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Not too long ago I replaced my alternator. The vehicle has been running with 12 to 13 volts while driving and drops to 11.9 at times. Everything works fine and the car turns over fine even when the volts reads 11.5ish with the key on. I don't know if my cars volt reader is faulty or if the alternator is defective. I think I should see around 14.xx volts while running right?
I left my parking lights on the other night and it killed the battery. Since then the cars been acting up more. It was very hard to get the car to take a charge and start. A test read the the bat is good but charging voltage is low. But the voltage has gone back up to 13ish now and reads normal.. I can replace the alternator under warranty. But not sure if that will fix the issue.
Make sure you have a good fully charged battery before testing charging system.
Check charging voltage across the battery and recheck at the alternator. Difference should be less than .3v. After start up with no loads should be 14+v. It should be 12.8 or higher at idle with loads on. When rpm's are increased it should go over 13v.
If it's low, check the connections at the starter.
Make sure you have a good fully charged battery before testing charging system. Check charging voltage across the battery and recheck at the alternator. Difference should be less than .3v. After start up with no loads should be 14+v. It should be 12.8 or higher at idle with loads on. When rpm's are increased it should go over 13v. If it's low, check the connections at the starter.
Thanks for the response. I did check all connection points including at the starter. I should have mentioned also that I replaced the battery at the same time due to age. This was 7 or 8 months ago. Optima yellow top. I work at a shop and our equipment reads that the bat is good and the charging system is faulty. So it's likely the alternator. But it's just hard to accept I guess seeing how it's brand new. It could maybe be an issue in the wiring since it's the second time this year.. Since it's free, I'll just replace the alternator under warranty.
But if the voltage stays low. What should I be looking for?
I remember reading on this forum sometime back that the vette alternator has some different stuff that a regular alt. doesn't, did you have the old one rebuilt or did you just replace it. This may not have anything to do with your problem but just remember reading that post. Good luck with the fix, let us know what U find
bjones7131 is correct that the C5 alternator is unique since it has an interface with the PCM as shown below. However I don't think that is your issue. Most of those issues result in Charge System Fault indication.
WHY did you replace the alternator in the first place?
bjones7131 is correct that the C5 alternator is unique since it has an interface with the PCM as shown below. However I don't think that is your issue. Most of those issues result in Charge System Fault indication. WHY did you replace the alternator in the first place? Charging System
I was having the charge system fault warning the first time. Not this time. Just stays below the necessary volts at all speeds and rpms it seems.
Many auto batteries do not take well to complete (deep-cycle) discharge, it can kill a battery for good. AGM batteries take a different setup to bring them back from the dead than just jumping them.
Put the ground of your meter on a clean spot on the engine block and then check the voltage at the alternator output stud and both terminals of the battery.
The stud and battery positive should read very close to the same voltage which should be >14V if there is little load on in the car. Heck, even with the headlights and AC running my car still has >14V at these points.
The negative terminal of the battery should read essentially 0V.
The new alternator is in, but I think I know the issue now. When cold, the volts read at 14.2. As I drive the volts gradually drop to the low 13s as the vehicle heats up. I've done a few cold starts now and it's the same. The volt reading is getting weaker as the vehicle heats up.
Also, they tested the one I turned in and said it was fine.
Not sure if that means the problem is in my wiring or something. Or if these crappy dura-last alternators have an issue with holding up to the C5s needs
Look at the charging system schematic provided. There is a FEED BACK CIRCUIT on the small red wire on ( PIN "D" )
That wire MUST provide proper system voltage to the alternator. Disconnect the connector on the alternator and read that pin to a proper engine ground and then a chassis ground. Compare it to direct battery terminal voltage when the car is HOT (Full Operating Temp)
List what each reads..
To get a full picture, you should actually read the resistance of that wire on PIN "D" END TO END. Its a FUSE LINK and they have been known to cause a voltage drop if they have ever been damaged or are heat soaked.
The other BATT Terminal to battery voltage test/readings that were recommended are also very important and help diagnose the problem.
You can connect a jumper wire DIRECTLY to the POS Battery terminal and to the BATT terminal on the back of the alternator.
If the charging voltage increases with the jumper attached, the wiring between the battery and the alternator or at the solenoid is compromised and causing a voltage drop. You can also disconnect the battery and read the resistance from the POS terminal to the alternator.
I pray that you are NOT using the IPC volt meter and or the DIC Digital volt meter as an indication of actual charging system voltage. IT DOES NOT provide you an accurate CHARGING SYSTEM VOLTAGE!
It provides you the voltage that the PCM, BCM, IPC ect etc sees "AFTER THE IGNITION SWITCH on the HOT in RUN and Start buss!"
If your battery voltage read 14.5 VDC and the IPC volt meter reads 13.0 VDC, the voltage drop is in or at the ignition switch/connectors.
Look at the charging system schematic provided. There is a FEED BACK CIRCUIT on the small red wire on ( PIN "D" )
That wire MUST provide proper system voltage to the alternator. Disconnect the connector on the alternator and read that pin to a proper engine ground and then a chassis ground. Compare it to direct battery terminal voltage when the car is HOT (Full Operating Temp)
List what each reads..
To get a full picture, you should actually read the resistance of that wire on PIN "D" END TO END. Its a FUSE LINK and they have been known to cause a voltage drop if they have ever been damaged or are heat soaked.
The other BATT Terminal to battery voltage test/readings that were recommended are also very important and help diagnose the problem.
You can connect a jumper wire DIRECTLY to the POS Battery terminal and to the BATT terminal on the back of the alternator.
