Multi Battery Isolator

[max e. rockafellow]

When I was just checking things our under the hood, I saw that the
isolator indicated that "Max Alternator Amps: 70" was printed on the
side. I know that the motorhome has a 80 AMP alternator. Could this be
a problem?

Max
76 Palm Beach

WebSite: http://www.gmcmi.com

 

[jim bounds1]

Max,
In the event that both of your batteries short out and present a massive
load throught the isolator and you do not notice the problem, it is
conceivable that the isolator to open.

You may want to look at the isolator as a fuse to fail safe in the event of
a system melt down and protect the alternator. After all, you are asking
the alt. to add current to 2 circuits and this is a rather heavy load to
begin with.

I have installed 130amp. isolators but there will be a bit more loss
through it to the batteries.

Bottom line is, the 70 amp. isolator has proven to be pretty reliable in
our application unless unusual expectations are asked of it. If you do not
whip your 12volt circuits and make them do difficult jobs, the 70 amp.
isolator will probobly do a good job for you.

Am interested in contrasting views, after all the "bigger is better" theory
was born and followed right here in the U.S. by many of us!

Jim Bounds
- ---------------------

>When I was just checking things our under the hood, I saw that the
>isolator indicated that "Max Alternator Amps: 70" was printed on the
>side. I know that the motorhome has a 80 AMP alternator. Could this be
>a problem?
>
>Max
>76 Palm Beach
>
>WebSite: http://www.gmcmi.com
>
>
>
Jim Bounds/Co-op Motor Works Orlando www.gmccoop.com

 

[dave1]

>In the event that both of your batteries short out and present a massive
>load throught the isolator and you do not notice the problem, it is
>conceivable that the isolator to open.

This also may happen when the batteries are substantially discharged. The
alternator will run at full output for a while to bring the batteries back
up to 14 volts or so.

>I have installed 130amp. isolators but there will be a bit more loss
>through it to the batteries.

I use a higher rated isolator too. The higher rated isolators have larger
cooling fins and thus run cooler at the lower (80 amp) load. It is not true
that the larger isolators have larger losses. All (diode based) isolators
will have a voltage loss of one diode drop (which is ~.7 volts). So your
power loss will be a function of the actual load on the alternator (.7
volts X 80 amps = 56 watts at full load). This is true regardless of the
size of the isolator. The advantage of the larger isolator is the fact that
it is designed to dissipate more power so it will run cooler when used at
power levels well under its rated capacity. A 130 amp isolator, rated to
dissipate 91 watts, should be very reliable when running at 56 watts. Where
as a 70 amp isolator, rated to dissipate 49 watts, will be overloaded
during the times when the alternator is producing its full output.

>Bottom line is, the 70 amp. isolator has proven to be pretty reliable in
>our application unless unusual expectations are asked of it. If you do not
>whip your 12volt circuits and make them do difficult jobs, the 70 amp.
>isolator will probobly do a good job for you.

I would not replace it unless it fails. But if/when it does fail, I would
use the larger unit as a replacement.

Dave
73 Sequoia