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I enjoy your updates. Especially since I bought an almost identical 84S in November.
Thank you for the kind words and your 84S looks great. I can't wait to get the car to a point that I am driving it with everything operational and worry free.
I thought I was doing something innovative, but after further research it appears I am not the first to use the CS144 alternator on the 928S.
Regardless, I will share the information I have gathered along with results. The alternator is a CS144 140 Amp alternator for a 1998 Chevy Tahoe V-8, 5.7L. I bought mine from Autozone for $124 along with the 3 wire pigtail for $9.99. I will post all the details after installation and testing. I was supposed to receive the stainless tubing to shim the factory bolt for the larger mounting holes in the alternator, but for some reason it did not show. I finished the wiring, which took all of 15min and got the appropriate Gates belt, which was 1" longer than stock. I bolted everything together and tensioned so I am literally just waiting for the tubing to finalize.
I should have pics with detailed information tomorrow for the alternator swap. I did receive the stamped metal brackets for the armrests today, but I am not going to touch the interior until the alternator is finished.
I might as well post some of the information now and the rest when I am finished. As previously stated I am attempting to use a CS144 from a 1998 Chevy Tahoe V-8, 5.7L from Autozone for $124 along with the 3 wire pigtail for $9.99.
A few things to consider when trying to make fit are physical space constraints and belt alignment. After verifying it would physically fit into the car with some adjustment capability I needed to make sure the belt would properly align. In the picture below I have attempted to line up the backside edge of the mounting pivot points to be in the same plane for both units, which is shown by the red line. I then overlay a piece of aluminum on the inner most pulley groove and confirmed they are in the same plane. Simply put, as long as I slide the alternator towards the rear of the car and use the "RED LINE" as a mounting surface the belt should align like stock. The other thing I have detailed is the width of the mounting point with the stock Bosch AL109X being ~2.210" and the CS144 being ~2.000". This is not an issue as long as you use a couple of washers that provide a total spacing of ~0.210", which should be added to the mounting side towards the front of the car.
The next challenge I had was the pulley differences. Most people just swap over the stock pulley onto the CS130/CS144 and you are good to go, but my stock alternator (Bosch AL109X) is an oddball and has a 14mm shaft as opposed to the more common 17mm shaft was used by the CS144 and other 928S alternators. If you are one of the unlucky ones like me that should not be an issue. In the picture below you can see the CS144 comes with a 6-groove pulley and the stock belt is 4-groove. It is ok to run a 4-groove belt on a 6-groove pulley. The only potential downside is the stock Porsche pulley is smaller, which will create higher alternator rpm's giving higher amperage at idle. If this does create an issue you can purchase smaller pulleys for ~$22 online. I am going to keep the pulley that came on the unit for now.
The next pictures gives you an idea of the size difference, which is minimal. The other thing I like about the CS144 is that it is a closed unit like the Bosch and because it sits so low to the ground it relatively sealed from dirt and debris from the road, unlike the CS130 and other high output options.
The final thing to report, for now, is the wiring. This is a very simple step and I have provided a diagram and pictures of the actual wiring. As previously mentioned I purchased a 3 pigtail connector for $9.99 from Autozone. Only 2 of the wires are used and only one has to be tied into the car. In the diagram below you will attach a ring connector to the larger red wire that is designated 'S' in the image below. This is then attached to the B+ terminal on the back of the alternator. You then tie in the brown wire, which is designated as 'L' in the image below. This is soldered directly to green/blue wire coming from the factory harness.
The image below is the wiring harness connected to the car. You can see I soldered the 'L' pigtail to the factory wire as well as the ring connector on the larger red wire. In case you are wondering about the third black wire, which is designated 'F' in the image above, I decided to just tape the end and apply heat shrink tubing instead of removing the wire. However, I can assure you it is not being used.
More to come once I get the stainless tubing...tomorrow.
BTW, I finally used my wife's camera to improve image quality because my camera must have taken a dump.
Last edited by 240Z TwinTurbo; 01-08-2015 at 09:03 PM.
I want to advise you here, the S connector on the alternator typically means the voltage sense lead. The 928 has the battery at the far back of the car, and the charge B+ wiring is long and complicated, first going to the jump post at the right front fender.
By sensing the voltage supplied at the B+ terminal on the alternator, you are not taking into account the various drops along the way from the B+ all the way back to the battery terminal. I would consider actually using the S terminal as intended, and run a 16Ga wire direct from the + batt terminal all the way up to the S terminal on the alt. This way, the alternator will provide the correct charge and float voltage to the flooded lead acid battery, and extend the life.
