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Calling Electrical Wizes - Charging Problems

gedmeyer

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May 17, 2003
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316
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upstate New York
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former L81 owner!
The last time I was out in my '81, I had the Battery and Choke lights illuminate. In addition, the Choke Relay started buzzing while at idle. The Battery and choke lights stay on all the time, w/ the battery light getting brighter w/ rpm. I've been troubleshooting this for awhile and can't figure it out...
  1. Batt. and Choke lights go out with green choke wire being disconnected. When connected, the choke is getting ~5.5V
  2. The batt voltage measured at the batt is 14.4V. Measured @ the alt, it is 14.75 V. The voltmeter in the dash shows about the same.
  3. I took the alternator to Advance AutoParts and they tested it as 'GOOD'. I'm not sure if their test checks the other connectors on the Alt.
  4. With the 2 connector plug disconnected from Alt, the #1 terminal (on the connector side) measures 11.8V at idle. The #2 connector shows 12.2V. Both terminals on the Alt. side show <0.1V.
  5. With this connector plugged in, the #1 terminal is 17.3V at idle and goes up with RPM. The #2 connector shows 14.4V, steady.
I know the service manual shows that one of these connectors should be 2-4V, but it's unclear on what to do if it's not in that range. Do I have a problem in my alternator or elsewhere? Car seems to run OK otherwise. The alternator is a year or two old (Delco) and has less than 3000 miles on it. The batter is 4 years old and has about ~6000mi?

I have not changed anything on the car this year, so there is no mods to look at...

-gedmeyer
 

wishuwerehere82

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Sep 6, 2003
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2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
Anytime more than one light on the dashboard come on that don't seem to be related to each other, I immediately think of the connector on the back of the console cluster. You can reach it by removing the glove box liner and reaching behind the gauges above the radio and check to make sure the connector is plugged in all the way.
 

Yoda

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4,884
Location
Amarillo, TX
Corvette
1981 UL5
General Info ;) from "learned" experiences :)

I've found when just the battery light comes on it was from NO output from the Alternator, e.g. loose or missing belt. Alternator Light was caused by charging circuit, e.g. loose or bad alternator connection, bad alternator, bad battery connections.

I chased an electrical problem (Altnator Light ~ Battery Light) for 5,000 miles during a cross country trip one year. Changed Alternator, not the problem ~ new battery, not the problem ~ new ground cable, not the problem.... then I was about to take the Altnator out to get tested (should have had the original tested :duh ) and one of the wires in the original connector came out of the connector :duh :mad replaced the connector $2.50+ problem FIXED ... that was 2 cross country trips ago..

Best guess, since you have done nothing since getting it out of storage, would be connection problem... do the trouble lights go away when the alternator plug is unplugged??

Not the most scientific help, but sometimes it doesn't have to be ;) Good Luck Tim getting Roxie out for some exercise :Steer

Bud
 

gedmeyer

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May 17, 2003
Messages
316
Location
upstate New York
Corvette
former L81 owner!
Anytime more than one light on the dashboard come on that don't seem to be related to each other, I immediately think of the connector on the back of the console cluster. You can reach it by removing the glove box liner and reaching behind the gauges above the radio and check to make sure the connector is plugged in all the way.

The battery and choke lights are related. They are on the same circuit. The connector going into the alternator was replaced a few years ago when I rebuilt the engine. All of the connections appear to be sound.
 

gedmeyer

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May 17, 2003
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316
Location
upstate New York
Corvette
former L81 owner!
Will someone be willing to go out to their 'vette and check the voltage on the #1 terminal of the 2-wire connector going to the alternator?

  • With the connector disconnected (engine running) I had 11.8V on the connector side.
  • With the connector plugged into the alternator (engine running), I measured 17.3V at idle.
I'm thinking I might have an overcharging problem? Unforunately, I can find any docmentation to indicate what the voltage should be at this terminal.

Thanks.
Tim
 

wishuwerehere82

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Rochester, NY
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Red '82 Coupe,Sebring Silver '98 Coupe
Yikes!!!
That's a voltage regulator if I ever saw one.
Take it to Autozone or some place like it and they can check it out.
I have an alternator shop down the street that will check it, rebuild it while I watch.
But after watching them a few times, I just take the bolts out and put in a new voltage regulator now. Easy!
 

gedmeyer

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May 17, 2003
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upstate New York
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former L81 owner!
After some more reading, I think I agree with you wishuwerehere. I was basically getting ign voltage on the connector when it was disconnected (and ignition ON). It only read 17+V with the connector plugged in, so the alternator must be back feeding voltage into the system. The excess voltage can't be coming through the fuse panel.

I'll replace the regulator tomorrow.
 

gedmeyer

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Location
upstate New York
Corvette
former L81 owner!
HEELLLP! I replaced the voltage regulator in the alternator and it didn't fix the problem. :mad
The symptoms remain the same...

However, I did notice that the choke/batter lights are barely on at idle. At the hit of any electrical draw (opening door, revving, turn on the defogger), the choke/battery lights go to full illumination and the choke relay starts buzzing.

As I mentioned, the autoparts store tested the alternator and says it puts out the correct voltage. Could I have a bum battery? The voltage at the battery is 13.9V while idling. The gages and choke fuses were OK and everything in the car works fine.

This is tweaking me out now. 3+ weeks since I've driven it for a grand total of about 400 miles this summer!!!
 

