3 Wire to 2 wire alt swap- can't turn off (1 Viewer)

[Kief]

OK so on my 'build I have a GM (Delco) 2 wire alternator, T1 and T2 are the terminals. T1 in factory configuration is from the charge light off of the ignition switch and the T2 is for the voltage sense on the battery.
On the '80 series it has IG (excite?), L (charge ind. light) indirectly wired off of the ignition before a diode, (S) which is voltage on the battery- before the ignition switch.

I ran hooked the T2 to the S and the IG to the T1 but it won't turn off, so I guess it is sending power back to the load (not hot) side of the ignition swich. I suppose the next step is to hook the L to the T1 lead and see if it likes that better. I know that the original set up allows power from the old L wire to go to ground until there is no potential when the alternator builds up equal voltage.. I thought maybe the GM alternator needed the T1 lead to excite the rotor.. I think if my first thought doesn't work I pick up a diode and put a check valve in that baby..

Even though it didn't turn off it was really fun starting it from the ignition..

 

[gnob]

Im not 100%
But i think gm uses the second wire as light or switch.
The lead is hot and colt sense.

Why not go one wire?

 

[ThreeEyedBandit]

Should be:

Wrong(IG -> T2)

S-> T2
L-> T1

Warning light/excite to T1 and remote load voltage sense to T2. This combined with the diode in the charge light circuit will keep the now excited alternator from keeping the ignition circuit live. Worse case, just wire the T2 to the battery lead on the back of the alternator(cleaner bur lower voltage) or its own separate lead to the battery (will keep batter voltage higher depending on load).

At least this has worked on many vehicles for me in the past.

Matt

 

[Kief]

I think the disadvantage of the one wire type is it can't compensate for voltage drop. and mine is on the opposite side of the engine vs. stock. There is a diode in the factory wiring for the charge light so I'll give it a go. I'm not sure of the logic of the OEM vs. the GM. I also noticed the OEM is center tapped on the "Y" 3 phase windings and the GM isn't but the center tap is grounded, I would think the GM is cheaper as it requires less diodes but it doesn't utilize the reverse flow of the current and maybe that is correlated to the voltage regulator and how the AC is rectified..

 

[ThreeEyedBandit]

I think the disadvantage of the one wire type is it can't compensate for voltage drop. and mine is on the opposite side of the engine vs. stock. There is a diode in the factory wiring for the charge light so I'll give it a go. I'm not sure of the logic of the OEM vs. the GM. I also noticed the OEM is center tapped on the "Y" 3 phase windings and the GM isn't but the center tap is grounded, I would think the GM is cheaper as it requires less diodes but it doesn't utilize the reverse flow of the current and maybe that is correlated to the voltage regulator and how the AC is rectified..

Yup, single wire doesn't compensate for the voltage drop. After looking at the wiring diagram for the 80, hook the 'S' to T2.

 

[D3fiant]

Um, I may have missed it, but why are you using a GM alt?

 

[Kief]

Its attached to the motor I've swapped in which has a HD 8 groove serpentine pulley system and also utilizes a particular mounting system that I didn't care to take the time to fab, my stock alternator won't take the same pulley and would require a bunch of fab to get it right if it did. The stock set up didn't eat belts so I didn't want to regress. I would like to upgrade to an internal fan, higher output alternator eventually and if a 3 wire I will go with that.