I have newish routers with built-in speed control and soft start. They're great. I also have older routers I like for other reasons that don't have those features. Is it possible to use a VFD controller on the older routers? I'm especially interested in using my laminate trimmers at lower speeds, mostly to reduce the high-frequency noise.
I have an old speed controller that doesn't do any load balancing (or whatever it takes) to keep the rotational speed constant at low speeds. It sort of works but I'd like something better.
Any ideas?
Variable Frequency Drive for Older Routers
Posts
Re: Variable Frequency Drive for Older Routers
#2The variable-frequency drives you reference are used with 3-phase motors. A controller for single-phase AC induction motors can be purchased but my understanding is they are expensive and can be picky about the motor it will work with. So for a router which is usually universal (AC or DC with brushes) you are out of luck using one of these.
What you need is a DC controller and as you found out, you need one that has a feedback mechanism to keep the speed constant under load. I think the usual method is to power the motor by variable pulses of current and in between the pulses it measures the back emf voltage which is an indicator of its speed and it can use this info to adjust the next power cycle. If you can find one for any old motor is a good question and I've never seen anybody post great luck with a speed controller for routers but maybe I'm too pessimistic.
Please let us know if you find a solution.
Re: Variable Frequency Drive for Older Routers
#3
A simple triac-based AC voltage controller very similar to a household dimmer switch should do the trick.
Harbor Freight 
Get variable-speed router control for better results in a wider selection of materials. This router speed control works with any universal AC/DC brush-type motor 8 amps or under.
Plug any router into the control unit and get instant variable-speed control
Works with any universal AC/DC brush type motor, 8 amps and under
Variable-speed dial for fine control
3-way rocker switch with Off/Full Speed/Variable Speed settings
https://www.harborfreight.com/router-variable-speed-control-dial-59386.html
Re: Variable Frequency Drive for Older Routers
#4The Harbor Freight speed control looks just like the 25-year-old one that find inadequate. It's mostly the loss of torque at lower speeds but also the difficulty of setting the right speed that aren't good enough.
I looked at some YT reviews from woodworkers who actually use routers a lot. The result is I'm going to buy a new laminate trimmer with soft start and speed control. I can keep my older trimmers set up for use with jigs I've made for them, but for general use I need a new trimmer.
Thanks, Bill and Peter, for the helpful information.
Re: Variable Frequency Drive for Older Routers
Edited #5
@Bill Howatt,
Yes, that would require rectifying AC to DC with a high-frequency PWM with a MOSFET and ideally a closed-loop feedback, and the cost for that would probably be more than getting a new router.
As an aside, the best way is mechanical reduction (pulley, gears, jackshaft) because that will increase torque with decreased RPM, which is often what you want. But for hand tools, that would have to built into the tool.