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What controls alternator output? Maggie'd 98 vert.
As in the title - What controls the output of the alternator? I thought that the PCM had some control of this, but after reading I find this is not the case. Or am I wrong?
I have blown the fusible links in my starting circuit. Again. Battery tested fine, need to retest the alternator (again), but this is a recurring problem.
I've looked at the schematic posted here in searches, read a lot of posts, and cannot find the answer. This is a sporadic problem. Car runs fine for weeks, then voltage drops off (after the links blow) and I end up stranded somewhere (or my wife does - it's her car). I'm kind of at my wits end.
As in the title - What controls the output of the alternator? I thought that the PCM had some control of this, but after reading I find this is not the case. Or am I wrong?
I have blown the fusible links in my starting circuit. Again. Battery tested fine, need to retest the alternator (again), but this is a recurring problem.
I've looked at the schematic posted here in searches, read a lot of posts, and cannot find the answer. This is a sporadic problem. Car runs fine for weeks, then voltage drops off (after the links blow) and I end up stranded somewhere (or my wife does - it's her car). I'm kind of at my wits end.
Help....
Scatter'd
The output is controlled by the voltage reg. that is internal in the alternator. If your burning up the fuseable links something is grounding to cause them to blow.
The output is controlled by the voltage reg. that is internal in the alternator. If your burning up the fuseable links something is grounding to cause them to blow.
A short to ground would do it, but it would be most likely be some where at/near the starter in order to pull too much current thru the fusible links. I don't see how an internal alternator short would do it. I'll have to think about that.
The PCM does not control the output, it only monitors the Duty Cycle that the regulator does to turn the alternator OFF and ON to control the charging voltage.
I did a full write up the other day to explain how alternators work and then more specifically how the C5 ones work. I was going to create a Thread to provide that.
The regulator in the alternator controls the alternator output voltage. The PCM provides a 10V current limited source to the L terminal when the key is turned-on. The current is used to "kick-start" the alternator and engage the regulator once the alternator begins rotating. All this is rather pointless for your issue though since the alternator is not capable of sourcing enough current to blow the fusible link.
I expect that the charging wire has a bare spot somewhere between the starter and the alternator that randomly shorts to the engine or a bracket on the engine.
The output stud of the alternator is connected to the diodes of the bridge rectifier. The parts are solidly mounted inside and plastic is used as the insulator. It's not very likely the assembly would suffer from intermittent shorts.
There are TWO alternator wires that connect DIRECTLY to the battery (Starter Solenoid BATT Terminal). The large BATT terminal on the back of the alternator and the small red wire on pin D. That is the feed back line to the alternator regulator. Both connect to the starter solenoid.
They are BOTH inline fused. If they are blowing, I would UNRAP the harness at the back of the engine and the one that runs down the drivers side of the engine and the harness that lays on top of the engine between the intake manifold and the head. They both get damaged and that could be your issue.
The one that lays on top of the engine between the intake manifold and the head bends around at the back of the engine and I've seen damage there..
Last edited by Bill Curlee; 11-20-2015 at 03:06 PM.
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.
The Gray wire (terminal C) just sends a signal to the PCM as to how the alternator is performing. This is called a Duty Cycle signal. The Regulator controls the output voltage of by turning the alternator OFF and ON to control the voltage. The PCM only monitors this and will throw a DIC Charging Fault message and code if it detects performance outside of preset parameters.
The Red wire (terminal B) from the PCM is called the “Turn On” signal. 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. As said before, 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.
Some common issues people have when replacing C5 alternators.
1. Many GM regulators look like the C5 ones but are not correct.
2. 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.
3. People get an alternator but it needs more PCM “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. These alternators are most likely similar to those in #1 above.
4. 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.
NOTE:
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. 145 amp ones can be used in all years.
6. Valaeo, a French company, was the supplier to GM for the C5. I think some were made by them in Mexico.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Nice write-up Sam.
The only thing I see that may need re-examination there is:
145 amp ones can be used in all years.
Although technically the 145A units will "work", meaning they physically mount up and charge, the pcms in the early cars go nuts and constantly kick on the "CHARGE SYSTEM FAULT" warning message in the DIC. Those pcms, which monitor alternator activity, are not expecting to see the duty cycle and/or output from a 145A alternator, will not "allow" the 145A units to be used in the early cars.
I wish that were not the case, as I would love to use the later, higher output unit in my '99.
Duty cycle is just a 0-100% PWM signal. There is nothing in the car that measures the alternator output current. So, there is no way the PCM can know that 100% duty cycle has changed to represent 145A instead of 110A.
Last edited by lionelhutz; 11-21-2015 at 11:48 AM.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Originally Posted by lionelhutz
Duty cycle is just a 0-100% PWM signal. There is nothing in the car that measures the alternator output current. So, there is no way the PCM can know that 100% duty cycle has changed to represent 145A instead of 110A.
Regardless, the 145A alternators will simply not work in the earlier cars, without generating a constant and ongoing warning message of: "CHARGE SYSTEM FAULT".
Regardless, the 145A alternators will simply not work in the earlier cars, without generating a constant and ongoing warning message of: "CHARGE SYSTEM FAULT".
BTDT
Where did the alternator come from? I'd bet money you had a problem besides installing a properly working 145A alternator.
