CTS-V alternator

[rolfer]

I am converting from a 2004 C5 alternator to a 2004 CTS-V alternator. I have a Speartech wiring harness. Even though my C5 alt has three terminals, the wiring harness only has the center two wired, red (turn on) and grey (field) wires. The CTS-V alt even has the third terminal removed. Both alternators use the exact same plug and are labeled F and L on the same terminals (can supply pics if needed).

my problem is the CTS-V alt is putting out 15.3V when the C5 put out 14.2V. It is about 55º outside. I drove the GTM around the block to warm the engine up to ~170º and the alt is still putting out 15V. The C5 alt when warm it would go down to 13.5V.

I double checked to make sure the two alt wires are going to the proper terminals on the factory ECU and they are. I have even put different 2004 CTS-V alt on it and it put out the same voltage so I do not think I had two bad alternators.

Am I going to fry my battery?

thanks
nick

[KGTM]

there are two type, older years, may 2004 to 2007 and and later version.

which one do you have? is this for GTM

[rolfer]

it is for my gtm.

i have the 2004 to 2007 alternator which uses the same plug as my old 2004 corvette alternator. the terminals are labeled the same on both alternators.

i should also add i am using a factory 2003 corvette ECU.

[Shoeless]

It sounds like you have one of the "newer" PWM controlled Alternators and since its not getting a commanded duty cycle to regulate the voltage, its defaulting at or near the highest setting. Below is a table of commanded output voltages I found a while back while researching this myself. The signal its looking for is 5V PWM signal at 128 Hz with a duty cycle of 0-100. If you are measuring 15V it would appear its defaulting at or near the highest duty cycle by not receiving the proper signal.

Commanded Duty Cycle Generator Output Voltage:
10% 11.00 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% 15.50 V

[KGTM]

ACDelco 25766345 this old one, has four pin connector, with this one you only need one connection to L pin ( this is Lamp goin back in time ) the ECU had a resistor from Battery to this pin to act like a alternator lamp, the other Pin F is not needed and this is how mine is, put out about 14.3v with light load., you can disconnect the F pin and se if it make any difference.

ACDelco 25925447 new one, I think this has two pin connector and not same as the 4 pin of the older units. and will need PWM on PIN F to control the output voltage.

Mostafa

[rolfer]

is there a way i can check with a DVOM, maybe 12v or 5v output? I do not have an oscilloscope.

here are pics of the plug and the old and new alternators. 138706138707138708



It sounds like you have one of the "newer" PWM controlled Alternators and since its not getting a commanded duty cycle to regulate the voltage, its defaulting at or near the highest setting. Below is a table of commanded output voltages I found a while back while researching this myself. The signal its looking for is 5V PWM signal at 128 Hz with a duty cycle of 0-100. If you are measuring 15V it would appear its defaulting at or near the highest duty cycle by not receiving the proper signal.

Commanded Duty Cycle Generator Output Voltage:
10% 11.00 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% 15.50 V

[rolfer]

cool i defiantly have the older one. do you think i should add a resistor? my computer says it is a 2003 Corvette.


ACDelco 25766345 this old one, has four pin connector, with this one you only need one connection to L pin ( this is Lamp goin back in time ) the ECU had a resistor from Battery to this pin to act like a alternator lamp, the other Pin F is not needed and this is how mine is, put out about 14.3v with light load., you can disconnect the F pin and se if it make any difference.

ACDelco 25925447 new one, I think this has two pin connector and not same as the 4 pin of the older units. and will need PWM on PIN F to control the output voltage.

Mostafa

[KGTM]

I have not used the vet ECU so not sure.

The resistor in series with L pin should be in ECU, but not sure about that and ecu needs to turn this off once ignition is off so it is somewhat controlled. the resistor should not affect the output voltage, if there is not one in series could damage the alternator.

