Alternator question...1970 340...externally regulated

[elevenssc]

...If I have bat voltage to the positive post, and nothing connected to either field spade terminal, and I ground either or both spade terminals while the car is idling, should the alternator be pushing 14+ V?

[Chryco Psycho]

no

[elevenssc]

If I apply alternator excitor voltage to one of the field spade terminals, and ground the other terminal, then I should get 14+V...correct?

[ShelbyDogg]

You'll get more than 14v and can blow your battery up.  What are you trying to do?  Test your alternator?     The 2 fields should go to the 2 pins on a GROUNDED voltage regulator with the center pin getting the 12v ref voltage. That should get you 13 to 14.5 if those 2 parts are working.

[mopar12372]

mancini racing has a great conversion to replace the old crappy mopar charging system.-->bill

[elevenssc]

I'm trying to de-bug/diagnose my charging system.  Took the alternator in to get tested and it does produce 14 V (brought my multimeter and aligator clips).  When I put it on the car, I'm only getting battery voltage...no charge.

I do have the center field spade getting excitor voltage.  I've tapped into the excitor voltage to feed the "IGN" terminal on the regulator.  The "outside" spade field terminal goes to the "FLD" terminal on the regulator.  The regulator is grounded.  I wanted to replicate the charging alternator in the car to isolate the component (regulator) that is not working.

I'm suspecting the regulator, but it is new, and I'm concerned that I may have installed wired incorrectly and blew it up...

oh the joys of electrical snafu's

[ShelbyDogg]

Hook a jumper cable from the positive battery post to the big terminal on the alternator and read the voltage there. This way you are bypassing everything inside the car.  What voltage do you get there?

[elevenssc]

Thanks ShelbyDogg...I'll get some data tomorrow...

[elevenssc]

Here's what I got...

Key in stop position, positive multimeter lead on positive battery lug, negative multimeter lead on negative battery lug. - Battery voltage = 12.63V

Key in stop position, positive multimeter lead on "hot" alternator post, negative multimeter lead on negative battery lug. - Voltage at alternator= 12.61V

The two numbers drop to 12.36V and 12.23V respectively when the key is switched to "run" (electric fan is juiced).

Key in run position, positive multimeter lead on alternator excitor wire (middle FLD spade terminal), negative multimeter lead on negative battery lug = 12.00V.  This voltage drops to 0V in the start position.

[CUDA JAS]

stupid question....did you test the alt with the car running?

[elevenssc]

Well, much to my surprise, the initial regulator that I thought was bad, wasn't.  I now have a charging system that works  (14.9V at 2000rpm) 

I painted the engine compartment over the winter and was relying on the fastener thread/firewall contact for my ground.  Tonight I sanded some of the paint away over the fastener holes (under the regulator) and now things work...go figure.  I guess the ground I thought I was getting before via my multimeter must not have been sufficient fot the regulator to operate.
 
CUDA JAS...I was hoping to bypass the regulator to verify alternator charging in the vehicle when I started this thread.  Guess I dont have to now 

Thanks to everyone for your patience, input, and advice.  It's nice to know I'm not alone trying to figure out 40 year old wiring/charging systems that were marginal when new.

I do have another volt meter question, but I'll start another post for that one...

[brads70]

Glad you got it figured out!   

[ShelbyDogg]

See my top post about a GROUNDED voltage regulator.

Glad that you got it charging.

Like my reply in another thread, I run a ground wire from the back of the block to the voltage regulator bolt then to the ECU bolt. I also run a cable between the block and frame.

[UKcuda]

Like my reply in another thread, I run a ground wire from the back of the block to the voltage regulator bolt then to the ECU bolt.............

Is it just a coincidence?   

Well done for getting it sorted.

[ShelbyDogg]

Is it just a coincidence?   

Well done for getting it sorted.

Well, you are close.  With mine, the ground wire that you have on your ECU plate, I would have right on the ECU itself and not 2 bolts away.