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  • VFD single phase input?

    I saw on another thread that using single phase input you recommended jumping L2 and L3. .si now I'm thinking "hmmmmm" I have a Mitsubishi vfd and I'm inputting 220single phase but this reduces capacity by 1/3 which is understandable. Can I jump one of the used inputs to the unused input? This would provide power to all three of the inputs but it would be out of phase. But would that matter because the vfd generates its own three phase output. So if this is possible then my vfd would nolonger be derated due to single phaseinput . Or is this only applicable to modern vfds? Mine is a Mitsubishi vfd z024. This is not mentioned in the manual.
    Last edited by ahidley; 09-16-2015, 11:49 PM.

  • #2
    The benefit of the jumper is limited to fooling any phase loss detectors so the unit will run. no benefit in operation to speak of.
    1601

    Keep eye on ball.
    Hashim Khan

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    • #3
      It depends on your VFD, and who makes it, does it not? Mine is rated for single phase input, I use L1 and L3, I believe.

      Comment


      • #4
        If rated single phase in, then there is no reason to do any jumper unless so directed by the manual.

        If not rated single phase, you may need it. And you should assume 50% derate unless otherwise stated. And there is a chance the VFD will not accept single phase even with ĵumper.
        1601

        Keep eye on ball.
        Hashim Khan

        Comment


        • #5
          I used to use Mitsubishi VFD's extensively, there is no benefit from jumpering as the input is simply a 3ph rectifier, there is however on some of the 1ph/3ph input types, two of the inputs are dedicated for the low voltage supply, so in 1ph use the power has to go on the recommended pair, on these models there is also an option of leaving the low voltage control on in standby and the main DC power off until ready for use.
          Max.

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          • #6
            Originally posted by J Tiers View Post
            If rated single phase in, then there is no reason to do any jumper unless so directed by the manual.

            If not rated single phase, you may need it. And you should assume 50% derate unless otherwise stated. And there is a chance the VFD will not accept single phase even with ĵumper.
            What Jerry said! it's generally a myth that you can get 2/3 power out with one phase missing. 50% is a good assumption, but some can be way worse. In my case, I have pair of high end 7.5hp VFDs that are only rated at 1.5hp on single phase. My Hitachi are roughly 50%.

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            • #7
              I have wired many VFDs and built well over 50 rotary and static convertors, and have been interested in single phase to 3 phase changes for 50 years. A few years ago I had the chance to talk to a VFD Engineer and it was an enlightening experience. let me talk about 3 phase to 3 phase VFD's only here:

              First, the input for each phase has a capacitor that stores the energy and provides power to a rectifier circuit which provides the power to the electronics that create 3 phase power. This electronic output could care less about 60 cycle current or incoming phases, it only wants a continuous source of DC power . If this level of incoming power is reduced, the VFD amperage output is reduced ( but voltage is maintained ).
              When you provide only a single phase input, the capacitors in that 1/3 portion of the input determine the total output, based on THEIR capacity.
              Some VFD builders have liberal caps used here, and some have only marginal capacity ...know that !
              He also said that not all the caps are the same--they may be rated the same--but electronic components are notorious to vary +/-10 %, so you need to try all three input possibilities to find the best for output performance.
              All 3 to 3 phase convertors will work on single phase input "IF" they do not have a voltage comparison circuit to prevent failure ( safety feature) . Most VFDS do have this feature however, but you may be able to disarm it.

              I have to assume the jumping of the terminals is an attempt to increase capacity --maybe it works--maybe it doesn't --try it and see as VFD's vary in design

              Rich

              I hooked up a Hitachi 200 to a 7 Hp motor in a 15 inch Nardini Lathe.
              The 10 HP VFD drives the 2 speed motor without issues and it has single phase input and
              there was a noticeable difference in the input terminals used.
              I have found Hitachi's to be the best in handling single phase loads
              Last edited by Rich Carlstedt; 09-17-2015, 12:30 PM.

              Comment


              • #8
                Originally posted by Rich Carlstedt View Post
                I have to assume the jumping of the terminals is an attempt to increase capacity --maybe it works--maybe it doesn't --try it and see as VFD's vary in design
                On all the VFD's I have stripped for parts, the majority have a 3ph full wave rectifier feeding a common capacitor bank for the DC. So strapping 2 phases effectively double up two of the rectifiers but has no effect on the DC.
                When I asked a Mitsubishi engineer on the question of output of 3ph over 1ph he said that the rated Kw it can supply applies for both 1ph or 3ph.
                Max.

