Battery disconnect.

[Iver]

I have two alternators on our coach.  One 24v for start batteries etc and one 12v for the house system. 
I usually turn off the battery disconnect switches on both systems when the coach is in storage.

When I occasionally have to move the coach out of my shop I switch on the start batteries, start the coach and move it out, shut it down and later on start it up and
move it back in the shop.

However I don't usually turn on the main 12v battery switch.  Is it harmful to the 12v alternator with the engine running to not have the 12v batteries connected?
    Thanks, Iver.

[eddiepotts]

No it is not hurting anything. Without the batteries hooked up it does not even rob HP. It is nothing more than an idle pulley during that time.

[Sean]

Actually, it depends on the alternator.  Some alternators can be destroyed if you run them open-circuit.

In part, it depends on how the field is energized.  If disconnecting the batteries also disconnects the field voltage, there should be no problem.  If, however, it is a self-exciting model, I advise against it.  I always recommend that the batteries be between the alternator and the disconnect switch to avoid alternator damage.

-Sean
http://OurOdyssey.BlogSpot.com

[luvrbus]

Iver, if it is a one wire alternator it won't hurt anything

good luck

[Jeremy]

My old Land Rover had a big metal plate in the engine bag saying 'Do Not Run Engine with Battery Disconnected". I didn't know what might happen if I did, but it was pretty clear that I shouldn't try to find out.


Jeremy

[Iver]

It is a "one wire" type.  However, I will close the switch in the future just in case.

My 'Link 1000' monitor requires disconnecting before switching off the batteries so it is just another wire to remember to unplug.
            Thanks, Iver.