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- Feb 17, 2013
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- 4,407
We're all pretty much here to help.I appreciate the input and the chart. I know it's difficult around here sometimes as many people are very seasoned here and they're here for like minded people. Then there are others (like myself) that are here to learn from the aforementioned. Some are very happy to give/shape/teach, you guys are very much appreciated.
I'm not sure I understand your question ... but it appears you're asking whether it's OK to put a capacitor across the "braking resistor" terminals of a VFD, instead of an actual resistor. If so, I'd recommend against it. Don't have a perfect understanding of how a VFD works, so I may be a bit wrong. But as far as I can tell, the braking function electronically connects the resistor across motor windings (which are acting as a generator).I know this isn't the place to pose this question, but I'm pretty sure I can (capacitors?) To my VFD for braking purposes, this would be huge for the whole "threading excitement" you spoke of.
Resistors and capacitors will act differently. My own VFDs (Teco FM-50) specify 100 ohm braking resistors. When first connected, the "resistance" offered by a capacitor is near zero (acting pretty much like a short circuit). It then rises to near infinity as it charges up to a voltage equal to the "driving" voltage from the motor. The initial near-zero resistance might be too low (and the inrush current too high) for the VFD circuitry to handle. Then you end up with a bunch of energy stored in the capacitor, which must be dissipated somehow. A power resistor, in contrast, will present a constant, known resistance to the VFD's circuitry. It dissipates the energy by producing heat.
If I absolutely had to substitute for a braking resistor on a VFD, my first choice would be a small space heater ... basically a large resistor designed to produce heat. I'd start be measuring the resistance across the AC plug, to verify that it's somewhere near the specified value. A large light bulb (say 100 watts) also comes to mind ... but the "cold" resistance of a light bulb filament is very low, so it might not be suitable.
Your best bet is to save up your pennies and buy an actual braking resistor. Here's one for just over $15:
uxcell 150W 100 Ohm Aluminum Housing Wirewound Braking Resistor: Amazon.com: Industrial & Scientific
Shop Amazon for uxcell 150W 100 Ohm Aluminum Housing Wirewound Braking Resistor and find millions of items, delivered faster than ever.
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