On Mon, 13 Aug 2007 04:37:04 -0000, wrote:

Okay - I'm new to boating, just bought my first. The guy I bought it
from has two batteries in the boat - a deep-cycle marine battery for
the starter, and a regular car and truck battery for the tilt motor,
lights, radio, etc. (both are 12 volt). The marine battery charges
itself from the magnets, but right now, the car battery just runs
itself down and has to be recharged frequently.

This doesn't seem efficient. Can I hook the batteries in together so
that the magnets are charging both at the same time? Or is it bad to
hook a marine and car/truck battery together? If I understand
batteries (and I'm not sure that I do!) I could connect the positive
terminal of the marine to the negative of the car/truck and that'd do
it. Is that right? Or would that screw with the voltage?

How should I approach this?

The easiest and cheapest solution is something called a combiner. It
is an automatic switch relay that will connect the two batteries in
parallel when there is sufficient charging voltage, and automatically
disconnect them when there is no charging voltage present. They are
inexpensive and easy to install, much easier and more fool proof than
an A/B switch.

Here's an example:

http://www.defender.com/product.jsp?path=-1|328|51495|606044&id=605576

or

http://tinyurl.com/2gsqak

On Mon, 13 Aug 2007 11:31:46 -0400, Wayne.B
wrote:

On Mon, 13 Aug 2007 04:37:04 -0000, wrote:

Okay - I'm new to boating, just bought my first. The guy I bought it
from has two batteries in the boat - a deep-cycle marine battery for
the starter, and a regular car and truck battery for the tilt motor,
lights, radio, etc. (both are 12 volt). The marine battery charges
itself from the magnets, but right now, the car battery just runs
itself down and has to be recharged frequently.

This doesn't seem efficient. Can I hook the batteries in together so
that the magnets are charging both at the same time? Or is it bad to
hook a marine and car/truck battery together? If I understand
batteries (and I'm not sure that I do!) I could connect the positive
terminal of the marine to the negative of the car/truck and that'd do
it. Is that right? Or would that screw with the voltage?

How should I approach this?

The easiest and cheapest solution is something called a combiner. It
is an automatic switch relay that will connect the two batteries in
parallel when there is sufficient charging voltage, and automatically
disconnect them when there is no charging voltage present. They are
inexpensive and easy to install, much easier and more fool proof than
an A/B switch.

Here's an example:

http://www.defender.com/product.jsp?path=-1|328|51495|606044&id=605576

or

http://tinyurl.com/2gsqak

That's what I was looking for - I couldn't remember if it was an
isolator or combiner.

Man, I'm getting old.

On Mon, 13 Aug 2007 12:58:11 -0400, Gene Kearns
wrote:

On Mon, 13 Aug 2007 11:31:46 -0400, Wayne.B
wrote:

http://tinyurl.com/2gsqak

I like the description of this one better:
http://tinyurl.com/2hw397

That's an isolator, not a combiner, big difference. The combiner is
an automatic switch and there are no voltage losses, basically a smart
relay.

An isolator uses diodes to keep one battery from discharging the
other, and the diodes have a forward voltage drop, typically 0.6
volts. That makes it impossible to bring the batteries up to full
charge unless the alternator has an external sense wire, and most do
not. It's possible that this may not make any difference with an
outboard but I'm not sure. The diodes will create power losses in any
case, that's why they are mounted on big heat sinks.

I've used both and greatly prefer the combiner. I've got two of the
150 amp units on my trawler so that both engines or either one can
charge the inverter bank when under way. They work very well and have
a lot of protective logic built into the switch.