Generator windings absorb moisture in high-humidity environments. Moisture weakens the insulation and leads to short-circuits, requiring replacement or rewinding.

To prevent this, the generator windings need to be kept slightly warmer than the ambient temperature.

New windings should have over 500 Meg-ohms from any winding to the frame. This must be measured with a meg-ohmmeter using 500VDC. NOTE: All leads, voltage regulators, etc, must be disconnected during a meg-ohm/insulation test, both to avoid damaging other equipment and to get accurate results.

Used generator windings may be between 50-100 Meg-ohms. If the measured insulation resistance is below 1 Meg-ohm, the generator should be taken out of service and the windings dried by a suitable method. The generator manufacturer can best advise on this. WARNING: Simply starting up a generator with low insulation resistance and a voltage regulator connected can cause a short circuit in the windings and permanent damage in just seconds.

Factory-supplied anti-condensation heaters operate at approximately +100C but are mounted on a bracket in front of the exciter. They depend on the heat conduction through the bracket to the generator frame. This does not seem to keep the actual windings warm enough to prevent moisture ingress.

We have been using regulated heat tape from Raychem, but the heat output decreases with temperature, and at 100F the output is below 1W/foot – providing less than 25 watts total output.

• Strip the base plate from two 1000W / 230VAC clothes irons
• Drill & bolt the bases to each side of the generator mounting foot/frame
• Connect to 120VAC
• If possible, save the indicator light from the iron and mount it so that it is visible when power is connected to the heater.

Operating at half voltage reduces power to 25%

• 1000W @ 240VAC = 250W @ 120VAC
• If 120VAC is not available, wire the two irons in series. Two 1000W irons in series @ 240V = 500W total, 250W each.

Top of generator frame is comfortably warm 12 hours after shutdown. This is ideal.

• Top of generator 95°
• Bottom of generator 114°
• Heater 175°

Ideal mounting position would be in the center of the bracket so that less heat is conducted to the mounting frame.