DC Motor speed control - for a laser...

[Gary Hair]

This really is for my laser, I added that to let the mods know it really belongs here.

I have a 24v dc motor that drives the Z axis on my fiber. It runs way too fast for fine adjustments and only has up and down push button switches. So, I'd like to add a speed controller to allow me to slow it way down and get the height exactly what I want it to be. I thought I might be able to use a rheostat or a potentiometer but I'm not sure a) if they will work? and b)is there something better to use? and also what value pot would be needed? They seem to range from 5K ohm to 1M ohm - at our local Radio Shack anyway.

Anyone know what to do with this?

Thanks!
Gary

[Keith Colson]

For a DC motor you want to use a PWM speed controller. A rheostat is what you used in the Edison days. They are linear and generate a lot of heat. They stall a lot easier too.

Search "PWM DC Motor Speed Control" on ebay and you will find one for a bout 5 bucks.

Cheers
Keith

[Gary Hair]

OK, so I looked a bit closer and now I'm more confused... sometimes it's scary how little that takes.

The spec sheet for the motor led me to believe it is 1PH220V yet the power supply that drives it outputs DC24V. I have an ac speed controller that I tried on the output of the power supply and it did nothing, the motor wouldn't even turn. I also discovered a sticker on the motor that matches part of the spec sheet but it's the diagram for a 1PH motor. I have the part of the spec sheet attached showing the diagram. All I really want to do is move the Z axis up and down and control the rate that it moves - easy, eh?

[Keith Colson]

That picture is a 3 phase AC motor and will most likely not be 24 volts, more like 110V. It also has a capacitor to "bodge" a phase shift. I think you might have your wires crossed with specs etc. See if you can find some more solid info on all the parts of your system

Cheers
Keith

[Bill George]

I don't think its a 3 phase motor but the capacitor is helping it start in either direction. Are you 100% sure the power supply is DC out, have you put a meter on it?

[Keith Colson]

The diagram shows this system in place, unless I am wrong which does happen.
http://www.gwm4-3phase.com/uands/static1.htm

If it were a "start capacitor" it would not be switched to a different leg of the motor as start windings have much higher current. The reason the capacitor is being switched to a different phase is to reverse the direction, not to start the motor. The diagram clearly shows "AC" in, which contradicts it being a DC motor.

If it is a 3 phase motor like I suspect you could run it with a VFD (variable frequency drive) I run my blower with one of these. I can dial in any speed I like and set how long it takes to get there. Try setting the meter to AC and see what voltage you see. Measuring AC with the meter set on DC can give untrue voltage readings.

[Bill George]

Its not a true start capacitor but a run cap which does not need to switched out of the circuit. Its just giving a out of phase boost in the other winding to help it start. Motor is called a PSC permanent split capacitor. A true three phase motor has three windings energized at any given time. A VFD is used on single phase sometimes but it still generates a true 3 phase variable Hz current. Just got done putting the single to 3 phase VFD on my 3 phase metal lathe. I have built a static/rotary phase convertor in the past, before VFD's got so cheap.

I think either the motor or the power supply is mis-labeled.

[Gary Hair]

I checked the power supply and it is definitely DC24V. That said, it's not apparent what role it plays in the whole thing... I'm trying to trace the wires and the -V (24v) goes to the up/down switches and I can't determine where the +V goes yet, but it's not to the switches, maybe a relay. The difficulty in tracing the wires is that they are fed through plastic channels and there are several of the same color/size going in and out so I'm not sure what starts and ends where!

The confusing part about the motor is that the part number on the motor is 4IK25RGN-C, which means it 1PH, 220V but the wires on the motor are black/blue/white, which indicate it's 3PH, then there is a sticker on the motor that has the 1PH wiring diagram... So I'm not positive what it is, 1PH or 3PH. I don't see a capacitor externally to tell me it's 1PH, I guess it could be internal?

Oh, there are also limit switches in the mix, the Z can only go so far in either direction. It's setup so that you can still travel the opposite direction when you hit a limit.

