Alternator testing?
Team Owner
Joined: Oct 2004
Posts: 23,831
Likes: 10
From: Springfield MO
St. Jude Donor '07
Step 1) remove alternator
Step 2) drive to parts store with alternator
Step 3) put alternator on parts store's handy-dandy testing machine
Other than that, I don't know.
Step 2) drive to parts store with alternator
Step 3) put alternator on parts store's handy-dandy testing machine
Other than that, I don't know.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
You can just drive the car to an Advance Auto Parts store and they can check the diodes with the alt. on the car with the engine running. I'm sure other parts stores can do the same.
Drifting
Joined: Jan 2006
Posts: 1,944
Likes: 22
From: Yooperville MI
I don't know how many people actually do this anymore or how readily available the parts are. But testing is interesting none the less. Depending on what alternator you have, I'm assuming it's one of 2 old styles.
Internal regulator (trio diode):
Remove the diode from the end frame and connect your ohmeter to the single connector and one of the 3 connectors. Write down the resistance and reverse the leads. Comparing the second reading, you should have one high and one low reading. Do this test on the the other 2 connectors. They should all have a high and low reading, if one has matching readings the diode is bad.
External regulator (6 diodes):
The diodes in the heat sink are positive and the diodes in the end frame are negative. On the bench, connect an ohmeter between the diode pin on a negative diode and the other lead to the heat sink and reverse the leads and compare reading as in the previous test. Check all 3. On the positive diodes, connect the ohmeter to the diode and the end frame and reverse.
I just remembered on the trio diode type as long as you have not completely dissasemble it, make sure the main connector on the diode is not grounding.
Internal regulator (trio diode):
Remove the diode from the end frame and connect your ohmeter to the single connector and one of the 3 connectors. Write down the resistance and reverse the leads. Comparing the second reading, you should have one high and one low reading. Do this test on the the other 2 connectors. They should all have a high and low reading, if one has matching readings the diode is bad.
External regulator (6 diodes):
The diodes in the heat sink are positive and the diodes in the end frame are negative. On the bench, connect an ohmeter between the diode pin on a negative diode and the other lead to the heat sink and reverse the leads and compare reading as in the previous test. Check all 3. On the positive diodes, connect the ohmeter to the diode and the end frame and reverse.
I just remembered on the trio diode type as long as you have not completely dissasemble it, make sure the main connector on the diode is not grounding.
Last edited by crazywelder; Mar 18, 2007 at 09:32 AM.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Very simple! Two types as previously noted. Tested or done with the engine running. [A] internal and [B] external regulated alternators. Similar proceedure for both. Remove the Alt plastic 2 wire plug. Connect a jumper wire to the bat [12 volt] hot wire connection on the back of the case and for [A] touch or cross both of the spade terminals where the plug was, carefull not to ground out against the case. For [B] touch only the [F] field treminal. If it energises or charges, the alt is ok. If not i`ll sell you a good one. 
Works for all styles of alternators. One could actually get fancy with the test wire. Buy the alt plug for the style you have and connect the wire or wires as the alt needs. The one wire for external and two wire for the internal. This is actually the principal of how the 'hot rod' one wire alternator works.
Works for all styles of alternators. One could actually get fancy with the test wire. Buy the alt plug for the style you have and connect the wire or wires as the alt needs. The one wire for external and two wire for the internal. This is actually the principal of how the 'hot rod' one wire alternator works.
Last edited by Ironcross; Mar 18, 2007 at 10:07 AM.
