CS-144 alt has a terminal for a tach, can i use a gasser tach?

[merlot566jka]

the 'p' terminal is connected to one of the stator winding on the 'cs' version of gm alts. this signal is or can be used to drive a tach. I am using the cs-144 140amp version on my burb

what do i need to make this drive a gasser tach cluster on my 6.2l burb?

what kind of signal is put out here? obviously 12v pulsing, but at what ratio compared to the crank? any way to figure that out with out taking a stab at the actual turn ratio of crank vs alt pulleys?

does the tach need a square wave or sawtooth?

i dont wanna buy the dakota digital converter if i can just build a conditioning ckt for this.

thanks

[rdurh]

I haven't tried it yet but I asked the same question on a different diesel forum and here's what was told about using a gasoline tachometer with a CS alternator:

"I think car tacks are looking for a spike from the ignition. ... Take your alt. wire and put a small capacitor in line with it. This will electrically integrate the square wave pulse into a spike!! That is what I did and it has been working for 5 years.
...
The size of the spike is not important, the important thing is that it is a spike. I remember just using something laying around the junk box. I also did this (like you ) in frustration and had my scope outside looking at the wave-shape, before and after. A large disc type , like the one on the gauge CVR it is I think .1mf . Try that, all you want to pass is the initial positive rising edge of your square wave. If it does not work go larger to a polarized electrolytic of say 2.2uf. Use a cap rated for 25v on your 12v spike.
...
My capacitor is a tantalum, 01 uF or 723000 pF @ 25+ volts.
It looks like a chick-let Its in line to the tach input pulse. I think any .01 disk @ 25v will work. I just, had this. You want to use something that moisture will not get to , hence the tantalum"

[merlot566jka]

yup, read that already. i guess that means no one knows?

[john8662]

Search the internet, and or go to DakotaDigital.com and browse their website for a diesel tach adapter module, this module utilizes that terminal on the alternator you're talking about, and allows you to use ANY gasoline tach with the module.

And, um, don't go sharing this with that other forum... :rolleyes:

[merlot566jka]

kinda wanted to build it myself.

[john8662]

That's cool, I was thinking that it was being built for the sake of the fact that few if any devices were known to perform the task wanted. I just happened to know of one already in existance, that I would use if I had such a project.

Keep us posted on making one though, I've got an interest in making things electronic too, and find this neat as well.

J

[merlot566jka]

ok well heres my plan....

im going to buy the dakota digital converter, copy its circuitry for the tach signal i need and figure out what it takes to use a gasser tach off of the p terminal on these alts.

from that i should beable to figure out the turn ratio of the alt vs crank, signal conditioning etc etc. basicly reverse engineer something that already works.

im going to use a photo tach for measurement of accuracy. ill keep this updated as i go along. parts should come in soon, but because of the holidays its going to be untill the new year before im able to be completely absorbed in this.

[john8662]

Well, making one from scratch is one thing, copying is another.

Buy it, install it, test it, be happy if it works.

Carefull, you might have to avoid the temptation to excersize the CLSA thing....

In lamens terms: respect other's hard work (or a company with engineers) and don't copy it...

[wade-ve7trw]

If you search this forum for tach and Dr. Lee, you will find a circuit already built and published here that works.
http://www.thedieselpage.com/members/features/swangertach.htm
found the reference for the info.

[merlot566jka]

thanks wade, i too have found that. but i was trying to avoid looking for a vacuum pump with the ESS on it. it seems hard to find.


yeah pretty crummy to copy someone elses work. I didnt think about it like that.

[wade-ve7trw]

You only need to check with various suppliers and order one. They are part of the California emission package. Or You can be inventive and adapt the circuit to work with the output of the alt