Another requirement when I initially went to variable speed on my lathe, was that the spindle had to stop inside of a second when I switched off or hit the e-stop. I built this in to take advantage of the fact that the G0602 doesn't have any form of braking, so screwcutting becomes a hairy proposition. So taking advantage of the contactor which is used for powering the motor I put a resistor rated at 10 Ohms/ 100W across the terminals so that when the contactor is de-energised the motor terminals are shorted through the resistor. Conversely when energized, the resistor is isolated from the circuit and power feeds the motor. This acts as a brake when connected to a DC motor and the energy directed at the resistor is dissipated by a heatsink externally mounted. I also drilled a series of breather holes on that back contactor cover to allow some convection cooling for the contactor and its coil as otherwise temperature buildup would cause the
coil to fail over time.
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The contactor is a quality unit so coil replacement shouldn't be difficult. This is also the original contactor by the way.
The resistor choice was my decision and works efficiently. If I had wanted a more gradual ramping down of spindle revs I would have gone for a higher Ohms value but kept the same Wattage.
This mod will work on any dc variable drive unit as long as the contactor has the necessary terminals to accommodate it. Please consult a professional sparky if you don't know what you're doing in this department because electrickery is unforgiving.