If the charging voltage increases with the jumper attached, the wiring between the battery and the alternator or at the solenoid is compromised and causing a voltage drop. You can also disconnect the battery and read the resistance from the POS terminal to the alternator.
I pray that you are NOT using the IPC volt meter and or the DIC Digital volt meter as an indication of actual charging system voltage. IT DOES NOT provide you an accurate CHARGING SYSTEM VOLTAGE!
It provides you the voltage that the PCM, BCM, IPC ect etc sees "AFTER THE IGNITION SWITCH on the HOT in RUN and Start buss!"
If your battery voltage read 14.5 VDC and the IPC volt meter reads 13.0 VDC, the voltage drop is in or at the ignition switch/connectors.
good answer Bill! I think after reading that he could also jumper from battery positive to the sensing terminal at the alternator and see if the charge voltage increases.
The new alternator is in, but I think I know the issue now. When cold, the volts read at 14.2. As I drive the volts gradually drop to the low 13s as the vehicle heats up. I've done a few cold starts now and it's the same. The volt reading is getting weaker as the vehicle heats up.
Where to start with this?
In my experience, this is completely normal. Your alternator will not charge at 14+ if not needed. The charging range you are describing is how your system should be acting with a good alternator, good wiring and a good battery. 12.6 volts is considered a full charge on a 12 volt battery. Now, if you are falling into the low 12 range or even 11's on the DIC or a meter then you need to start looking for problems. It could be any number of things. I would start with alternator. You have. Next the battery. Check. Then the wiring. The readings you get with a meter either on the alternator post or the battery post will be .3-.5 volts higher than your DIC indicates but will stay relevant to each other.
I am running a 300 amp alt from DC Power and it is running 1 Die Hard Platinum and 2 Red Tops, through a Perfect Switch Dual Rectifier Isolator with 0 gauge run directly from the alternator to the isolator. All of this is running everything normally in the car + almost 5000 watts of Old School TRUE WATT amplifiers fused at 550 amps, not todays "phony wattage". I did have my alternator built without the de-coupler pulley as I feel it is a weak link. It is not a true sprag de-coupler pulley as someone on here suggested recently. It is a clutch type decoupler that can and will get weak over time. A weak de-coupler will also get weaker with temp increase. My voltage readings are just about like yours. I KNOW that I am getting maximum charging because when I put full load on the system I have zero light dimming and the DIC indicates a .1 volt drop at most. The alternator is responding almost immediately. At cold crank in the morning, I get 13.7 to 14.2 on my DIC and 14.2 to 14.7 under the hood. Within 30 minutes I am reading 13.2 to 13.6 on the DIC and 13.6 to 14.0 under the hood. But keep in mind, it takes a fair amount of power just to turn on the amps along with all of the regular accessories in the car.
Why don't you post exploded pictures of the "clutch" that is in the decoupler pulley. It seems you don't understand how friction works when metal is sliding against other metal instead of grabbing and locking together...
I just cleaned the main connections under the hood a few months ago. After an hour of driving my voltage reading on the DIC is still 14V with the HVAC, aftermarket stereo + amp and 100W headlights on. The only time I see the voltage start to drop is with the above plus the the high speed fans when idling and that is likely caused by the 25% under drive damper.
With the Duralast alternator it's possible they used a lighter gauge of wire in the stator or rotor and the alternator internal voltage drops are higher when it is hot. You can't get any more output from an alternator once you apply full-voltage to the field.
Last edited by lionelhutz; 11-01-2014 at 11:26 AM.
lionelhutz, I posted links and even a video. The clutch is NOT A ONE WAY SPRAG CLUTCH. Get it or don't get it. I don't care. The clutch can and will wear to a point where increased load will cause it to slip but still spin some and only let the alternator partially charge at the rate it is supposed to. I posted links to the clutch and also a video in this thread.
As far as you seeing 14V continuous, if it were my car, I would think something was wrong somewhere. The DIC doesn't display battery voltage when the car is running. It displays alternator charge voltage. If my alternator was continually trying to put out 14V it would tell me that I had a wiring problem, alternator problem or battery problem. If your alternator is continually sending 14V to a good battery...your battery is not long for this world...
So it's not necessarily a bad thing that it reads less volts? I just remember it was ways around 14+ volts when I got it. But maybe the type of battery affects that. I went from a diehard to an optima yellow top. This is considered a deep cycle bat, so maybe it doesn't need a lot of charging volts continually..?
The new alternator is in, but I think I know the issue now. When cold, the volts read at 14.2. As I drive the volts gradually drop to the low 13s as the vehicle heats up. I've done a few cold starts now and it's the same. The volt reading is getting weaker as the vehicle heats up.
Where to start with this?
Originally Posted by NukeC5
So it's not necessarily a bad thing that it reads less volts? I just remember it was ways around 14+ volts when I got it. But maybe the type of battery affects that. I went from a diehard to an optima yellow top. This is considered a deep cycle bat, so maybe it doesn't need a lot of charging volts continually..?
That could very well be the case. If the battery doesn't require 14V and your wiring is good, you will not see 14V on the DIC.
Do you have a picture that shows this 1-way clutch that isn't a sprag design or not?
A decoupler pulley on an alternator basically has of a 1-way sprag-type clutch and a spring coupling the pulley to the shaft to absorb some or the belt drive harmonics. If the sprag isn't locking then it's sliding metal on metal.
I'm also going to stick with the 14V and ignore your advice about my charging voltage.
10-30-2014, 01:09 AM
Defective alternator?
good answer Bill! I think after reading that he could also jumper from battery positive to the sensing terminal at the alternator and see if the charge voltage increases.
