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Amperage draw versus Air flow VFD Fan

  1. Nov 19, 2013 #1
    I have a VFD fan that pushes air through a filter. Over time, downstream resistance gets higher due to the filter. Fan speed remains constant. We have looked at amperage draw and it has remained stable even with this added resistance. Does that mean that air flow remains constant?

    Kind of confused that we are getting constant amperage. I'm inclined to think that we should be seeing a decrease in amperage draw since we should be pushing less air to due added downstream resistance.
  2. jcsd
  3. Nov 19, 2013 #2
    Fans come in many blades some for CFM others for presser . it is probable that your air flow is stalling . This would not show in a amp test. Did you check the static presser downstream . You could remove the filter then if air stalling was the problem the amp should show a higher reading. A stall air flow will still hold a press downstream.
  4. Nov 19, 2013 #3


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    Staff: Mentor

    What is the VFD doing? Is it under any sort of control?

    How much? Are you actually measuring it?
    Not necessarily. Filter loading is not always a linear (or parabolic) relationship between airflow and pressure and the fan curve can have different shapes, so if resistance goes up and airflow goes down, the amperage could stay the same. That's not common, but it is possible.

    Do you have a way of reading the airflow?
    That would be the expected result, yes.
  5. Nov 20, 2013 #4
    No control. Just for additional operational flexibility.

    Between 2-3 in. H2O

    BHP is constant since P = IV and both voltage and current are constant in my case. I guess that means that my increase in delta static pressure across the fan is exactly proportional to my decrease in air flow no?

    That is the next step.
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