20 vs 30 amp voltage regulator

I doubt anyone where you bought the VR has any idea whatsoever of what Field amps/duty cycle that VR is rated for, let alone the max field current rating of your existing genny !!!!! !!!

Buttttt ttt it could work fine n last a long time, theres just no sure way to tell sititn here with no specs or data whatsoever. I can say Ive used 6 volt gennys n made em work n charge at 12 volts SIMPLY by changing to a 12 volt VR and they never seemed to get hot. Thats NOT the engineering correct or any good way to do it, Im ONLY saying it worked and it may well have been pumping more field current then the genny was rated for, it charged but at no super high rate lol A genny dont really know what its output should be exactly, its increased by turning it faster and/or pumping more amps through its field windings.

Better be safe then sorry although if in a bind and the tractor was needed desperately for a short while I doubt that 30 amp VR would fry the genny in any short period of time or even ever BUT I JIUST CANT SAY FOR SUREEEEE EEEEE E

John T

Running a wire (like those in the armature) at 30 amps when it was designed for 20 amps will more than double the power loss and so the temperature rise in the winding. (1.5 squared = 2.25).

On the other hand there is considerable thermal inertia in copper and battery charging after a start tapers off from the peak current rapidly so the time duration of that peak current for battery charging isn't long.

Another way to limit the current is through the resistancce of the wire betweeen the generator regulator and the battery. I have a run of 10 gauge on my JD 4020 with an alternator. Since the alternator is regulating the voltage at the alternator, the peak current even after a hard start is only 30 amps. If I had a fatter charging wire that peak current would be greater. But it charges the battery fast enough for me so I'll not change the wire. A 12 gauge charging wire 6' feet long would limit the peak current on your 20 amp generator to probably stay close to within its ratings. You might want that wire to have good high temperature insulation. My 10 gauge wire is rated to 250 degrees C. Its silicone insulated with a fiberglass braid. I don't worry about it being close to the engine hot parts like exhaust manifold. That's overkill, but I have a spool of it on hand.

But if you load that 20 amp generator to 30 amps with a lot of lights, its going to smoke. Brushes first, then commutator, then the armature windings.

Gerald J.

Take care Gerald,

John T

But in any case its the wire in the armature and the brushes that limit the continuous current capability. That along with the temperature rating of the armature insulation. Modern insulation will handle a lot greater temperature rise, but the typical vintage tractor generator will have used the least expensive paper insulation with the lowest practical temprature rise because in those days saving copper didn't save enough money to pay for high temperature insulation. Today saving copper does pay. Look at the tiny starters even on trucks these days.

A good automotive electric shop might be able to readjust the current limit without wrecking the voltage regulation or have a far greater selection of regulators to get the right one for that 20 amp generator.

Gerald J.