Not sure where to go from here, but I may have to give this up for now - paying jobs are calling me away from my quest...

edit: would it harm the motor, or anything else, to turn it manually? there is a handle on the opposite end of the lead screw that it turns and I could adjust it by hand if it won't hurt anything.

[Bill George]

Three phase motors can only be powered by AC. There are exceptions to this.... as a pulsed DC power supply could mimic the AC sine wave, all you really need is three phases or out of phase connections on three legs so it can rotate. Reverse the phase sequence and you reverse the motor.
I know they make 3 phase stepper motors but I really don't know how they are powered. But for all either AC or pulsed DC you would need three wires.

If your Really sure the PS or motor is bad and want to use the hand crank I would disconnect the motor wiring.

[Gary Hair]

If your Really sure the PS or motor is bad and want to use the hand crank I would disconnect the motor wiring.

There is nothing wrong with the motor or the PS, I just want to adjust the speed.

[Dan Hintz]

Gary, are you POSITIVE it's a DC motor and not a stepper?

[Gary Hair]

Gary, are you POSITIVE it's a DC motor and not a stepper?

It's definitely not a stepper. At least not according to the spec sheet I linked. Oops, I thought I linked it... Here it is: http://www.sei-automation.com/products/ACMotor/ACSpeed/2011-4IK-25W-SP.pdf

[Keith Colson]

Hi Gary

That data sheet shows a single phase induction motor which none of use guessed. It is a totally different beast to all the motors discussed so far.. The induction motor speed is set from the AC frequency of 60 hertz in your case. You will still need a VFD to change the frequency. The VFD only needs to be a single phase VFD although a lot of 3 phase VFD's have a single phase connection option.

You should still measure the AC voltage at the motor to confirm what voltage you have I suspect the 24 volts is for the limit switch logic and not the motor itself.

[Gary Hair]

Hi Gary

That data sheet shows a single phase induction motor which none of use guessed. It is a totally different beast to all the motors discussed so far.. The induction motor speed is set from the AC frequency of 60 hertz in your case. You will still need a VFD to change the frequency. The VFD only needs to be a single phase VFD although a lot of 3 phase VFD's have a single phase connection option.

You should still measure the AC voltage at the motor to confirm what voltage you have I suspect the 24 volts is for the limit switch logic and not the motor itself.

Well I guess I have some wire tracing to do... I'll see if I can run down where everything goes and what is connected to what. It's pretty tight quarters and with a few well-hidden splices, it's not going to be quick and easy, but I should be able to have something either later tonight or tomorrow.

Thanks to everyone for their efforts!!

[Gary Hair]

OK... I have a bit more info but not the exact wiring diagram - that would mean more disassembly than what I really want to get into.

The DC24V PS powers two relays that are controlled by two switches, one up and one down. The output of the relays is AC235V and each relay lights up when it is energized. I haven't actually measured the voltage on the motor, the wires are tucked up pretty good and would be very difficult to get to without some major contortion and disassembly - it seems pretty obvious that it is AC although I'm not sure why they ran 240V through the limit switches!

If it would take a VFD to control the speed, then it's not likely to be in the cards. About the cheapest VFD I'm finding is around $150 - for that much I'd swap out the motor and redo the Z drive with a stepper - I have an mpg, all I would need is a drive and the stepper - maybe $75-$100. Unless, of course, someone has a better idea?

[Bill George]

So the DC is for the control relays. The motor is AC 60 Hz. Wonder if a light dimmer would work, in series with the AC line feeding those relays. You would need to find a 240 volt dimmer.

You might look at a place like Surplus Center they have a good website or other surplus electronics sources, who knows you might find a OEM VFD for not much money.

[Gary Hair]

Would something like this work? http://www.amazon.com/gp/product/B00GMBYFRK/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

[Bill George]

Would something like this work? http://www.amazon.com/gp/product/B00GMBYFRK/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Well for less than $7 and shipping you could find out. It says motor speed control, and one guy (not recommended) uses on a furnace blower motor.