In cars where there is a large 2Ga or 0Ga short wire from the alt to the nearby batt in the engine bay, this isn't so much an issue. As with all situations --- the 928 is once again an outlier.
<edit; I found an online explanation with a diagram, but strangely enough even this diagram doesn't show the sense lead all the way to the battery terminal. Hmmmpf, they got it right in the text, and wrong in the diagram. Oh well, just run the lead from the batt + to the S on the alt and you are home free. http://chargerr.com/Alternators/ALT.HTM >
I would consider actually using the S terminal as intended, and run a 16Ga wire direct from the + batt terminal all the way up to the S terminal on the alt.
This sentence confused me, did you mean to write "and run a 16Ga wire direct from the + batt terminal all the way up to the B+ terminal on the alt."?
If so, would you recommend a route for that wire? Like most others, I have to replace my battery about every 2 years at a significant cost, anything I could do to correct that problem would be welcome.
This sentence confused me, did you mean to write "and run a 16Ga wire direct from the + batt terminal all the way up to the B+ terminal on the alt."?
If so, would you recommend a route for that wire? Like most others, I have to replace my battery about every 2 years at a significant cost, anything I could do to correct that problem would be welcome.
Regards,
The 'S' wire on the alternator connector is supposed to get a signal direct from the 'B+' terminal on the battery to accurately provide electrical needs based on what the battery is experiencing. I was under the assumption one of those two wires that connect to the 'B+' post on the alternator went directly to the battery, but it appears it does not.
I spent a minute and crawled under the car and it appears the large 0g wire from the 'B+' on the battery is running directly to the starter. From the starter I think it is then running to the 'B+' on the post of the alternator. I found an image in the post below that would indicate this to be true.
If this is the case I don't think it is that bad how I have it configured, but it might make more sense to run the 'S' wire to the starter since that is directly connected to the 'B+' on the battery by a large 0gwire.
It might be wise to run large gauge wires direct from the battery terminals to the alternator housing and 'B+' terminal.
the S is the sense wire. It offers a closed loop value of the voltage at the battery, or at the major point of the load, without carrying any of the current supporting that load. Think of it as a cruise control for the voltage output of the regulator which is best suited for the type of battery installed in a circuit.
Now, consider the case where we jump in, start the engine and drive off. When the S lead is connected directly to the B+ on the alternator, the sense wire does not see the sag in voltage caused by the starting current. So, the alternator starts charging the battery based on the voltage present on the B+ terminal but NOT on the voltage at the battery. This situation leads to a charge voltage that is insufficient to recharge the battery in a timely way. It will be charging at a lower rate than if the sense line were actually sensing the battery voltage, which is lower than the alternator B+ voltage, because of the resistance of the large charge wire and connections, and the loads on the battery from the running car.
So, the sense wire should be used as it was designed by connecting it to the battery + terminal, and this provides the actual battery voltage to the alternator so it can either raise, or lower it's voltage charging rate as required by flooded lead acid batteries. I presume you have a standard flooded lead acid battery. If not, and you have an AGM battery, you may want to investigate the charge and float voltages for those types of cells.
It does not make sense to run the sense wire to the starter lug as the starter is a high current load with no charging, and it is a temp load, not a sustained load. The 928, depending on year has several taps on the primary alternator B+ for various loads. The most important point to sense the voltage is at the battery, as that is the storage point for ALL loads and will provide the best support for the battery. It does not carry current, so the size isn't too important, just that it be large enough not to get warm and become inaccurate. 16Ga should do it fine, or if you are really concerned about the gauge go down to 14, because the alt and the battery are so far away in the 928.
This sentence confused me, did you mean to write "and run a 16Ga wire direct from the + batt terminal all the way up to the B+ terminal on the alt."?
If so, would you recommend a route for that wire? Like most others, I have to replace my battery about every 2 years at a significant cost, anything I could do to correct that problem would be welcome.
Regards,
No. The wire goes from the + batt to the S terminal on the alternator. It must not be connected to the B+, or you defeat the purpose of remote voltage sensing. I don't know what alternator you have, or if it has a Sense connection on it. Your battery will last longer with the sense connected, but 928s are tough on batteries as a matter of design.
the S is the sense wire. It offers a closed loop value of the voltage at the battery, or at the major point of the load, without carrying any of the current supporting that load.
This explanation makes more sense because of the lack of current that would flow through the 'S' wire. Thank you for providing this explanation. I have it currently running to the 'B+' on alternator, but I will run a new wire this weekend.
