What triggers the "Volts" idiot light?

[FlaBoy]

I know the obvious answer is improper voltage, but I'm looking for some specifics. A few days ago my voltage light came on dimly and it hasn't gone away. I say dimly because it's barely visible in daylight, and when the key is on, engine off (and the voltage light is lit as it should be) it is MUCH brighter. The alternator is only a few months and a few thousand miles old, and the belt doesn;t seem to be slipping. My Scanmaster reads anywhere from 12.5-13.5 volts, which seems about right to me. I haven't gotten quality readings from a multimeter yet to verify the scanmaster, though I guess that would be next.

My main question is what parameters will trigger a volt light, is it just a lower bound (anytime voltage dips below 'x') or an upper and lower bound (anytime voltage is less than 'x' or greater than 'y')? If so, does anyone know what the upper and/or lower bounds are? Also, Since my actual voltage seems to be normal, and the light is lit only dimly, are there other things that could erroneously trigger the 'volts' light? I have noticed for a while now that the readout for fuel remaining (i have the digital dash) will occasionally blink to "--" for an instant so maybe theres something goofy going on in the dash wiring? (though the fuel level thing has been going on for a while, whereas the volts light is new).

Any light you guys can shed would be helpful... its not a major problem, but it certainly is annoying. Oh, and my car is a hot-air if that makes any difference wiring-wise. Thanks!!

 

[TURBOTWIN2]

Sounds like the diode trio is going out, giving you probably only 2/3rds of your amperange output, while stays good (voltage regulator=OK). Get it tested with a professional type on the car system. Most parts stores have these and will do it for free. Be sure they do or look at the possible diode "ripple". That will tell the tale.

 

[Bruce Urie]

Take your alternator apart and test all the diodes with your volt/ohm meter. The diodes only allow current to run in one direction only...so if you find a diode that lets your current run in both directions, it's bad. Just put plus on one side and minus lead on the other, then switch. Read your meter that's set on connuity. The diode should be good when you switch and lets current go in only one direction. You should have only one reading on your meter after switching leads. Then when you find the bad one...replace it. Simple and saves you money.:smile:

Bruce '87 Grand National

 

[FlaBoy]

Are alternators that simple to dis- and re-assemble? I've had bad luck in the past with motors and stuff, sometimes they can be a huge pain to get back together (lining up bearings and shafts, holding back carbon brushes so you can slide it all back together etc.). If the alternator's not too tricky, I'd love to take care of it myself and save some money. Testing the diodes I can handle, but I have never messed with removing/replacing them in an alternator. Where can I buy replacements, and what specs will I need to make sure I get the right ones? Again, thanks for the help so far!

Kinda wishing I'd paid more attention in my circuits and other EE classes... kept telling myself "eh, I'm a mechanical engineer, what do i need this for?" :biggrin:

 

[TURBOTWIN2]

A paper clip is the trick tool for putting the alternator back together. There's a small hole in the back to insert it to hold the brushes in place while fitting the two halves back together. Everything else inside is bolt on and available from NAPA and other parts outlets.
Give it a try, you're an engineer. It's not like you'll screw it up or anything.
(Walks off laughing)

 

[FlaBoy]

Give it a try, you're an engineer. It's not like you'll screw it up or anything.
(Walks off laughing)

:biggrin::biggrin:

 

[TURBOTWIN2]

:biggrin::biggrin:

Good, so you DID figure out that I was just kidding.

 

[Bruce Urie]

Are alternators that simple to dis- and re-assemble? I've had bad luck in the past with motors and stuff, sometimes they can be a huge pain to get back together (lining up bearings and shafts, holding back carbon brushes so you can slide it all back together etc.). If the alternator's not too tricky, I'd love to take care of it myself and save some money. Testing the diodes I can handle, but I have never messed with removing/replacing them in an alternator. Where can I buy replacements, and what specs will I need to make sure I get the right ones? Again, thanks for the help so far!