[Ray Scott]

This picture shows a SINGLE PHASE motor. The capacitor is used to cause a phase lag. The phase lag is what causes the direction to be controlled. This is NOT a 3-phase motor.

The motor is definitely AC. I have seen this type of motor controlled by 24VDC relays. The relays control which direction the capacitor is arranged.

You cannot use a "Dimmer" to control the frequency. Light dimmers only work correctly with resistive loads (non-CFL). They don't change the frequency...
(1) The cheap dimmers might add a resistive load in the control. That method reduces the light output by "voltage dividing" part of the power to a resistor. By having less amplitude in the AC wave... the light is less bright. This can be applied to a motor. But the result is less correct. The motor may go slower, but only because it has less torque to overcome friction. If you could feel the speed of the motor, you would observe a constant "stutter". The definitive reason for AC motors to go a certain speed is due to the number of internal poles and the AC frequency. The torque is from the quality of the poles, windings, AC voltage, ...etc.
(2) The good dimmers change the power to the light by clipping off part of the AC waveform. The circuit turns off the AC signal as the sine wave crosses zero and then turns the AC signal back on during some portion of the half sine wave. The result is a partial sine waveform. No resistor is used to divert the power. It is MUCH more power efficient. This method works great for devices that might as well work as DC appliances ...such as Router motors, DC motors, LEDs, resistive filament lights...and more. It is NOT recommended for AC motors that need direction control.


If you want to do your project right.... I can help. It really isn't that hard to do.

Choice (A) .. buy a small VFD. You need to make sure I have one to match your needs first. What horsepower? What voltage? What control signals? ..Does it switch the phase lag correctly for your single-phase motor? You need to check the user manual of the VFD. Many VFDs (2.2KW and less) are capable of running single phase and 3-phase. .. ebay .. $60 .. 60 day warranty.

Choice (B) (a more work and more fun project) .. buy a small stepper motor to take the place of the AC motor. Check the torque required. Check the shaft diameter required. Mount the motor in place of the AC motor. Get a matching stepper motor amplifier. ... Buy an Arduino board. I already wrote the code to do basic stepper motor movement. I wrote the project for controlling a laser machine worktable height. As I finished the code project, the factory got smart and changed the table motor to Stepper motor. I now have the kit running in my home lab as a "nearly forgotten" demo of using stepper motors and Arduino.

Choice (C) switch to a DC motor and use a Router speed controller (dimmer box)

Choice (D) get a gearbox to do the speed reduction for you. You only have one speed, but it would be closer to what you want.

[Bill George]

(2) The good dimmers change the power to the light by clipping off part of the AC waveform. The circuit turns off the AC signal as the sine wave crosses zero and then turns the AC signal back on during some portion of the half sine wave. The result is a partial sine waveform. No resistor is used to divert the power. It is MUCH more power efficient. This method works great for devices that might as well work as DC appliances ...such as Router motors, DC motors, LEDs, resistive filament lights...and more. It is NOT recommended for AC motors that need direction control.

Ray the device he has highlighted or bookmarked is a Motor Speed controller. True its not a VFD but people are using them all the time on non-DC motor loads. Uses an SCR and clips the waveform to produce a low cost motor speed control. I have seen them used as fan speed controllers and someone on the Amazon site is using to control his furnace fan motor, Not Recommended by me! Why can't it be used with a reversing switch? Your in series with the lead feeding the reversing switch.

[Ray Scott]

That product looks like fun to try out. You need to buy $35 worth of stuff to get free shipping... but looks like I could find more stuff to buy from Amazon. I doubt it would hurt the motor to try this. I have considered the switch and capacitor also.. they shouldn't be damaged by the PWM with an SCR method. The only question is if the motor will be faked by the trick.

[Gary Hair]

You need to buy $35 worth of stuff to get free shipping...

I have Prime, so shipping is included - 3 day no less...

[Keith Colson]

Beware that an induction motor is a phase controlled motor so a dimmer will not change the speed, it will drop the torque until it stalls. Dimmers are effectively current controlled devices. You need frequency control.

