Someone asked if this router speed control would be okay to use with a
typical non-variable speed 1/2" drill motor (5 Amps or so).:

http://www.mlcswoodworking.com/shops.../speedcon.html

I called to get a little more info and the seller says that it is for
use with "brush type motors of up to 15 Amps" and that it is a
"voltage sensitive device that maintains constant torque".

If I understand it right, this must do more than simply drop the
voltage. I wonder if this is like a VFD in that it can vary speed
without overheating the windings? Anyone want to venture a guess on
how this works?

I'm reluctant to tell someone to do something that might fry their
drill motor. If it works as they say, for $24 and free shipping, I
might get one myself.



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I can't vouch for their use on a drill, but I bought my dad one to use
with larger bits in his 3hp router. Seems to work well with the router.

Jack Erbes wrote:

Someone asked if this router speed control would be okay to use with a
typical non-variable speed 1/2" drill motor (5 Amps or so).:

http://www.mlcswoodworking.com/shops.../speedcon.html

I called to get a little more info and the seller says that it is for
use with "brush type motors of up to 15 Amps" and that it is a
"voltage sensitive device that maintains constant torque".

If I understand it right, this must do more than simply drop the
voltage. I wonder if this is like a VFD in that it can vary speed
without overheating the windings? Anyone want to venture a guess on
how this works?

I'm reluctant to tell someone to do something that might fry their
drill motor. If it works as they say, for $24 and free shipping, I
might get one myself.



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

--
--------------------------------------------------------------------------

James P Crombie

Summerside Machinist
Prince Edward Island Amateur Astronomer
Canada 3D Designer

E-mail
Astronomy webpage http://www.jamescrombie.com
Rhinoceros 3D webpage http://www.jamescrombie.com/rhino/
Mirror Grinder page http://www.jamescrombie.com/pics/
--------------------------------------------------------------------------

ok, you asked. these are triac based controls that duty cycle modulate the
input AC power - basically they delay the turn on of the AC to the motor
until a desired phase angle is reached - the later the turn on (each half
cycle) the less power is delivered to the motor. It's the same as a lamp
dimmer, but with a few parts (and a more rugged triac) to accommodate the
reverse voltage from the inductance of the motor. I have a few spare
controls scrapped from drills - if you want one, I'll send you one for a
couple of $$ postpaid.


"James P Crombie" wrote in message
...
I can't vouch for their use on a drill, but I bought my dad one to use
with larger bits in his 3hp router. Seems to work well with the router.

Jack Erbes wrote:

Someone asked if this router speed control would be okay to use with a
typical non-variable speed 1/2" drill motor (5 Amps or so).:


http://www.mlcswoodworking.com/shops...l/pages/speedc
on.html

I called to get a little more info and the seller says that it is for
use with "brush type motors of up to 15 Amps" and that it is a
"voltage sensitive device that maintains constant torque".

If I understand it right, this must do more than simply drop the
voltage. I wonder if this is like a VFD in that it can vary speed
without overheating the windings? Anyone want to venture a guess on
how this works?

I'm reluctant to tell someone to do something that might fry their
drill motor. If it works as they say, for $24 and free shipping, I
might get one myself.



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

--
--------------------------------------------------------------------------

James P Crombie

Summerside Machinist
Prince Edward Island Amateur Astronomer
Canada 3D Designer

E-mail
Astronomy webpage http://www.jamescrombie.com
Rhinoceros 3D webpage http://www.jamescrombie.com/rhino/
Mirror Grinder page http://www.jamescrombie.com/pics/
--------------------------------------------------------------------------

"william_b_noble" wrote in message
...

ok, you asked. these are triac based controls that duty cycle modulate
the input AC power - basically they delay the turn on of the AC to the
motor until a desired phase angle is reached - the later the turn on
(each half cycle) the less power is delivered to the motor.

That sounds like PWM. Is that what these controllers are?

It is my understanding that a PWM drive will offer max torque over the speed
control range because the motor always sees peak voltage (but that the
voltage is chopped so that the average current determines the speed).

I am trying to build a power table feed for a mini mill. I've got a
high-torque 24VDC gear motor, but I'm still looking for an electronic
circuit to drive it. I know some people have used a light dimmer with the
output routed through a step-down transformer; perhaps a more version would
use one of these universal motor speed controllers in place of the light
dimmer.

