Re: 1 wire alternator confusion

Posted by DavidPackard On 2022/12/8 16:58:54

Humanpotatohybrid:

I found the binder!

Just a bit of background: I converted my Model A from 6 to 12 volts. The previous owner had installed a Delco 10-SI alternator equipped with internals to regulate at 7.2 volts (aka 6 V), positive ground. My conversion was to 12 volt negative ground, with a Delco 10-SI alternator. The car was initially wired with one wire connected to the B+ terminal (that’s the big one), with the other two terminals covered with a rubber plug. As far as I know that alternator had no objectionable characteristics, so I wired the 12 volt alternator exactly as the previous. That alternator had what I considered an objectionable characteristic of ‘late cut-in’. Since the Model A has a ridiculously low idle speed and a rather small crank pulley diameter, both of the alternators were fitted with the smallest diameter pulleys available.

The small terminals should be identified on the casting, but if not the number 1 terminal is closer to the B+ terminal. Terminal 1 appears somewhat of a ground when the alternator is ‘off-line’ and will transition to output voltage when the alternator is ‘on-line’. The plot thickens a bit because Delco has many internal regulators . . . voltages of 6, 12, and 24, and both ‘one-wire’ and ‘three-wire’ configurations, terminals 1 & 2 connected, and a few regulators that have only one of the small terminals.

The Delco manual is quite clear that the rotor is excited by the current applied to terminal #1. My testing on the Model A was guided by a circuit in a shop manual for an Oldsmobile where a 10 ohm resistor was in parallel with a low candle power indicator lamp. From that I assumed that the target current flow to terminal 1 should be about 1 amp. I actually tested 0, 0.25, 0.50, 0.75, and 1.0 amps (50, 25, 16.7, and 12.5 ohm resistance), in conjunction with a LED indicator (trivial current flow). The cut-in speed was definitely reduced each time the terminal 1 current was increased. For quite a long time I had the 1 amp configuration mounted in a plastic project box, with the LED indicator, and an ON/OFF switch. I would start the car, and then a bit later after turn the excitation ON, which excited the rotor and the alternator transitioned to ‘on-line’ smartly.

Let’s move on to terminal 2. That’s the terminal that I understand what the purpose is, but I’ve actually run with nothing connected to it, which has me baffled. The Delco information identifies this as the remote sense terminal, meaning if a wire is connected from a specific location in the car’s electrical system to terminal 2, then the voltage at that specific location will equal the regulated voltage, and the output as measured at terminal B+ will likely have a higher voltage. At the Saturday night car shows I’ve frequently seen short jumper wires from terminal 2 to the B+ terminal. I have dated circuit diagrams for the voltage regulators, so there may be an up-dated version that uses the Zener alone if terminal 2 falls below a certain level.

In summary we have both run Delco 10-SI alternators without the two small terminals connected, and other than late cut-in the alternators seem to have worked just fine. Later I modified the car’s electrical system by connecting terminal 2 to a location much closer to the battery, and connecting terminal 1 to a power source that was current limited to approximately 1 ampere. In that configuration the alternator seem to work just fine, and the late cut-in speed had been adjusted closer to the engine’s idle speed.

If it was my car I would connect terminal 1 to a key activated circuit that is current limited to 1 ampere, and then connect terminal 2 to either the B+ terminal or the main binding post of the wiring harness (likely the battery side of the solenoid).

Now on to a bit of speculation on my part. I’m thinking of an engineering meeting at Delco when the failure modes and effects were being discussed, and the subject of what should happen if the indicator bulb fails. It seems that having a late ‘cut-in’ was an acceptable effect. Moving on to the robustness of the design if the customer didn’t need the remote sense feature. I think the regulator was design to allow the customer decide whether that feature was necessary.
I’m looking at a Delco illustrated parts catalog and see both 6 volt, 12 volt, and 24 volt regulators that are identified as ‘one-wire’, and they have both small terminals. There are also regulators that have terminal 1 and terminal 2 connected with a ‘bridge’ that can be cut in the field if remote sense is desired. There are also regulators that have only one of the small terminals. I have not found in the Delco catalog a 10/12-SI regulator without the small terminals.

For those members that have installed Delco 10-SI or 12-SI alternators, and use the car regularly, I would use the three-wire design . . . only because that design was used by GM for many years. They’re available at a reasonable price at a typical ‘big-box’ auto parts store, and if the clocking is not correct that can easily be changed without removing the pulley. Clocking refers to the location, aft looking forward, of the small terminals with respect to the threaded mounting hole.

To ‘Big Kev’s question about whether the alternator is a ‘1 wire’: If the only short coming is a late cut-in speed I would presume the alternator is a ‘3-wire’. The link to the red & white wire connector that Cli55er provided was the one that I used, but it was from the local auto parts store. I somewhat take exception to the comment that 3-wire alternators won’t charge if connected as a 1-wire. My experience suggests the 3-wire does work when only the B+ terminal is connected, but the cut-in speed is objectionably high (excited by only residual magnetism). And given the infinite combination of pulley diameters and final drive ratios the alternator may never ‘cut-in’, which would lead to a conclusion that would be correct for that car, but not all cars.

What is the diameter of the alternator pulley? I’ll presume that the Packard doesn’t have quite the octave range as say a SBC.

dp