Putting a series resistor does not hurt but if too high of value in total series resistance will make the initial file current too low and cause the output be below or at battery until you rev the engine and then once it get to regulation then the field current will be set internally

I would try removing the F pin and also make sure the the L and F are not swapped.

CTS-V new alternator version without the L ( corrected this was F before) pin connected to PWM it will have output voltage of about 13.5V and will need PWM to set it to 14.3 or so.

Mostafato

[rolfer]

I disconnected the F pin and it made no difference so either way I guess the F is not needed. It is still putting out 15.2 when I start it.

I did check to make sure the red L pin wire is going to the proper terminal on the ECU.

The L pin is putting out ~1V lower than the car voltage so i am going to assume it does have an internal resister.

[KGTM]

what is the voltage on this pin with ignition on only and connected to alternator?

what happens when you rev the engine? does it regulate the voltage or voltage goes up?

Mostafa

[KGTM]

One more thing

You said "The L pin is putting out ~1V lower than the car voltage so i am going to assume it does have an internal resistor."

This should be lower before you start the car but should be same or higher once the car starts, so one possible reason could be you may not have resistor in series from your ECU and that might have damaged the alternator, I have heard this issue, by just bad alternator design.

So one way to test this might be start the car and remove the connector from alternative or from any other place ( it is hard to get there with car on ) if voltage goes low then bad alternator.

generally Alternator only need this to start and there is no need after until next restart.

Mostafa

[rolfer]

i did find this in the factory 2004 corvette manual:

138763

it explains why you do not really need the F terminal wire. the engine might die when the car is idling and the alternator is drawing a heavy load but that is about it.

sorry i do not know why it is rotated to the side. the original is not rotated.

[rolfer]

I just wanted to give you guys a quick update.

I took the car up to my local auto parts store where they tested the alternator on the car while it was running. The diodes and everything else look good. When I first start it up it charges at 15.3V and as it warms up goes down to about 14.9V. When I turned on the accessories like headlights and air-conditioning and the blower motor the voltage stayed exactly the same so that tells me the voltage regulator is functioning properly it's just a little high.

I have an odyssey AGM style battery so I called up odyssey and they told me AGM batteries like to be charged at a little higher rate than normal batteries. They told me when it's cold it is not unheard of to go above 15V and when they're warm they normally like to be charged at about 14.7V. They did tell me 15V if it is 100° or more outside would be overcharging.

I think my best course of action is to wait until the weather gets warmer and if I need to I can replace just the voltage regulator. All the diodes and everything else is OK so that might be the way to go if the voltage is still too high.

I want to thank all the people that have helped me on this issue.
It has been a huge help!!!

[KGTM]

Here are some more info, made some measurement for rolfer, thought be good for others so added here also.

Talked to a friend here that has a shop and builds custom cars GT40 and so on, he said he has has issues with these alternator and some have gone bad without resistors he said something about regulators changing indesign to make them cheaper and this has been the side effect on some alternators, so I decided to make some measure on mine as this was no easy.

These are measured on the Orange wire on crate ECU going to alternator.

With ignition off , 0v, 100k to ground
With ignition on , 0v, 100k to ground
With ignition on, car running and not connect to alternator ,5V battery at 12.1V
With ignition on, car running and not connect to alternator but 2.2K load to ground 4.55V, battery at 12.1V
With ignition on, car running and connect to alternator ,4.9V so about 10K load from alternator, battery at 14.2V

So if you have 12V that is bad, and this may be why my friend is saying he is damaging then until he added resistor, he also said most of his damage one where higher than 15.2v but was no sure and some did not work at all.

I would add at least 10K and and keep testing at what value will work if any and see what happens. or figure out why your ECU putting out 12V.

Mostafa

[KGTM]

ACDelco 25766345 this old one, has four pin connector, with this one you only need one connection to L pin ( this is Lamp goin back in time ) the ECU had a resistor from Battery to this pin to act like a alternator lamp, the other Pin F is not needed and this is how mine is, put out about 14.3v with light load., you can disconnect the F pin and se if it make any difference.

