New alternator ???

-
Yote

Yote

Well-Known Member
Joined
Aug 30, 2015
Messages
1,404
Reaction score
731
Location
far eastern Colorado
installed a new (rebuilt) alternator . Started car, belt squealing on alternator pulley, ammeter slams to right about 40 amps. New regulator and belt and yes it was tight. And of course I can't go to parts store today so I thought I would ask if you guys have Any idea what's going on?????
Yote
 
Might be the battery is dead and nothing is wrong?

Check running voltage at battery. If it's 14V or so, it's "just charging."

If the voltage goes very much higher, and higher with engine RPM, say, 16, then you have..........

..............Problems in the field circuit / wiring, most likely. WHY did you replace it? And for the record what are you working on, and what are you using for a regulator?

On the 70/ newer vehicles IT IS COMMON to get rebuilts which are AFU. Aaaaaa....eeeehhhhFFFF ....Uuuuuuu....

Sometimes one or the other of the two field connections is GROUNDED. This can be very bad, if you get the blue wire hooked to the grounded one by mistake, it will BURN UP WIRING

Take an ohmeter. Check resistance from each field connection to the alternator case. They should both be open / infinite
 
Working on 72 demon 340. With field wires hooked up no resistance when grounded to case. With wires unhooked no reading from alternator terminals to case. Wires to ground only , blue wire shows no resistance , green wire has 9 ohm .Replaced because alternator was not working at all. Just used the alternator and regulator parts store said was correct.
Yote
 
Battery is showing 12.7 volts. Wouldn't think it should try to put out 40 amps. What about the belt slipping on the alternator pulley ? Is that just because it is charging so heavily??? Does it make a difference which wire hooks to the two field terminals?
Yote
 
Last edited:
At what RPM did you check battery voltage. I should have mentioned, you want to bring up RPM to simulate "low to medium cruise"


I think your battery is just low. Shut the car off, turn the lights on for about 30 seconds and then with everything off, measure battery voltage. I bet it's "dead."
 
I don't know much about this stuff and at my age if I learn it I won't remember. Anyway, a squealing belt, hot pulley, and 40 amps just seems like a lot of issues to recharge 1 volt in my semi adult mind.
Yote
 
12.7 at the battery disconnected sounds pretty well charged. With the ammeter pegged, then alternator is for some reason trying to put out well past normal voltage, IMHO.

So is this the original type regulator? The flat pack type with the modular 2 prong connector? Make sure its case is well grounded; scrape the paint from the back to be sure.

Check the following voltages while running:
1- Main alternator output to see if it around 14-14.5 volts
2- Check field lead to alternator with blue field wire; should be within .5 volts or so of the main output
3- Check the green field wire to the alternator; should typically be 2-3 volts below the blue field wire

Disconnect the green wire and see if it stops charging.
 
Main alt output 15.35-15.83v .
Blue wire 14.71 v
Green wire 12 variable v
Disconnect green wire stopped charging. Regulator is original style and grounded . Hope this helps, you have been a valuable resource for me .
Yote
 
Hmmm the output voltage is somewhat high but not like wide open high. And the voltage difference between the blue and green wire connections to the field is in the right range to indicate that the regulator is actually regulating around a set point.

BTW did you measure these voltages at fast idle or just regular curb idle speed? If at curb idle, re-measure at fast idle. Sorry, I did not specify that it should be done at fast idle.

I'd think:
1) a ground problem somewhere. Could be at the regulator case to body, the ground lead from firewall to head, or from the block to the battery -.
2) the new regulator is just off in its internal set point.

BTW, it would not hurt to trickle charge the battery overnight and then re-check. But the high output won't be fixed by that.

BTW, trace back the blue wire from the field and make sure it is connected to the same source at the blue wire into the regulator, and that there is not a corroded or oddball connection leading to the blue wire to the regulator. Both of the blue wires to the regulator and to the field need to come from the same source. Sometimes wiring mistakes get made; we found one where the regulator blue wire feed was connected AFTER the ignition's ballast resistor, not before, and that was sure mucking up the regulation.
 