The alternator has been installed and I can happily report it is working without issue. I finally received the stainless tubing to make the stock metric bolt resemble a 3/8" bolt. I ordered 1ft of 304L stainless tubing from McMaster Carr that is 3/8" OD with an 0.28" wall, which fits the stock bolt perfectly. I cut two 2.0" pieces for the two mounting points on the alternator. The picture below is the tubing placed over the bolt. Make sure you put three metric washers on the front of the alternator mount to make up the ~0.210" difference. My washers actually measured ~0.190" so good enough for government work.
McMaster Carr Part # 8457K55 (~$7.00)
I then installed the alternator to show the two different extremes of mounting. Prior to taking the pictures I made sure the power steering pump was in the as used position with belt tightened. In the fully up position I put a red mark to make sure I did not exceed this mark with the alternator tightened, which would mean the alternator was hitting the power steering pump.
In order to get the belt on I completely removed the adjustment mechanism and then installed after the belt is placed on the pulley. Make sure you place another set of three metric washers on the front to maintain proper spacing. I have detailed this in the picture below.
You can see in the picture below the red marks I made to make sure the alternator did not hit the power steering pump. I ended up using a belt that was ~0.500" longer than the stock belt. With the adjuster installed I ended up not having to tighten the adjuster as the belt was snug enough. I used a pry bar to install the adjuster. If you feel the belt is too tight you need to increase the slot on the mounting arm for more negative travel. I tried a belt that was ~0.500" longer than the belt in the picture below, but when tightened it was almost touching the power steering pump.
Below is the belt I used that is 0.500" longer than stock.
Measuring voltage at the battery with the car started and idling at ~700rpm I am seeing ~14.0V.
If I turn on the headlights and blower on high I am seeing ~12.4V idling at ~700rpm.
I had my wife give the car a little throttle and with the headlights on and blower on high the battery voltage is 14.0V. I will drive the car for a while, but I might need a slight increase in alternator rpm, which will necessitate the smaller pulley. This should give me no lower than 14.0V no matter what condition.
Last edited by 240Z TwinTurbo; 01-08-2015 at 10:44 PM.
Once more, I would advise you. The IV/RPM curve of a modern alternator is not remotely linear. It will reach a pretty high current even at lower revs. Unless you spend a lot of time idling with the AC, lights, and blower on you can leave the pulley as it is. This will benefit by lower torque use from the alt, better tracking, and less pressure on the bearings in the alt(Mu = torque*SIN(theta)).
So, if you use your car on modest drives where you can run it off idle plenty and have the S wire hooked up right stay with what you have until you measure the specific gravity after a few use cycles.
Once more, I would advise you. The IV/RPM curve of a modern alternator is not remotely linear. It will reach a pretty high current even at lower revs. Unless you spend a lot of time idling with the AC, lights, and blower on you can leave the pulley as it is. This will benefit by lower torque use from the alt, better tracking, and less pressure on the bearings in the alt(Mu = torque*SIN(theta)).
So, if you use your car on modest drives where you can run it off idle plenty and have the S wire hooked up right stay with what you have until you measure the specific gravity after a few use cycles.
While the overall response curve for the CS144 is non linear, at lower rpm the curve is quasi linear so a small change in rpm has a significant impact on output current. While not a deal breaker, I would personally prefer a more consistent voltage.
Regarding your equation, I think it is wrong. Also, I think you meant force and not pressure, which is force per unit area. Finally, specific gravity is a measure of density relative to water so I am unsure how this term applies.
Specific gravity of the battery is the preferred method for measuring the quality of the charge in a flooded lead acid battery. Typically done with a dipping hydrometer. This will tell you the state of charge of the battery once you drive it a bit with your current pulley, letting you know if the alternator is doing it's job maintaining the state of charge, or if you need to use a smaller pulley, and increase the torque taken from the crank.
Thank you for providing clarification regarding the specific gravity. I suspect the current pulley configuration is likely sufficient to satisfy the needs of the battery, but my need for 14.0V at idle is going to make me buy a smaller pulley and not a dipping hydrometer.
I posted an update in the alternator swap thread, but essentially I have charged the battery and the battery shows 13.2V at idle with everything on in the car (blower high, high beams, fog lights, doors open).
I finally finished the trunk upgrades by installing a new OEM catch/spring as well as the liner for the catcher as shown below.
Now that the car is on the ground I am going to switch focus and finish the door panels. I ordered some nice 1/8" foam, leather printed black vinyl, and the correct spray adhesive for car interiors. I will post pictures over the weekend of my first time to recover a door panel. Should be interesting.
01-07-2015, 10:18 PM
