Gain extra benefits by becoming a Supporting Member Click here find out how!

Classic Performance Products Nu-Relics Power Windows
American Auto Wire Hellwig Products IncPerformance Rod & Custom
Danchuk Catalog



Username Post: Strange Alternator Problem        (Topic#305301)
Majoraslayer 
Member
Posts: 318
Majoraslayer
Age: 33
Loc: Tennessee
Reg: 02-22-04
11-26-13 01:21 PM - Post#2402832    

I'm having trouble figuring this one out.

Keep in mind this is in my 1978 Camaro, but as I've mentioned before, all the engine wiring matches up to a 1995 C1500 so we'll pretend thats what it is.

I first noticed that each time I started the car, it seemed to have less and less power to turn the starter. My first thought was a short somewhere pulling down the battery, but if it was slow enough to still have cranking power after sitting a couple of days then the alternator SHOULD have at least charged it back up a little after running for a while. After a test drive yesterday, the engine shut down and when I tried to restart it, the battery was too low to get any cranking at all.

This battery is brand new; I just bought it two weeks ago. Its not impossible its a bad battery, but its at least improbable. I thought for sure that meant a bad alternator, so I pulled it off and took it up to AutoZone. They tested it and, at least according to their machine, it passed all tests. So, perplexed, I brought it home and put it back on the car. Just to make sure there wasn't a grounding problem, I added a ground strap to one of the alternator bolts. I charged up my battery and started it up.

I recently picked up one of those battery chargers that also tests the alternator. I would have used it in the first place, but the car has to be running for the test, so I just let AZ test it. When I tested it with my tester (engine running, headlights on), I was only reading 12.5 volts. According to my reference, anything lower than 13.6 indicates a problem with the charging system.

Next, I tested the big wire going to the alternator; it shows 12.5 volts, meaning the output of the alternator SHOULD have a complete connection to the battery for charging it. I tested that to the casing of the alternator and got the same voltage, so I shouldn't have a loose ground.

I'm not sure exactly how the AZ tester tests the alternator; all it does is show a PASS or FAIL light. The plug on the alternator only has one wire on it, which as I understand it drives the battery gauge. I don't have a battery gauge, so that wire is currently disconnected under the dash. Does the gauge somehow activate the regulator to start charging the battery, or do I have a bad alternator?

www.autozone.com



 
0utlaw 
Very Senior Member
Posts: 2794
0utlaw
Loc: US East Coast
Reg: 09-10-02
11-26-13 02:20 PM - Post#2402839    
    In response to Majoraslayer

Because Alternators vary, I will give you some basics. You need to excite the alternator once during starting to turn it on... however this is done.......
it can be done internally as in a hot rod one wire alternator...which excites when revved a bit. On some GM products, a wire from the starter solenoid which is hot only during starting, then shuts off.... is all you need. Yours may be done through the gauge which is excited through the ignition switch only during starting and then back fed for a reading. Just Guessing.
Once started and charging, a quick check with a metal object (a screwdriver works)will stick to the magnet core in the back. If it is not charging, it will not stick.Saves you running around looking at the gauge or voltmeter every time you want to check it..
The alternator quits charging when the engine stops...and will need to be excited again on restart.
On my old hot rod, once in a while the alternator does not turn on. On mine, I can restart and get it to work, but one day , it had been 20 miles before I noticed the gauge on discharge. I didn't dare shut it off. I took 12v off the big terminal and jumped to the smaller terminal using a paper clip...and that turned it on. HOWEVER>>>> You need to know what you are doing.



 
Majoraslayer 
Member
Posts: 318
Majoraslayer
Age: 33
Loc: Tennessee
Reg: 02-22-04
11-26-13 05:01 PM - Post#2402882    
    In response to 0utlaw

I traced down the wire in the harness that originally ran to the truck's battery gauge, but I don't have one in the car. Should I just hook this up to receive 12V when the key is turned on (i.e. the ACC wire), or do I need to add a load to it by installing an aftermarket gauge?

My Chevys (I.E. What I'm Asking About)
------------------------- -------------
-1988/1989 C/K1500 5.7L w/700R4 ('88 C Body, '89 K Everything Else)
-2003 Avalanche Z71, Auto, 4x4


 
bowtie44s 
Valued Contributor
Posts: 4290
bowtie44s
Age: 38
Loc: wv
Reg: 08-29-12
11-26-13 05:45 PM - Post#2402906    
    In response to Majoraslayer

Is it a 1 wire or 3 wire alternator? If it's 1 wire it's self excited. If it's 3 you can run a short wire off the charge stud to the excitor spade terminal and that will work fine. What is your voltage with the engine off?

