Tako Kichi

Hi Folks,

I have searched fruitlessly up to now for a suitable circuit and thought I would pick your collective brains (again...lol).

Basically all I am trying to do is have a variable speed control for a wood router/laminate trimmer/PCB drill type motor.

I know some people are using light dimmers but laminate trimmers can draw up to 4 amps in use and I am not sure if a simple lamp dimmer would handle that. Running motors on lamp dimmers can also generate big spikes apparently and generally they do not last long.

As this will be used in a home-built CNC engraver/router/PCB mill I don't fancy having large spikes around stepper motors, computers etc.

Does anyone have a link to a suitable controller, or has anyone here built something similar that they would be willing to share?

This project is an extremely low budget affair (more to see if I can do it than anything else) and if I can build a controller so much the better. I am already 'dumpster diving' and ebay searching for materials....lol.

Thanks in advance for any pointers/help.

Larry Green

TillEulenspiegel

Is the motor AC or DC?
A very simple design uses a 90vDC motor on the far side of a rectifier bridge a cap to smooth ( NP if the motor is bi-bidirectional) supplied by a commonly available 15-20 amp light dimmer.

AC is a different story most industrial use variable frequency drives ( expensive). lower end drives use a phase scheme where the current is turned on for a fraction of the sine wave. Inductors don't like that much , but if it's intermittent use You should be OK.
http://www.fairchildsemi.com/an/AN/AN-7511.pdf

Styx

you say you want speed control?
do you want "true" speed control, ie even when the load changes the speed stays at the speed that was demanded (you need someway of measuring present speed to close a speed-loop)

or are you just after a variable speed controller?
you say it is an AC machine, i take it that it is a Induction machine and not a syncrous machine?)

If it is a induction machine just search the net for "slip" control - really easy.
If it is a syncrous machine than you will need to generate a sin-wave and have an AC inverter to drive it

Tako Kichi

Hi folks and thanks for answering my question.

The motor will be AC (laminate trimmer/mini router...probably) and it is just a simple variable speed control I was after.

It turns out that Harbor Freight (in the US) has some router speed controllers on sale right now for less money than it would cost me in parts. I have a buddy down there that can get one and ship to me (in Canada) so I think that might be the way to go. A lot less work for me...lol.....I have enough work lined up building the machine and the control board.

Thanks for your help.

Larry Green