Fan Array Start Method

Fan Array Start Method

Today’s Fun Fact Friday is about using a single variable speed drive (VSD) to run multiple motors on an HVACR fan array. There are various topics that require addressing, so I will divide them into separate posts. This week let’s focus on the moment the VSD is given a Start Command.

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At this moment, there are (3) different scenarios to consider:

  1. The fans are stopped.
  2. The fans are spinning roughly at the same speed.
  3. The fans are spinning, but at different speeds.

Scenario 1 is easy, as the motors are all stopped, most drives won’t have an issue here.

Scenario 2 is more challenging, but a quality VSD can catch the spinning motors and ramp them to the setpoint.

Scenario 3 is where we separate the basic VSDs from the advanced VSDs. I won’t get into the techy details, but a VSD essentially starts at the “average” speed from all those motors combined, and this results in a large current spike by the motors – which may result in a drive fault.

The ACH580 solves the challenges of Scenario 3 first by braking all the motors and then ramping them to the setpoint. For those interested in technical details, check out the related Technical Note.

ACH580 drives family
ACH580 drives family


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