Testing Alternator

[69340]

I am having some problems with the Alternator on a 1969 Dart. The question i have is should i get 14.4 volts if i go direct from the battery output on Alternator to the battery. I currently get the same voltage as i have on the battery about 12.5 volts. I have tried 2 different alternators that i have had tested on a alternator bench tester and i still can not get alternator to charge?. I have a new battery and i have fully charged it up . the car has electronic voltage regulator. I have tested the wiring from alternator to plug in on firewall all ok . I even bypassed the Ammeter gauge as i am aware they create problems. Any ideas out there?

 

[redfastback]

so your volt meter is red on the bat post of the alt and the black to ground? take it above idle and check voltage.

 

[69340]

wont go above 12.5 volts even when increasing rpm. Actually reads whatever battery voltage is.

 

[fishy68]

Is the regulator good? That would be the next thing to test. Just because it's an electronic type don't mean it's good.

BTW: You should get approx. 14 volts testing accross the battery when running and battery charged. I've seen it as little as 13.8 and as high as 15 volts but 14.4 is considered best.

 

[69340]

How can i test regulator? . I tried another regulator that i had on a shelf in my shop same problem? I will try a new one this weekend. I also unhooked the battery when the engine was running and the motor quit immediately? i am told this is an indication of a bad Alternator. I tried this with both Alternaters that i had tested at the shop and was told that both passed the bench test?

 

[Eric_S68]

I recently had a similar problem. It's an easy test to check the alternator. If you unhook both the field terminals (2 smaller wires) One should read battery voltage...(key on) plug that one, back in. On the other terminal run a wire to ground and start car. Note Voltage. Shut off car. You don't wanna do this for a long time as you'll see the voltage will be some where between 14-16 V. If you do see 14-16 V the alternator is ok.

Dont forget the voltage regulator needs a good ground to its case!

Hope this helps. Eric

 

[fishy68]

To test the regulator just take it to most any local auto parts store and they usually have a tester. Unhooking the battery and the car dying is a sign the charging system isn't working, not necessarily the alternator. The alternator is only 1 part of the charging system.

Eric has a good point about the regulator needing a good ground. Also make sure your battery has a 10-12 gauge groung wire running from the negative post to the fender in addition to the large wire running to the engine block or head. And the engine should have a ground wire running from the back of the intake to the firewall. Any bad ground can also cause your problem.