Team Chevelle banner
1 - 5 of 5 Posts

·
Registered
Joined
·
224 Posts
Discussion Starter · #1 ·
I have a problem which seems to have gotten worse over time and was hoping someone could point me in the right direction.

The charging system has been modified to eliminate the external regulator and a alternator with an internal regulator was installed. A jumper was added from one of the field terminals to the BAT terminal, I guess to energize the field. I wish I had more info on the alternator model but it has the two wire connector and a BAT terminal. I believe the second terminal goes to the charge light in the dash.

This work was done 4-5 years ago. The alternator seemed to work fine and was putting out 14 volts at about 1000 rpm. Not so good for long idling but this engine isn't one to sit idle for long!

Anyway, last summer I began to have problems with keeping the battery charged even after highway cruising. The alternator output doesn't seem to kick in until I get the rpms up around 2200. Interestingly, the dash light does not light up during this time. If I let the idle drop far enough, it will come on.

I've taken a number of alternators apart to replace brushes or regulators but they usually were obviously toasted. So I'm not afraid to crack the case and replace something but I don't know what this could be.

Any idea what could cause this to happen? Other things to check?
 

·
Premium Member
Joined
·
2,173 Posts
Most places that sell alternators will test one for you for free. The test device usually will tell you if the diode tree is leaking or the VR is bad. Otherwise, it's difficult to tell without disecting and metering the diode tree, etc. etc.

If you're still serious about cracking the case, there are some simple things you try. The brushes or armature could be getting cruddy or wearing out. I'd do the new brushes thing first since it's the cheapest. Clean the armature surface where they ride with a little 1000 grit paper and use a VERY FINE pointed tool, like the tip of an ice pick or even a razor knife to clean the segment dividers. Just scrape the crud (usually carbon dust) out from between the copper pads. This buildup of carbon dust deteriorates the performance of the unit.

If this doesn't cure it and the tester doesn't say the diode tree is leaking, you could then try replacing VR. (unless you wanted to do that while you had it open) Aside from the bearings, there isn't much else to replace. If these things don't cure it, it's probably got some windings shorted. In that case it's replacement time (which I would do anyway since this stuff is a pain, costly and time consuming. You could spend well over $30 bucks on brushes and other parts and still have a bad unit.)

14 volts at idle isn't bad. In fact, 13.9 to 14.3 is pretty normal.
 

·
Registered
Joined
·
224 Posts
Discussion Starter · #4 ·
Thanks for the tips and pointers!

There's no unusual noise from the alt when running. There's no parasitic drain with the engine off so the diodes are at least not shorted. I can test them when I crack the case open.

It used to have 14 volts at just above idle. Now, it doesn't begin to supply current until well above 2000 rpm.

I'll bet it's the poor brush contact or carbon deposits as suggested. The internal parts are fairly cheap and so I think I'll take a shot at replacing the VR and brushes while I'm in there. If it's a winding short, oh well. I'll try to find a new donor to wrap in my chrome case.

Thanks again!
 

·
Premium Member
Joined
·
2,173 Posts
Don't blame you a bit!! That's what I'd do if mine were chrome.

Yeah, you might try lifting one end of each diode and checking it both ways.

I've resurected many a unit just by burnishing the stator, cleaning the gaps and flushing out the case (go easy around the bearings).

I'm curious so pls le me know what you found.

Good Luck
 
1 - 5 of 5 Posts
Top