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#11
Posted to sci.electronics.basics,sci.electronics.repair,rec.crafts.metalworking,alt.engineering.electrical
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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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