Variable Frequency Drives : Why you don't need a bypass

When I think about variable frequency drives (VFDs) and bypasses I am reminded of the story of the family of women cooking a ham at Christmas. The young girl notices that her mother cuts each end of the ham off before

putting the ham in the pan to cook it. She asks her mother, “why did you cut the two ends off?” The mother replies, “well that is the way my mom taught me to cook a ham.” The girl then finds her grandmother and asks her the same question, to which her grandmother responds, “that is the way my mother taught me.” The girl’s great-grandmother is still living and when the young girl asks her why she cut both ends off of the ham before she cooked it she responds, “I had a small pan and it was the only way the ham would fit.”

Bypasses have been around as long as VFDs have been used. And until recently it made sense to have a bypass on your VFD. There were two very good reasons for always having a bypass: 1) VFD’s were unreliable, had a high failure rate, were complicated to set up, and required a highly trained specialist to install, set-up, or fix your VFD. 2) A bypass was required to allow your fan or pump to run while you waited for a specialist to come and replace your variable frequency drive.
With the massive improvements in VFD quality resulting in thousands of hours of run time between failures and ease of installation and setup (see how to set up a variable frequency drive in 36 seconds) the need for VFD bypasses are few and far between. Given that most bypasses cost more than the VFD it makes much more sense to by a back up VFD that can be installed and working in the time it took your grandfather to call the VFD specialist.
If you are in Georgia or Florida you can call the Control pros at Stromquist & Company for all your variable frequency drive needs. If you are located in another part of the country one of our affiliates at Controls Group North America can be of assistance with your variable frequency drive applications.

Eric Stromquist

Eric Stromquist

Eric has been in the controls industry since 1979. His passion for controls and the desire to provide an easy way for HVAC professionals to keep up with the rapid changes in controls technology inspired him to create Controltrends.

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Comments

  1. says

    That was a great story to match with the way logic and reasoning get bypassed just because ‘that is the way it is done’.

    Now a days VFDs are relatively easy to replace and with proper programming of the detachable keypads you can literally program the new drive exactly the same in just a few key presses.

    Everyone wants to cut dollars and it can be done by including the cost of one or two spare VFDs available for swapping out rather than matching bypasses on each drive.

  2. says

    I totally agree, and it sure is amazing how far technology has come over the years, and continues to progress. What will life be lie 30 years from now?

  3. says

    Having a VFD on the shelf might be a good idea, however don´t forget to “exercice” capacitors in VFD. They don´t like to be with out power for long time (year), they might explode in those case. Put some main voltage on input once every 6-12 month to avoid a unplecent supprice.

  4. elai says

    l had inquiry… is there a practice where u have a VFD then u still had a back-up soft starter??

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