There were some stupid claims here in the past that a 145A gives a 145A PWM signal which goes past the 110A alternator PWM signal. But that is hogwash because it's not how a PWM signal works. A PWM sginal can only go from 0% to 100% duty cycle. Both alternators will give the same PWM signal varying between 0% and 100% depending on how much voltage is applied to the field winding. The signal is the same for both alternators - 0% when the field has no voltage applied up to 100% when the field has battery voltage applied.
Don't you tune your car? Just turn off the F terminal in the system settings and the problem goes away. If it still doesn't work then the alternator you're trying to use is defective.
Last edited by lionelhutz; 11-21-2015 at 11:37 PM.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Originally Posted by lionelhutz
Where did the alternator come from? I'd bet money you had a problem besides installing a properly working 145A alternator.
And you'd lose that bet. One came from GM (new 145A, NOT rebuilt) and two (180A also new) came a well known aftermarket manufacturer of high output alternators who claimed up and down they should work. NONE of'em did. I put the original OE unit back on the car and no more issues.
Like I tried to tell you before, BTDT, but you know best!!
The problem plaguing replacement C5 alternators is the L circuit. The circuitry in the PCM that feeds the L terminal of the alternator doesn't provide enough current to energize certain aftermarket regulators. The manufacturers build an alternator designed to work with a light bulb because they copy other alternators which use a light bulb. But, the end result is an alternator incapable of properly working with the current limited 10V circuit in the PCM.
The F or PWM circuit is nothing special. The CS130 and CS144 alternators have the same PWM terminal which works the same way.
Is the aftermarket alternator you're talking about the Billet Tech alternator? I've seen group buys running and they have been around here a fair bit. There are many people running the 170A Billet Tech in 2000 or older cars. Some get the charge system fault message intermittently when they start their car but once they rev the engine a bit the alternator starts charging and works fine. That rev is required because of the L circuit, not the F circuit. The same thing happens on 2001+ car so it's not an issue unique to the older C5's or the 97-00 PWM F circuit.
I also saved a link to www.nationsautoelectric.com since some people are successfully running their 240A alternators, even in pre-01 C5's.
If you're believing the posts about the PWM duty cycle going over 100% as the alternator current goes above 110A which causes a charge fault, then too bad for you being sucked in by such stupid BS. It is NOT POSSIBLE for the duty cycle of a PWM signal to go above 100%. Then, there's the small fact that the PWM signal represents the voltage applied to the field winding, NOT the charging current. But hey, believe what you want....
Last edited by lionelhutz; 11-22-2015 at 02:46 AM.
LoneStarFRC, I am doing some research on the different years and how the Duty Cycle feed to the PCM varies to create P01638 and give the Charging Fault message. There are differences I did not know existed.
There is a another thread about the C5 alternators that's simultaneously going on here on the C5 Tech area.
I think reading both of them gives a better perspective on the subject because they complement each other. This particular post brings some interesting details to the table.
LOL, I already knew he was full of crap but I unblocked him just to find more. What a waste of time.
First strike, it's a Valeo alternator, not a CS130D.
Second strike, he's implying the L & F is different only on the 00 & 01 cars and they are the only ones with replacement alternator issues.
Third strike, he found another schematic besides the one he claimed he found earlier in the thread. Yet, I bet he will never produce either of these schematics he claimed he has found.
Fourth strike, the L terminal doesn't have anything to do with ramping the output voltage of the alternator when then the car is started. The regulator circuitry itself is built to ramp-up the field voltage as it turns on. It's likely called something like soft-starting. If you actually search for regulator IC's you will find this is a feature you can get in different regulators. The PCM in a C5 has NO, ZERO, ZIP, ZILCH control over the charging voltage of the alternator. Besides all this, i have no idea what the sudden loading of the alternator has to do with the belt drive. It was basically added due to variations in engine speed causing harmonics in the belt drive.
Fifth strike, he also claimed the L circuit is special and that has 0 current flow. Well, explain this. PCM produces 10V on L circuit without the alternator connected. The alternator has 0V on L terminal without PCM connected. Then connect them and the voltage on the L circuit becomes something like 0.5V. So the PCM voltage is pulled down to 0.5V while the PCM being connected to the alternator puts 0.5V onto the alternator terminal. I bet he can't produce any kind of circuit description which duplicate that result without any current flow.
Sixth strike. He claims the regulator doesn't switch the L terminal to ground if the regulator detects a fault. Odd because the write-up in many different years of service manuals specifically say it does.
Seventh strike. His crap about why aftermarket alternators need to be revved is wrong. It's not because the regulator is leaking current. It's because the L circuit is providing a small amount of current to the field, except the current is too low and creates too weak of a magnetic field on the rotor to "kick-off" the alternator at an idle. At least he got the rpm vs magnetic field strength part right. Once a higher rpm is reached, the weak magnet field in the rotor cuts through the stator coils faster which produces a higher AC output voltage and eventually the regulator sees enough AC voltage on the stator to switch-on and begin supplying a current to the field to regulate the field.
He also goes on about how the proper alternator keeps the voltage in the 13V to 14V range which is better than 14.5V continuously. Now, 14.5V could be a wee bit high, but if you posted a poll I bet MANY members here wish their alternator would maintain around 14.2-14.4V regardless of the electrical load on the car.
Ok, I'm just going to block him again and try to never read anything else he might post.....
Guys I finally 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 tell there are only two things that can create the Charge Fault message 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.
11-20-2015, 11:16 AM
What controls alternator output? Maggie'd 98 vert.
