PWM Motor Speed Control

Unless it has brushes, you can't change the speed by dropping the voltage. Induction motors use the line frequency to set they're speed Dropping the voltage may slow them a bit as there isn't enough magnetism generated to overcome the load and you get slip. They generate a LOT of heat then and very little torque.

Greg
 
Unless it has brushes, you can't change the speed by dropping the voltage. Induction motors use the line frequency to set they're speed Dropping the voltage may slow them a bit as there isn't enough magnetism generated to overcome the load and you get slip. They generate a LOT of heat then and very little torque.

Greg
Greg,
Would I see exterior brush caps if my motor has brushes or are some internal?
 
Your split phase phase motor won't have brushes Dick. Things like treadmills use them to easily get variable speed as do hand drills. Most power hand tools use DC motors as they develop high torque in a small package.
One more caution Dick. Some really old AC induction motors had brushes. They were called repulsive / induction motors. They won't work with a variable voltage either.
Unless the plate says DC or AC/DC it won't slow down. Or not for long anyway.

Greg
 
Thanks, Greg

I will probably use the drill press as it is. It is an old Toro that I rebuilt and it is wired for forward and reverse, but it is inconvenient to change belt positions on the step pulleys. If it was a Walker Turner or old Delta it might be worth the effort.

Dick
 
Not cheap to do but you could replace the motor with a 3 phase one and use a VFD variable frequency drive to change speeds.
Or there have been many posts with people using a treadmill motor and the PWM controller to get variable speed.

Greg
 
This may sound like like a silly question, but how can a motor be both AC and DC?

Dick
That is not a silly question, but an excellent question. AC/DC or also known a universal motors are usually small motors that you find on portable tools and small appliances such as vacuum cleaners. Universal motors are basically a series wound DC motor with some modifications. The main mod is a added compensating winding so it will run on AC better. Usually a thyrister controller is used. You know those lamp dimmers for regular light bulbs. Same type of control. Since the motor is only 1/4 hp. you may be able to use an old appliance motor with a dimmer switch. Just make sure the dimmer can handle the current.
 
PS an old sewing machine motor might work.
I'll offer a cautionary note here. Picked up a relatively new looking Singer sewing machine at Goodwill a couple years ago, just to check out the motor and speed controller. The motor's nameplate says 120V 60W (or about 1/12 HP). That's way too small for a drill press (which is what the OP was asking about). Might be OK for a micro drill press, though.

<Edit added> - My used sewing machine motor, previously offered, has been given away.
 
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I'll offer a cautionary note here. Picked up a relatively new looking Singer sewing machine at Goodwill a couple years ago, just to check out the motor and speed controller. The motor's nameplate says 120V 60W (or about 1/12 HP). That's way too small for a drill press (which is what the OP was asking about). Might be OK for a micro drill press, though.

If anybody wants to experiment with it, I'll be happy to send them the motor and foot pedal for just the cost of postage. PM me.
Red face department. You are right. Should have check it out.
 
I have an old drill press having a 1/4 hp AC 115 volt split phase motor from the 1950's.
Can I use a PWM motor controller to control the motor speed? There are several available on EBay.
I am looking for a quick way to adjust speed other than changing belts. Most all my work is with smaller drill bits.

Dick
No. You cannot. AC motors are trickier to control. Some AC motors (like fans) can have some kind of crude speed control. 3 phase AC motors can be controlled very accurately. Same goes for DC motors. Your drill press is not one of them. Use your belts to change speeds.

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