alternator

[canalman1946]

I have two alternators, the one that charges the engine battery is getting very hot after only 5 minutes running. I'm getting 14.5V, so its working, just getting very hot! any ideas?

A little more info.. the red charging light stays on and there's no output, if I bypass the light, it charges. I've changed the relay switch.

Edited June 27, 2011 by canalman1946

[Gibbo]

...I'm getting 14.5V, so its working...

 

...the red charging light stays on and there's no output...

 

These seem rather contradictory to me!

[canalman1946]

These seem rather contradictory to me!

Yeah, I know what you mean, but If I bypass the bulb, it charges?

[RobinJ]

I have two alternators, the one that charges the engine battery is getting very hot after only 5 minutes running. I'm getting 14.5V, so its working, just getting very hot! any ideas?

A little more info.. the red charging light stays on and there's no output, if I bypass the light, it charges. I've changed the relay switch.

Where are you getting 14.5V?

The charging light illuminating is indicating no charge, bypassing it will simply make the alternator try and generate more power, making it get hotter!

This could be caused by a fualty alternator, or a short or a high resistance in the positive to the battery? More information is needed and you should check things out carefully!

[Gibbo]

Getting hot very quickly but still "sort of" charging is indicative of a blown rectifier in the alternator.

 

ETA: But that's not the only thing that can cause it

Edited June 27, 2011 by Gibbo

[cereal tiller]

are the two excitation fields powered from the same battery bank?

it may be that current is flowing from the bulb into the "other battery bank,allowing it to glow.

the "second alternator" should be excited via a relay from it's own bank.

[Robin2]

I have two alternators, the one that charges the engine battery is getting very hot after only 5 minutes running. I'm getting 14.5V, so its working, just getting very hot! any ideas?

A little more info.. the red charging light stays on and there's no output, if I bypass the light, it charges. I've changed the relay switch.

 

When you go to the doctor you are asked for your medical history (iirc ).

 

You haven't given us any history of this alternator problem.

 

When was it last working correctly?

 

Has anything electrical been changed by anyone since then?

 

 

And as a separate thread of thought ...

 

Is it possible there is a short circuit? (usually accompanied by a smell of burning ) If the alternator is getting hot it means there is a lot of current flowing somewhere. Of course the short may be internal to the alternator.

 

ETA

 

If it was mine I think I would stop the engine; disconnect the B+ wire from the alternator (and make sure it could not touch any metal part of anything) and connect a bulb (several watts - not an LED) from B+ to ground. Then I would start the engine and measure the voltage across the bulb and at the field wire connection. If the field voltage is normal (about 13.9v) and the bulb lights with same voltage across the bulb AND the alternator overheats then there is an internal fault. If the voltage across the bulb is low or high there is an internal fault. If the voltages are normal and there is no overheating there is an external problem.

 

... Dons flak jacket ...

Edited June 27, 2011 by Robin2