Brainstorming? Quantifying braking resistor usage?

[einnh]

Hi All,

I am trying to figure out a way to quantify the power required for our machines VFD braking resistors. We don't currently have a way to quantify the braking requirements due to the nature of how the machine is used so to date we have just sized them for continuous 133% power. This has been fine, however I think it is oversized as the resistors never get much above room temperature from my limited spot checking.

We have a new machine being built and I was trying to figure out a way to monitor the resistor circuit or equipment closer to try and determine the relative usage for the next machine, to more appropriately size the resistor (smaller overall packaging will help the design of this machine significantly).

Any ideas how how I could monitor it? My thoughts were:

Monitor current - difficult as it's done in high frequency pulses through the resistor.

Monitor temperature - monitor ambient and surface temperature of the resistor to determine heat loss. This would require quite a bit of physical knowledge of how the resistor is built but do-able.

Any other ideas?

 

[damica1]

If your VFD has "Modbus" capabilities, then you could monitor all the different parameters that would help to make that decision.

Example: you could monitor "Current, Hz, Voltage, Regen-Voltage, Duty-Cycle, RPM, and probably about anything you needed."

Just an Idea.