Soft-Starting Electric Motors Jim Forgette Important Caution The permanent-magnet"type motors used for washer converting and other machinery produce an usually strong, abrupt starting torque -- more stress than many ac appliances were designed to withstand. In the older washers with belt-drive and metal gears, a 12 or 24 VDC conversion seemed to be able to handle this excessive starting torque, although over the long haul it will undoubtedly shorten the transmission's service life. I have found that the 115 vac conversions can produce an even more severe, sudden start than the 12 or 24V. Most newer washers use plastic type tranny gears instead of metal. Direct-drive washers washers do not have a drive-belt to help dissipate this sudden jerk. The worst-case-scenario is a plastic geared, direct drive washer converted in 115 vac. This example could produce severe damage, in the short term, to the transmission gears. Other detrimental effects from this strong start: 1) It prematurely degrades contact points of any relays used in conversion circuit (arcing); and 2) it can prematurely weaken (de-magnetize) the permanent-magnets in these motors. In certain industrial appliances using these motors, a protection sometimes called "Soft-Start" is included, which greatly mellows this high amperage jerk start (see graph showing difference). Machinery you convert should also have this protection. I've researched this and put together a simple, effective soft-start module using Rodan SG220, SG210 or SG260 thermistors. Two should be used for reversing-type washer/machinery designs. You must know the motor horsepower rating and full load amps (common info on motor I.D. plates or from the factory/dealer). INSERT GRAPH Main summary This circuit is useful to greatly reduce power consumption of many 115 vac appliances & machinery in the 1/4 to 1/2 horsepower range. Even though the new motor is DC, the appliance's power input is still 115 vac. In this way, the existing ac supply/wiring can still be used. Improved efficiency will vary with application. Be sure to ground the DC motor's case to the frame of the appliance. Before removing the old ac motor, turn on the appliance and note direction that the motor turns. If the new DC motor runs in the opposite direction, simply reverse its DC power wires. If the new DC motor's RPM is low, then increase the value of the capacitor to 350 æF. Be sure to disconnect the power source from the appliance before working on it, otherwise you can get a nasty shock. In a washing machine, expect a 3-fold increase in efficiency. The circuit can also be used in most conventional dryers, wringers, pumps, shop machinery, swamp-coolers, large attic fans, etc. If a larger horsepower application is desired, the amperage rating of the rectifier, fuse and "soft-start" must be increased accordingly. Horsepower ratings of these 180 VDC motors are commonly available up to 3 hp@ 1,750 RPM (15 full load amps, consumes 4 watts) for about $1,000. (2hp-$750, 1hp-$375, 3/4hp-$300, 1/2hp-$259). INSERT SCHEMATIC This type of circuit is basic to anyone in electronics. But for practical usage, what makes it worth showing here is the specific ratings of each component and the addition of "soft-start". Some of these ratings were found only after much R & D, especially the motor and capacitor. Under load, the DC side of the circuit is about 145 VDC. If a newer motor's horsepower rating is the same or slightly higher than original ac motor, these circuit specifications will yield an RPM very close to the original 1750 RPM ac motor. This allows the original motor pulley/gear size and any drive belt to be re-used in the conversion. The fuse in this circuit is especially important to include. Both amperage draw and torque of these PM motors "goes out the roof" if it is ever forced to stall by a locked- up/malfunctioning appliance. The user's load-center fuse/circuit breaker is usually too high a rating (10, 15, 20 amp) to protect the appliance and circuit from possible severe damage if this should ever occur. Access Jim Forgette, Wattevr Works, POB 207, San Andreas, CA 95249 ù 209- 754-3627. Wattevr Works sell these soft-start thermistor modules for $18 each for 12V, $15 each for 24V and $12 each for 115V. The 12 & 24V modules are wired into a NON fuse holder and have ample terminals for larger-sized wire.