Alternator Rotor test - CorvetteForum - Chevrolet Corvette Forum Discussion

Register FAQ Search Today's Posts Mark Forums Read Vendor Directory

C3 Tech/Performance
V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

Alternator Rotor test

Reply
 
 
 
Thread Tools Search this Thread
Old 05-21-2012, 11:17 AM   #1
TWINRAY
CF Senior Member
Thread Starter
 
TWINRAY's Avatar
 
Member Since: Aug 2005
Location: Working on the car NY
Posts: 2,380
Thanked 6 Times in 5 Posts
Default Alternator Rotor test

I went to test an alternator that I suspect is defunct. The diode trio tested OK as did the Rectifier diodes. I went to test the rotor which (according to the book) has 2 tests. The test performed touching the meter to the slip rings tested OK. The other test whereby you touch one probe to a slip ring and the other to the shaft gave me no reading (each slip ring tested individually to the shaft) –the book said a low reading means NG. Just for the fun of it, I had the original alternator to my 1969 which was performing OK until 2002 but I took it out and put in a Rebuilt unit. With nothing better to do, I took that unit apart. A similar test gave the same result. Am I doing the test wrong or are both units bad?
TWINRAY is offline   Reply With Quote
Old 05-21-2012, 02:57 PM   #2
TimAT
CF Senior Member
 
TimAT's Avatar
 
Member Since: Oct 2006
Location: Gladstone MO
Posts: 5,097
Thanks: 0
Thanked 16 Times in 16 Posts
Default

A low reading on an ohm meter means a good (low resistance) path. A high reading means a very poor path or open.

The slip rings on the rotor should have a very low reading between them, but individually to the shaft should be open.

TO maybe help get an idea of how this all works, a simple test. When you touch the meter leads together (meter on ohms) the meter (digital) will read .05 or somewhere close. Apart, the meter reads 0. or has a dash. Lots of different ones out there and rarely manufacturer's use the same indication.
OK not hold one lead in each hand between your thumb and forefinger- What's the meter reading? Remember that number. It'll probably be jumping around a bit so maybe get a rough average- right here this is not a real accurate test- Just a simple rough idea to give you a idea of how the meter reads- Got your average number? Good, now wet the fingers you were holding the meter leads with and grab them again just like you had them. DOn't worry, not enough voltage or current here to even feel it. Now look at the numbers on the meter again- they will be lower- the water on your fingers makes you a slightly better conductor.
Not a real scientific test, but it may help shed a little light on how a meter reads.

If you already know- sorry, I am not trying to make anyone look bad- but someone else may be trying to work thru a meter and this might help them too. And the way things are worded sometimes make a ohm meter as confusing as it can be and when you tie that with some guys are (rightfully) afraid of anything dealing with electricity ------
TimAT is offline   Reply With Quote
Old 05-21-2012, 03:52 PM   #3
Peterbuilt
CF Senior Member
 
Peterbuilt's Avatar
 
Member Since: Aug 2006
Location: mount holly NC
Posts: 4,199
Thanked 112 Times in 101 Posts
Default Basic test...

You should have continuity between each slip ring.
You should have an open circuit from the slip rings to the shaft.
Peterbuilt is offline   Reply With Quote
Old 05-23-2012, 11:31 AM   #4
TWINRAY
CF Senior Member
Thread Starter
 
TWINRAY's Avatar
 
Member Since: Aug 2005
Location: Working on the car NY
Posts: 2,380
Thanked 6 Times in 5 Posts
Default

Thanks to you both for your advise and explanations. I have wasted already too much time on taking this alternator apart and putting it back together with no definative explanation as to why it is not working. I'm going to pick up a new unit. thanks
TWINRAY is offline   Reply With Quote
Go Back   CorvetteForum - Chevrolet Corvette Forum Discussion >
Reload this Page
  • Alternator Rotor test
  •  
     
    Reply

    Related Topics
    Thread Thread Starter Forum Replies Last Post
    Battery POWER DRAIN Question MaSTeRofDZaSTeR C4 General Discussion 10 03-11-2011 07:44 PM
    Alternator Diode Question firefighter C-3 C3 Tech/Performance 8 07-17-2008 08:50 PM
    Alternator/Regulator Explained and Tested plaidside C3 Tech/Performance 2 05-21-2007 01:44 AM
    Alternator/Regulator Explained and Tested plaidside C1 & C2 Corvettes 2 05-20-2007 11:36 AM
    Where to buy alternator diodes (and other parts) 66since71 C1 & C2 Corvettes 7 05-11-2007 08:38 PM


    Tags
    alternator, rotor, test

    Thread Tools Search this Thread
    Search this Thread:

    Click for Advanced Search

    Posting Rules
    You may not post new threads
    You may not post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are Off
    Pingbacks are Off
    Refbacks are Off

    Forum Jump


    All times are GMT -4. The time now is 10:12 AM.