Alternator Load?

[SierraPilot123]

Does anyone know how or why a failed alternator creates an additional load on the electrical system?

I can't find this answer for the life of me.

It must create an additional load because all the checklist specify to isolate the failed alternator from the rest of the electrical system.

Thanks

[Berkut]

There are a couple of concerns I can think of.

You don't want to keep feeding current to a device that's failed. It could be arcing, overheating, or just plain old on fire.

As far as load goes, the short version is that an alternator contains an electromagnet which requires a small amount of current, in order for the alternator to produce a large amount of current. It's possible for the alternator to fail in such a way that it still uses current to maintain the magnetic field, yet isn't generating any electricity. That field current would drain the battery.

It's also possible for a malfunctioning alternator to damage or destroy the belt.

I don't know if these are the specific reasons the checklist authors had in mind. There might be more I'm not thinking of.

[trafficinsight]

shouldn't create an additional load, however, an alternator has no permanent magnet so it uses current to work. By isolating it you are cutting off the field current which reduces the load.

[B767Driver]

My Warrior electrical schematic shows a diode between the alternator and the alternator switch. I would not think that the alternator would be a load for the battery.

However, turning off the alternator switch could isolate a short between the switch and the alternator...which definitely could cause problems.

[trafficinsight]

Originally Posted by B767Driver

My Warrior electrical schematic shows a diode between the alternator and the alternator switch. I would not think that the alternator would be a load for the battery.

However, turning off the alternator switch could isolate a short between the switch and the alternator...which definitely could cause problems.

The voltage regulator varies output of the alternator by varying field current, in essence it's varying the strength of the magnet. In the case of a failed alternator, the alternator is putting out zero voltage and the battery voltage is low so the regulator is sending full current to the alternator field to try and "wake it up."

Actually I guess in terms of the original question the failed alternator would cause an additional load until the voltage regulator was shut off.