When a car's idle is erratic and low, should this affect the alternator output voltage? My idle was below 500 and voltage was low 11.high-12.low... but if engine is revved it would go up. Now the idle problem is fixed )maybe or maybe not) but for now its idling at 750 and the voltage is 14.2 ish . I know this is ok, but I am worried about the low voltage with the low rpms... I think this might be normal considering the alternator is turning slower than its supposed to...

Just need some confirmation I guess.

Thanks!

 

the alternator needs to hit a certain speed in some cases to start charging at 14. though once it starts it's supposed to keep that voltage regardless of the rpms

 

Just like IA said...

Its normal when alt is not pushing voltage up, that appliance drag will cause voltage drop. Like u said during low rpm...

Check out voltage ign off, should be around 12.5V or more. 12.3V is still healthy reading...

 

Thanks... just what i thought and needed to comfirm..

 

Our alt's burn out b/c of a flaw in the rotors material. The brushes are burning channels into the rotor, it should be the other way around where the brushes wear out. So the diameter of your rotor is smaller and less charge transfer can occur, and at low rpm you'll have that voltage drop. Esscentially your alt is on its way out, but it would have lasted another 100k if the brushes wore and not the rotor.

 

hmmmm.. thats interesting considering that I've had to rebuild my alternator twice already. I wonder if different materials can be used on the next rebuild so that this doesnt happen.

Right now the voltage is at 14.2-14.3 so it looks good for now.

I guess I should learn to rebuild myself instead of paying someone 85 $...

 

Not be argumentative but thats plain nonsense.

The diameter of the rotor surface where the brushes run has got squat to do with the capacity of the alternator if there is still good contact between the brushes and rotor (there is after-all only a few Amps running there)

Sure if the brushes are too short or the springs pushing the brushes against the rotor surface is losing tension then local arcing will result that will eventually wear "grooves" into those brass/copper surfaces - all alternators and motors experience the problem with age.

If you find grooves on a shiny new and smooth rotor surface after the alternator has been "rebuilt" its because of non-spec and too hard brushes have been fitted. (or you are driving in real sandy environments with the car's bottom protection covers removed causing mechanical wear)

Alternators are probably the most robust and reliable item on the car and should last the life of the car plus - just keep sand and rubbish out of it and replace the brushes as soon as any funny business starts happening on the charging system.

By way of example - my VG has 240K Km on it - original alt and regulator/brushes assembly - stripped and cleaned the alt the other day and guess the brushes has another 240K to go before their operating limits will be reached - so sorry - rotor material is fine in my experience.

 

Agreed. But still your alt is top example.

After five? yrs the alt grounding may start to lose contact with engine block, and may start floating. That will burn regulator and destroy batt. One solution: Make new add on wire from alt to chassis.

see http://www.cardomain.com/memberpage/748507/10