Alternator works better with a load versus no load.. weird

[jar25201]

Alternator works better with a power load (a/c) versus no load at idle.. weird

So like the title says, I am testing this alternator in an 99 LX and with my dc plug battery/alternator tester its shows that when at idle, its a weak alternator and then when i add a load like the A/C it shows a green good light.

I am just curious if anyone else has encounter this problem and what the outcome was.

 

[lethal6]

They all go up when under load. That is it's job.

 

[jar25201]

If you drive the RPM's up yes it should increase the voltage charge output.

But for me when at idle with no power load it shows weak alternator and good battery. With a power load (a/c) it shows a good alternator and good battery while still in idle, also when driving.

Sometimes I get what I normally expect, at idle good alternator and good battery. With a power load (a/c) it shows a weak alternator and good battery while still in idle range. During this same time if you rev or drive it shows both alt. and battery good.


I'v checked the resistance between alternator and positive battery terminal and seemed fine with a reading at first of .5xx ohms and then a jumping range from .3xx-.4xx ohms sometimes a quick moment in the .2xx ohms.

and a 13.7 volt while running and 12.x while off.

 

[Trekk]

They are built to be spun at a certin rpm to produce max power. Idle isn't enough, with the ac on your rpms increase a decent amount.

 

[jar25201]

What would cause the RPM's not too increase when the a/c is engaged? If i remember correctly it is supposed to gain 300 rpms give or take a few.

My 80 amp fuse-able link is okay and so is the 7.5 amp #15 fuse.

 

[Trekk]

Yes the rpms are suppose to increase with the ac on, that's my point, now the alt is spinning faster so alt is putting out more power. If the alt is 100% effective at say 1500 rpms, at 650 rpms it's only 40% or so (quick guess) effective at those speeds.

Example. If you have a dead battery you can jump start the car and let it idle in your front yard for an 1/2 hour, chances are when you turn it back off it won't have enough of a charge to start. If you instead drove the car around for 10-15min it would have a much stronger charge after.

 

[mymmeryloss]

Yes the rpms are suppose to increase with the ac on, that's my point, now the alt is spinning faster so alt is putting out more power. If the alt is 100% effective at say 1500 rpms, at 650 rpms it's only 40% or so (quick guess) effective at those speeds.

Example. If you have a dead battery you can jump start the car and let it idle in your front yard for an 1/2 hour, chances are when you turn it back off it won't have enough of a charge to start. If you instead drove the car around for 10-15min it would have a much stronger charge after.