Alternator test question

[55 50 Ron]

How accurate do you think these tests are when done at NAPA, Auto Value, or O'Reilly's? I'm not convinced that they are correct.

My reason for saying this is that I bought a new voltage regulator and installed it after determining the other parts of the alternator were good. The free alternator test at one of the parts stores, then said the regulator (this brand new one!) failed but rectifier and lamp/diode trio both passed.

Thanks for your comments.

 

[wsmm]

Could have been a bad part right out of the box. It happens from time to time.

 

[Steve@Advance]

The regulator test is only good if it was properly installed, and even then I doubt the test would know if the field was open or shorted.

Is this a Delco 10SI?

This could also apply to other alternators too. There are several insulator washers under the regulator mounting screws. If any were omitted or installed where they don't belong, it could have an open field which would cause no charge, or a grounded field which would cause unregulated over charge.

 

[guido]

55 50 Ron,

The diode trio is inside the alternator. Field wires (3) go to each of the 3 diodes,
The other side is now DC voltage. That is regulated by the voltage regulator.

They took the alternator apart and tested the diode trio?

Some tester will detect a leaky diode.

Guido.

 

[used red MN]

Of the 3 bolts that fasten the brush holder and regulator in the case 2 of the 3 have integrated insulated washer and sleeve. The 3rd is bare and goes in the hole closest to the center bearing. There is also a U shaped clip that a bolt can pass through that I am also pretty sure is on that bolt hole of the brush holder to transfer a ground connection from that bolt head back to the top face of the regulator. This rarely comes off and usually has to be forcefully removed.
Did you check continuity between the slip rings of the rotor and for no short to ground? Did you check for continuity between all the 3 legs of the stator and that none were shorted to ground? These last two things are rare problems but so happen. Usually a stator will only test bad if the winding insulation visibly shows signs of burning from overheating.
Guido, I take it Ron had the alternator apart to check the items he mentioned as passing testing.

 

[UncleTom]

Used the free test once and they were wrong.

 

[pete 23]

The tests I have seen at auto stores only see if it charges or not and check voltage. Different alternators specify different voltages also. IH lowered the voltage on the 86 series tractors to extend battery life and it threw a lot of guys off who were watching the reading on their volt meter in tractor. When I tested an alternator I tested for rated output of the particular alternator by applying a load. A 10 si and most other 12 volt alternators should show full rated amperage at 13 volts or more when you apply a load to them.

It takes a good test stand to pull 100 amps out of one. Another thing is the test stand should have variable speed so you can tell at what rpm the alternator starts to charge.

The old Allen test bench bit the dust at the dealer and the new test stand they got was basically worthless as far as I was concerned. Even worst checking generators than alternators.

 

[55 50 Ron]

Yes, I had the alternator apart and checked the diode trio and rectifier using my Fluke 73 III on diode position. All that checked good. I did not check slip rings or stator areas. The 3 bolts for the regulator and brush holder all looked good and were removed and re-installed easily.

My next move will be to install it back on the tractor for a test run.

Yes, it is a 10 SI Delco.

Thanks for your help.

 

[timcasbolt]

(quoted from post at 18:06:53 06/11/22) How accurate do you think these tests are when done at NAPA, Auto Value, or O'Reilly's? I'm not convinced that they are correct.

My reason for saying this is that I bought a new voltage regulator and installed it after determining the other parts of the alternator were good. The free alternator test at one of the parts stores, then said the regulator (this brand new one!) failed but rectifier and lamp/diode trio both passed.

Thanks for your comments.

suspect it's easy to hook up one of those testers the wrong way and get false negatives.

 

[Hobo,NC]

You can bypass the regulator thru the D hole.

To check rotor use a small battery charger touch lead to a slip ring and the other lead to the other slip ring. It should read/draw 1 to 2 amps. I have seen them pass a ohm test but fail a load test.

Its rare I have seen the pass thru bolt opposite of the battery lug/bolt for the rectifier be broken are a bad ground.