Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Taco 705-2 Variable Speed Injection Control with ECM Pump?

JGC Member Posts: 2
Anyone know if it is OK to use the Taco 705-2 controller with one of the newer ECM pumps (eg. Grudfos Alpha 15-55)?
The manual for the controller says it is compatible with a "permanent capacitor pump motor". I presently have a Taco 008 pump as the injection pump but I want to put in a more energy efficient pump. The plan would be to leave the Grundfos Alpha pump on "maximum speed" mode and let the 705-2 control its speed.


  • SWEI
    SWEI Member Posts: 7,356
    Short answer: It will not work (at least with currently available ECM circulators.)

    Longer answer: The Taco drives an induction (PSC) motor using a phase-chopping and then PWM driven TRIAC (similar to a lamp dimmer.) ECM circulators rectify the incoming AC power to DC and then invert that to a multi-phase variable voltage and frequency output which drives a permanent magnet synchronous motor.

    In order to make this compatible with a phase-chopping dimmer, the input circuitry actually has to analyze the incoming AC waveform, interpret that to derive a modulation percentage, and apply the result to the control portion of the internal inverter circuitry. This is pretty much what happens inside quality "dimmer compatible" LED light fixtures, BTW.
  • JGC
    JGC Member Posts: 2
    Great, detailed answer. Thanks so much.
  • hot_rod
    hot_rod Member Posts: 22,147
    Some of the larger size ECM pumps can be controlled, and speed varied from the boiler control. I see Lochinvar offers some of their boilers with the Grundfos Magna series pumps now.

    Smaller sizes ECM circulators, like the one you mentioned are available in the European market, if you could work with a 220V motor.

    It's common to see solar pumps with with PWM ECM motors in Europe, and most of the solar controllers have the output to run them. This is a drawback pump with the PM controlled motor.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream