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I just swapped the regulator in my alternator from 4 pin to 2 pin, so now it's like a 2006 or newer alternator. Why??? Because GM thinks it's better than the older 4 pin one and they must know something.
Oh but everyone says you need a late model 2006+ ECM/BCM to run it or it only gives you 13.7 volts. Not necessarily.
Here's the secret why GM puts it in later model cars. The computer can command the alternator to put out any voltage from 11V to 15.5V.
Before the late model engine is started, and also after its shut off, GM can check the condition of your battery. Then they can decide how to charge it and they command the alternator to put out the voltage needed to maintain the battery. Also, the alternator tells the computer if it's having trouble putting out the voltage that the computer commanded. To help the alternator, the computer might raise the idle speed for example.
The L pin is the command voltage pin. A 5V PWM signal is sent from the ECM/BCM at a frequency of 128hz. If the duty cycle is less than 10% or more than 90% or just plain not connected, the alternator will go into default mode and put out about 13.7 volts. Enough to keep your car running, but not enough to charge the battery well. Here are the voltages and duty cycles:
10% = 11.0 V
20% = 11.56 V
30% = 12.12 V
40% = 12.68 V
50% = 13.25 V
60% = 13.81 V
70% = 14.37 V
80% = 14.94 V
90% = 15.5 V
The F terminal is also a PWM signal. But it's put out by the alternator and read by the computer. The lower the duty cycle the easier the alternator is working. If you want to use the alternator and aren't connected to the correct ECM/BCM then you don't need to connect the F terminal.
It remembers the last setting even after it's turned off so once you set it, that's where it will stay. Set the frequency to 128 and then set the duty cycle to whatever voltage you want the alternator to put out. Let's say you're at the track and you want a little more voltage for you fuel pump and coils. Easy. Just raise the duty cycle. Or you left the lights on and your battery is low.... Easy.
Here's how you wire it:
Ignore the Power input -. Apply 5V to the Power input + terminal. You can probably use the 5V signal from the ECM. The PWM controller takes very little power. Connect the ground to signal ground and connect the PWM out to the L terminal of the alternator.
Now go pull that 2 pin alternator out of the trash bin.
7/2021 update. I upgraded my alternator to one of the newer, higher efficiency, higher current, 6 phase hairpin winding designs in anticipation of the higher demands of my new more powerful radiator fan setup and getting my A/C in order. It's controlled by the same 2 pin connector so the PWM generator will work great with these as well. Lots of folks with huge stereo loads are using these alternators for their extra capacity and smoother DC (6 phase) and now they can control them with the PWM generator as well.
Last edited by LSswap; 07-24-2021 at 09:51 AM.
Reason: update
is that a gen 2 i pod in the middle? lol what beats you jammin to?
I'm jamming to the heartBEAT of america... Chevrolet. LOL
Nah, it's a tiny scope that has a similar case to the ipod. Another Ebay find $40.
Originally Posted by WFO_SS
surely this could be useful on aftermarket ecm's, no? holley dominator, etc.
Absolutely yes.
To be honest, I don't need that PWM generator in my car. I drive it directly from my DIY 4L80E/car controller.
I don't have a Holley... however... You would need a 5V PWM. I know Holley can put out a 12V PWM and also a ground sourced PWM. But I havn't seen if it can put out a 5V pwm. But I would bet that you can use the 12V PWM with a pair of resistors to make it work with the Holley. Or a resistor and a zener diode. I can draw up a diagram if someone wants to try it.
I'm jamming to the heartBEAT of america... Chevrolet. LOL
Nah, it's a tiny scope that has a similar case to the ipod. Another Ebay find $40.
Absolutely yes.
To be honest, I don't need that PWM generator in my car. I drive it directly from my DIY 4L80E/car controller.
I don't have a Holley... however... You would need a 5V PWM. I know Holley can put out a 12V PWM and also a ground sourced PWM. But I havn't seen if it can put out a 5V pwm. But I would bet that you can use the 12V PWM with a pair of resistors to make it work with the Holley. Or a resistor and a zener diode. I can draw up a diagram if someone wants to try it.
Is the signal to the L terminal pwm+ or pwm-? I have a Dominator and there is no option for a 5v pwm signal, only 12v, either PWM- or PWM+
Is the signal to the L terminal pwm+ or pwm-? I have a Dominator and there is no option for a 5v pwm signal, only 12v, either PWM- or PWM+
Andrew
There are ways to wire up either the PWM+ or PWM- port on the Holley, but it will be easier to use the PWM+. 5V zener Diode
The zener diode is 35 cents quantity 1.
Here's how I would try it. Keep in mind I've never seen or smelled a Holley. I'm fairly confident it should work.
Hey, good information. Thanks for sharing. I've always wondered how the PWM alternators operated.
This would be a great solution to keep the same alternator, but keep in mind this will give you the performance of a one wire alternator without the simplicity. The voltage won't adapt with load so you will see voltage fluctuations as things turn on and off.
