12-volt alternators on a 6-volt (and now 12-volt) 9N

When I bought my 9N, it had a new 6-volt battery, a Delco-Remy 12-Volt "one-wire" alternator, and a new 6-volt solenoid (in other words, it was still a 6-volt system). I can't determine the actual alternator model since some of the numbers are ground off.

However, there is a stud on the back marked BAT. Immediately above the stud is the letter R. There is a black cap covering two spade terminals on the top. Below the cap, there are two markings: a 1 on the left and a 2 on the right. There is an R below the 1 and an F below the 2. (I think someone on this board said that the R is for Relay and F is for Field and this alternator requires external voltage regulators, but I'm going from memory). Is this a 10SI (17SI) or some other oddball GM alternator?

The alternator was wired as follows: a 10 ga wire running from the BAT stud to the ammeter and a wire from the ammeter to the starter keyswitch. There are no other wires attached to the alternator.

Here's the catch: in the 6-volt setup, the 12-volt alternator was putting out 6 volts and the ammeter showed a minimum of 10 A-15A (if it took a while to start the tractor, the alternator may put out almost 30A). To be fair, the alternator was putting out 6 volts when connected as indicated above, but over 12 volts when completely disconnected.

When I converted the tractor to 12-volt, all I did was add a dropping resistor (about 1.5 ohms), installed a 12-volt Ford car solenoid and swiped the battery from my truck. The 9N starts right up now. When I'm running the starter, the ammeter shows a slight discharge (about 1-3A), but once I turn the key back to run, the ammeter never actually shows a positive charge (I've even tried running the engine at full throttle). The voltage at the BAT terminal of the alternator is 12.47V, however.

One of the articles here at YT suggest that on 12-tractors, a voltmeter is better, since these 12-volters don't draw much current (and that as long as the alternator is putting out 12-14V all is OK). Is this ammeter-showning-a-charge-at-6-volts-but-not-at-12-volts a problem? Should I add a voltmeter?

Thanks

All of the comments below refer to your description of how it operated when set up for 6V operation.

The evidence for it being a 6V alternator is that the charge rate changes depending on how far down the battery was. This proves that the alternator was charging and voltage regulation was taking place. Further, since we know that the regulator was active, it almost has to be a 6v alternator since if it were a 12v, the charge rate wouldn't drop to the 10-15A that you report.

The only thing I can't explain is why the charge rate doesn't drop down further. (Did it ever drop to a lower current?) If it were still a 6V system, I'd ask you to measure the voltage and current more accurately to help figure out what's going on.

The 1-3A discharge when cranking is the current to the ignition circuit.

chuck
436244

Batteries are great limiters. A 12v alternator will not "show" 12v if it's lugged down to a 6v battery, however, this is not a good setup and will destroy the 6v battery in time.

I think you're on the right track and you may see a charge from your alternator, once you tie those two lugs to the BAT lug.