ACDelco 25925447 new one, I think this has two pin connector and not same as the 4 pin of the older units. and will need PWM on PIN F to control the output voltage.

Mostafa

correction for alternator with PWM requirement.

I believe PWM is on L pin and not F pin, just in case someone actually read this, F pin still field pulses.

Mostafa

[KGTM]

I just wanted to give you guys a quick update.

I took the car up to my local auto parts store where they tested the alternator on the car while it was running. The diodes and everything else look good. When I first start it up it charges at 15.3V and as it warms up goes down to about 14.9V. When I turned on the accessories like headlights and air-conditioning and the blower motor the voltage stayed exactly the same so that tells me the voltage regulator is functioning properly it's just a little high.

I have an odyssey AGM style battery so I called up odyssey and they told me AGM batteries like to be charged at a little higher rate than normal batteries. They told me when it's cold it is not unheard of to go above 15V and when they're warm they normally like to be charged at about 14.7V. They did tell me 15V if it is 100° or more outside would be overcharging.

I think my best course of action is to wait until the weather gets warmer and if I need to I can replace just the voltage regulator. All the diodes and everything else is OK so that might be the way to go if the voltage is still too high.

I want to thank all the people that have helped me on this issue.
It has been a huge help!!!

Generally output voltage change VS temperature is very small, depending on design in side the regulator this could be only 1 to 3 mv per degree C, so may be at best 200mv, the change with load is normal and will depend on wiring, these alternator do not have voltage sense wire so voltage is only regulated at the Alternator post, measuring at battery will have all the wire drops.

So this will not be fixed in summer by itself, hope full by adding resistor as we discussed will help.

Good luck

Thanks,
Mostafa

[rolfer]

another update.

the factory 2004 GM manual says the L terminal wire when unplugged should read 5V. for some reason mine is reading about 1V lower than battery voltage.
thanks to Mostafa telling me if that wire receives too much voltage it will cause the regulator to put out too much voltage. i could have put a resistor inline to drop down the voltage as well but i did not feel like trying to find the proper resistor.

i had a 5V reference terminal on the computer that was not used so i plugged the L terminal wire into that one. i found a new regulator on eBay and replaced my old one. now i am getting the proper voltage!

[KGTM]

Thanks for kind word and update.

So the learning here is if you are using CTS-V newer or old before you plug the connector from ECU in it, make sure it puts out 5v and not 12v, in some cases you may have to run the car before this voltage is present to measure, I have heard if you leave as 12V it may work for a while but will go bad over time.

The level should be 5V for older CTS-V and 5V PWM for the new one, if just 5V you will get about 13.5V for the newer versions which is no enough to fully charge your battery especially if you have LiFePO4.

Thanks,
Mostafa

[beeman]

I have a cts-v alternator, how do I tell if it's a newer one or older one?

[rolfer]

the older one uses a plug that will take up to 4 wires even though they only use 2. on the newer style the plug will only take 2 wires.

I have a cts-v alternator, how do I tell if it's a newer one or older one?

[Shoeless]

the older one uses a plug that will take up to 4 wires even though they only use 2. on the newer style the plug will only take 2 wires.

Unfortunately, I don't believe its that easy, I'd have to go back and review all my notes and re-read every post I saved on it.

Here are some PNs I have in my notes:
Old - 25766345
New - 25925447 or 23480515

[KGTM]

Unfortunately, I don't believe its that easy, I'd have to go back and review all my notes and re-read every post I saved on it.

Here are some PNs I have in my notes:
Old - 25766345
New - 25925447 or 23480515

25766345 needs 5v control to turn on no PWM, 14.2V or so output. this is what I have.

New - 25925447 or 23480515 needs PWM

I have heard there might be 4 pin plugs version that need PWM also, but have not seen one.

Mostafa

[beeman]

Thanks guys