15 Amp vs. 30 Amp Stator/altenator

[BigRedD180 1]

I am in the process of a repair of my Crank, Flywheel, and Stator. I bought a used flywheel and stator to find that the stator is a 30 amp. This unit is much beefier than the 15A that was original and has 2 extra wires coming out of the stator:

I am an electronics tech by trade but I am a little confused by this set up and would like some others input.

I have 3 wire rectifier/regulator (that i dont know if it is any good any more since the stator shorted out and the "magic smoke" was let out of the wire that shorted, the unit doesnt "smell" fried but ya never know):

This is the set up for a 30 Amp system with the 4 wires (2 10G Black and 2 20G Red). The black is definitely the AC output for the stator but what the heck are the red wires for? They have to be a separate circuit because the testing procedure indicates different ohm readings when measuring across each pair. From the drawing below, one red goes to gnd and the other goes to the reg of the 30 A rect/reg:

If my 15 Amp rect/reg is OK (any testing methods would be greatly appreciated), Can I just hook up the 2 black wires and cap the reds? I really hope that this will work because I REALLY dont want to pay $60+ for a new rect/reg, debating on going to radio shack for a full wave bridge rectifier and a voltage reg to make my own.

I hope to some day repay the knowledge that you all have given me over the past month, :thumbs:

[Save Old Iron 1,563]

The 15 amp stator matched to the 15 amp regulator are designed to compliment one another - the 15 amp stator, by design will not be able to supply more amperage than the regulator can handle. The regulator is protected from destruction in the case of a heavy current demand in the tractor's circuits.

A 30 amp stator will need its flywheel "mate" to produce the 30 amps. More magnets on the flywheel usually are all that is need to produce more amperage and the heavier gauge wires on the stator are able to support this flow. Possibly using the 15 amp flywheel will limit the amount of current the charging system can develop thru the beefier stator.

A 30 amp stator will not start "giving up" if asked to supply a current greater than 15 amps. Current flow over 15 amps could fry the 15 amp regulator.

A regulator will regulate the VOLTAGE to the battery / load.

The regulator will not regulate the maximum CURRENT to the battery / load.

I don't own a D but purely from an electronics point of view, the 30 amp stator could fry the lower rated regulator given the right set of circumstances - low battery charge / shorted battery / lots of power accessories, etc.

I too would be interested in what the 20AWG wires would carry - by gauge only - must be a low current supply - less than 5 amps I would guess.

[MikesRJ 552]

I believe the two red wires are AC bias voltage to the regulator circuit, which is used to maintain regulator output voltage at low engine rpm. When the AC frequency decreases at low engine RPM, the RMS voltage from the alternator decreases as well. The two red wires supply bias voltage to the regulator and the output voltage of the regulator is internally increases in order to maintain a steady ~13.5 volt output from the regulator to the battery/equipment.

[BigRedD180 1]

I think that this is going be some trial and error (hopefully not too costly error). Soon as I get the engine running, I will have to dig out the o-scope and look at the outputs before and after the 15A rect/reg to see if it is working and if it does not then I will probably have to break down and buy a 30Amp Rect/Reg.

I would think that the 15A Rect/Reg would work as long as the load demand stays in check, probably add an Ammeter to the dash to keep an eye on the draw if the 15A is in working condition and does its job with the 30A Stator.

I will report my findings with the O-scope, pretty curious how this all works.

Thanks for the info

[Save Old Iron 1,563]

This is a bit of a charging archeology dig, but I do have an answer to this question. Why do 30 amp stators have dual sets of windings?

 

The secondary set of stator windings are wound in an opposite direction to the main winding. When the rectifier / regulator allows controlled current to flow thru the "opposite" secondary winding, the secondary winding "inhibits" the primary windings from producing additional power. So the secondary set of smaller gauge windings control the output from the primary windings. Of course, the rectifier / regulator determines the amount of opposition power in the secondary winding.