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Sweet spot for inexpensive VFD?

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  • #46
    Originally posted by PStechPaul View Post
    That's only 1000 uF, so perhaps my calculations were off by a decimal point.
    Come on now. You know a digit off for high capacity capacitors can in discharge a tremendous of energy. Like a LiOn going off.

    I want some please I like Caps. And Inductors. Resisters? No thanks. JR
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

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    • #47
      Originally posted by lakeside53 View Post
      Click image for larger version Name:	hitachi L300p caps resized.jpg Views:	0 Size:	65.2 KB ID:	1848186

      Above is the capacitor bank for a Hitachi L300P, an older 15hp 480v vfd. This just slides in and is secured with 4 screws that are also the power connections. I'm replacing them on 2 VFD tomorrow. Just "preemptive maintenance"... these VFD have been running at 100% power (huge air cleaner system) 10 hours a day, 270 days a year for 13 years, in an 80F+ room. This calcs out to 35K hours, but the run meter shows 44k so look like these been left on for a "few" weekends when no one is around. The 4 VFD cooling fans get changed out also.

      Anyhow... you can see these are 400v, and in "series pairs". Given Hitachi guidelines, these would be suitable for 7.5hp on single phase.
      Big time. JR
      My old yahoo group. Bridgeport Mill Group

      https://groups.yahoo.com/neo/groups/...port_mill/info

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      • #48
        Originally posted by PStechPaul View Post
        That's only 1000 uF, so perhaps my calculations were off by a decimal point.
        You can get away with a LOT less capacitor if feeding with 3 phase. You barely need any capacitor with 3 phase, other than just as a bypass, the rectified 3 phase is always at or above 86% of peak voltage..

        For single phase, you do need a fair bit of capacitance, single phase goes to zero volts twice per cycle.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #49
          That is true, but Hitachi guidelines (their devices) imply single phase is only 2x the capacitance of 3 phase. i.e. there array above from a 15hp vfd is good for a 7.5 hp vfd on single phase. Someone with EE 101 can calc the ripple voltage. 1/2CV^2 etc. Assume 17.5 amps each phase out, 60hz. (or Paul can put it into his fancy spice program).

          Changed out the 2 sets of capacitor banks and fans this morning, blew out a ton of filth. All fired up fine! Maybe get another 13 years out of them. Sure is nice to be able to pick up the phone and get oem parts for older units.

          One nice feature of this VFD is that it has an LED down by the power lead/screws that stays on until the capacitor bank has discharged after the power is removed Takes about 5 minutes.
          Last edited by lakeside53; 01-12-2020, 12:33 PM.

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          • #50
            I must have slipped a decimal point. Here is a simulation showing acceptable ripple with 480 VAC 60 Hz single phase input and roughly 4.7 kW (6 HP) output load, with just 1000 uF total capacitance. Voltage peaks at 720V and stays above 625V. I have also attached the ASC file for LTSpice (remove .txt - .asc not allowed)

            Click image for larger version

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            Attached Files
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

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            • #51
              Originally posted by PStechPaul View Post
              [SIZE=16px]I must have slipped a decimal point. Here is a simulation showing acceptable ripple with 480 VAC 60 Hz single phase input and roughly 4.7 kW (6 HP) output load, with just 1000 uF total capacitance. Voltage peaks at 720V and stays above 625V. .......
              That is almost perfectly theoretical for no capacitance, even. about 14% ripple as percent of peak. 3 phase never falls below that.

              How much you use for single phase depends on how much ripple you can stand.
              1601

              Keep eye on ball.
              Hashim Khan

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              • #52
                My TD400 VFD on my lathe will take either single or 3phase input. Should I run it off the RPC?

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                • #53
                  if it's designed for either I'd just leave it on single.

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                  • #54
                    So I've been reading the manual for the $130 Lapond SVD-PS Series, and it doesn't look like it can operate on the momentary contact switch system I like. This is from http://www.soyan-tech.com/uploads/20...ser-Manual.pdf page 138. There's several more configurations, but they don't improve the situation.

                    Click image for larger version

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                    As opposed to what I want with the momentary contacts for the buttons, which makes it easy and foolproof. I think this was the problem with the Toshiba also.
                    Click image for larger version

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                    Location: Jersey City NJ USA

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                    • #55
                      I guess I'm not going to do better than that 2 wire config above. Is there any reason I can't use a nice 35A STDP switch I have for the low voltage circuit? I'll get a SPST switch for the direction.

                      Click image for larger version

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                      Location: Jersey City NJ USA

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