                Comment


                • #9
                  Originally posted by Rich Carlstedt View Post
                  I have wired many VFDs and built well over 50 rotary and static convertors, and have been interested in single phase to 3 phase changes for 50 years. A few years ago I had the chance to talk to a VFD Engineer and it was an enlightening experience. let me talk about 3 phase to 3 phase VFD's only here:

                  First, the input for each phase has a capacitor that stores the energy and provides power to a rectifier circuit which provides the power to the electronics that create 3 phase power. This electronic output could care less about 60 cycle current or incoming phases, it only wants a continuous source of DC power . If this level of incoming power is reduced, the VFD amperage output is reduced ( but voltage is maintained ).
                  When you provide only a single phase input, the capacitors in that 1/3 portion of the input determine the total output, based on THEIR capacity.
                  Some VFD builders have liberal caps used here, and some have only marginal capacity ...know that !
                  He also said that not all the caps are the same--they may be rated the same--but electronic components are notorious to vary +/-10 %, so you need to try all three input possibilities to find the best for output performance.
                  All 3 to 3 phase convertors will work on single phase input "IF" they do not have a voltage comparison circuit to prevent failure ( safety feature) . Most VFDS do have this feature however, but you may be able to disarm it.

                  I have to assume the jumping of the terminals is an attempt to increase capacity --maybe it works--maybe it doesn't --try it and see as VFD's vary in design

                  Rich

                  I hooked up a Hitachi 200 to a 7 Hp motor in a 15 inch Nardini Lathe.
                  The 10 HP VFD drives the 2 speed motor without issues and it has single phase input and
                  there was a noticeable difference in the input terminals used.
                  I have found Hitachi's to be the best in handling single phase loads

                  nope.....

                  Same capacitor is used for ALL phases, that is not the issue.

                  The jumper may fool the unit into accepting all 3 phases as working. Done.

                  Limits are because 3 phase rectified with NO capacitor is good DC, only about 14% ripple. So the capacitor is just for a bypass, and may be very small. voltage never goes below about 86% of peak, and input current is quite steady.

                  With single phase, input drops to zero volts (!) twice per cycle. So the capacitor must be perhaps 100 x larger. AND input current is very "peaky". It is zero when onput voltage is below the DC, and high when the voltage is at peak, and the capacitor is being re-charged.

                  3 important limits are at work

                  Limit 1 is that the small 3phase capacitor may not hold voltage up high enough, so you get an undervoltage trip-off.

                  Limit 2 is that the single phase current peaks may be far more than the 3 phase rectifiers can take, because they were sized for 3 phase input current (lower).

                  Limit 3 is that the capacitor on 3 phase has to supply a lot of current when volts are low, and is charged with a high pulse of current when input volts are high. A capacitor that is selected for the small variation on 3 phase may not be able to take the higher current on single phase.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    I have a Toshiba(would have to look at the model) in my lathe. It does a little better than 50% de-rate for single in. I have a 5hp drive with a 3hp motor and no issues. I talked to a tech there before I got it and he told me a 3hp drive would be border line but would probably work for a 2hp motor with single line in.

                    Comment


                    • #11
                      Those are some very good points, and I have little to add. However:

                      1. Some VFDs have a transformer connected between two of the input phases, probably used for fans or control circuitry. It should be easy to tell by checking resistance on the input terminals. And a VFD like that cannot be run on DC unless you bypass the rectifiers and supply a separate AC source or DC for that purpose. I found that on a very old VFD that I have now stripped down, and modern units probably are not built that way.



                      The space in the corner is where this transformer and power supply was mounted:



                      2. What is needed to operate a VFD on single phase at full power is a PFC front end that is basically a boost switching regulator that uses most of the input waveform near the zero crossings so as not to need so much at the peaks to keep the main bus capacitors fully charged. Here is a schematic of a PFC circuit used in a 10 kW EV charger - the complete kit is less than $1500 so the PFC section probably could be built for under $500:



                      Here is the power section:



                      3. It might be possible to increase the power output by connecting a motor run capacitor from one of the single phase AC lines to the unused third phase, similar to how a 3 phase motor can be driven from single phase, and also similar to simple phase converters. The capacitor would need to be sized so that it would draw the full phase current at the input voltage and the power being delivered. So a 10 HP (7.5 kVA) VFD on 240 VAC would draw about (7500/240)/sqrt(3) or 18 amps which would be a reactance of 13 ohms and a capacitance of C=1/(2*pi*60*13) = 199 uF.
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