One question, why not power it with 12V rather than trying to source a 5V?
Good stuff here. Someone either needs to bump this thread everyday, or make it a sticky.
I spent a lot of time looking for good info about wiring up my alternator. So many threads, and so much confusion. I didn't feel I got a straight answer as to which one I had and how they work. I'm not one for just blindly listening to someone say hook this here and your'e done, I need to understand why. There is alot of incorrect information about a topic that doesn't need to be complicated.
Originally Posted by Che70velle
Just read through your Corvette build thread. You sir are a genius. Absolutely amazing electronics work in that C3.
I havn't let the cat out of the bag on some stuff I'll be testing on the Vette.
Originally Posted by gofastwclass
Nice work man, thanks for sharing!
The little PWM gizmo would be good for testing lots of things like PWM fan controllers and flex fuel sensors too. Guess what just got ordered?
Actually I already did a thread about that PWM module and fan controllers. I never thought about it for E85 sensor, but that would work. It's an easy tool to use as technology in our cars goes more digital.
Originally Posted by Pop N Wood
Hey, good information. Thanks for sharing. I've always wondered how the PWM alternators operated.
This would be a great solution to keep the same alternator, but keep in mind this will give you the performance of a one wire alternator without the simplicity. The voltage won't adapt with load so you will see voltage fluctuations as things turn on and off.
One question, why not power it with 12V rather than trying to source a 5V?
Sorry, you are incorrect. The voltage will adapt to load as things go on and off. The PWM to the alternator is like a command... "Give me exactly 14.5 volts!!!" The regulator inside the alternator has it's own separate PWM to control the field coils, to automatically adjust everything internally so it puts out the commanded voltage no matter what. The only time it won't be able to maintain the commanded voltage, as with any other alternator is when it's turning too slow.
Virtually all alternators are PWM controlled internally. This one has an additional PWM input, externally, to tell it what voltage to put out.
The 5V is not power. It's more an instruction or a command. I have not tried it with 12V. It might work or it might destroy the regulator. Let us know if someone gets it working with 12V.
Well, I've never thrown away one of those alternators, but I have removed them from a couple of low mile engines for swaps for simplicity reasons, so I'm sitting on a couple of real good ones. Finally a use for them, I'll have to try this out! Thanks for posting this!
I spent a lot of time looking for good info about wiring up my alternator. So many threads, and so much confusion. I didn't feel I got a straight answer as to which one I had and how they work. I'm not one for just blindly listening to someone say hook this here and your'e done, I need to understand why. There is alot of incorrect information about a topic that doesn't need to be complicated.
I havn't let the cat out of the bag on some stuff I'll be testing on the Vette.
Actually I already did a thread about that PWM module and fan controllers. I never thought about it for E85 sensor, but that would work. It's an easy tool to use as technology in our cars goes more digital.
Sorry, you are incorrect. The voltage will adapt to load as things go on and off. The PWM to the alternator is like a command... "Give me exactly 14.5 volts!!!" The regulator inside the alternator has it's own separate PWM to control the field coils, to automatically adjust everything internally so it puts out the commanded voltage no matter what. The only time it won't be able to maintain the commanded voltage, as with any other alternator is when it's turning too slow.
Virtually all alternators are PWM controlled internally. This one has an additional PWM input, externally, to tell it what voltage to put out.
The 5V is not power. It's more an instruction or a command. I have not tried it with 12V. It might work or it might destroy the regulator. Let us know if someone gets it working with 12V.
Is this not similar to what the S terminal does on the older 4 pin alternators?
Also, do you know the exact strategy that is used to control the output voltage? In other words, under what conditions (I assume there are many) would the BCM command different duty cycles? I am just trying to think through how this might be implemented with the Holley ECU. For instance, for fan control I set up a table with coolant temp on one axis and speed on the other and the cells are populated with duty cycle to control fan speed.
Well, I've never thrown away one of those alternators, but I have removed them from a couple of low mile engines for swaps for simplicity reasons, so I'm sitting on a couple of real good ones. Finally a use for them, I'll have to try this out! Thanks for posting this!
That's what this thread is all about.
And for those of you who are a little more adventurous.... you could also drive this with an Arduino nano ($3) and a potentiometer instead of the PWM generator. Wiring is almost as simple and I'll write the program and post it here if anyone is interested. Then you could have the alternator set to a real low output for some time to keep the alternator from trying to compensate to very low battery voltage while the starter is on and then work it's way up to the voltage you have dialed in with the potentiometer. This is a great project for those of you who have always wanted to get your feet wet with Arduino.
Also, do you know the exact strategy that is used to control the output voltage? In other words, under what conditions (I assume there are many) would the BCM command different duty cycles? I am just trying to think through how this might be implemented with the Holley ECU. For instance, for fan control I set up a table with coolant temp on one axis and speed on the other and the cells are populated with duty cycle to control fan speed.
