My alternator is only charging at 11 volts when it's on the car and running, therefore, not charging the battery. When I take it to have it tested, it cranks out 14 volts. What's up?

Voltage regulator. Do a search of this forum for voltage regulator. You should find a good descripton of how to check it out. Also John Muha has mentioned a replacement, AutoZone I think, pretty cheap. You should find that in your search results also.
EDIT: Not to familiar with the 72, I assume it has an external regulator. Does the voltage go up if you bring the engine rpms up or does stay at 11v?

Stays the same voltage even when the engine is revved

BTW the engine is a 327...

Engine size doesn't matter. You need around 14.5 volts.
The Zone or Kragen will check your charging system for free. If you need a regulator Autozone carries a Wells #VR715 solid state for around $11.00. Kragen only carries "offshore" mechanical replacements.
Be sure to disconnect the battery before installing the Wells unit.

So you think it's the voltage regulator? I've had Kragen check out the alternator and when it's off the car, it does 14 volts

I don't even know if it has a voltage regular...Where will it be?

It has one Marci. If you have the charcoal canister it's right behind that. Look on the left side of the radiator. Behind the round canister there's a square box screwed down to the radiator support. Have to move the canister to change it out.
Unless you are into correct restoration, may consider loosing the external regulator set-up and going with a more modern internal regulated alternator. I buy the newer style down here for around $20.00 (used junkyard).

If it has a voltage regulator, how does the alternator still show 14 amps at Kragen? Please forgive me, this electrical stuff is beyond me....

Their test should show that it runs above 16.5 volts (not amps). Without the regulator, like a governor on an engine, the alternator should put out maximum voltage. Somewhat like running a car engine wide-open-throttle (WOT).
Running WOT is great. It shows that the alternator can really deliver. Problem is that the battery and other stuff doesn't like that high of voltage. The regulator controls what the alterator delivers. Too high a voltage, the battery gets cooked and the headlights pop. Too low a voltage and the batery won't charge and the headlights dim at a stop sign.
Yes, a stock 72 has a regulator just where I indicated.

Thanks for your help. I was just talking to the "car" guy that's been helping me out and he said (listen to this) that "he unplugged the voltage regulator because it's not needed"!!!! graemlins/sad.gif Looks like I need another car guy.. BTW I meant volts, just for some reason I'm thinking amps. Thanks again!!!

It's possible that he installed a newer style alternator in his car. The 72 came with a DN style alternator. Later 70s Chevys changed to an internally regulated alternator (SI) that got rid of the mechanical regulator. It's a popular upgrade and both the DN and SI have the same case so it drops in.
http://www.chevelles.com/techref/ftecref14.html

AARRGGHH If both alternators look the same, how can I tell if an external voltage regulator is needed?! This is so confusing. :confused:

Not really. The cases are the same but the connectors are different. GM made a connector change so the wrong one would not be installed.
In order to do the the conversion shown in Wes's article the alternator connector has to be changed or there are conversition plug kits available for $15.00. No soldered required.
The orginal DN has its pins going this way ( II ) while the SI goes (--).

Regardless off which style it sounds like the alternator is not putting out anything. The 11v is probably battery voltage. If the alternator really is good then either it needs the regulator, old style alternator or the conversion to the new style was not done correctly.

The alternator puts out 14 volts at the auto parts store......how would that happen?

Originally posted by Marci:
The alternator puts out 14 volts at the auto parts store......how would that happen? Because their test equipment has a regulator built in so they can properly test it, I assume. As John mentioned before it should be capable of putting out more that 14v. 14.5 is nominal when regulated, max should be more that that, 16 > 18 I think. Anyway you know it can put out more than the 11 you see while it's in the car.
I would suggest before you do too much more that you put a charger on the battery. It sounds like it's draining down. You don't want it too low then try to charge it up with the alternator when things get straightened out. Charging a drained down battery with the alt can fry the alt. Just a word of caution don't want to cause more problems.

Thanks for all your advice, you two. I feel like an idiot when it comes to that charging system. If I have any more questions, you know you'll see them posted here somewhere.. :D

I dug this out from before, hopefully it help. If not, just post or send me your questions.

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.

Peter

Peter is the guy on charging systems. Thats what they pay him the big bucks on. Might I suggest that you convert that car to a more modern internally regulated alternator. If you do the alternator either works right or doesn't work right. Takes all the guess work out of it.

Thanks Peter! I had to print that baby out!! After this whole fiasco, I'm definitely changing to an internal voltage regulator!! Thanks for your advice, you guys are the best!! graemlins/thumbsup.gif

A good upgrade is to change to an internally regulated alternator. The 10SI type alternators are available everywhere and if you do a web search you'll find tons of info on them. They're also one of the cheapest alternators to buy. If you're never going to run any electric fans then a 10SI will work just fine. There's really no need for the more expensive CS130 alternators.

If you're looking to run electric fans then you need to find something 100A or so to keep up the voltage when you're idling since this is when you really need the fans to work their best. This is where the CS130 series alternators shine.

The externally regulated alternator will work OK for a car without much extra electrical load beyond stock. Some people leave them for origionality reasons or so they don't have to modify the car. Just replace the bad part and keep going.

Peter

Marci,
In addition to the tech section on this forum, there's also good info on this conversion at www.madelectrical.com. (http://www.madelectrical.com.)

Are you measuring your 11 volts at the alternator output post or somewhere else? If you get 14 v or so at the output post, it may be a wiring problem after the alternator. (which could mean your regulator is OK)
Good luck!
-Bill

Originally posted by docaudio:
Are you measuring your 11 volts at the alternator output post or somewhere else? If you get 14 v or so at the output post, it may be a wiring problem after the alternator. (which could mean your regulator is OK)
Good luck!
-Bill That's a good point, I assumed it was taken off the car and tested. If that's not the case then the problem may not be alt or regulator.