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Alternator Design and Issues

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Old 05-23-2016, 10:25 AM   #1
dadaroo
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Default Alternator Design and Issues

I put this together to try and provide factual information. If anyone finds an issue I will be glad to correct.


How alternators work.

The alternator has a Rotor in the center with wire windings that spins on two bearings. Surrounding that is the stationary Stator with its own windings that you can see through the air cooling openings. If adequate DC voltage and current is applied to the Rotor while it spins it creates a rotating magnetic field and that induces an AC voltage and current in the Stator. This is called “flashing” the field in the Stator. The alternator has a regulator that converts this AC output into DC for charging.


Here is how the alternator works in the C5. Also refer to the schematic below.


Big picture, the large Red wire on the far left in the schematic below is the DC voltage output from the alternator to charge the battery, via the starter. The smaller Red wire (terminal D) to the right of it is used to monitor that voltage there and provide “feedback” to the alternator regulator in order for it to provide (regulate) the correct charging voltage.

The 2 wires (Gray and Red) on the right are interfaces with the PCM (Powertrain Control Module).

The Red wire (terminal B) from the PCM is called the “Turn On” signal and is also called the L terminal. The PCM provides this when you turn the ignition to ON. It is just DC voltage and current that is fed to the alternator Rotor which is the part that spins. As it spins it creates a rotating magnetic field that produces an AC voltage and current in the Stator which is stationary. The regulator senses that the Stator is producing voltage and now takes over control. It also converts the AC to DC. Some of this DC is now used to power the Rotor while most of it is used to provide the charging voltage. The regulator also can turn OFF and ON the alternator output to regulate the charging voltage. It does this by turning OFF and ON the power it provides to the Rotor. This aspect is discussed next.

The Gray wire (terminal C) just sends a signal to the PCM as to how the alternator is performing. It is also referred to as the F terminal. This is called a Duty Cycle signal which is a Pulse Width Modulated (PWM) signal. The Regulator controls the output voltage by turning the alternator OFF and ON to control the voltage. This Duty Cycle signal can be from 0 to 100% with 100% being the regulator has the alternator fully “ON” providing voltage and 50% would mean it is “OFF” half the time.. The PCM only monitors this and will throw a DIC Charging Fault message and code P1638 (99-04) if it detects performance outside of preset parameters. I can’t find where 97 and 98s show this code in their FSM (Factory Service Manual).





The only thing controlling the current output of the alternator are the loads throughout the car. Based on the loads the alternator will provide as much current as it was designed to do. The regulator just works to try and maintain the correct charging voltage over the range of current loads it experiences. Ohm’s law is at work. Voltage=Current X Resistance.

One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM.


Some common issues people have when replacing C5 alternators.


1. Many GM regulators look like the C5 ones but are not correct.

People get a replacement that does not have the feedback design to the PCM for monitoring the Duty Cycle. This causes a PCM Charging System Fault DIC message but the alternator can still charge the battery.

2. People get an alternator but it does not immediately create “Turn On” voltage or current for the Rotor to activate/flash voltage and current in the Stator. In some cases one has to rev the engine to 1500-2000 rpms before the alternator starts charging on its own.

3. People turn in their core before they get a functioning replacement. That prevents their ability to have theirs rebuilt. This happens quite often as seen here on this Forum.

NOTES:

1. From 97-00 all Automatics had a solid alternator pulley.

2. From 97-04 all Manual cars had a solid alternator pulley.

3. From 01 to 04 the Automatic cars had a Decoupler pulley to help "synchronize" the belt drive system for improved engine efficiency, reduced Noise/Vibration/Harshness (NVH) and increased component life. It helps eliminate the influence of the alternator on the serpentine belt drive. It is kind of like a suspension for your alternator. I have heard GM used them on the automatics to improve idling characteristics.

The alternator decoupler pulley will have a spring and a clutch inside. The internal spring absorbs vibration from the engine belt. The clutch inside the pulley allows the alternator rotor to coast to a stop after the engine has been shut off. The clutch also allows the alternator to spin faster than the engine during hard shifting thus eliminating annoying belt chirping. I can’t say why the manuals didn’t get the design.
Decouplers can to used/added to manuals

4. From 97-02 all C5s were 110 amp. In 03-04 they were 145 amp. Some of the 2002 cars might have been 145 but I can’t confirm.

5. Valeo, a French company, was the supplier to GM for the C5. I think some were made by them in Mexico.

6. 145 amp ones can be used in all years and will charge. HOWEVER, in the 97-00 years they will probably throw a Charge Fault. From 01-04 the PCM Duty Cycle monitoring is the same and not like the earlier years. I plan to use one of my NOS 145 amp Valeo ones to test that theory in my 01 in the near future.

See the following FSM info on PCM Duty Cycle monitoring.

Part Number Information:

I have tried to identify the original GM part numbers for each year alternators. If you find an error please let me know.

From 97-2000 they used a 110amp one with P/N 10246634

From 2001-2002 on Manual cars they used the 110amp 10246634 also.

From 2001-2002 on Automatics they used a 110 amp 10316182 since they used a decoupler. It should have been identical to 10246634 except it had a decoupler.

