Adding a W terminal to alternator

[martinriches]

I need to open up my tachometer to add a W terminal which will be a sensor for a Faria tachometer.. It is a a Hitachi 35a from a Yanmar 2GM20.I have found some information on how to do it which seems fairly simple. It wasn't however on this particular alternator.Has anybody made the connection on the Hitachi ?


Martin

 

[VicS]

Hitachi alternator: P is the "W" connection

Sometimes the W connection is I believe a tap on the coil giving IIRC ony 8 volts.

provided your tacho is happy with the full voltage (or you can drop it) the above should show the way

 

[martinriches]

Thanks Vic. I have one marked BAT & and one E. There are two other unnamed terminals but they have no effect on the tacho. I have read that there isn't one on this particular alternator.

Martin

 

[VicS]

Thanks Vic. I have one marked BAT & and one E. There are two other unnamed terminals but they have no effect on the tacho. I have read that there isn't one on this particular alternator.

Martin

I think normally the tachometer on the GM engines gets its signal from a separate sensor on the engine rather than from a W terminal on the alternator.
So you don't expect to see a W terminal on an alternator from a GM series engine ..

Diagram I posted I think came from a Beta engine manual

 

[Upnorth]

Martin,

I'm wanting to do exactly the same thing as you. If you ever get it sorted I would be obliged if you could let me know.

Mike

 

[earlybird]

VicS is correct, GM's don't use a "W" terminal for the tacho.
I think that your only solution is to open the alternator and solder a wire to one of the 3 stator coil connections where it joins the diode pack.
Or take it to an auto-repair shop to do the job.

 

[ianj99]

Martin,

I'm wanting to do exactly the same thing as you. If you ever get it sorted I would be obliged if you could let me know.

Mike

Its easy to do, you simply solder a wire onto the winding side of one of the diodes - as shown by the P connection on the above diagram.

Be sure to insulate & route the wire adequately so it doesn't chafe or become trapped when you reassemble the alternator.

The voltage will be the charging voltage plus about .5v but its the frequency that is driving the tacho.
The tacho will need to have some sort of adjustment because the actual frequency & therefore rpm reading will depend upon the alternator speed and no of poles. (most are 6)
I

 

[martinriches]

Thanks for the replies. I will have a go at soldering a wire on. Mike. I will let you know how it works out.


Martin

 

[dgadee]

I took mine to a car electrics place I use and they charged me £20 to add the w lead. Then I decided that the alternator was a bad fit and caused belts to wear out (put in by the previous owner) and didn't use it.