Twin alternators w/tach

[turbonator]

Hi, we have our ''Pugg'' motor running now and are just fine tuning and prepping before the install.

We are running twin alternators on brackets that jeff set up. I have the two alternators connected in parallel. Everything works fine with only a 0.2v difference in the output voltages. Figure its a good install; no belt movement when under load, the outputs match well and good tach signal from alt#1.

The place that we run into problem is that when both alternators are connected at the same time, our diode tapped signal circuit to the tach cancels out or goes to zero. The signal is taken from alt#1 (tapped center diode) and I was wondering if anyone else has an idea on how to isolate this signal from the other alternator.

Thank you in advance....:)

[rogers]

Is this for the truck in your signature? How many and of which colors are the wires on the back of each of the alternators?

[turbonator]

No, not going into the 3500 in signature, this is an 18:1 compression that we built to go into a GMC C5000.:)

Both of the alternators are the old style with the large red wire on the battery terminal and the two blade connector. The connector has a red wire to battery and a brown wire (field excitation) that goes to the alternator light in the dash.

On alt#1, I tapped the center of the diode trio to have a tach signal, this wire is green.....:D

The alternators are connected in parallel and work fine together. It is just that my tach signal disappears when both are plugged in.

Tell me what you think......

We need to update our sig, there's 4 missing.....:)

[JohnC]

This question is from total ignorance, but are you on the stator side of the diode? Otherwise, unless the other alternator is exactly phased with the first, I'd expect it'll blot out any signal.

[rogers]

I had an older alternator(94) that I just tossed, otherwise I could walk through this a little better with you. However, there should be 4 terminals or markings other that the battery wire. The terminals should be labeled P, S, F, and L. The terminal labeled P is the one to use to drive the tach. This P terminal corresponds to one of the outside of the diode trio(at least on the wire diagram). L is the brown wire and S and F are not used. I hope that helps to make things as clear as mud.:rolleyes:

[JohnC]

Can you post the diagram?

[turbonator]

The tap that I put on is on the center diode, only one side of diode is accessible will try to verify with my diagram here and get back to you whether or not it its tapped stator side or not.

The colors of wires is arbitrary, because they are my rebuilds. I try to keep to factory coding, these alternators are from the 80's.

Thanks guys, BRB, jim.

[rogers]

Sorry, I should have thought of that! Here is the charging circuit and alternator terminals.
http://www.thedieselpageforums.com/photopost/data/500/medium/Charging_circut.jpg


http://www.thedieselpageforums.com/photopost/data/500/medium/Alternator.jpg

Hope this is some help. I may have read them wrong, so if I did please correct.

[turbonator]

Okay thanks guys I need to take an alternator apart and remove the trio that is in it. I never thought at all about the phasing being out of sync, that can be big problem in generation with one alternator ''hunting'' for the other...... not sure if we need to do something here since the voltage is rectified before the one meats the other.....

Will get back to you all, thank you both, jim.

These diagrams are much more in depth than the ones we have from the Haynes repair manuals..:)

[turbonator]

Okay John, I pulled another alternator apart, to verify and yes, I am tapped to the stator side, directly to one of the stator winding wires. I used a connector to the center pin.....

Tried to upload a photo...... computer challenged I guess....:)

[GMC Hauler]

Does the signal come back if you turn on more loads, like the blower motor in high, headlights on????

[turbonator]

Does the signal come back if you turn on more loads, like the blower motor in high, headlights on????

Will have to get back to you on that, we noticed the problem with motor on the tuning stand, test the alternators with multimeter and battery tester (old toaster style).

We just installed the motor in truck today, so will be about 1 week before we can test again.......

First we got to go make some money.....then continue. Will deffinately update when motor is running again.