For 2003-2004 they used a 145 amp alternator. 10305776 for manuals and 10353440 for Autos with decoupler.

Some information says some 2002s came with 145 amp units.

110 amp units use a Valeo Regulator M530

145 amp units use a Valeo Regulator M520

PCM Duty Cycle Monitoring: This was done to try and address Note 5 above.

I know a knowledgeable person who tried to put a new Valeo 145 amp unit in his 99 and it threw a Charge Fault.

I had a chance to go thru every year C5 in my GM database to provide the following information. I make no conclusions from what I found. I am still trying to absorb what I found and did not find.

As far as I could find there are only two things that can create the Charge Fault message which are:

Low voltage or high voltage as detected by the PCM

P1638 related to the Duty Cycle monitored by the PCM

97 and 98:
I could not find any information that P1638 is even a code there. Not listed in the DTCs or diagnostics. I even have access to Prodemand.com database (like Alldata) and found nothing.

99 and 00:

P1638

Circuit Description
The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.

When there is low demand from the electrical system on the generator, a low duty cycle
percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100%. A normally functioning generating system will never reach 100% as indicated on the scan tool.

Conditions for Running the DTC
The ignition switch in the ON position or the engine is operating.

Conditions for Setting the DTC
• The F Terminal indicates a duty cycle not between 10 and 40% with the ignition ON and the
engine OFF or the duty cycle is less than 5% with the engine running.
• All conditions met for 6 seconds.

01 thru 04:

P1638

Circuit Description

The PCM uses the generator field duty cycle signal circuit to monitor the duty cycle of the
generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the Charge System Fault message


Conditions for Running the DTC

Key ON Test
No generator, CKP sensors, or CMP sensor DTCs are set.
• The key is in the RUN position.
• The engine is not running.

Run Test
• No generator, CKP sensors, or CMP sensor DTCs are set.
• The engine is less than 3000 RPM.

Conditions for Setting the DTC
• During the key ON test, the PCM detects a PWM signal greater than 65 percent for at least
5 seconds.
OR
• During the RUN test, the PCM detects a PWM signal less than 5 percent for at least
15 seconds.

Related DTCs:

P0562, P0563, and P1637 can be related to the alternator and charging circuit but I have not included them as I was focusing on Charge System Fault DIC message issues.


Mr. Sam

Last edited by dadaroo; 05-23-2016 at 10:27 AM.
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Old 05-23-2016, 11:09 AM   #2
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Thanks for your time and knowledge !!!
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Old 05-23-2016, 12:55 PM   #3
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WOW!!! THIS has to be a NEW STICKIE!!! Great stuff Sam

Thank you for making this so that even a novice can follow and understand almost all of what you have laid out for us...

Last edited by 73Corvette; 05-23-2016 at 01:11 PM.
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Old 05-28-2016, 09:47 AM   #4
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This could be Sam's last contribution (of Many) to this great forum !!!!
I wonder if God had a Vette problem ????? RIP Dadaroo !!!!!!
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Old 05-28-2016, 11:53 AM   #5
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Quote:
Originally Posted by akapounder View Post
This could be Sam's last contribution (of Many) to this great forum !!!!
I wonder if God had a Vette problem ????? RIP Dadaroo !!!!!!
He will be greatly missed here on the forum. My condolences to his family!

RIP, Mr. Sam (Dadaroo) and thank you for all your contributions!
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Old 05-29-2016, 01:03 AM   #6
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Old 06-13-2016, 06:12 PM   #7
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I've got a replacement alt on my 97 that doesn't create a turn on voltage, any way to fix this short of a 300-400 dollar alternator?
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Old 06-28-2016, 12:56 PM   #8
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Quote:
Originally Posted by Sgt. Spuds View Post
I've got a replacement alt on my 97 that doesn't create a turn on voltage, any way to fix this short of a 300-400 dollar alternator?
It's probably too late, get the OEM alternator rebuilt...
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Old 07-01-2016, 08:50 AM   #9
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Quote:
Originally Posted by Sgt. Spuds View Post
I've got a replacement alt on my 97 that doesn't create a turn on voltage, any way to fix this short of a 300-400 dollar alternator?
YES! I wasn't aware of this till today.... great link.

https://www.corvetteforum.com/forums...post1591319135

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Old 07-17-2016, 11:58 PM   #10
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Old 08-08-2016, 12:19 PM   #11
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I was interested to see this:

"One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM."

I recently noticed when coasting up to a light (6sp) with the AC blazing away - the idle stays higher for a moment or two and then settles back down again. I wonder if this "idle increase mechanism" is at work?
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Old 08-08-2016, 03:58 PM   #12
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Quote:
Originally Posted by jjc508520 View Post
I was interested to see this:

"One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM."

I recently noticed when coasting up to a light (6sp) with the AC blazing away - the idle stays higher for a moment or two and then settles back down again. I wonder if this "idle increase mechanism" is at work?
mine does the same !!!!
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Old 08-08-2016, 08:27 PM   #13
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Probably the throttle kicker. The alternator duty cycle would have only increased once the rpm dropped to idle.
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