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Control for fractional HP motor needed

zepfanzepfan Member Posts: 294
Does anyone know of a control, or an Inexpensive VFD that could be used on a 115 volt 1/10 hp motor? The application is an an exhaust fan for a lab that is served by a VAV box. The board in the vav box would send a 0-10 volt signal to the exhaust fan’s control, the signal would increase as the damper in the box opens. A vfd may be the only way to go, but the fan is so small that this me be overkill. I did not know if anyone had a like experience, and what control they used for this. Thanks to all


  • Jamie HallJamie Hall Member Posts: 12,862
    Is this a standard AC squirrel cage motor? If it is, the speed it runs is fixed by the frequency of the power fed to it, so a variable frequency drive is going to be the only hope. If it is the type with brushes, you might be able to control the speed by varying the voltage applied (think Lionel electric model trains!).
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,057
    120 volt VFDs are available, mostly Chinese made.
  • zepfanzepfan Member Posts: 294
    Thanks for the responses. We have not received the motor yet and the submitalls do not state weather it is PSC, shaded pole, or ec. Normally we would use a wall mounted scr to very the speed of the fan, but that requires manual adjustment. We are looking for something that is automatic
  • Jolly BodgerJolly Bodger Member Posts: 209
    What type of lab? Sounds like you need to keep the room negative. Seems like a 1/10hp motor might be small for controlling space pressure. I have come across some of the newer ECM motors have a 0-10 input.
  • pecmsgpecmsg Member Posts: 1,429
    Not a very big exhaust fan. If a squirrel cage fan just control a damper.
  • hot_rodhot_rod Member Posts: 13,318
    a trial relay might be all you need, if you have a way to send it a signal. 20 bucks or so for a small relay able to switch 1 hp or so. We added them to our solar controllers when the load exceeded 1 A.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • mikeg2015mikeg2015 Member Posts: 1,178
    > @pecmsg said:
    > Not a very big exhaust fan. If a squirrel cage fan just control a damper.

    Modulating damper tied directly to VAV.

    Honestly for a fan that small, just leave it running.
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