testing a 12si capacitor? how? What say the Wisdom of the Brotherhood?

[mudbuggy]

Got my parts alternators for the tiganator, started going through all of the parts to see what fails the bench tests. I picked up 4 alternators for 40 bucks, 1 - 10si, and 3 - 12si, a small bracket and a thermostat housing (for the temperature coolant switch for the efans) From the yard I went to autozone to have them tested, 3 failed, one 12 si passed. So I came home and did the web homework, then went to work and did the 'professional homework' too. Problem is that nowhere in either the web or the GM manual is anything printed about testing the capaciters. I have included a quick pic (it's not the best, since I'm drunk and using the blackberry for the picture) for reference. Don't know why there are two different styles, I'm going to look for replacements now , but I might pass out drooling on the keyboard so I figured I'd ask the Wisdom of theBbrotherhood.

 

[Fordum]

Well, when you come to and actually post the pic.....

You can do a quick and dirty test with an ohm meter.
X100 scale, I'm guessing its the single wire type capacitor, put the positive lead on the wire, the negative on the casing.
Should show almost a short for a second, then swing to open circuit.


To be sure, you need a capacitor checker. They are built in to many digital meters, or you can do a search for a watsco cappy capacitor tester.

There ought to be a few hundred of them out there cheap.

 

[diesel4me]

I think the capacitor is only in there for radio supression,it doesn't do anything as far as the charging...the DIODE TRIO and RECTIFIER are the main electrical items in there that matter,along with the brushes,regulator and feild coil windings & stator...

You can test a diode trio using a ohm meter--set it so the meter buries the needle with both eads touching each other,then touch one lead ro each "leg" on the trio ,to the other side ,it should only pass current and allow the meter to read in one direction,but not the other,when you reverse the leads...

 

[Fordum]

I think the capacitor is only in there for radio supression,it doesn't do anything as far as the charging

Yep, pretty sure that is all its for, but what the heck, he wanted to test it.......

I figured once he woke up, he might realize that.

 

[mudbuggy]

yep I'm awake and yep you is right! I figured I would put them all back to oem then test them again. That way I know what each one is putting out. If it came stock like that then it will be tested stock, only after it passes will it be considered for modification. No use to beat my head through the wall if I don't need another hole (in the wall that is)!

 

[nsxxtreme]

Yep, pretty sure that is all its for, but what the heck, he wanted to test it.......

I figured once he woke up, he might realize that.

It's to short any remaning AC signal after rectification to ground. So the output should be very close to DC. It's not easy to test a capacitor and even a capacitor tester in an DMM can screw it up. To get an accurate and reliable reading you need an expensive piece of equipment.

Also to use a capacitor meter you need to disconnect it from the rest of the circuit.

 

[diesel4me]

WE used to "test" capacitors in vocational school by charging them up all morning on a power supply,and take them with us to the cafeteria at lunch time---if the freshman you poked with the two leads jumped about 6 feet off the bench,then it was GOOD!...