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How To Upgrade Your Farm's Electric Power
Variable frequency drives (VFD's) let you use 3-phase motors without paying for 3-phase power. What's even better, they provide infinitely variable speed control on big electric motors and the tools they drive.
"Three-phase power is typically 150 percent more efficient than single-phase and allows smaller motors to be used," says Philip Myers, Myers Machine & Mfg.
These cost savings, explains Myers, are why 3-phase motors are used almost exclusively in industrial applications. As a result, used motors are readily available and economically priced. Myers frequently finds them in good condition for $5 to $10 per horsepower.
To use them, Myers buys VFD's. They rectify incoming AC power to DC current and back to higher quality AC power that can be controlled.
"A VFD provides infinitely variable speed control, up to double or more than the 60 cycles the motor was originally designed to run at," explains Myers. "It also gives control of the rate of acceleration and deceleration with dynamic breaking and stopping. Another advantage is that torque doesn't drop off as speed decreases."
Standard single-phase AC induction motors switch on or off at full voltage supply. VFD's let a motor develop 150 percent of rated torque while drawing less than 50 percent of rated current.
"VFD's eliminate the need for gear reduction because of the way you can adjust the electrical power," says Myers. "We put them on all our shop equipment. It's amazing to be able to easily adjust speeds."
For a number of years, Myers used 3-phase motors on single-phase current by using static converters or rotary phase converters. However, when he switched his shop from manual controlled machines to CNC (computer numerically controlled) machine tools, the power provided by the converters wasn't high enough quality.
"They required purer 3-phase power," says Myers. "The $24,000 estimated fee from the power company for bringing 3-phase power one mile to our farm provided the incentive to search for another solution."
The answer Myers found was the VFD. He bought a 125-hp, 230V drive for about $6,000 and coupled it to a 50 kW, 480V, 3-phase generator. This gave him a dependable power supply for his entire shop at roughly half the cost of the electric company fee, plus it was a cheaper power with no extra demand charges.
Myers also uses individual VFD's on each motor. He has used one drive on a 3-phase, 5 hp lathe for 14 yrs. with no problems. Myers cautions that drives and motors must be connected directly without a switch or transformer between them. "Drive voltage must match that of the motor, and you need to use a drive with 30 to 50 percent higher hp rating than the motor if input is single-phase," he says. "The exception to that is 3 hp drives and under."
Myers stocks used and new surplus drives from hp drive with 115V single-phase input and 220V, 3-phase output for between $130 and $150, depending on enclosure.
"We've used these drives to power our 3-phase, 10 hp screw compressor, lathe, forging hammer and variable hydraulic pumps, pressure washers, conveyers and more," says Myers. "My nephew uses one to provide variable feed and auto reverse on his band saw. A local fire department bought one to power their 3-phase siren. We've sold them to woodworkers, farmers and manufacturers. Any heavy power usage will provide energy savings over time."
Contact: FARM SHOW Followup, Myers Machine & Mfg., 587 Thomas Rd.. Hollsopple, Penn. 15935 (ph 814 629-9632).

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2010 - Volume #34, Issue #2