The way I see it is a VFD for 150 bucks is a lot cheaper than modifying the mechanics or adding steppers etc. Its a simple wire in job versus loads of work for all the other approaches. You won't need relays anymore either. Just connect the up/down buttons direct to the VFD.

[Gary Hair]

Beware that an induction motor is a phase controlled motor so a dimmer will not change the speed, it will drop the torque until it stalls. Dimmers are effectively current controlled devices. You need frequency control.

The way I see it is a VFD for 150 bucks is a lot cheaper than modifying the mechanics or adding steppers etc. Its a simple wire in job versus loads of work for all the other approaches. You won't need relays anymore either. Just connect the up/down buttons direct to the VFD.

What about the control I linked on Amazon?

[Bill George]

What about the control I linked on Amazon?

That I think will work, its worth a try. I believe all AC motors are Induction motors, at least that's what I was taught anyway over 40 years ago They can be 3 phase, single phase capacitor start, split phase, PSC, shaded pole or whatever... lots of variations . Your motor for the Up / Down we are discussing looks like a PSC motor. Read the reviews on Amazon, they are using on several motor types with that Motor Speed Controller. Sure its not a VFD which I have used and installed on customers equipment and my own. But its a form of speed controller, clips the waveform and uses an SCR based control system.

Oh, and standard VFD's can not be used on single phase motors, needs to be 3 phase. Been there, tried that.

[Scott Shepherd]

Oh, and VFD's can not be used on single phase motors, needs to be 3 phase. Been there, tried that.

They can't? I thought my CNC router used a VFD to control the speed and it's single phase. I've also been told that you can use a VFD on single phase to make 3 phase work on single phase. I have a huge compressor that's 3 phase and we don't have 3 phase power here, and I was told to buy a VFD and it would run it.

You're saying that hasn't been your experience, Bill? (I'm asking, not telling, as my experience with electricity is right in line with my experience with brain surgery).

[Gary Hair]

They can't? I thought my CNC router used a VFD to control the speed and it's single phase. I've also been told that you can use a VFD on single phase to make 3 phase work on single phase. I have a huge compressor that's 3 phase and we don't have 3 phase power here, and I was told to buy a VFD and it would run it.

You're saying that hasn't been your experience, Bill? (I'm asking, not telling, as my experience with electricity is right in line with my experience with brain surgery).

Since I have the same experience with brain surgery and a bit less with electricity, I google everything. It turned up quite a few sites, this wiki page being one of them.

From wikipedia:
AC Motor[edit (http://en.wikipedia.org/w/index.php?title=Variable-frequency_drive&action=edit&section=2)]The AC electric motor used in a VFD system is usually a three-phase (http://en.wikipedia.org/wiki/Three-phase_electric_power) induction motor (http://en.wikipedia.org/wiki/Induction_motor). Some types of single-phase (http://en.wikipedia.org/wiki/Single-phase_electric_power) motors can be used, but three-phase motors are usually preferred. Various types ofsynchronous motors (http://en.wikipedia.org/wiki/Synchronous_motor) offer advantages in some situations, but three-phase induction motors are suitable for most purposes and are generally the most economical motor choice. Motors that are designed for fixed-speed operation are often used. Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA (http://en.wikipedia.org/wiki/National_Electrical_Manufacturers_Association) Standard MG-1

[Bill George]

They can't? I thought my CNC router used a VFD to control the speed and it's single phase. I've also been told that you can use a VFD on single phase to make 3 phase work on single phase. I have a huge compressor that's 3 phase and we don't have 3 phase power here, and I was told to buy a VFD and it would run it.

You're saying that hasn't been your experience, Bill? (I'm asking, not telling, as my experience with electricity is right in line with my experience with brain surgery).