Anyone have suggestions for either an economical off-the-shelf solution, or
a schematic for a basic PWM circuit?

Thanks!

Shunt wound or permanent magnet DC motors are inherently constant torque
devices because the magnetic field is constant at or below base speed. Any way
to get variable armature voltage will produce variable speed at constant
torque. Most AC supplied DC motor controllers are phase controlled SCR bridges
with freewheeling diodes. PWM supplies, variac (autotransformer) with diode
bridge, or power resistor will all work.

Brush type AC/DC motors (universal motors) as found in most hand held power
tools are series wound meaning the armature current also provides the field
excitation. That is why they will run (sort of) on AC -- the magnetic field
and the armature current both reverse at the same time. The speed of a series
motor can be controlled by controlling terminal voltage. That is what simple
triac controllers and light dimmers do -- but simply reducing the terminal
voltage will also reduce the available torque. Slightly more sophisticated
controllers have a feedback circuit that senses when the motor starts to slow
below the intended speed and increases the voltage to maintain the intended
speed. This feedback allows the motor to produce constant torque. Many
variable speed power drills depend upon the operator's finger to provide this
feedback -- pushing the trigger down to maintain something like constant speed
as the tool is loaded. The better controllers, and probably the more expensive
router speed control that started this string, have an electronic feedback
circuit of some kind. The cheap HF controller that did not work very well
probably does not have an electronic feedback feature.

Mill


"william_b_noble" wrote in message
...

ok, you asked. these are triac based controls that duty cycle modulate
the input AC power - basically they delay the turn on of the AC to the
motor until a desired phase angle is reached - the later the turn on
(each half cycle) the less power is delivered to the motor.

That sounds like PWM. Is that what these controllers are?

It is my understanding that a PWM drive will offer max torque over the speed
control range because the motor always sees peak voltage (but that the
voltage is chopped so that the average current determines the speed).

I am trying to build a power table feed for a mini mill. I've got a
high-torque 24VDC gear motor, but I'm still looking for an electronic
circuit to drive it. I know some people have used a light dimmer with the
output routed through a step-down transformer; perhaps a more version would
use one of these universal motor speed controllers in place of the light
dimmer.

Anyone have suggestions for either an economical off-the-shelf solution, or
a schematic for a basic PWM circuit?

Thanks!

"MP Toolman" wrote in message
...

Shunt wound or permanent magnet DC motors are inherently constant torque
devices because the magnetic field is constant at or below base speed.
Any way to get variable armature voltage will produce variable speed at
constant torque. snip

Thanks for all the good info. But it is my understanding that there is a
difference in the output torque of DC motors depending on the means by which
the speed is controlled. In fact, isn't that why expensive PWM drives are
preferred over other supply circuits?

Below are some quotes that I am basing some of my assumptions upon.
Additional comments & clarifications would be appreciated!

Posted by Harvey White (msg #53845)

The SCR is capable of being turned on with a gate signal, but unlike a
FET, the SCR latches on until (basically) power is removed. The supply to
the motor and SCR is raw pulsating DC, coming from a bridge rectifier. A
gate signal is generated from a ramp synchronized to the DC waveform coming
in (this is one way of doing it). With a ram rising from , say 0 to 10 volts
repeating each 1/120 of a second (for 60 Hz power), you compare the ramp
voltage against a pot voltage (speed control). When the ramp voltage exceeds
the pot voltage, the comparator flips on, and this signal is used to turn on
the SCR. The circuit resets when the rectified DC voltage falls below the
SCR's holding voltage/current limit.

For full speed, you trigger at the beginning of the half cycle, so you get
the benefit of the full AC voltage half cycle, 0 to peak to 0. At half
setting, you trigger at the middle of the cycle (and get your worse spike
for this circuit). You've "ignored" the first 1/2 of the half cycle. At low
RPM, you trigger very late in the cycle, and you're getting the part of the
waveform that's at, say 25 volts descending to zero going to the motor.

Since Motor torque is related to the supply voltage, The torque falls from
half speed down to zero. It's the same effect as if you had a variable DC
supply. That's why running a DC motor off a variable DC supply gives you
"bad" low end torque, low motor voltage/current.