Kinda wishing I'd paid more attention in my circuits and other EE classes... kept telling myself "eh, I'm a mechanical engineer, what do i need this for?" :biggrin:

I'm a mechanical engineer, too. Whoopie. Yes, it's not hard to disassemble, just mark the two casings with a scratch awl so you can line them up for reassembly. There's a 3 page section in the Buick shop manual that shows disassembly and testing of the alternator of your car. I also believe it's on the CD Turbo Shop manual available here by a board member. Shows how to do everything. As TurboTwin said, he's right with his suggestion. Really not hard to do. The paperclip trick always works, not hard at all. After you put the two casings together, put in the four long casing screws, pull out the clip and the brushes will pop right against the armature rotor. You might want to lightly sand the armature roto copper rings where the brushes go with some emery paper. Do your diode check and your bridge rectifier check, too. Same proceedure..current in one direction..your diode trio is as follows...put ohmmeter lead on single connector, then reverse lead connection. You should have high and low readings. If not, replace it.you'll do alright, or walk away laughing.:biggrin:

Bruce '87 Grand National

 

[The Darkside]

My voltage light started doing the same thing you describe & after doing a search on here, found out that a loose connection behind the idiot light can cause these symptoms...All I did to fix it was push in around the voltage light & the problem went away....

The Darkside

 

[FlaBoy]

I'm a mechanical engineer, too. Whoopie.

Wasn't trying to toot my own horn, or brag about being an ME by any means (though i realize on re-reading that it may have sounded that way). The point I was trying to make was that I wish I hadn't let my blinders as an ME student keep me from taking more of an interest in EE or electrical-related classes. I'm paying for it now, since all the problems with my car lately have been electrical, and my research relies heavily on this stuff... luckily I've got my dad and brother (both EEs) to help me out when I need it. And trust me, they love to lord it over me when I come to them for help . Thanks for all the help and advice so far, i might actually have free time this weekend to tackle this problem, and I'll let you guys know how it turns out. Now I half want to take apart my alternator just to play around with the insides, always been curious about it, but was to afraid i wouldn't be able to get it back together again and ruin a perfectly good alt.

Darkside, I was poking around back behind the instrument panel a few weeks back trying to get at my odometer cable to fix a squeak, so you may be on to something there, thanks for the suggestion, I will see this weekend what the problem is (hopefully).

 

[Bruce Urie]

Wasn't trying to toot my own horn, or brag about being an ME by any means (though i realize on re-reading that it may have sounded that way). The point I was trying to make was that I wish I hadn't let my blinders as an ME student keep me from taking more of an interest in EE or electrical-related classes. I'm paying for it now, since all the problems with my car lately have been electrical, and my research relies heavily on this stuff... luckily I've got my dad and brother (both EEs) to help me out when I need it. And trust me, they love to lord it over me when I come to them for help . Thanks for all the help and advice so far, i might actually have free time this weekend to tackle this problem, and I'll let you guys know how it turns out. Now I half want to take apart my alternator just to play around with the insides, always been curious about it, but was to afraid i wouldn't be able to get it back together again and ruin a perfectly good alt.

Darkside, I was poking around back behind the instrument panel a few weeks back trying to get at my odometer cable to fix a squeak, so you may be on to something there, thanks for the suggestion, I will see this weekend what the problem is (hopefully).

Hey, FlaBoy, no problem. I didn't mean it that way at all. I should have left off the whoopie. And believe me, I know how it feels to have father and brother "lord it over".:biggrin: Haven't heard that expression in a long time. I see and understand your point exactly. No hard feelings. I have trouble sometimes putting my thoughts into the correct contex. I guess that's a disadvantage of getting old. Maybe that's why I own two "Buicks"...a car I told my Dad years ago you'd never catch me dead in. Dad was a true Buick man all 82 years of his life. I grew up seeing them as "old people cars." Me, fast, loud cars, Corvettes, etc., no way a Buick for me.:redface: And now look...I sure ate my words grandly. Dad grinned until the day he died about his Grand National. I will be owning this Buick until the day I die also. And by the way, I consider all mechanical and electrical engineers the cream of the crop and good friends.:smile: They are the icons of the industry.

Bruce '87 Grand National

 

[The Darkside]

Just checking to see if you found the problem yet?

The Darkside

 

[FlaBoy]

No, my schedule has been insane the past few weeks. Between work for the classes I am taking (papers, design projects, research projects, etc.) and the work for the classes I teach (grading papers, design projects, tests) and add in the fact that I have a big grant proposal due in the next week to fund my personal research, and I have not had any free time to spend on the car.

I was planning on tackling it this weekend, but i barely had enough time free to shower and feed myself. I hate the end of the semester! Since whatever the issue is doesn't seem to be causing any driveability issues, it may just have to wait until christmas break when my time frees up to take a look, unfortunately.

I appreciate the concern though, and whenever I figure it out, I will definitely post back and let you folks know.