A VFD is one way to run a 3 phase motor off single phase. There are other ways. Scott my guess is your CNC router spindle is 3 phase and its running off the VFD wired to single phase. Of course you could wire it to 3 phase but most home shops don't have it available. You can even get up to I think 1 Hp max VFD that will take 120 VAC single phase and convert it to 240 volt 3 phase. I was considering that route on my three phase EMCO Super 11 metal lathe, but I was borderline on the Hp and decided not to risk. Its now happily running on single phase 240 VAC circuit.

The Wiki post on single phase motors on a standard VFD needs edited. Not going to happen unless you get into the motor windings and make some changes. I have never seen a "special" invertor duty motor used very often, unless the machine was brand new from the factory. In fact the older motors, with cast iron or steel construction and copper windings are one of the best for a conversion. The newer pot metal and aluminum winding motors don't fare well, hence the Invertor Duty, pot metal and aluminum winding motors.

[Scott Shepherd]

Well, now you know why my compressor is just sitting there, and has been for the last 4 years ;)

I have absolutely no idea what Gary or Bill said.

[Dan Hintz]

Well, now you know why my compressor is just sitting there, and has been for the last 4 years ;)

I have absolutely no idea what Gary or Bill said.

You can run that compressor with a VFD... or for the likely size of that compressor, it will likely be cheaper to find a used rotary phase converter, as a VFD sizable enough to run a compressor will be big bucks.

[Keith Colson]

Hi Gary, that unit does current control so I suspect it will not work as you want.

[Keith Colson]

Bill there are many kinds of motors, and there are single phase motors that can be run of VFD's. Phase controlled motors are controlled with VFD's and current controlled motors are controlled with dimmers. They do not interchange.

A good example of a single phase motor that can be run off a VFD is a shaded pole motor.

[Gary Hair]

A VFD is one way to run a 3 phase motor off single phase. There are other ways. Scott my guess is your CNC router spindle is 3 phase and its running off the VFD wired to single phase. Of course you could wire it to 3 phase but most home shops don't have it available. You can even get up to I think 1 Hp max VFD that will take 120 VAC single phase and convert it to 240 volt 3 phase. I was considering that route on my three phase EMCO Super 11 metal lathe, but I was borderline on the Hp and decided not to risk. Its now happily running on single phase 240 VAC circuit.

The Wiki post on single phase motors on a standard VFD needs edited. Not going to happen unless you get into the motor windings and make some changes. I have never seen a "special" invertor duty motor used very often, unless the machine was brand new from the factory. In fact the older motors, with cast iron or steel construction and copper windings are one of the best for a conversion. The newer pot metal and aluminum winding motors don't fare well, hence the Invertor Duty, pot metal and aluminum winding motors.

Well George, you have gone way above my pay grade... I can copy and paste from a Wiki, albeit wrong info, but that's about the extent of it. I get the gist of what you are saying but not enough to know exactly what it all means.

[Bill George]

Also they do make a special Single Phase VFD, if I remember right its just for PSC and shaded pole motors. Nothing with a switched circuit like a capacitor start motor. Its kind of pricey as only one company that I could find anyway makes and sells it. All low starting torque motors like on a fan or low power application.

I think I will order one of those Amazon motor speed controllers just to see how well it works. The folks leaving the reviews all think it works fine.

[Keith Colson]

Here is some interesting info on connecting a single phase permanent split capacitor motor to a VFD. It can reverse with out switching the capacitor

See
http://www.kollmorgen.com/en-us/products/drives/discontinued/230-430pto/bronco_vfd_manual_en-us_reva/
Page 20 and 21

[Bill George]

Got one on order, thanks Amazon Prime no shipping and 3 day shipping. I don't have a reversible motor setup to try it on, but I suspect it will work on the motors I have in my junk/inventory supply. True its not a VFD or a control to vary the frequency for speed control, but it re-shapes the waveform to lower the supplied voltage and current to the motor. But its more than a simple dropping resistor, variable or otherwise. And the price was right to do some experimenting.