Where a PWM controller is superior is that the motor voltage is always the
full value. Since the supply is switched on and off at a rapid rate, the
current flowing through the motor (when it stabilizes) is always the design
normal value, and the torque in the motor is always (or mostly) the same,
regardless of speed setting. Since the motor is an inductor, and since you
can't change the current through an inductor instantaneously, there will be
a practical limit to the minimum width of the pulse through the motor. Below
this limit, the current through the motor does not have the opportunity to
reach full value, and the motor torque drops. However, the theory says that
with a good PWM supply, the motor torque is higher at low speeds than with
an SCR supply.

However, SCRs are more robust than FETs, so they go poof less....

There used to be devices called GTO SCRs, for Gate Turn Off SCR (SCR is
Silicon Controlled Rectifier). You could turn them off, you could turn them
on.

Ironically, you could make one with an SCR and a MOSFET....


Posted by Rick Dickinson (msg #53864)

For those that aren't familiar with PWM, here's the Cliff Notes version:
Pulse Width Modulation uses some sort of fast, low resistance, electronic
switch (like a MOSFET) to turn the DC voltage driving the motor on and off
thousands of times per second. By changing the percentage of the time that
the switches are "on" rather than "off", the average power being applied to
the motor varies proportionally, and the speed varies as well.

By contrast, an SCR-based motor controller uses devices called "Silicon
Controlled Rectifiers" to turn on and off the power to the motor. On the
"pro" side, SCRs are very robust devices, and hold up well to abuse without
releasing their magic smoke. However, on the "con" side, they are peculiar
devices: they can only be turned on by a triggering signal, not off. How do
you use a switch that you can only turn on, not off, to control the power
going to a motor? By taking advantage of one other feature of SCRs: they
actually do turn off when the voltage across them drops to zero. So, if you
use them with an AC signal (a 60 Hz 110V RMS sine wave from the power
outlet, for instance), you can turn them on at whatever point in the sine
wave you want, and they shut off all by themselves every time the voltage
passes zero (120 times a second, for 60 Hz AC). Rectify the output, so that
all of the "humps" of the sine wave are positive, and you've got a robust
source of pulsing voltage that can be controlled as to what percentage of
total power it delivers by changing at what point you turn the SCRs on.

Now, since MOSFET-based PWM motor controllers turn on and off thousands of
times per second, you have very fine granularity across the whole range from
full on to full off. However, SCR-based controllers are dependent on the 60
Hz AC sine wave from your power outlet. If you've ever looked at a sine
wave, you can see that the curve slopes a lot more right near where it
crosses zero than it does near the peaks. This means that, at the low end of
the power curve (near full off), a small adjustment makes a big jump in
speed. Also, no matter what speed is selected for a PWM-controlled motor,
the motor always sees pulses of full voltage, which means that the motor
always gets a full-strength "kick" to get it started moving as soon as the
pulse hits it. An SCR-based controller is sending rounded pulses (shaped
like part of a sine wave). At low speeds, the motor never sees full peak
voltage, which makes it more likely that the motor will stall at low speeds.
So, to summarize: PWM with MOSFETs gives smoother control over the whole
range of speeds, while SCR-based controllers are more robust, and give their
best control at mid-to-high-range speeds.

MP Toolman wrote:

Shunt wound or permanent magnet DC motors are inherently constant torque
devices because the magnetic field is constant at or below base speed.

Closer to constant speed devices. If the armature and power supply had
zero internal resistance speed would be constant independent of load. A
Variac and a bridge rectifier will do a pretty decent job for a power
feed.

http://www.metalworking.com/dropbox/_1999_retired_files/PWRFEED.TXT

Ted

In article , MP Toolman says...

Shunt wound or permanent magnet DC motors are inherently constant torque
devices because the magnetic field is constant at or below base speed. Any way
to get variable armature voltage will produce variable speed at constant
torque.

This is true, but there are many cases where shunt wound motors
are run to keep the torque high at low speeds.

The hardinge feed motor setup is like this. Originally they would
have the armature voltage controlled with a variac, so the
voltage increased to speed the motor up, and at the same time
the field voltage was controlled with a large variable resistor,
ganged to the variac shaft, so the field current was decreased
as the arm. voltage went up. This way the field was at full
strength as the control was set to lowest speeds.