Andrew
Andrew.
I figured you'd be the first to try this with the Holley.
I don't have an ECM/BCM but I've read their strategy is very complex, I think it's called Regulated Voltage Control (RVC)..... takes into account batter temperature and whatnot. I don't think there is enough flexibility in the Holley or any aftermarket engine management to fully mimic this strategy.
If I were configuring something like a Holley, I would try a table where below idle RPM, it's low duty, then as you approach idle, it works it's way up to a modest duty. Then as you are in reasonable RPM, your full desired duty. This all depends on how you plan to use the car. Also, it might be good if the Holley knew when the starter was on and you could tie this table to not requesting a high voltage while the starter is dropping the voltage of the entire system.
Originally Posted by Project GatTagO
Is this not similar to what the S terminal does on the older 4 pin alternators?
Andrew
I don't have enough experience with the S wire on other alternators to make a definitive statement. I do however have a theory that the S wire is a voltage Sense that the other alternator used to know what the voltage was at the battery so as to not get fooled by various voltage drops in the car. So if that's the case, the alternator would compensate based on the voltage at the sense wire rather than at the output post. You could test this by putting different voltages on the S wire and see what the alternator does.
Before I posted this, I tested the 2 pin alternator on my Vette, with the PWM module, to make sure it did what I posted.
Andrew.
I figured you'd be the first to try this with the Holley.
I don't have an ECM/BCM but I've read their strategy is very complex, I think it's called Regulated Voltage Control (RVC)..... takes into account batter temperature and whatnot. I don't think there is enough flexibility in the Holley or any aftermarket engine management to fully mimic this strategy.
If I were configuring something like a Holley, I would try a table where below idle RPM, it's low duty, then as you approach idle, it works it's way up to a modest duty. Then as you are in reasonable RPM, your full desired duty. This all depends on how you plan to use the car. Also, it might be good if the Holley knew when the starter was on and you could tie this table to not requesting a high voltage while the starter is dropping the voltage of the entire system.
I don't have enough experience with the S wire on other alternators to make a definitive statement. I do however have a theory that the S wire is a voltage Sense that the other alternator used to know what the voltage was at the battery so as to not get fooled by various voltage drops in the car. So if that's the case, the alternator would compensate based on the voltage at the sense wire rather than at the output post. You could test this by putting different voltages on the S wire and see what the alternator does.
Before I posted this, I tested the 2 pin alternator on my Vette, with the PWM module, to make sure it did what I posted.
The PWM table can have numerous conditions under which it is activated. So it can easily be disabled with a minimum RPM command. So basically it wouldn't do anything unless RPM is say 300, something above cranking speed, but below normal idle RPM.
I guess ultimately (for me) there is no real advantage so using a 2 wire (besides science project coolness or if I already had one), over what I already have. I have a 4 wire alternator and I power the L terminal from the Dominator with a resistor. I also have the S terminal going to a major power distribution junction and my normal voltage output is between 14.2 and 14.7 volts (as seen but the ECU, which is connected directly to the battery.
There have been multiple thread on the Holley forum about this, because people have these alternators, but can't seem to figure out (you did and thank you for that!) how to make it work with the Holley EFI.
The PWM table can have numerous conditions under which it is activated. So it can easily be disabled with a minimum RPM command. So basically it wouldn't do anything unless RPM is say 300, something above cranking speed, but below normal idle RPM.
I guess ultimately (for me) there is no real advantage so using a 2 wire (besides science project coolness or if I already had one), over what I already have. I have a 4 wire alternator and I power the L terminal from the Dominator with a resistor. I also have the S terminal going to a major power distribution junction and my normal voltage output is between 14.2 and 14.7 volts (as seen but the ECU, which is connected directly to the battery.
There have been multiple thread on the Holley forum about this, because people have these alternators, but can't seem to figure out (you did and thank you for that!) how to make it work with the Holley EFI.
Andrew
Agreed, not much benefit in your case unless you had different modes of operation in your project since you already have it working with the 4 Pin. When you start your engine, do you momentarily notice a belt squeal? If so, you might consider turning on the the 12V to the resistor only after the engine is running. Only a theory, havn't tried that yet.
It would be cool if you could try this and get the Holley community straightened out with the 2 pin alternator. Hell, it they sponsored me, I'd swap my AEM infinity and drop in the Dominator is a heartbeat.
There have been multiple thread on the Holley forum about this, because people have these alternators, but can't seem to figure out (you did and thank you for that!) how to make it work with the Holley EFI.
Andrew
Andrew,
Do you have a scope? Even if you don't install this alternator, it would be great to connect the resistor and zener as above, to one of your free PWM+ ports and look at the waveform. If it looks like a 5 volt square wave, then it is highly likely to work with the 2 pin alternator.
12-21-2018, 01:45 AM
2 pin 2006 + alternator. Don't throw it away!! 
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