[Bill George]

Here is some interesting info on connecting a single phase permanent split capacitor motor to a VFD. It can reverse with out switching the capacitor

See
http://www.kollmorgen.com/en-us/products/drives/discontinued/230-430pto/bronco_vfd_manual_en-us_reva/
Page 20 and 21
Keith I'm pretty sure that can be done. Did not read the PDF but a PSC would be an ideal candidate for that sort of conversion. I guess for Gary's application I was thinking cost.

I did go look at the pages you noted 21-22. It looks like they removed the run capacitor and connected all the windings as you would for a 3 phase motor. That would work, and may be a good way to go in some cases.

[Gary Hair]

Well the speed controller on Amazon didn't work... Turn the knob fully counter-clockwise and the motor doesn't run at all, fully clockwise and it runs slightly less than full speed. Turn it slowly counter-clockwise and about halfway the motor stops, it never changes speed, just from about 90% to 0%. Since a VFD is out of the question due to price, I'll have to live with what I have - or take the parts I do have and use a stepper instead.

Thanks again to everyone for their help and suggestions!

[Bill George]

When mine gets here I will try on the motors I have. The guy on Amazon is using on his furnace motor which I am sure is a PSC motor about like yours.

Is it chain drive to the table? I wonder If you could change the motor sprocket to slow down the speed?

[Gary Hair]

When mine gets here I will try on the motors I have. The guy on Amazon is using on his furnace motor which I am sure is a PSC motor about like yours.

Is it chain drive to the table? I wonder If you could change the motor sprocket to slow down the speed?

It's connected directly to the leadscrew. It's not moving a table, it moves the galvo head up and down. I can, in theory, change the gearing to slow it down, but then it would be too slow to make gross changes. In an ideal world I would have two speeds, fast and slow. Ain't gonna happen...

[Keith Colson]

If you know some electronics you could make a divide by 2 counter and connect it to a triac, this would drop your ac frequency to 30hz instead of 60hz. This would halve you motor speed. Probably about 10 components worth 5 bucks. It would be an interesting little circuit to make. You could then switch between divide by 2 and no division for full speed and half speed. Many years ago I designed a VFD, this would be so much simpler and not require any microcontroller.

Cheers
Keith

[Bill George]

If you know some electronics you could make a divide by 2 counter and connect it to a triac, this would drop your ac frequency to 30hz instead of 60hz. This would halve you motor speed. Probably about 10 components worth 5 bucks. It would be an interesting little circuit to make. You could then switch between divide by 2 and no division for full speed and half speed. Many years ago I designed a VFD, this would be so much simpler and not require any microcontroller.

Cheers
Keith

Keith and Gary, could the motor be replaced with a DC one? Or is it a special size and nothing else would fit?
Like one of these > http://www.surpluscenter.com/Electrical/DC-Gearmotors/DC-Gearmotors/?page_no=1

[Gary Hair]

Keith and Gary, could the motor be replaced with a DC one? Or is it a special size and nothing else would fit?
Like one of these > http://www.surpluscenter.com/Electrical/DC-Gearmotors/DC-Gearmotors/?page_no=1

It is a special size due to the mounting holes, but I'm sure that it's not so special that something couldn't be found to replace it. Even I could figure out how to vary speed and change direction on a DC motor! I'll see if there is anything that would bolt in to replace it.

Thanks Bill!

[Bill George]

It is a special size due to the mounting holes, but I'm sure that it's not so special that something couldn't be found to replace it. Even I could figure out how to vary speed and change direction on a DC motor! I'll see if there is anything that would bolt in to replace it.
Thanks Bill!

I got my Amazon speed controller today and can't play with it yet. Need to finish cutting up a downed tree. But not at all impressed with the controller. There is no way that heat sink or anything on it is going to handle 25 amps.
Be aware there are couple of those DC gear motors that look like they involve more than reversing the leads for motor direction. They also sell just DC motors. I have purchased from Surplus Center for years, they are slow to ship but otherwise fine.

Here is yet another Surplus place in Nebraska. Since there are a number of Air Force bases in that area they get a lot of that stuff too. Check out the gear motor section they have a couple of interesting DC ones.
Link> http://www.surplussales.com/index.html