The Stovebolt Site Forums The Shop Area The Electrical Bay Alternator, Can't be, right?

69 Chev stepside, 250. System not charging.

Alternator tested "passed" by Autozone. New regulator. Good ground. Battery test excellent (9 mos old). No fuses blowing, no spark at battery terminal when disconnect (ie no shorts).

Re-checked the wires, all show proper voltage/continuity. Still no charging.
battery static is 12.48v, when running 12.22v, when lights and heater fan on 12.03v revved to 2000-3000.

I'm beginning to think, although the alternator tested fine, that it must be the alternator. Any other thoughts??

Curious though, I can take short trips, 3 to 10 miles 10 times and the battery voltage never drops. If I go 100 miles, I run out of juice and it has to be jumped. And even though there wasn't enough juice to start the engine, once started it will go another 50 miles. (still won't start if you shut it off though) Wonder if this is significant?

Have you tried bypassing the regulator? I'm assuming you've got a 10SI alternator with the built-in regulator. There's a D-shaped hole in the back of the housing near the position of the 2-wire plug on the outer perimeter. If you use an ice pick or a thin-bladed screwdriver to ground the field circuit to the case by putting it through the hole and touching the tab on the regulator, thh voltage should go up a noticeable amount. If the engine is revved up a little with the field grounded, voltage will go to 15-20 volts, so don't race the engine. Also be sure the #2 wire in the 2-wire plug has battery voltage on it at all times. The #1 wire (usually white) gets switched voltage from the ignition, or it serves as a ground for the idiot light.

I'm not surprised at the unit passing the check at the parts store- - - -I've seen them pass one with the brushes removed!
Jerry

No, this is an alternator with an external regulator. Brand new VR.

A side note here, the glove compartment sticker says "42 amp generator". Would this late a year originally have come with a generator? I also have a '65 I bought new and that came with an alternator.

Try connecting a jumper wire from a known source of battery voltage such as the big main battery lead at the alternator to the "field" terminal at the 2-wire plug in the back of the alternator. This bypasses the regulator and puts the alternator into full output. "New" is not necessarily "good" where those 4-pin extrnal regulators are concerned, particularly the new design solid-state ones without the magnetic contact points inside.

No, that vehicle would have an alternator as original equipment. The 42 amp alternator was one of the earliest ones. They quickly increased the capacity to 65 amps or more.
Jerry

Thankyou, thankyou, thankyou!

When I went to hook up the jumper wire, I checked the colors going to the VR and found that the 2 wire plug in the back of the alternator was reversed. The field wire was going to the stator terminal #2 on the VR and the stator wire to #1 the field. Who knew the plug could be reversed and still fit. Obviously (now) I must have reversed it after cleaning and buffing the alternator when re-connecting.

Excellent! I have battery static 13v
idling 13.80
revving 14v

5 weeks I've been fooling with this problem, and over lunch you helped to solve it.

Thanks again Hotrod Lincoln

As long as I have you here, one more question: Under the VR tab #4 there is another tab. Is this the return through the ignition switch for the indicator (charge) lamp? And, can I just connect an amp guage in the series in place of the indicator lamp?

Hmmmmm- - - - -there's supposed to be a tab that prevents the square plug from getting reversed. Sometimes it gets worn away or broken off. It's been so long since I worked on the external-regulator rigs that I'll need to dig out a wiring diagram to answer your question about the extra terminal. I think it might be a connection for an external ground wire. No, it won't be possible to substitute an ammeter for the idiot light, as there was a different circuit and a shunt-type ammeter for the trucks that had the ammeter option. There was also a resistor built into the ammeter-equipped trucks to prevent enough current backing up through the circuit to keep the ignition working as the switch was shut off. The idiot light restricted the current enough to prevent the run-on situation. It would be possible to wire an aftermarket ammeter into the main charging circuit between the battery cable terminal at the starter and the alternator. Other locations would not allow the proper charge/discharge indication at the ammeter.
Jerry

The extra tab underneath the VR is actually on the same post (#4) as topside. (and, of course, insulated from the housing).

I do have the dash panel with the ammeter, temperature, and oil pressure guages. Could I use that ammeter in the charge light circuit? I was going to use aftermarket guages, but if these would work....
Otherwise, I will do as you suggest with an ammeter in the main charging circuit.

If the connectors on the two dash panels are the same, you can probably interchange them without making other modifications to the wiring. The only circuit diagrams I can find in my collection show the "no charge" light circuit, but I'm sure I've dealt with the ammeter-equipped ones in the past. There's a built-in shunt on the dash panel and only a fraction of the actual charging current goes through the ammeter. I don't recall if the heavy-current charging circuit has to be modified in order to use the original-equipment ammeter. It won't hurt to give it a try!
Jerry

Thanks again Hotrod Lincoln. This may be awhile. I'm back to sanding, now that I have the charging working again. I have to be sure I can drive the truck to the car show (Madison Classics) the end of the month, and I know once I get into the dash there will be a lot of things taken apart.