Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old September 10th 07, 09:07 AM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?


William Noble wrote:
the speed control is a triac based phase control, the same as a light
dimmer - typically it has two wires, just short the two wires together and
the dremel will run full speed all the time.

by the way, typical failure is just noisy pot, try cleaning carbon track


Mine had a smd triac BT134W which was faulty.

I replaced it (easy!!) with a new one, and
the dremel has worked years after that. The
triac costs about 1 usd.. The parts are on a
white ceramic circuitboard.

Kristian Ukkonen.

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Old September 10th 07, 09:42 AM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?


"James Sweet" wrote in message
news:[email protected]

wrote in message
ups.com...
Just take it apart, I'm pretty sure it's just a "potentiometer"
(variable resistor) so it would only have 3 leads, one from the external
wire to the pot., one from the pot to the motor, and one from the other
external wire to the other lead of the motor.

Cut things off, plug the external leads directly to the motor.



Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.


Of course it's not gonna be a pot, it would have to be far too big and
burn up a lot of power. Instead they use what is essentially a light
dimmer. The semiconductor you see is a triac, the diode is a diac to
trigger it, if you just jumper together the right two pins on the triac,
the motor will be forced on.

Don' it just hurt to the core, James ... ? !!! ;~)

Arfa


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Old September 10th 07, 11:35 AM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?

hillpc wrote ...
I'm on my second electronic variable speed control inside my Dremel
model 395 tool. This one just crapped out with the same temperamental
symptoms as the last one. I need to use the tool tomorrow night, and
would like to bypass the internal variable speed circuitry to simplify
it; maybe buy an external control later.

. . .
Can anyone help?


This is one of those cases where "If you don't know already, you probably
shouldn't be doing the job".

The wiring should be simple enough to do it by inspection. If it isn't, you
really need the schematic and the ability to understand it.

Unlike the other poster, I really doubt that the motor speed control is just
a pot.


--
Bill Fuhrmann


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Old September 10th 07, 01:25 PM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?

Thanks, folks. This discussion is exactly the type of info I
needed.

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Old September 10th 07, 07:14 PM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?

Michael A. Terrell wrote:

Claude Desjardins wrote:

wrote:

Just take it apart, I'm pretty sure it's just a "potentiometer"
(variable resistor) so it would only have 3 leads, one from the external
wire to the pot., one from the pot to the motor, and one from the other
external wire to the other lead of the motor.

Cut things off, plug the external leads directly to the motor.


Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.


I doubt they have put a stepper motor in there, they wouldn't sell for
20$ each! -- You still should only have two leads coming out of the
motor. Confirm?




Every Dremel tool I've had apart used a universal motor, and the
speed control was a simple dimmer circuit. This one might be PWM, and
run the motor on DC.

Most of the cordless drills these days use PWM power FeT drivers.

I modified a cordless drill with a mini PIC and Bridge to
perform regulated torque control, auto reverse and then forward
again until maximum torque was no longer peaking. Did this so that
the drill would have a TAP mode in it. I stuck a mini pot on the back
side of the handle to set the torque level.

if his dremel is also cordless, It may also be using it a PWM?
who knows. how ever, with the part count, I'm guessing he's using a
corded unit with a phase control.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

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Old September 10th 07, 08:06 PM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?

Jamie wrote:

Michael A. Terrell wrote:

Claude Desjardins wrote:

wrote:

Just take it apart, I'm pretty sure it's just a "potentiometer"
(variable resistor) so it would only have 3 leads, one from the external
wire to the pot., one from the pot to the motor, and one from the other
external wire to the other lead of the motor.

Cut things off, plug the external leads directly to the motor.


Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.


I doubt they have put a stepper motor in there, they wouldn't sell for
20$ each! -- You still should only have two leads coming out of the
motor. Confirm?




Every Dremel tool I've had apart used a universal motor, and the
speed control was a simple dimmer circuit. This one might be PWM, and
run the motor on DC.

Most of the cordless drills these days use PWM power FeT drivers.

I modified a cordless drill with a mini PIC and Bridge to
perform regulated torque control, auto reverse and then forward
again until maximum torque was no longer peaking. Did this so that
the drill would have a TAP mode in it. I stuck a mini pot on the back
side of the handle to set the torque level.

if his dremel is also cordless, It may also be using it a PWM?
who knows. how ever, with the part count, I'm guessing he's using a
corded unit with a phase control.



None of those I've seen used an IC in the speed control. Also, he
didn't mention a filter capacitor, so id may be a simple dimmer
circuit. It's hard to tell from such a vague description. Part numbers
would have been a big help.

BTW, have you seen the small DC powered clone at Harbor Freight? It
runs on 12 VDC, and comes with an AC adapter. I was thinking about
using one (or more, with different sized drills) with a homebrew CNC
machine to drill PC boards.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Old September 10th 07, 08:53 PM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Default how to bypass dremel tool internal variable speed control?