                      Comment


                      • #12
                        Originally posted by PStechPaul View Post
                        3. It might be possible to increase the power output by connecting a motor run capacitor from one of the single phase AC lines to the unused third phase, similar to how a 3 phase motor can be driven from single phase, and also similar to simple phase converters. The capacitor would need to be sized so that it would draw the full phase current at the input voltage and the power being delivered. So a 10 HP (7.5 kVA) VFD on 240 VAC would draw about (7500/240)/sqrt(3) or 18 amps which would be a reactance of 13 ohms and a capacitance of C=1/(2*pi*60*13) = 199 uF.
                        I never tried a cap to feed the unused phase input but have always wondered if that wouldn't work fairly well. There should be about a 90 degree phase shift across the cap which would somewhat simulate 3 phase input but not at the balanced 120 degree phasing of true 3 phase. Its a interesting concept though and I have never seen it attempted.

                        Your calculation using sqrt(3) may not apply with the unusual phase relationship obtained with the cap method of generating a 3rd leg. Using sqrt(3) to calc a effective voltage is the standard for normal 3 phase with 120 degree phase relationships. I believe the phasing with a cap generated 3rd leg would be 0/90/180, do you agree? This would no doubt unbalance the current draws and invalidate the cap size calculation.

                        Another interesting consideration would be the ripple frequency on the VFD internal filter caps. The ripple would be 180hz with true 3 phase input, 120hz with single phase input. It makes my head hurt to contemplate what it would be with the cap generated 3rd leg and resulting strange phase relationship. It would have a effect on the VFD sensing ripple current though, and many VFD's use that for determining input phase loss.

                        I will be interested in your comments. I just bought a 7.5hp cnc lathe with a 5.5kw yaskawa vfd internal to it. I will never load the lathe up to its 7.5hp level but would sure like to run it off single phase. Alternately I will run the electronics off a 120 circuit and the VFD off a 15hp rotary phase converter. I wonder if the cap method would work for me, I will probably try it and see.
                        Last edited by Sparky_NY; 09-17-2015, 03:54 PM.

                        Comment


                        • #13
                          Originally posted by J Tiers View Post
                          nope.....

                          Same capacitor is used for ALL phases, that is not the issue.............
                          You missed it Jerry, not all VFD's have a single cap !
                          And that is the issue

                          The quality range of VFD's is immense
                          You can buy them with small caps, large caps or maybe with 'micro" caps you mentioned
                          The ability to convert power from one form or another is subject to the quality of the tool.

                          As I said , both from my experience and talking to others "you sometimes have to give it a try"
                          Telling anyone they can...or they can't.. is a fools game when you don't know what they have for a tool

                          My best
                          Rich

                          Comment


                          • #14
                            Originally posted by Rich Carlstedt View Post
                            You missed it Jerry, not all VFD's have a single cap !
                            And that is the issue

                            The quality range of VFD's is immense
                            You can buy them with small caps, large caps or maybe with 'micro" caps you mentioned
                            The ability to convert power from one form or another is subject to the quality of the tool.

                            As I said , both from my experience and talking to others "you sometimes have to give it a try"
                            Telling anyone they can...or they can't.. is a fools game when you don't know what they have for a tool

                            My best
                            Rich
                            I don't think Jerry missed it. Yes there can be many types and sizes of caps but they form a single filter bank. Your original post claims the caps feed the rectifiers, that is way wrong, exactly reversed. They are configured as a standard 3 phase line fed rectifer followed by a standard bank of filter caps to form the DC bus. Single phase rated VFD's would have much higher value filtering caps due to the lower ripple frequency.
                            Last edited by Sparky_NY; 09-17-2015, 04:37 PM.

                            Comment


                            • #15
                              In the case of a motor, or a balanced resistive/inductive load, the phase of the voltage on the third leg will depend on the complex impedance of that point. The capacitor will supply current at 90 degree phase to that of L1-L2, but the load, which appears as resistance, capacitance, and inductance across all three phases, cause an additional phase shift. If you established a center point between L1 and L2, where single phase is applied, you could generate a third phase at 90 degrees that would form the third phase on L3. The amplitude would be 240*sin(60) or 208 VAC. The neutral of the resulting three phase power would be at 240*sqrt(3) or 138V to each phase. So I am not sure if my value for the capacitance is correct. However, it should be "in the ballpark". I will try a simulation to see how things look. It is difficult to simulate a VFD and a motor, but an ideal motor should be close to a set of three resistors with a small amount of series inductance for a motor with 95% or so PF running a constant full load. I think a three phase motor actually draws a constant current from the DC bus. So it will be interesting to see the input waveforms depending on capacitor size and load.
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

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