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Braking resistor for AC Tech vfd

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  • Braking resistor for AC Tech vfd

    A batch of 2hp single-phase AC Tech vfds have been on ebay for a while and I finally pulled the trigger for $100 w/shipping.

    All my other VFDs have terminals for a braking resistor and it was easy to cobble up something suitable from Radio Shack, but AC Techs don't offer that arrangement: instead you're supposed to buy an add-on device that's more expensive than the vfd itself and has a transistor inside.

    There are comparably-rated new units on ebay that are about $150 w/ shipping, and they look just like Teco's, but they don't inspire much confidence.

    Anyway, does anyone here have the wherewithal to describe what I might build to add dynamic braking to an AC Tech unit?

  • #2
    Your best bet will be to buy their brake package.


    • #3
      yes, a nasty suprise -same with Hitachi L or X series...


      • #4
        When you use the VFD to brake the motor, the motor generates electricity rather than consuming it. Without a braking resistor and the associated control, the VFD's DC bus voltage would increase beyond the breakdown voltage of the diodes and capacitors in the input section. To dissipate the generated power, the VFD dumps current through an IGBT (normally) into the braking resistor. What you are missing is the control circuitry for this, the IGBT and the braking resistor. Without technical details (schematic and software) it will be difficult to add this feature.


        • #5
          I have the FM50 TECO and the BR for a 3 horse motor was only 28 bucks. So the VFD and the BR was just over $200.00

          Can you have to much equipment ????


          • #6
            The brake add-on can be pretty simple, a voltage detector that turns on an IGBT.

            When the brake is internal, the brake often has settings, such as maximum duty (% on time). External ones may have it also, in different form.

            Fundamentally, it is a shunt voltage regulator. Companies such as PowerOhm sell modules for large systems. We have a 50A unit in the shop right now, as part of a setup for a client.

            The add-on types such as Powerohm are usually variable duty modulated to hold a max voltage which is settable.

            The add-ons for a vfd may be different by brand and model, and depend on having access to the + bus and -bus.
            4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

            Keep eye on ball.
            Hashim Khan

            Everything not impossible is compulsory

            "There's no pleasing these serpents"......Lewis Carroll


            • #7
              Originally posted by MetalHead
              I have the FM50 TECO and the BR for a 3 horse motor was only 28 bucks. So the VFD and the BR was just over $200.00

              yes.. but that's just the resistor.. the easy part.