I once worked for a livestock equipment manufacturer. We manufactured a small hog waterer that screwed into a half-inch pipe. When the hog bit the waterer, fresh water was supplied. Compared to a heated device with a standing tank of water, it was a great product and quite economical. We made them in high volume out of 304 stainless steel on a specialty eight-station machining center.
To reduce tool wear, I had a frequency control module installed on the threading head so we could accelerate and adjust the threading speed of that station. Every day after lunch, the frequency drive was faulted. Incoming voltage was the indicator. We reset it at first, thinking it was an abnormality, but it happened 100 percent of the time.
We set up a meter and waited. Sure enough, right at the end of the lunch period there was a voltage spike and the frequency control faulted. As it turned out, the factory had a capacitor bank to level out the incoming requirements and thus lower the electric bill. To further lower the bill they had put the capacitors on timers and shut them off unless needed, such as during the lunch period. We did not fault out the frequency control in the morning since the machine was turned off when the capacitors were energized.
At noon, when the capacitors were cycled down and then later back on, the voltage spiked and then stabilized while the machine was on. The frequency control caught it every time. The solution was not to cycle the capacitors at noon. We had spent much more on the phantom issue than the electric reduction. We realized that our equipment would not appreciate the high inrush that cycling the capacitors would generate.
Roger Vreeland is an advanced manufacturing engineer with Lennox Industries Inc.
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