12v conversion wiring - Farmall H

I am in the process of wiring up the Hitachi 14231 alternator on the H, and want to thank everyone for their great information (Bob M for his wiring diagrams, Dean O for his threaded rod photo, Jim N for his comments, plus all others I've failed to add).

I do have one comment regarding the wire size of the 1N4001 diode - it is on the thin side, I would think it defeats the use of 16 ga wiring after it? Granted, I am not an electrical guru.

I know you folks have been doing it for years without problems. Comments, anyone?

The diode is fine, wire is over sized, which is also fine.

It requires very little current to initially excite the alternator, I don't have any exact amount, but 20 gauge and smaller wire would likely handle it just fine. HOWEVER for simply improved strength and vibration 16 gauge etc may be commonly used. Likewise, a higher amperage rated diode (say a 5 amp or more) with bigger leads (more strength) could suffice, even if not needed.

Instead of a diode and if one just wants to have the added strength, I have used like a 5 or even 10 watt rated 10 ohm resistor instead of a diode as it provides at least somewhat higher degree of safety current limiting and has bigger stronger leads.

ALSO if a person were to use (instead of a diode or resistor) a small tail/marker automotive 12 volt incandescent light bulb, the needed current limiting PLUS a charge indicating idiot light is now at your disposal!!!

FINALLY if you wanna really get fancy I think my friend Bob M has suggested an idiot light in parallel with a resistor so excitation can take place if the bulb were to burn out!!!!!!

BOTTOM LINE you can use a bigger diode,,,,,,,,,,or a 10 ohm resistor(what I usually do) ,,,,,, or an incandescent idiot light

The diode thing is whats been passed down over the years (now an old wives tale or urban legend) as THE way to do it although there are certainly better and other ways to allow for initial alternator excitation plus prevent run on when ign is off when using the Delco 10SI and similar family of three wire alternators

John T

Like John T says, 16 ga wire is required for mechanical strength only.

The current carried by the excite circuit is only a couple tenths of an amp. So theoretically a very fine wire (like AWG #30) would be sufficient. But minimize risk of failure of the wiring from vibration, abrasion, etc., 16 ga wire is specified.

IH used all three methods to energize the alternator. They used a diode for gasoline engine tractors and a resistor for diesel engine tractors in the excite circuit for the 10SI alternator. For the 10DN alternator on tractors like the 806 they used a light bulb on the dash along with a resistor at the regulator to provide the initial voltage to energize the alternator field.

When I did a Super H I put the diode several inches away from the alternator, put heat shrink over it, then tied that wire and the big charge wire to the brace bar above the valve cover.

Radio Shack 276-1661 has heavier leads and higher amp rating.

I am very happy with a little $5 idiot light I got from NAPA. It's an Echlin ECH TGA10. I don't sweat the bypass resistor--that little Hitachi will excite just fine without it once you get her up to about 2/3 throttle as it did before I put the light in. The bulb is non-replaceable, but I'm sure it will last a good long time and it looks right in the dash of my 140--just needs a 3/8" hole to mount.


http://www.napaonline.com/Catalog/C...Switch-Accessory-Lamp/_/R-ECHTGA10_0006539451

Here is my wiring for my SA using the Hitachi 14255, same wiring as the one you're using, just a little bigger. Any diode with at least 1A 50v rating will work, I used a 3A Radio Shack diode just because that's what was in stock. I added a 10 resistor in series with the diode just for protection in case I fat fingered the connector wire when testing. The resistor will protect the diode from momentary shorts to ground. Not required, you may want to not use it. I highly recommend a fuse at the alternator B terminal to protect your alternator, wiring, and battery.

Thank you all for the abundance of knowledge you willingly share; always appreciated! -Paul

If you are going to put a fuse in the alternator to battery wire it should be at least as large as the maximum alternator output. In this case it would be 50 amps. If you have a 30 amp fuse for an alternator that is capable of producing 50 amps is would be possible to blow the fuse if the battery were low and the engine rpms allowed the alternator to produce the full 50 amps.

(quoted from post at 09:13:49 10/24/13)
If you are going to put a fuse in the alternator to battery wire it should be at least as large as the maximum alternator output. In this case it would be 50 amps. If you have a 30 amp fuse for an alternator that is capable of producing 50 amps is would be possible to blow the fuse if the battery were low and the engine rpms allowed the alternator to produce the full 50 amps.

Click to expand...

True to a point, but on Farmall tractors, the highest RPM is about 1600 and with a about a 2:1 ratio on the crank/alternator pulley, the max alternator RPM is about 3000 RPM. At these RPMs, the alternator can provide about 60% of it's rated output. For the Hitachi 14255, that is about 30 amps. If the fuse blows, try a 40, but it is not a good idea to run the alternator unfused.