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I need to replace the rotary potentiometer of a VFD DELTA variator with a slider potentiometer to control the speed of a motor. I have tried some of those slider potentiometers for stereo and mono use, but they went up in smoke.

I suppose that they are made for 5V and not for the 24V that the variator needs. Is there in the market those slider potentiometers for variator use? How can I make it work with those mono slider potentiometers? Here is the last one I am using.

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  • \$\begingroup\$ It depends how it is connected by source and load current and maybe needs a wirewound type \$\endgroup\$ Jul 8, 2021 at 18:52
  • \$\begingroup\$ i will look for that, thanks \$\endgroup\$ Jul 8, 2021 at 19:04
  • \$\begingroup\$ What is a "variator"? Where is the potentiometer used? What was the resistance and power rating of the original potentiometer? \$\endgroup\$
    – Transistor
    Jul 8, 2021 at 19:09
  • \$\begingroup\$ variator means a speed variator or motor driver. Those VFD delta are well known \$\endgroup\$ Jul 8, 2021 at 19:48
  • \$\begingroup\$ To replace, one must specify, R, Pmax and taper (linear or exp.) These Variable Resistors are called either Rheostats or Potentiometers. \$\endgroup\$ Jul 8, 2021 at 19:59

1 Answer 1

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I am coming from a different domain, where people often use potentiometers.

  1. Find markings on the original potentiometer, for Resistance and Power. If no markings, then measure the resistance using a multimeter, the largest value between two terminals out of 3 combinations. Power is: P = (V x V) / R = (24 x 24) / R. In consideration of the operating margin (headroom before burning), I would choose at least 1.5 times bigger power. What causes smoke is the "rated power".

  2. "www.digikey.com" -> search "potentiometer", -> "Slide Potentiometers": "https://www.digikey.com/en/products/filter/slide-potentiometers/78?s=N4IgTCBcDaIG4EMBOBLBAjANgUwAROwGcVCAXAeyRAF0BfIA"

  3. Specify "resistance" and "power", then "Apply All".

I use "Mouser.com" as well.

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  • \$\begingroup\$ according to the manual of any VFD Delta those potentiometers are from 0-5KOhm, 0-10VDC and 0-20mA, meaning a 0.2W \$\endgroup\$ Jul 8, 2021 at 19:50
  • \$\begingroup\$ I probably am wrong to see far difference: 5Kohm 10V is 0.02W. 20mA on 5Kohm is 100W. Is there any marking on the original potentiometer? Otherwise, 5K with 24V (is it?) is 0.1152W. You would be fine with 0.25W or 0.5W potentiometer, providing the numbers, 5K & 24V, are correct. \$\endgroup\$
    – jay
    Jul 8, 2021 at 21:33
  • \$\begingroup\$ Hi user3177225, It just came in my mind; If the connected circuit (I assumed it is on the center pin, wiper) loads, then it has to be considered as well. Unless I see the detail, I wouldn't be able to tell. Do you have link to the datasheet, user guide, or schematics? I only know the principle of VFD but not field applications. \$\endgroup\$
    – jay
    Jul 9, 2021 at 2:28
  • \$\begingroup\$ ok, here is the manual: deltaacdrives.com/Delta-VFD-V-User-Manual.pdf page 10(or3-2) \$\endgroup\$ Jul 11, 2021 at 19:52
  • \$\begingroup\$ Hi user3177225, In the Wiring Diagram, 5Kohm resistor is on 10V supply. Power on the 5Kohm pot is P = V * V / R = 10 * 10 / 5000 = 0.02W or 1/50W. Maximum loading current through the wiper (AVI) is insignificant, less than 10V/47k < 0.3mA, can be ignored. Point is; almost any of 5K slider on DigiKey exceeds 0.05W, safe to use. If it smoked, probably incorrect wiring caused so. Make sure the center (wiper) terminal gets connected to AVI, and other two terminals to 10V & ACM. If wiper terminal goes to 10V or ACM, it can smoke, around at the edge of the slider. \$\endgroup\$
    – jay
    Jul 12, 2021 at 15:41

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