I'm adding a second battery to my 19' bowrider, 3 liter MerCruiser powered.
I primarily want the redundancy of a second battery in case the first one
fails, but I have added radar, GPS, VHF and a utility outlet to power other
stuff like a searchlight.
Already had the battery, switch and an isolator; went to buy the necessary
wires and connectors and came home with a combiner and zap-stop to use
instead of the isolator.
Anybody have any suggestions or preferences of isolator/combiner?

A combiner won't suck any current from your batteries when it isn't
being used, I'm told. I've one for two years and like the concept of
never messing with my A/B switch unless I run my house batteries down
too low to start the engine.

Capt. Jeff

Warning: I've never used an isolator so anything I say
about them is only from reading the catalog and thinking...

I think for your size boat & electrical needs that a small
battery combiner will be simpler, smaller, and cheaper
and still do the job. That's what I use. It nicely separates
the batteries so the "backup" one can't get drawn down
yet connects them when the altenator (or generator in my
case) is putting out charge - so both stay charged. My
1/2/ALL switch is now simple to operate - OFF or 1 is all
I ever need unless I run the main battery down.

Looking at the description of isolators it would seem they
perform the same basic funtion (separate the batteries from
each other) but would be needed when....

If your two batteries or banks of batters were of different
types, ratings, etc., you might never want them conneted
to each other. The battery combiner *does* connected them
when the system is charging (voltage over some level). The isolator
keeps them separated (via diodes) at all times.

Hope that is rignt and helps or at the least sparks more
conversation.

Gary

"Bill Andersen" wrote in message
news:Atqdb.7221$Rd4.6684@fed1read07...
Already had the battery, switch and an isolator;


The phrase: "If it ain't broke, don't fix it" comes to mind here. With the
isolator, you can leave the switch on just one battery and both batteries
will still charge. The downside of the isolator is that unless the voltage
regulator has remote sense it can significantly reduce the rate of charge
you will get. Based on your description of the loads, however, this doesn't
seem like it would be a big concern.


Anybody have any suggestions or preferences of isolator/combiner?


One issue with the battery combiner is that they are subject to failure.
The combiners have a current limit, and if you exceed that limit you can
destroy the combiner. The combiner connects the two batteries, and a sudden
heavy load on one can start to draw current from the other until the
combiner disconnects. Repeated disconnects under heavy load can take its
toll. You may not realize that it is no longer working until your "reserve"
battery is dead.

The isolator only deals with the current from the alternator. If it is
sized according to the maximum output of the alternator, it should never see
an overload, hence they are much more fail safe.

If you need or want the additional charge rate, then go with the combiner.
Otherwise, I would stay with an already installed and working system.

Rod McInnis

"Rod McInnis" wrote

The phrase: "If it ain't broke, don't fix it" comes to mind here. With
the
isolator, you can leave the switch on just one battery and both batteries
will still charge.

Same as for a combiner.


One issue with the battery combiner is that they are subject to failure.
The combiners have a current limit, and if you exceed that limit you can
destroy the combiner. The combiner connects the two batteries, and a
sudden
heavy load on one can start to draw current from the other until the
combiner disconnects.


I didn't know of think of that. Could happen on my boat it I shut down the
engine
and then restart it within the 5 or so seconds before the combiner
disconnects.
Now that I know that I'll take the time to see exactly how long the combiner
stayed connected after the engine if off (voltage has dropped). Then I'll
not restart the engine until after that time passes. (Not a likely scenario
except
maybe when troubleshooting something.)



You may not realize that it is no longer working until your "reserve"
battery is dead.

Good point. I'm pretty good at having safety habbits and am making up some
check-lists.
One thing to add to my mental & physical list is: Look at the combiner and
see that it's
indicator is on when it should be.


Thanks,
Gary

Thanks for all who responded. I guess I'll go with the combiner instead of
the isolator. (Hate to change my mind, the isolator was free and is already
mounted.) The combiner has two indicator lights, so I guess I'll mount it on
the outside of the engine cover so I can see them without having to remove
the rear two seat and the engine cover.

Bill
"Gary Warner" wrote in message
...

"Rod McInnis" wrote

The phrase: "If it ain't broke, don't fix it" comes to mind here. With
the
isolator, you can leave the switch on just one battery and both
batteries
will still charge.

Same as for a combiner.


One issue with the battery combiner is that they are subject to
failure.
The combiners have a current limit, and if you exceed that limit you can
destroy the combiner. The combiner connects the two batteries, and a
sudden
heavy load on one can start to draw current from the other until the
combiner disconnects.


I didn't know of think of that. Could happen on my boat it I shut down
the
engine
and then restart it within the 5 or so seconds before the combiner
disconnects.
Now that I know that I'll take the time to see exactly how long the
combiner
stayed connected after the engine if off (voltage has dropped). Then I'll
not restart the engine until after that time passes. (Not a likely
scenario
except
maybe when troubleshooting something.)



You may not realize that it is no longer working until your "reserve"
battery is dead.

Good point. I'm pretty good at having safety habbits and am making up
some
check-lists.
One thing to add to my mental & physical list is: Look at the combiner
and
see that it's
indicator is on when it should be.


Thanks,
Gary