They ultimately changed this, and made the field be basically
PM by running it constant current, and using a fed-back
SCR control circuit to maintain torque at low speeds.
They adjust the firing angle of the scr based on the
back EMF of the armature as far as I can tell. I've
got the reverse engineered schematic, and I would be
interested to get a 'real' EE's take on it.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

On Wed, 29 Oct 2003 06:30:18 GMT, "DeepDiver"
wrote something
.......and in reply I say!:

"william_b_noble" wrote in message
...

ok, you asked. these are triac based controls that duty cycle modulate
the input AC power - basically they delay the turn on of the AC to the
motor until a desired phase angle is reached - the later the turn on
(each half cycle) the less power is delivered to the motor.

That sounds like PWM. Is that what these controllers are?


Sort of similar, but use the sine wave. Imagine a sine wave. then
switch it on at a certain time within each half cycle, and only to be
turned off at the end of that half cycle (a triac is fired by a
trigger pulse of very short duration, and will turn off only when the
_supply_ voltage reaches zero again). The earlier you turn it on in
the half cycle, the more power gets to the driven motor etc.

Check out Thyristor. A Triac is two thyristors back to back and
reversed, to control AC in both directions of current flow.


It is my understanding that a PWM drive will offer max torque over the speed
control range because the motor always sees peak voltage (but that the
voltage is chopped so that the average current determines the speed).

I doubt it. Torque is pretty much tied in with applied average power,
all other factors being equal. Shorten the pulse, lower the power. To
obtain max or constant speed, you need to usually measure either the
speed of the motor, or the back EMF from it, or current draw for
applied voltage, and provide more or less power as needed in each
pulse.

To make the triac parallel, you will see a loss of torque and power as
soon as you start to delay the firing of the triac, even though the
currtent still passes through peak until you reach a quarter cycle.


I am trying to build a power table feed for a mini mill. I've got a
high-torque 24VDC gear motor, but I'm still looking for an electronic
circuit to drive it. I know some people have used a light dimmer with the
output routed through a step-down transformer; perhaps a more version would
use one of these universal motor speed controllers in place of the light
dimmer.

Anyone have suggestions for either an economical off-the-shelf solution, or
a schematic for a basic PWM circuit?

Not being smart. Try googling PWM circuits. To get a constant torque
************************************************** ****************************************
Whenever you have to prove to yourself that you are
not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

Anyone have suggestions for either an economical off-the-shelf solution,
or
a schematic for a basic PWM circuit?

This kit might work:

http://electronickits.com/kit/complete/motor/ck1400.htm

I used one to power a 90VDC 1/2 HP motor for a potter's wheel for my wife.
I had to replace the MOSFET with one that could handle more current but
otherwise it worked as is.

It doesn't use any kind of feedback so the speed isn't held constant but it
provides a good amount of torque so it hasn't been a problem.

If you want something more stable watch eBay for a Minarik controller that
fits the bill. You can check specs on the different ones that are listed at
their site, http://www.minarik.com.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"

On Tue, 28 Oct 2003 21:16:37 -0800, "william_b_noble"
wrote:

ok, you asked. these are triac based controls that duty cycle modulate the
input AC power - basically they delay the turn on of the AC to the motor
until a desired phase angle is reached - the later the turn on (each half
cycle) the less power is delivered to the motor. It's the same as a lamp
dimmer, but with a few parts (and a more rugged triac) to accommodate the
reverse voltage from the inductance of the motor.

I think it's better than a lamp dimmer because they claim constant
speed with varying load. They may use something like the TDA1185A
chip and associated circuitry. This chip accomplishes tachless speed
control of universal motors with positive feedback.

On Tue, 28 Oct 2003 21:16:37 -0800, "william_b_noble"
wrote:

ok, you asked. these are triac based controls that duty cycle modulate the
input AC power - basically they delay the turn on of the AC to the motor
until a desired phase angle is reached - the later the turn on (each half
cycle) the less power is delivered to the motor. It's the same as a lamp
dimmer, but with a few parts (and a more rugged triac) to accommodate the
reverse voltage from the inductance of the motor. I have a few spare
controls scrapped from drills - if you want one, I'll send you one for a
couple of $$ postpaid.


Thanks for the good explanation. So the output is intermittent 60
cycle 115V AC. That explains why they do not overheat the windings.

I can answer the question with confidence now. And thanks for the
generous offer, I like the packaging and switching concept (off, full,
variable) on the one I referenced so if I were going to use one I'd
probably just pick one of those up.



