving down the highway
in a mis-matched parallel set-up. That is not the best thing to do
unless there's an emergency.

[smile4...@bellsouth.net]

This is a common practice to charge a starting battery and deep cycle
in parallel.. what would be the problem?

Jim

[H...@nospam.nix]

<smile4...@bellsouth.net> wrote in message
news:1138562644....@f14g2000cwb.googlegroups.com...

It is better to use an isolator, so that the fully charged battery is not
discharged
into the flat one. The electronics to do it are cheap and simple.

[William R. Watt]

Thanks for the replies, but I don't understand why it costs extra fuel. The
alternator belt stays connected turns the alternator whether it's
charging anything or not. You are just using wasted power to charge the
extra battery, are you not?

[Lawrence Glickman]

On 31 Jan 2006 22:40:43 GMT, ag...@FreeNet.Carleton.CA (William R.
Watt) wrote:

It causes extra load because the more current the alternator has to
deliver, the harder it is to rotate.

[Steve]

William R. Watt wrote:

No, you are NOT! I wish I knew where this crazy idea came from and why
it keeps popping up all the time. The alternator does NOT waste a bunch
of power when its not needed!!!

When the battery is full, the alternator is just supplying the regular
electrical load of the car. But when it is charging a dead battery, it
is putting out a lot more power, and therefore it draws much more power
from the engine. In simple language, the more current the alternator has
to put out, the harder it is for the engine to turn it. You can hear a
lot of small car engines slow down when you turn the headlamps on at
idle- the load the alternator puts on the engine is NOT constant!

[Scott Dorsey]

Get a little permanent magnet motor. Spin it, and feel how loose it is.
Now short out the leads. Spin it, and you'll feel that it isn't so loose
any more.

The mechanical resistance depends on the electrical load.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."