I would like to have a router speed controller that can keep constant torque at all speeds. I will be running the router at around 5000 rpm or lower. I tried a triac controlled commercial unit once but it did not have enough torque at the lower speeds. Does anyone have a circuit for a controller that really maintains constant torque or are there commercial units available that really work well? Thank you!

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    \$\begingroup\$ Don't you mean constant speed under varying torque? \$\endgroup\$ – Rocketmagnet Sep 8 '12 at 0:16
  • \$\begingroup\$ You can't do that with a Triac. it is open circuit when off and the high impedance state means no torque. You need a variable AC source that maintains low impedance to deliver the power assuming the motor can handle it. It would look like an inverter with variable amplitude mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/… \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 16 '12 at 3:52
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    \$\begingroup\$ As @rocketmagnet points out, your question is technically impossible. Torque is a function of motor speed and motor loading. If you want constant torque given constant speed, the only variable to play with is the load (which is obviously not what you want). Perhaps you meant constant torque -- changing speed to hold torque, given load; or constant speed -- allowing torque to fluctuate (as load fluctuates). \$\endgroup\$ – DrFriedParts Dec 12 '12 at 22:45

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