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On Wed, 29 Oct 2003 10:21:54 -0500, Jack Erbes
wrote something
.......and in reply I say!:

I thought there was actually quite a high danger of overheating,
unless the motor was designed to run under load at lower revs. It's
one of the things warned against regarding fitting aftermarket seepd
controllers to tools.

I reckon this would apply even more if the feeding device increased
power on demand.

Thanks for the good explanation. So the output is intermittent 60
cycle 115V AC. That explains why they do not overheat the windings.

I can answer the question with confidence now. And thanks for the
generous offer, I like the packaging and switching concept (off, full,
variable) on the one I referenced so if I were going to use one I'd
probably just pick one of those up.



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************************************************** ****************************************
Whenever you have to prove to yourself that you are
not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

Jack Erbes wrote:

Someone asked if this router speed control would be okay to use with a
typical non-variable speed 1/2" drill motor (5 Amps or so).:

http://www.mlcswoodworking.com/shops.../speedcon.html

I called to get a little more info and the seller says that it is for
use with "brush type motors of up to 15 Amps" and that it is a
"voltage sensitive device that maintains constant torque".

If I understand it right, this must do more than simply drop the
voltage. I wonder if this is like a VFD in that it can vary speed
without overheating the windings? Anyone want to venture a guess on
how this works?

I'm reluctant to tell someone to do something that might fry their
drill motor. If it works as they say, for $24 and free shipping, I
might get one myself.

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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

It should work fine with a brush type motor in a drill.

IIRC those speed controls sense the "generated" back EMF during the portions of each
half wave cycle when their controlling triac is "off" and use that voltage as a
feedback signal to help keep the motor at a constant speed in the face of varying
torque loads.

IIRI, someone please correct me...

FWIW, I picked up a similar appearing speed control device from HF when it went on sale
for less than $10 and it's worked well for me the few times I've used it on my router.

Jeff


--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to place the
blame on."

I also bought one of these from H/F and have found it to be totally
useless. As I slow the speed down the torque plunges. When the rpm gets down
to about 15000 just putting the bit against a board brings the bit to a
stop.
Dick

--
Building and repair of fine custom cues at affordable
prices for real poolplayers. Over 35yrs. exp.
Richard H. Neighbors 318 Linden st. Cinti. OH
ph.# (513) 242-1700
web-site: http://www.dickiecues.com



"Jeff Wisnia" wrote in message
...
Jack Erbes wrote:

Someone asked if this router speed control would be okay to use with a
typical non-variable speed 1/2" drill motor (5 Amps or so).:


http://www.mlcswoodworking.com/shops.../speedcon.html

I called to get a little more info and the seller says that it is for
use with "brush type motors of up to 15 Amps" and that it is a
"voltage sensitive device that maintains constant torque".

If I understand it right, this must do more than simply drop the
voltage. I wonder if this is like a VFD in that it can vary speed
without overheating the windings? Anyone want to venture a guess on
how this works?

I'm reluctant to tell someone to do something that might fry their
drill motor. If it works as they say, for $24 and free shipping, I
might get one myself.

-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

It should work fine with a brush type motor in a drill.

IIRC those speed controls sense the "generated" back EMF during the
portions of each
half wave cycle when their controlling triac is "off" and use that voltage
as a
feedback signal to help keep the motor at a constant speed in the face of
varying
torque loads.

IIRI, someone please correct me...

FWIW, I picked up a similar appearing speed control device from HF when it
went on sale
for less than $10 and it's worked well for me the few times I've used it
on my router.

Jeff


--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone
to place the
blame on."

On Wed, 29 Oct 2003 04:23:27 GMT, "rhncue"
wrote:

I also bought one of these from H/F and have found it to be totally
useless. As I slow the speed down the torque plunges. When the rpm gets down
to about 15000 just putting the bit against a board brings the bit to a
stop.
Dick

I'm wondering if the HF one is as "smart" as the one I referenced. If
I understand the replies (which answered my question very well) it may
be that the HF one is cheaper but does not use the feedback from the
motor to keep the power level up and the speed constant.

When I was stationed in Korea we used to get a lot of things that
looked great and were pretty well made but just as good as the
original item. We used to call it the "Land of not quite right". Now
it appears that China has taken over that market.



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