[Mace1971]

I purchased a Summit alternator https://www.summitracing.com/parts/sum-810344
which is billed as "1-wire or 3-wire capable." Summit's alternators are the only ones I can find that are billed as both 1 and 3 wire, all the other alternators I've looked at are one or the other. I started thinking that this alternator is in fact just a 1 wire but with the additional plug to allow it to be wired as a 3 wire for appearances sake (and probably to enable the alternator light). Summit claims that the third wire does provide remote 12V sensing but does anyone have experience with these alternators and know that it actually functions as a 3 wire with remote sensing?

[OrigOwner77]

https://www.summitracing.com/parts/tff-7127

That's the alternator I have on my '80 T/A. Also has the same type of voltage regulator you describe (1 or 3 wire hookup).

From what I've learned, this type of alternator will self-excite at startup to begin charging immediately. Traditionally, the exciter circuit uses either an idiot light or resistance wire to trigger. If that wire is open / disconnected, the alternator won't charge at startup/idle until the motor is revved.

I've tested mine with / without the 2-wire plug connected. There was no difference in operation. It started charging immediately.

With a stock alternator, if the 2 wire plug is disconnected, you can start the car and only see about 12v until the alt kicks in (rev the motor), whereby the voltage comes up to +/- 14.4v.

The only difference should be if you're running a load on the charging system (headlights, wipers, heater). With the 2-wire plug connected, the alt will sense voltage and output more/less as needed to maintain the regulator setpoint (14.4ish volts). With the 2-wire plug disconnected (1-wire hookup) the output will be whatever the regulator setpoint is, no more, no less. Regulator setpoints vary from around 14.2 to 14.7 volts.

Electrical gurus, please correct me if I'm wrong.

[george kujanski]

With the 3 wire connection, the voltage at the end of the sense wire will be controlled to the set point.

With the one wire connection, the voltage at the alt output will be at the set point.

The difference in the system voltage is at high output currents. With the one wire, the voltage at the load will be less than the set point due to voltage losses in the harness.

With the 3 wire, since the battery voltage is controlled, the system voltage is dependent more on the harness connections and the harness voltage drops between the battery, harness, and alternator.

Since the battery charge state is probably the most important factor for the life of the battery, the 3 wire connection is preferable.

George

[Mace1971]

You guys have gotten to the problem, remote sensing. It's good that it will self-excite regardless of one or three wire but the remote sensing is something else that seems important. I'm just not understanding how a single alternator can actually operate as either one or three wire with no modifications given that I've seen no others (besides the Summits) which make this claim. I'm still wondering if this alternator actually works as a three wire with remote sensing or not. OrigOwner...have you actually checked the voltage under load both with and without the additional wires connected? I don't know if that's the right way to check this or not but don't know for sure.

[johnta1]

It's probably jumpered internally with that plug?

My alternator on my dragster is the original type on mid-70's Bird, but I have jumpered the plug to make it like a one wire.
(only one wire used on it to the battery)

Basically both wires on plug connect to the big post on alternator then one wire to battery.

[connman]

My 2 cents. The farther away that the senseing wire is located from the alternator the better it charges cause it is reading the whole circuit not just inside the alternator. My understanding is that most cars , the senseing wire is spliced near the stsarter.