Battery question - hooking two batteries (marine and car/truck) together
 

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?

Matt

Battery question - hooking two batteries (marine and car/truck) together
 

In article . com,
says...
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?

Matt



You need an A/B switch. Here's several options:

http://www.westmarine.com/webapp/wcs...iteSearchView?
catalogId=10001
&Ntx=mode+matchallpartial&keyword=battery+switch&N tt=battery+switch&N=
377+710&y=0&x=0&storeId=10001&Ntk=Primary+Search&d dkey=SiteSearch


or just do a search on battery switch at westmarine.com


Sexton

Battery question - hooking two batteries (marine and car/truck) together
 

DO NOT hook them up as you described,that will double the voltage and
probably burn out a lot of things,You could hook the pos to the pos and neg
to neg.That will charge both at the same time.However it is not a good
solution.If one battery goes bad it will drain the other one.The correct
thing is to buy a battery switch .you can then select one at a time to
charge, or both at the same time with the switch,
wrote in message
ups.com...
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?

Matt

Battery question - hooking two batteries (marine and car/truck)together
 

Battery question - hooking two batteries (marine and car/truck) together
 

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

How should I approach this?

First off, do not wire the batteries in series - that doubles the
voltage. Second, do not wire the batteries in parallel - that doubles
the amperage available. An A/B switch is a potential solution but
that has problems also.

You need to determine what the charging rate is for your alternator.
As Rob said, it should be somewhere around 6 to 8 amps. I don't think
you mentioned the size of the engine - that would help a little.

That said, I would put put everything on a deep cycle, group 27/28
marine/rv battery and keep the second battery on an A/B switch as
insurance.

That would be my solution - not the best, but the easiest.

Battery question - hooking two batteries (marine and car/truck)together
 

Short Wave Sportfishing wrote:

That said, I would put put everything on a deep cycle, group 27/28
marine/rv battery and keep the second battery on an A/B switch as
insurance.

That would be my solution - not the best, but the easiest.

Tom,
When you switch it to "Both" on the A/B switch, are you just charging
both or are you running them in series?

Battery question - hooking two batteries (marine and car/truck)together
 

Gene Kearns wrote:
On Mon, 13 Aug 2007 10:53:12 -0400, "Reginald P. Smithers III"
wrote:

Short Wave Sportfishing wrote:

That said, I would put put everything on a deep cycle, group 27/28
marine/rv battery and keep the second battery on an A/B switch as
insurance.

That would be my solution - not the best, but the easiest.
Tom,
When you switch it to "Both" on the A/B switch, are you just charging
both or are you running them in series?

Not as easy a question as you might think!

What is happening if the A/B Switch is set for "Both" and Battery "A"
has 11.5 Volts, Battery "B" has 9.5 Volts, and the engine is providing
12.5 Volts????

Now, imagine what is going on if Battery "B" has 9.5 Volts because it
has a weak cell.....

I have always thought Battery B would drain battery A to equalize the
voltage if they were not being charged, but if it was charging both
batteries, they would only charge up to about 13 volts and then the
charger turns off.

I always use Battery B for when I am at anchorage, but switch it to both
when I am ready to start the engine. I am using the rational that it
would take awhile for the B battery to drain the A battery and the
engine is always started in less than 30 sec from the time I switch the
perko to Both.

I was told whatever you do, don't switch the Perko switch when the
engine is running. Something about the end of the world as we know it.

Battery question - hooking two batteries (marine and car/truck) together
 

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

Battery question - hooking two batteries (marine and car/truck)together
 

Gene Kearns wrote:
On Mon, 13 Aug 2007 11:11:52 -0400, "Reginald P. Smithers III"
wrote:

Gene Kearns wrote:
On Mon, 13 Aug 2007 10:53:12 -0400, "Reginald P. Smithers III"
wrote:

Short Wave Sportfishing wrote:

That said, I would put put everything on a deep cycle, group 27/28
marine/rv battery and keep the second battery on an A/B switch as
insurance.

That would be my solution - not the best, but the easiest.
Tom,
When you switch it to "Both" on the A/B switch, are you just charging
both or are you running them in series?
Not as easy a question as you might think!

What is happening if the A/B Switch is set for "Both" and Battery "A"
has 11.5 Volts, Battery "B" has 9.5 Volts, and the engine is providing
12.5 Volts????

Now, imagine what is going on if Battery "B" has 9.5 Volts because it
has a weak cell.....
I have always thought Battery B would drain battery A to equalize the
voltage if they were not being charged, but if it was charging both
batteries, they would only charge up to about 13 volts and then the
charger turns off.

I always use Battery B for when I am at anchorage, but switch it to both
when I am ready to start the engine. I am using the rational that it
would take awhile for the B battery to drain the A battery and the
engine is always started in less than 30 sec from the time I switch the
perko to Both.

I was told whatever you do, don't switch the Perko switch when the
engine is running. Something about the end of the world as we know it.

A properly built A/B switch has a make-before-break feature. You don't
want the alternator to sense a really low voltage situation (break)
and go to *infinite* charge. Toast.......

So it would be the end of the world as we know it. ;)

Battery question - hooking two batteries (marine and car/truck) together
 

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.

Battery question - hooking two batteries (marine and car/truck) together
 

On Aug 13, 7:54 am, Short Wave Sportfishing
wrote:

You need to determine what the charging rate is for your alternator.
As Rob said, it should be somewhere around 6 to 8 amps. I don't think
you mentioned the size of the engine - that would help a little.

Wow - great response. Thanks to all - I'm soaking up all the info I
can. To answer this question, I'm running a 115 hp Johnson outboard.

Matt

Battery question - hooking two batteries (marine and car/truck) together
 

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.