Alternator “W” terminal?

[FDo5g]

greetings and salutations, I just got my hands on a Dakota Digital gauge system and I’m in the process of adding tachometer capability. I can either use an inductive sensor for the tooth flywheel, or the “W” terminal from the 24 V alternator. Does anybody here have any experience doing either of these options on a BJ 40 or BJ 42?

 

[mcaz5]

I just added a W terminal to my 2LT LN65. Pulled the alternator, soldered a wire in, and ran it to the Dakota Digital.

Not familiar with B engine pumps, but the ‘w’ wire is a pretty universal solution

 

[4Ruster]

I just added a W terminal to my 2LT LN65. Pulled the alternator, soldered a wire in, and ran it to the Dakota Digital.

Not familiar with B engine pumps, but the ‘w’ wire is a pretty universal solution

Do you mind telling us how you did it?

 

[mcaz5]

Do you mind telling us how you did it?

Sure! You just solder a wire to one of the 3 diodes (have to remove the rear case). Check continuity from the solder joint to the end of the wire. Run the wire to the Dakota digital, and then run that to the tach. The Dakota digital has to then be manually calibrated to output the correct rpm signal.

No point in doing this if your pump has the rpm pickup. Mine didn’t, hence why I went this route.

 

[-MaTTi-]

greetings and salutations, I just got my hands on a Dakota Digital gauge system and I’m in the process of adding tachometer capability. I can either use an inductive sensor for the tooth flywheel, or the “W” terminal from the 24 V alternator. Does anybody here have any experience doing either of these options on a BJ 40 or BJ 42?

View attachment 3504656

View attachment 3504658

This is how the W is connected to BJ42’s alternator (yellow wire soldered):

 

[mginn68]

This is how the W is connected to BJ42’s alternator (yellow wire soldered):
View attachment 3520786

Great finding this post. Can you go into more detail on the wire install. I have new alt for my 3b and I’m looking for the “w” pickup for my Dakota also.

 

[-MaTTi-]

Great finding this post. Can you go into more detail on the wire install. I have new alt for my 3b and I’m looking for the “w” pickup for my Dakota also.

Sorry, I haven’t done this/no more pics or info. That’s my friend’s alternator.

 

[relaxedcruiser]

A alternator has basicly three stator windings which are all producing A/C curent.
The W connection is basicly just the A/C current of one of those windings before the diode . That signal can be used for tachometers.
Some alternators have the W connection ready, some don't. I have soldered those in before - easy thing to do if you are happy to take your alternator apart.
I believe that is how it is....it is just a basic explanation out of the back of my mind.

 

[Dougal]

I put a cheap scope on the W terminal on my Isuzu alternator and the resulting wave is really really noisey. I think you'd get a much cleaner signal from an inductive pickup sensor.
On a previous vehicle (Nissan) I soldered in a wire (and diode) for a W terminal where it didn't have one. I was able to successfully drive an aftermarket tach with it but had no luck driving a factory dash tacho.

 

[george_tlc]

I used an inductive pickup for years on my stock alternator - I found they died over time. Unless your inductive pickup is automotive rated and 'shake proof' they will be subject to a pretty harsh environment.

I went to a new alternator (when my old one wore out, dead bearings etc). I added a W wire, basically it is just one of the stator wires. And yes, it's a pretty noisy signal, so definitely needs to be conditioned and cleaned up before being fed into a tacho. In my case a built my own converter (with a microcontroller) to take the alternator W pulses and convert them to the appropriate frequency to drive me stock dash tacho. 50Hz = 1000rpm on my old nissan patrol.

I created a very noisy signal (the green) and then ran it through a filter circuit (the blue) and then a schmitt (the red) to feed to my microcontroller. This is a simulation so I could tune the component values for the maximum rpm (4400 on the nissan sd33 diesel) and factoring the crank-alternator pulley ratio and the 6 pole pairs).

Final result works great and has been installed more than 10 years.

I presume the Dakota unit does the necessary filtering to clean up the 'dirty' W signal, similar to my home brew solution.

cheers,
george.