Delco Alternator Sense Terminal

[dustybarn]

While I was driving 1776 this summer, the alternator abruptly stopped charging. So while I had the back end of the car apart to fix the valvetrain I took the opportunity to have the alternator tested, and sure enough, it was bad. It was a big Delco CS144, and I replaced it with another. While I was in there I also replaced all of the battery and alternator wiring.

Although the CS130/144 can be run without the sense wire connected (and indeed, this is how it was wired when I got the car), I decided to connect the sense terminal "S" to the positive passthrough under the coil cover. Now the voltmeter shoots up to ~14.5 V as soon as the engine starts, and never varies regardless of electrical load. It was nowhere near that robust before, even when the old alternator worked.

Has anyone else tried hooking up the sense wire? I think it may have made a difference.

[Ron]

According to Delco, it is not "needed" but makes the regulator do its job better (fyi- it calls for a 5 amp fuse on the feed).

[Jeffu]

II know this thread is fairly old, but is there anyone else out there utilizing the "sense" terminal on their Delco Alt? I know a person could probably just run a small section of wire off of the sense output tab on the alt and connect it to Batt stud on the back of the alt (like Scenario A). But I think it would be wiser to run the sense wire directly to the poss post of the Batt itself (like Scenario B).

Anyone else have any real world examples of utilizing your sense terminal? Positive results....Negative results?? (no pun intended :biggrin: ) I would love to hear about it.

23054

[David T]

II know this thread is fairly old, but is there anyone else out there utilizing the "sense" terminal on their Delco Alt? I know a person could probably just run a small section of wire off of the sense output tab on the alt and connect it to Batt stud on the back of the alt (like Scenario A). But I think it would be wiser to run the sense wire directly to the poss post of the Batt itself (like Scenario B).

Anyone else have any real world examples of utilizing your sense terminal? Positive results....Negative results?? (no pun intended :biggrin: ) I would love to hear about it.

23054

I would try attaching the sense wire to something that gets power when you turn the ignition on. You do not need power on the sense wire when the motor is not running. That could cause a drain on the battery when the motor is not running. Also if you just wire it into any place you should use a fuse on it just in case the internal regulator in the alternator fails or the wire gets grounded somehow.

[Josh]

Wiring the sense to the positive terminal on the alternator will give no advantages. The sense is already connected to the positive terminal inside the alternator. If you want to do it this way, save yourself a half hour and just leave the sense disconnected.

The whole point of the sense is to probe for the voltage of the system. Hooking the sense to or very close to the battery gives the most accurate voltage reading, and allows the alternator to output the ideal voltage to the charging system.

[Josh]

Scroll about half way down the page, it is well explained in two pictures.

http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html

[Jeffu]

I would try attaching the sense wire to something that gets power when you turn the ignition on. You do not need power on the sense wire when the motor is not running. That could cause a drain on the battery when the motor is not running.
On our cars what would that "ideal" location be that is closest to the batt that would be switched?? I am not sure if the OP was talking about the "jump start post" stubbed into the side of the body in the engine compartment when he was referring to the "possitive pass through under the coil cover"? :hmm:


you should use a fuse on it just in case the internal regulator in the alternator fails or the wire gets grounded somehow. Yes, I completely agree.

[Jeffu]

Scroll about half way down the page, it is well explained in two pictures.

http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html

Yes, that is the website that I was reading and where I grabbed my attached image from earlier. That is why my thinking was if I were to utilize the sense wire it would make the most "sense...ha,ha" to terminate it right at the positive post of the battery. However, that connection not being "switched", and like Dave mentioned might be a potential for battery drain?? I certainly would not want to create a situation where after any length of time the battery would drain. That being said, I do have a manual battery disconnect switch that I turn off any time I know the car will sit longer than like a week or two. So perhaps I don't really need to worry about a potential drain......

[Jeffu]

Wiring the sense to the positive terminal on the alternator will give no advantages. The sense is already connected to the positive terminal inside the alternator. If you want to do it this way, save yourself a half hour and just leave the sense disconnected. Agreed!

[Bitsyncmaster]

I deal with a lot of power supplies that have remote sense lines. On those if you leave the sense line open the power supply goes to full voltage. I would think the alternator would be the same unless it has some circuit that detects an open circuit to shutdown the sense.

Those of you that don't have the sense line tied to +12 volts, have you checked your voltage?

It does not make sense to have a sense line since your battery cable to alternator is most likly 4 AWG or 2 AWG and you would not be dropping much voltage there even if you were pumping a 100 amps into the battery. Your car draws 50 amps or more so the most your battery will charge is 55 amps anyway.

[dustybarn]

On our cars what would that "ideal" location be that is closest to the batt that would be switched?? I am not sure if the OP was talking about the "jump start post" stubbed into the side of the body in the engine compartment when he was referring to the "possitive pass through under the coil cover"? :hmm:

Yes, I completely agree.

I didn't connect the sense lead to the jump start post. I connected it to the "Engine Compartment Battery Post" mounted in the same plate as the bulkhead connectors. The other end of this post supplies power to just about everything in the car.

[Ron]

On our cars what would that "ideal" location be that is closest to the batt that would be switched?? I am not sure if the OP was talking about the "jump start post" stubbed into the side of the body in the engine compartment when he was referring to the "possitive pass through under the coil cover"? :hmm:

Ideally, you would put it as close to the input side of the highest drawing device (on a D, it is the fans...heavy draw, long route for feed and ground -- Hot side of relay 112 would be a good place. It will not draw the battery down even though it is hot at all times).
Normally GM puts it right off of the hot side of the ignition switch...which is the same as at relay 112 (but it will then see the voltage drop... ).