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Majoraslayer 
Member
Posts: 318
Majoraslayer
Age: 33
Loc: Tennessee
Reg: 02-22-04
11-26-13 05:50 PM - Post#2402910    
    In response to bowtie44s

I know the alternators you have in mind, but its the original alternator from a 1995 C1500. So ,it actually has two wires; one wire goes to the hot side of the battery and charges it, and one wire goes to a rubber plug that clips into the regulator. That one wire runs to the gauge in a truck's cluster; as I understand it, I think the gauge excites the regulator through this wire as well when the switch is turned on.

So, I'll have to set something up to excite the regulator through this wire either by adding an aftermarket gauge, hooking it straight to switched battery power, or calling in some strippers and telling it I'm giving it a lot of money.

My Chevys (I.E. What I'm Asking About)
------------------------- -------------
-1988/1989 C/K1500 5.7L w/700R4 ('88 C Body, '89 K Everything Else)
-2003 Avalanche Z71, Auto, 4x4


 
bowtie44s 
Valued Contributor
Posts: 4290
bowtie44s
Age: 38
Loc: wv
Reg: 08-29-12
11-26-13 09:06 PM - Post#2402945    
    In response to Majoraslayer

This is 140 amp, 105 is cheaper, 200 is more. http://www.summitracing.com/parts/tff-7861g6g/ove r... I'm not familiar with the alternator you're talking about but you should be able to excite it off of the alternator. I've always hooked up 3 wire alternators that way and left the 3rd one empty. The 3rd one is for a light or gauge or something like that.

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
0utlaw 
Very Senior Member
Posts: 2794
0utlaw
Loc: US East Coast
Reg: 09-10-02
11-27-13 03:28 AM - Post#2402966    
    In response to Majoraslayer

If your alternator has an internal voltage regulator, CHANCES are you can pick up an EXCITER wire from your starter solenoid. There should be 3 terminals on your solenoid. Find the tiny terminal on your starter solenoid. Attach a voltmeter plus to this terminal and a minus to a ground. Start your car. The voltmeter should read 12volts just until you move the key to "run", then go dead. This can be the wire you are looking for to get this working.
If you have an external regulator, you need to find a wiring diagram or at least find a wire that is 12v while cranking and no voltage while running. This CAN BE the "EXCITER" wire.




 
0utlaw 
Very Senior Member
Posts: 2794
0utlaw
Loc: US East Coast
Reg: 09-10-02
11-27-13 04:17 AM - Post#2402969    
    In response to 0utlaw

I found this on the web...it should help you to understand the alternator and how it works.
OUTLAW




http://www.autoshop101.com/forms/alt_bwoh.pdf



 
Majoraslayer 
Member
Posts: 318
Majoraslayer
Age: 33
Loc: Tennessee
Reg: 02-22-04
11-27-13 08:18 AM - Post#2403042    
    In response to 0utlaw

Every 1988 - 1995 C/K truck I've seen with a V8 has had the same alternator; one wire goes to the battery to charge it, and there is a plug with one wire in it that clips into an actual connector on the alternator, NOT spade terminals like older model alternators. Most of the information I've found on Chevy alternators lists a one-wire or three-wire alternator; the one-wire is self-exciting and only has the wire going to the battery, and the three-wire has two blade terminals in addition to the battery wire; one terminal is used for the battery light/gauge, and one terminal is used to excite the regulator.

This two-wire model our trucks use (which I'm pretty sure applies to at least everything '88-'95, since the plug is part of the wiring harness)has the battery wire, and one wire going to the the little plastic plug that clips onto the alternator. They are internally regulated. After some reading I did find the answer I was looking for, so I'm going to share it here for anyone else who might need to know.

The wire that goes into the regulator plug comes from the battery warning light (not necessarily the gauge). When the key is turned on, the warning lamp receives 12v switched power from the battery, and the ground from the bulb is connected to the one wire running to the alternator. The bulb adds a load to the circuit, so its not an exact 12v at the actual regulator plug; I measured on my actual truck, and with the key on you should get 10v. Voltage from the battery light actually excites the regulator.

So, when the key is off, the light doesn't receive any power and stays off, and the regulator doesn't excite. When the key is on, voltage runs through the battery lamp, illuminating it, and grounds through the regulator, exciting it. Once the engine cranks, +12 volts is still applied to the battery light, but the action of the regulator feeds back +12 volts to the other side of the lamp when the regulator is activated and the alternator is in charge mode. With 12+ applied to both sides of the lamp, no current flows and it doesn't illuminate. Thats why if the regulator fails or the alternator doesn't produce a charge, the light will illuminate; the balancing voltage won't be sent back to the bulb to keep it from illuminating.

