permanent magnet motor control

[grizzly]

Hi. I'm a new member, found this great site by accident. Anybody had any experience with controlling PM motors (Grizzly Mini-mill) with a router speed control?? Since these controls maintain torque by sensing back-emf of the field and the PM has no field windings I'm wondering if it would work. Would like to know before I smoke something. I have a couple of these mini-mills I bought at Grizzlys tent-sale as fixer-uppers and rigged one with an old treadmill control which works ok, but need a control for the other one. Also, has anyone tried any of those aluminum replacement gears some guy is advertising on the Ebay? Am wondering if they are noisy and what you would use to lubricate them....light grease maybe??? In the one I have running, I bought stainless steel gears from Stock Drive Products and spent a lot of time modifing them to fit. They work great, but it's a lot of work and I'm thinking of going the ready-made route for the second one. Thanks for any info. Grizzly

[Al_The_Man]

You need to know the control type, Because many routers are Universal motor type (AC/DC) the controller may be triac phase angle control, if so you cannot use on a PM DC motor, but there are many out there, (All Made by one Manuf,) Baldor and others that are full-wave SCR control and you can use these, and pick them up for ~$100.00 new, or $20~$25.00 on ebay.
Al.

[sch]

PWM (pulse width modulator) controllers are better than SCR/60hz controllers at least in the lower speed range as the SCR controllers are working at on either 30 or 60 herz pulses depending on whether the power supply is half or fullwave and these can get kind of coggy near the low end or speed. The sponsor for the forum (Electronickits.com) among others sells dual 555 controllers for dc motors for $12-18 that can be adapted to FET transistors at any power rating you need. If the power transistor (sometimes a FEt, others a darlington power transistor) is not rated for the supply you need just look through a catalog for FET power transistors and you will find ones from 400V + at 10amp to 60-100amps at 50V for under $2. The 555 runs in the low thousands of herz and can smoothly control speed from 10 to 100%
without the cogging of the 30-60hz SCR circuits. www.littlemachineshop.com sells the controllers for minimills with the built in failsafes and connectors and from the wiring diagrams these would work with PM motors. Price is about $130. Not clear if they are feedback speed controlled or not, but I suspect not. Router speed controllers generally work over the top 50% of the speed range of the router, ie there is not much reason to reduce router speed below 40-50% of its rated max.