Announcement

Collapse
No announcement yet.

VFD Braking Resistors - another question.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    I use either 300W 120v (48 ohms) and 1500W 240v (39 ohms) elements on the Hitachi 3hp vfd. Dirt cheap, They work fine and exceed the 35 ohm minimum resistance requirements. The problem with using close to minimum resistance is that your braking duty cycle goes way down. Often it's better to pick one that is not as low (aggressive) and have better overall usage results. All depends on how you use your machine.

    One thing NOT to do is blindly (no pun intended) use incandescent light bulbs. The resistance varies widely as they "light up". Could be pretty though.

    Comment


    • #32
      I remember using the heating element cartridge out of a tumble dryer once, long time ago, I can’t remember the resistance but there was a hell of a load on it, I think it’s still in use (it was a small reversing mill for samples)
      Mark

      Comment


      • #33
        Originally posted by lakeside53 View Post
        I need to play with the PLD on my vfds - in theory I can read a selector switch and auto-set parameters - would be nice to have multiple changes at the flick of a switch. I can already set 2 "different" motors, so I guess I could have two discrete sets of parameters entered.
        Mine has the "two motor" option also. On my KOC100 I believe there's up to four start/stop time parameters available but their selection is via the DI (digital input) terminals. I'm not educated on how the DI terminals would be implemented. I guess you would need some external circuit to supply that.

        Comment


        • #34
          Most digital Inputs are pretty simple.. switch to ground (NO or NC) or +24 depending on how you program them. You might have to read the manual

          Comment


          • #35
            That's for the Analog Input (AI) terminals. How would you input a value of "23" with a switch?

            Comment


            • #36
              With difficulty. The switch(es) via digital inputs would be used to select preprogramed parameters, like "second motor set", or a sequence held in the internal PLD (not all VFD have access).

              Comment


              • #37
                Originally posted by lakeside53 View Post
                I use either 300W 120v (48 ohms) and 1500W 240v (39 ohms) elements on the Hitachi 3hp vfd. Dirt cheap, They work fine and exceed the 35 ohm minimum resistance requirements. The problem with using close to minimum resistance is that your braking duty cycle goes way down. Often it's better to pick one that is not as low (aggressive) and have better overall usage results. All depends on how you use your machine.

                One thing NOT to do is blindly (no pun intended) use incandescent light bulbs. The resistance varies widely as they "light up". Could be pretty though.
                The Ohmic rating is only 1/2 half otr the data needed. The whatage is much more important for braking resistors. The Higher the wattage the more often you can use the braking funstion as a higher wattage rating has the ability to get rid of more heat. Resistors in parallel with give you a higher wattage.

                Comment


                • #38
                  resistors in series give you increased wattage too! but seriously.. you need the right ohms and a minimum sufficient wattage.

                  Increasing the wattage of the resistor has little effect on duty cycle after a nominal point (i.e. "big enough"); it's more related to duty cycle capability of the VFD. The resistor part is easy - how hot can it get hot and survive? The VFD is much more limited.

                  1500w is HUGE comparison to what you need for a typical 3hp motor at any reasonably sustainable duty cycle. Advantage of elements is that they are dirt cheap and can can take "red hot" temperatures. 300W works well for 2-3hp, never gets "red" or even smokes on mine even if I use it as much as possible before the vfd limits.
                  Last edited by lakeside53; 04-20-2018, 12:26 AM.

                  Comment


                  • #39
                    Originally posted by kf2qd View Post
                    The Ohmic rating is only 1/2 half otr the data needed. The whatage is much more important for braking resistors. The Higher the wattage the more often you can use the braking funstion as a higher wattage rating has the ability to get rid of more heat. Resistors in parallel with give you a higher wattage.
                    My first reaction to this post was "HUH??"

                    No offense intended, but (in a technical forum (this one)) I'd expect as a licensed Advanced Radio Amateur licensee (judging by your handle) you would not make up your own terms.

                    There is no such thing as an "ohmic rating". As you certainly should know, it's resistance or impedance. There is no such thing as "wattage". It's power rating.

                    73, KF6R
                    There are no stupid questions. But there are lots of stupid answers. This is the internet.

                    Location: SF Bay Area

                    Comment


                    • #40
                      Somehow it slipped into the language

                      watt·age
                      ˈwنdij/Submit
                      noun
                      a measure of electrical power expressed in watts.
                      the operating power of a lamp or other electrical appliance expressed in watts.

                      Jerry : where are you when you are needed? get over here and argue both sides
                      Last edited by lakeside53; 04-20-2018, 01:08 AM.

                      Comment


                      • #41
                        Originally posted by lakeside53 View Post
                        Somehow it slipped into the language

                        watt·age
                        ˈwنdij/Submit
                        noun
                        a measure of electrical power expressed in watts.
                        the operating power of a lamp or other electrical appliance expressed in watts.

                        Jerry : where are you when you are needed? get over here and argue both sides
                        There are no stupid questions. But there are lots of stupid answers. This is the internet.

                        Location: SF Bay Area

                        Comment

                        Working...
                        X