Blue wire at 14.7 does not sound that bad, "a bit" towards high, but actually typical.

I think either your battery is discharged or has something wrong with it

It is ALSO possible the alternator has something wrong internally, like a shorted stator, etc. Only way to tell is to perform a full output test, read the shop manual, and you'll need a carbon pile tester. You might also see if a local parts store has an alternator tester BUT TAKE THOSE with a grain of salt
 
If he has that connector on the back of the block for the alt output harness it could be hidden back behind the motor on the passenger side and partially grounding to the block, firewall, or even within the connector.
That could explain all this.
It's even easy to pinch when the engine or trans gets R&R'd.

67Dart273 said:
You might also see if a local parts store has an alternator tester BUT TAKE THOSE with a grain of salt
Click to expand...

Yea, like if they drop it on the concrete floor and it tests good. :D
I bought a starter and it would work about 25% of the time or less, so I decided it was probably an armature brush hanging up because when it didn't want to work I could tap the back end of it with something and it would work again.
So one day when it stopped working I pulled it to get it replaced, they tested it and said there was nothing wrong with it.
Well, OF COURSE YOU DON"T SEE ANYTHING WRONG, because you just dropped it on concrete and jarred the brushes loose.
 
Last edited:
Dang, you guys are working my rear end off. BUT I fully appreciate it. The tests I did were more than 1.3 minutes
ago and I didn't take good enough notes. Wireing harness appeare to be factory though PO said it was replaced (gave me old harness). New ground wire from firewall to head and re did ground from block to battery. Charged battery as suggested but did not recheck voltage. Belt still squealed for about a minute then quit. Ammeter still showing more charge than I think it should. Parts store tested alternator before I took it and it tested well according to them. I'll refer to your replies tomorrow and then respond. IF I REMEMBER!!!
Yote
 
Last start up with no belt squeal.
Ran at 1600 rpm, alternator output 15.6 v. Blue wire 14.6 v, green wire 12.4 v, all using my old regulator. After 5 minute run battery had 12.7 v disconnected.
Which of these voltages charge the battery? If it's 15.6 v I would think it would decrease battery life by overcharging?
Yote
 
It is the 15.6 alternator output, minus any voltage drops in the wiring back to the battery +, and also voltage drops in the ground circuit, which would be from the alternator case, through the engine, and then the ground lead from the front of the block to the battery -.

How long has the battery been setting before you hooked this up? Maybe discharged somewhat (as suggested in post #2).

What is the battery voltage after sitting overnight?

Your voltage regulation point is a bit on the high side. Not like it is running wide open. Modern systems regularly run up around 15 volts. Can you drive the car? The voltage will drop as the system heats up. I'd be interesting to see what it was after 30 minutes of driving.
 
Battery was setting for about a week before installing new alternator. I'm sure battery was probably somewhat low at that time but engine still spun over readily. Will check voltage again tomorrow am. Will be driving to show Saturday, can check again when I get there.
Yote
 
"Which voltage" Try to get as close to the VR blue wire as you can. The point you mentioned at 14.6 is it. This shows the VR is close. Also, you must measure "warmed up" for accuracy, because the VR is temperature compensated. Look in the service manual. 13.8--14.2 warm is optimum. Much over 14.5 warm you need to look into.
IT IS NEARLY ALWAYS voltage drop between the battery and the VR blue wire terminal, "ign" terminal.

Another way to measure this is to turn the engine off, but turn the key to "run." Put your meter, one probe right on the battery POS post, and the other "as close" to the VR ign terminal as you can get. The ballast, originally, or the alternator field blue wire. You are directly measuring the drop in the harness, all the way from battery to the VR. You are hoping for a very low reading, the lower the better. More than .3V or so (3/10 of one volt) you need to look into things. This is why I occasionally suggest a relay to run underhood ign loadds.
 
You must log in or register to reply here.
-

Back
Top