Variable speed control device

eyeeatingfish

eyeeatingfish

Joined
Dec 9, 2003
Messages
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I have a belt sander but it only runs at one speed. Does anyone know a device I can hook up or wire in to control the speed of the belt? I checked out a speed switch for a fan but it wasnt high enough amps. My motor runs 6 amps, 120 volts I believe.
 
you need a DC setup or you could get a 3 pulley setup

as far as i know there might be something you can grab to set it up
 
Someone mentioned a router speed control device, however it was something like $60 bucks... that seems awfully expensive.
 
eyeeatingfish said:
Someone mentioned a router speed control device, however it was something like $60 bucks... that seems awfully expensive.
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:cool:...They might have been talking about This...Not sure if it'll work but it's a thought...:)...Looks like it has enough amps for ya...
 
I haven't set up one of those myself, but I was told the torque would be so low as to make them useless. A variable speed motor / controller is generally a $500 - $1000 option so $60 would be almost free.

If you decide to risk it, let us know how it works out.

Rob!
 
All I really rember is that most things that LIMIT power unless they are digital will have to consume that power and turn it to heat in most applications

but its a big world and im a small person lol

60 dollars isnt much.... a pair of good pulleys will cost that much at least
think of it as an investment and timesaver
 
DC motors have a long standing rep of being the only motors you can vary the speed on AND KEEP THE TORQUE! But DC motors have alot of issues such as brushes, etc not to mention most folks don't have DC volatage at their home or buisness! ALot of folks get confused when you talk AC Motors. There are TONS of varieties of AC motors! Shaded pole motors such as fans etc etc that HAVE OR CAN TAKE NO TORGUE can be slowed by simple rheostats that simply lower the voltage! BUT when you have a AC motor that needs slowed AND NEEDS TO KEEP THE TORQUE you can only do it presently with a VARIBABLE SPEED DRIVE! VSD's change the hertz, or to keep it simple the alternating sine value that is a standard 60htz in the USA. VSD's have came down in price considerably lately and probably will come down more with the "world economy" but till then that's the only option for someone that wants to push a piece of steel up against a rubber wheel till it can't take no mo! lol Even then there are trade offs!
 
LCoop said:
DC motors have a long standing rep of being the only motors you can vary the speed on AND KEEP THE TORQUE! But DC motors have alot of issues such as brushes, etc not to mention most folks don't have DC volatage at their home or buisness! ALot of folks get confused when you talk AC Motors. There are TONS of varieties of AC motors! Shaded pole motors such as fans etc etc that HAVE OR CAN TAKE NO TORGUE can be slowed by simple rheostats that simply lower the voltage! BUT when you have a AC motor that needs slowed AND NEEDS TO KEEP THE TORQUE you can only do it presently with a VARIBABLE SPEED DRIVE! VSD's change the hertz, or to keep it simple the alternating sine value that is a standard 60htz in the USA. VSD's have came down in price considerably lately and probably will come down more with the "world economy" but till then that's the only option for someone that wants to push a piece of steel up against a rubber wheel till it can't take no mo! lol Even then there are trade offs!
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Any recomendations?
 
I assume you don't know that an induction motor has no brushes, that is why it is an induction motor. DC motors have brushes as do some smaller AC motors.Synchronous AC motors have brushes, some of these are variable speed,like in a flexshaft unit.
Stacy
 
bladsmth said:
I assume you don't know that an induction motor has no brushes, that is why it is an induction motor. DC motors have brushes as do some smaller AC motors.Synchronous AC motors have brushes, some of these are variable speed,like in a flexshaft unit.
Stacy
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What would happen if I used a variable speed control that is designated for electrict motors with brushes on a brushless motor?
 
If the motor current draw was more than the unit could handle, smoke would happen.
Even if the unit didn't burn up there would be little likelihood that it would give any satisfactory results. The speed controls for dremmels are not rated for the current draw of larger tools like belt sanders. Router speed controllers are more robust, but as said, are for a different type of motor.

Motor speed in an AC motor is a function of the frequency of the power supply (hertz) and the way the motor is wound. If the speed is to be varied, something has to be changed in the equation. Since the motor usually has to stay the same in use, the power supply is what is changed. The voltage can be dropped, causing a loss in power, which is seen as a lower speed, but is terrible inefficient. The frequency can be changed, allowing most of the torque to be retained, but the external power control system to chance the frequency is not cheap.

So the two main solutions are a VFD ,to change the frequency, or a DC motor, which runs on variable voltage.

Believe me, if there was a simple, cheap, and efficient way to vary the speed of a motor above fractional HP, it would be on every shop tool in existence.
Stacy
 
Believe me, if there was a simple, cheap, and efficient way to vary the speed of a motor above fractional HP, it would be on every shop tool in existence.

Truer words have never been spoken or written! Dremel tools have brushes for the record as do electric hand drills that have variable speed! Variable Speed Drives VSD's have came down considerably in price in the last few years and I expect them to come down even more BUT I doubt they will ever come down to the price of being "cheap". If they were to, like Stacy said they'd be on every electrical motor out there. Right now IF you really need VSD (slowing an AC motor down and keeping torgue) they do it a at a reasonable price PLUS if you don't have 3 phase power you can use a VSD to produce 3 phase with variable speed as a great option.
 
surpluscenter.com

check em out. they usually have some nice sutff. i know two guys who bought a speed control from these guys.. they still sell the same model... and they're been running it on their KMG's for about 8 years
 
Stacy and LCoop are right on about what can and cannot be done to control the speed of different types of motors.

No one has come up with a fundamentally new way to control the speed of an electric motor for something like 15-20 years. All the papers related to motor control that I have seen published or presented at conferences are all talking about refinements of the same basic methods. Most of these refinements are really only relevant to applications above 50-100 hp. The best deal that I have seen so far are the Lenze drives since they are dust proof.

If your sander is a bench model, you can consider using an external motor with step pulleys and driving the sander with a belt. The existing motor in the sander would not be powered. There was a thread a few weeks ago about how some people did this but the search function is not working this evening.

Phil
 
A sewing pedal is just a rheostat (variable resistor). It would burn up at about 5 amps, maybe less. It would only work on a motor with brushes anyway.

You need to rethink this problem from what DOES work, not what might(not) work. A VFD or a DC motor setup will work. Any other setup won't. Plain and simple. Find a system you can afford, or save up to get one later. The price range starts at a set of multi pulleys - $about $10 each, to a high end VFD and matched motor for couple grand.
Stacy
 
How many horsepower is your motor? What is the style of the motor housing? How is it currently installed on your grinder?
 
bladsmth said:
A sewing pedal is just a rheostat (variable resistor). It would burn up at about 5 amps, maybe less. It would only work on a motor with brushes anyway.

You need to rethink this problem from what DOES work, not what might(not) work. A VFD or a DC motor setup will work. Any other setup won't. Plain and simple. Find a system you can afford, or save up to get one later. The price range starts at a set of multi pulleys - $about $10 each, to a high end VFD and matched motor for couple grand.
Stacy
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I wish to save my trusty bench sander but im not sure how to rig up pother wheels and belts. Would it be something akin to the top of a drill press? Would I just slide the motor back and maybe add wheels of different diameter?
 
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