KOPBET

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Jan 31, 2003
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Tulsey Town
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'73 Silver LS4 4 speed
The choke coil is probably chattering because of AC at the coil. Check the rectifier diodes, one or maybe two are probably shorted.
 

bill81vette

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Jan 17, 2004
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4,321
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Troy,NY
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1981 dark blue metallic
Tim, voltage should be 14.2v.when mine was overcharging last year the,the diode trio(?) ended up being my problem,so far no more problems.if you need a hand give me a call...
 

gedmeyer

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upstate New York
Corvette
former L81 owner!
I real skeptical of replacing more parts in the alternator... It has no more than a few thousand miles on it. The voltage on the post of the alternator is a steady 14.xx volts. Plus, I had it tested at the auto store and they said it's output is good.
 

KOPBET

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Tulsey Town
Corvette
'73 Silver LS4 4 speed
I real skeptical of replacing more parts in the alternator... It has no more than a few thousand miles on it. The voltage on the post of the alternator is a steady 14.xx volts. Plus, I had it tested at the auto store and they said it's output is good.

Electronics don't pay attention to the odometer and I didn't suggest you replace any more parts, I just suggested you check the diodes. Just because the output is measured as an average of 14.xx DC volts does not mean there is not an AC component riding on top of it. You can also read the AC volts with the AC function of the volt meter. Very little AC should be measured. Apparently you already have a VOM, so you can also check the diodes with the ohmmeter and see if they are shorted. Put the ohmmeter leads across one diode at a time and note the reading. Then reverse the leads and again note the reading. If a diode reads the same resistance in both directions it is bad. If it is shorted the resistance will read zero or close to zero ohms in both directions.


:w
 

gmjunkie

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Old Fort NC/Vero Beach FL
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03 Z-51,78 L82 Coupe
Electronics don't pay attention to the odometer and I didn't suggest you replace any more parts, I just suggested you check the diodes. Just be cause the output is measured as an average of 14.xx DC volts does not mean there is not an AC component riding on top of it. Apparently you already have a VOM, so you can check the diodes with the ohmmeter and see if they are shorted or you can throw parts at the rest of the car. Put the ohmmeter leads across one diode at a time and note the reading. Then reverse the leads and again note the reading. If a diode reads the same resistance in both directions it is bad. If it is shorted the resistance will read close to zero ohms in both directions.


:w
Kop is exactly right!!!! Just because it's got plenty of output don't mean that AC voltage is not present!!!!AC voltage slipping past the Diodes can and will make a DC system do all sorts of weird things!!!Including and not Limited to Burning things up like ECM's,Relays,Electronic Ignition Moguls,Coils,Fuel Pumps,Fan Motors,Headlamp Motors,Wiper Motors,Battery's and other Pertinent Components!!!!!:eek:hnoes:eek:hnoes:upthumbs
 

gedmeyer

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May 17, 2003
Messages
316
Location
upstate New York
Corvette
former L81 owner!
Electronics don't pay attention to the odometer and I didn't suggest you replace any more parts, I just suggested you check the diodes. Just because the output is measured as an average of 14.xx DC volts does not mean there is not an AC component riding on top of it. You can also read the AC volts with the AC function of the volt meter. Very little AC should be measured. Apparently you already have a VOM, so you can also check the diodes with the ohmmeter and see if they are shorted. Put the ohmmeter leads across one diode at a time and note the reading. Then reverse the leads and again note the reading. If a diode reads the same resistance in both directions it is bad. If it is shorted the resistance will read zero or close to zero ohms in both directions.
:w

My multimeter indicated that the voltage drop across each of the diodes is approximately .6V. Switching the leads showed 0 and that the diode is not shorted.
 

KOPBET

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Jan 31, 2003
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Tulsey Town
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'73 Silver LS4 4 speed
My multimeter indicated that the voltage drop across each of the diodes is approximately .6V. Switching the leads showed 0 and that the diode is not shorted.


How many diodes did you check? Six in the bridge and three in the trio.

Here's a good write up http://www.4wheelnoffroad.com/alter.html

Have you measured the AC ripple voltage across the battey with the engine running and with a load on the Gen?
 

gedmeyer

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May 17, 2003
Messages
316
Location
upstate New York
Corvette
former L81 owner!
How many diodes did you check? Six in the bridge and three in the trio.

Here's a good write up http://www.4wheelnoffroad.com/alter.html

Have you measured the AC ripple voltage across the battey with the engine running and with a load on the Gen?

I checked the 3 diodes in the diode trio.

I took out the battery and brought it to the autostore and had it tested... It failed after charging for 40min, so I bought a new one. Unfortunately, this did not solve the problems.

My multimeter shows ~28-30 ACV across the battery with the alternator running.

Can the alternator really be the culprit? I did have it tested and it came out good.
 

KOPBET

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Jan 31, 2003
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Location
Tulsey Town
Corvette
'73 Silver LS4 4 speed
My multimeter shows ~28-30 ACV across the battery with the alternator running.


:W:eek:hnoes:W:eek:hnoes Yikes!!!! You should have less than 0.1 VAC

I checked the 3 diodes in the diode trio.


Did you check the 6 diodes in the rectifier?

I took out the battery and brought it to the autostore and had it tested... It failed after charging for 40min, so I bought a new one.

A new one or a re-man one ?
 

gedmeyer

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May 17, 2003
Messages
316
Location
upstate New York
Corvette
former L81 owner!
Well, atleast I'm getting good at taking apart the alternator.

I will crack her open and see if I can find the bum diode.
 

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