Alternator Cut Out Switch

[dale farley]

What is the purpose of this switch? I don't think I have ever used it for anything, but it must be there for a reason.

[Donnie Myers]

There are several different scenarios. The one I see the most is the regulator going bad and "full fielding" which causes the alternator to output up to its max and could be as high as 38 volts! Which alternator do you have? When Delco Remy lost the patent on their old square style regulator, Transpo started producing a knock off ( which is hands down better than the Delco) the new Delco can be identified as black and silver with two "lumps" potted in. The "lumps" are internal fuses. These regulators WILL full field! Anyone with this regulator should consider changing to the Transpo which looks exactly like the old Delco. I have been seeing this scenario for many years and it doesn't matter the conversion. If you have a 12v or 24 volt Delco 50dN this should be a concern.

Another scenario would be if you had cooked batteries and trying to drive to service center you could just flip it off and not have to smell the rotten eggs! Hope this helps!

[Gil_J]

It is generally not a good idea to disconnect the output of an alternator from its laod when it's operation. However, Donnie points to a scenario where a switch would help protect systems from a regulator failure.

I can also see value in a alternator disconnect switch for the house battery bank if it is charged from the same alternator that charges the chassis. I don't remeber if you had a 24 volt house battery bank charged by the chassis alternator.

While on the topic of regulators. I'm amazed how few converters unsed intelligent regulators for alternators that are dedicated to the house batteries. Automotive regulators make the alternator a dumb charger. Do you really want to charge your $5K house bank of Lifeline batteries with a dumb charger? There are several intelligent regulators available that will provide an intelligent multi-stage charge very similar to your intelligent inverter/charger. They are available from Ample Power, Victron, Xantrex, and I'm sure many other supliers.

[Donnie Myers]

Gil, while in theory, those "smart regulators" are awesome, but in real life, they have not been reliable and have fried more batteries than they have helped. Especially on larger banks of batteries. A "dumb" regulator set around 27.5-28 volts charging a bank of 6-8 four d or 8 d batteries would need to run continuously for a couple days nonstop with no load to fry a set of Lifeline batteries. NASCAR and entertainer coaches are about the only coaches we see a problem with that. Now a full bus air coach with dedicated twin Bosch alternators for the house would be the exception. The house batteries would not have any load on them so an over charge is likely. There are exceptions to every rule but for sure, do not turn off that disconnect while engine is running.

[dale farley]

This is the alternator that I have.