For my retrofit application, I'll have to wire up that one wire to the GEN light in the dash; I thought I had it that way, but over the course of 35 years its possible the bulb is history. So an interesting note; if the regulators in these alternators aren't being excited, it could possibly be caused by the battery warning lamp bulb going out in the cluster. For anyone who stumbles across this thread in a search, just watch for the battery light to come on when you turn the key on without starting.

My Chevys (I.E. What I'm Asking About)
------------------------- -------------
-1988/1989 C/K1500 5.7L w/700R4 ('88 C Body, '89 K Everything Else)
-2003 Avalanche Z71, Auto, 4x4


Edited by Majoraslayer on 11-27-13 08:19 AM. Reason for edit: No reason given.

 
0utlaw 
Very Senior Member
Posts: 2794
0utlaw
Loc: US East Coast
Reg: 09-10-02
11-27-13 01:43 PM - Post#2403117    
    In response to Majoraslayer


Hope we helped. By now, I bet you got it working fine. OUTLAW



 
Majoraslayer 
Member
Posts: 318
Majoraslayer
Age: 33
Loc: Tennessee
Reg: 02-22-04
11-27-13 03:40 PM - Post#2403139    
    In response to 0utlaw

It seems to be working great now. I appreciate everyone's input! The main difference between the alternator on these trucks and the older three-wire alternators is that the two blade terminals are essentially combined into one pin for the plug, and the battery lamp itself excites the regulator. I wired it up, started up the car, and tested again with my alternator tester; it passed with 14.6 volts.

Thanks again!

My Chevys (I.E. What I'm Asking About)
------------------------- -------------
-1988/1989 C/K1500 5.7L w/700R4 ('88 C Body, '89 K Everything Else)
-2003 Avalanche Z71, Auto, 4x4


Edited by Majoraslayer on 11-27-13 03:44 PM. Reason for edit: No reason given.

 
King Neptune 
Silver Supporting Member
Posts: 2
King Neptune
Loc: SW USA
Reg: 06-14-21
06-17-21 10:08 AM - Post#2821722    
    In response to Majoraslayer

Got a question for the group. It has been interesting to read all the posts about alternator issues, although they all seem a number of years old now (2013). None of them, however, exactly describe the problem I’m having.

For background, I’m trying to troubleshoot a charging system problem. I have an ’85 Chevy K10 with A/C. The engine is a 350, and I’ve recently replaced the alternator with a 150A alt from Summit. It’s a modern one-wire, internally regulated alt. I’ve also replaced the battery, an Optima Red Top.

Here are the issues. With the engine off, I measure 12.38V. There’s a two-conductor plug going into the side of the alternator, with one red and one brown conductor. I unplugged this from the alternator to make the measurements. On these I measure 12.38V and 0.0V respectively.

With the engine at idle, 550 rpm, I measure a battery voltage of 14.32V, and the red and brown (plug on the alt still disconnected) read 14.29V and 13.51V.

Now with the A/C on, I get 12.60V at the battery, and 12.42V & 11.11V at the connector.

Next I disconnected the battery at the negative post. Voltages measured, in the order I listed above, were 11.8, 11.93, and 10.69.

I find it really surprising that the alternator, at 150A, cannot seem to carry the whole load.
I’m at my wit’s end trying to figure this one out.




Edited by King Neptune on 06-17-21 10:44 AM. Reason for edit: No reason given.

 
Shepherd 
Frequent Contributor
Posts: 2305

Loc: Lake George, NY
Reg: 11-11-15
06-17-21 11:44 AM - Post#2821726    
    In response to King Neptune

How big is the pulley? How much amperage is it putting out ac on at 12.6v. Remember as the load goes up, and more amps are required, the voltage will drop.



Edited by Shepherd on 06-17-21 11:46 AM. Reason for edit: No reason given.

 
King Neptune 
Silver Supporting Member
Posts: 2
King Neptune
Loc: SW USA
Reg: 06-14-21
06-17-21 03:26 PM - Post#2821738    
    In response to Shepherd

Standard pulley, V-belt driven.

A very good question about the current, but I have not measured it. Yet. I'll do that this evening when the weather cools off a little.

I'll take two readings, both from the alt. output: one with the A/C off, and the other, on. The battery will be disconnected in both cases.



 
Shepherd 
Frequent Contributor
Posts: 2305

Loc: Lake George, NY
Reg: 11-11-15
06-17-21 05:08 PM - Post#2821740    
    In response to King Neptune

Do not disconnect the battery when checking this.



 
65_Impala 
Very Senior Member
Posts: 4797

Reg: 12-29-02
06-20-21 07:03 PM - Post#2821878    
    In response to King Neptune

The voltages on the disconnected plug don't mean anything.

Do not disconnect the battery to test.

Check the voltage at the main output stud of the alternator with the AC on. Measure between the alternator case and the stud.



 
Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

18763 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.01 seconds.   Total Queries: 10   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 06:09 AM
Top