Michael A. Terrell wrote:

Jamie wrote:

Michael A. Terrell wrote:


Claude Desjardins wrote:


wrote:



Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.


I doubt they have put a stepper motor in there, they wouldn't sell for
20$ each! -- You still should only have two leads coming out of the
motor. Confirm?



Every Dremel tool I've had apart used a universal motor, and the
speed control was a simple dimmer circuit. This one might be PWM, and
run the motor on DC.


Most of the cordless drills these days use PWM power FeT drivers.

I modified a cordless drill with a mini PIC and Bridge to
perform regulated torque control, auto reverse and then forward
again until maximum torque was no longer peaking. Did this so that
the drill would have a TAP mode in it. I stuck a mini pot on the back
side of the handle to set the torque level.

if his dremel is also cordless, It may also be using it a PWM?
who knows. how ever, with the part count, I'm guessing he's using a
corded unit with a phase control.




None of those I've seen used an IC in the speed control. Also, he
didn't mention a filter capacitor, so id may be a simple dimmer
circuit. It's hard to tell from such a vague description. Part numbers
would have been a big help.

BTW, have you seen the small DC powered clone at Harbor Freight? It
runs on 12 VDC, and comes with an AC adapter. I was thinking about
using one (or more, with different sized drills) with a homebrew CNC
machine to drill PC boards.


Hmm, No, I haven't checked into Harbor Freight in some time how ever, I
think you'll find that a lot of named brand tools we know are now being
made by the same people that make the no-name brands from China.
For example, I have a rotary tool that in all respects is a dremal.
bu t the name isn't of course.
As far as drills with PWM, the Craftsman 1/2 drive chuck cordless uses
PWM driver board which is mounted as part of the trigger. the speed pot
slider is on the board. It employs an IC chip with a logic level Power Fet.

We have some electric real movers that are still being modified by the
manufacturer because they can't seem to get one to last any longer than
2 months in our shop. First they had drive problems where it wouldn't
start half the time. This was an elaborate board with a micro driving
what looked like a Mosfet H-bridge.

Any ways, we sent them back, the next set that came our way, they
modified with the speed control in the handle of the unit. All they
did was employ a speed control trigger slide switch from some existing
cordless drill system.
Those were very simply units, a single Power Fet with a 555 timer
driving it. Not sure if it was variable freq pulsed or PWM? Anyways,
those have a switch in the slide that initially connected the + batt
lead to the Vcc and Drain of the Powerfet. the Minimum speed was too
much on initial start. Those would burned them self's up in the switch.!
oh well, so much for engineering.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

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Old September 11th 07, 02:39 AM posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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Posts: 5
Default how to bypass dremel tool internal variable speed control?

Michael A. Terrell wrote:
Jamie wrote:
Michael A. Terrell wrote:

Claude Desjardins wrote:

wrote:

Just take it apart, I'm pretty sure it's just a "potentiometer"
(variable resistor) so it would only have 3 leads, one from the external
wire to the pot., one from the pot to the motor, and one from the other
external wire to the other lead of the motor.

Cut things off, plug the external leads directly to the motor.

Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.

I doubt they have put a stepper motor in there, they wouldn't sell for
20$ each! -- You still should only have two leads coming out of the
motor. Confirm?


Every Dremel tool I've had apart used a universal motor, and the
speed control was a simple dimmer circuit. This one might be PWM, and
run the motor on DC.

Most of the cordless drills these days use PWM power FeT drivers.

I modified a cordless drill with a mini PIC and Bridge to
perform regulated torque control, auto reverse and then forward
again until maximum torque was no longer peaking. Did this so that
the drill would have a TAP mode in it. I stuck a mini pot on the back
side of the handle to set the torque level.

if his dremel is also cordless, It may also be using it a PWM?
who knows. how ever, with the part count, I'm guessing he's using a
corded unit with a phase control.



None of those I've seen used an IC in the speed control. Also, he
didn't mention a filter capacitor, so id may be a simple dimmer
circuit. It's hard to tell from such a vague description. Part numbers
would have been a big help.

BTW, have you seen the small DC powered clone at Harbor Freight? It
runs on 12 VDC, and comes with an AC adapter. I was thinking about
using one (or more, with different sized drills) with a homebrew CNC
machine to drill PC boards.



I took a look at google images for his model and the dimmer really is
just a dimmer ... providing they sell brushes kits (2) for his model,
the principle was ok from the first post; plug it right to the input.

If the person who originally posted the question still follows the
discussion; it is strongly suggested that you do NOT use the tool wired
that way for too long as the motor will overheat and break (or some of
its internals will melt down)... take it as a temporary fix only.


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