"Bob" wrote in message
...

I am not sure what amp rating I need for the combiner and switch. Can
someone help with this. I don't care about saving pennies, want the
best system for safety.


Well, if money is no object, get a combiner that has more capacity than the
maximum output of the alternator.

If you would rather spend your money on more useful stuff, the 50 amp model
you have selected will work fine. Note that the ratings on this unit are 50
amps continuous, and 100 amps for 5 minutes. It is very unlikely that you
would ever end up charging the backup battery at more than 50 amps, and
unless the battery is very large or you had multi-stage regulator on the
alternator I don't think you could charge it at more than 50 amps for more
than 5 minutes. Even if you did, the combiner has a thermal shutdown that
would protect it.

Where you could get into trouble with such a device is if you have two
battery systems, such as a cabin battery and starting battery. If your
cabin system is using a lot of current (such as running an inverter) and the
engine is running then you could end up passing the full alternator output
to the cabin circuit via the combiner. If the second battery is just for
reserve, then you shouldn't have any issue.

As for the switch, get a good one. Since all your starting current has to
pass through this switch at all times, you don't want it to cause you any
problems. Keep the cables from the batteries to the switch and switch to
engine as short as possible.

Rod