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Thread: Variable speed 1/4 hp motor
12-02-2008, 05:37 PM #1
Variable speed 1/4 hp motor
What would be the best and cheapest way to make a 1/4hp single phase motor variable speed? And I stress cheapest! TIA
12-02-2008, 05:54 PM #2
The only method I know of is with a VFD.
What is the application?
12-02-2008, 06:37 PM #3make a 1/4hp single phase motor variable speed?
If it's an AC induction motor, gears or pulleys would work, as would a variable speed gearbox.
If it's an AC/DC universal (brush type) motor, a router speed control would do.
If it's a DC permanent magnet motor, you'll need a PWM motor drive.
To use a VFD, the motor must be three phase.
12-03-2008, 04:17 AM #4
SIngle phase induction motors don't work with VFD's. Period.
Your best bet for cheap is a spring loaded variable speeed pulley with the motor on a swing mount. You can get about a 3:1 speed variation from that. You can get about 7 to 1 with a two pulley V/S drive.
Here's a source:
12-03-2008, 05:50 AM #5
Cheapest way I know of is to pick up a 3 phase 1/4 ph motor for free and add a VFD. Depending on the VFD you get, a new VFD will cost between $99 and $120. $99 for the 1/4 hp VFD and $120 for the 1hp version. You will have all the variable speed you need.
12-03-2008, 12:25 PM #6Your best bet for cheap is a spring loaded variable speeed pulley
I've used Browning adjustable pitch sheaves, which are similar because the pitch diameter is variable.
Screw in the threaded side to increase PD, screw it out to decrease PD. The motor still has to be on a hinged or spring loaded mount.
12-03-2008, 06:49 PM #7
If you want to control an existing 1ph motor, then as mentioned already, VFD is out,
I would either look at 3ph motor and VFD, or get a surplus 90v DC motor and SCR controller, these are relatively cheap, you do not need PWM.
120v or 240v can be had on ebay for ~$25.00.
These run direct of the 120v supply.
If the motor has a tach, you get the bonus of closer speed control, as the Baldor or KB SCR drives will run with or without tach.
If you need extremely high rpm, then a Universal motor and TRIAC (router) controller would do it.