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Help wiring a VFD to motor

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  • #31
    Originally posted by EVguru View Post
    The motor will be 415V in DELTA and 720V in Y/Star. The 720V configuration is not for running off that high a voltage, but is instead used on 415V for soft starting. I've seen quite a few motors like this and often the higher voltage is not marked, presumably because it's not intended that the motor be 'run' at that voltage.
    Are you sure about this? The DSG that I occasionally use does not sound like a star/delta starter when the motor is started up. I think most (all?) DSGs have a clutch and that means that the motor starts under nearly zero load, so it is not like (say) a compressor that needs serious help with starting.

    We need someone with a wiring diagram for a similar DSG. There are parts manuals on the Shamrock site, but I haven't seen any wiring diagrams - they may be there somewhere.

    If it is designed for star/delta starting then certainly the current and torque will be low when connected in star.

    Of course some motors in this size range are star only; their star point is buried in the windings. No way to run them in delta without some surgery.


    Originally posted by EVguru View Post
    The VFD is a 415V input/output model that has been modified.

    The DC bus capacitors may already have been arranged as two lower voltage units in series. Making a connection between the incoming neutral and the mid point of the capacitors creates a voltage doubler circuit (as used to be common in PC power supplies that had the slide switch for 120/240V operation). You now have a DC bus voltage more than high enough to generate three output phases at 415v.
    Yes this is my impression of the method used by Drives Direct to get their 240V in 415V out spec. As far as I know this particular VFD is just a standard TECO model that someone has 'upgraded'. My question is whether TECO stand behind this approach. It probably doesn't matter but would be good to know.
    Bill

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    • #32
      Originally posted by willmac View Post
      Are you sure about this? The DSG that I occasionally use does not sound like a star/delta starter when the motor is started up. I think most (all?) DSGs have a clutch and that means that the motor starts under nearly zero load, so it is not like (say) a compressor that needs serious help with starting.
      We know from the first post...
      The problem I have is that there are 6 wires coming back from the lathe motor labelled A1,A2,A3 and B1,B2,B3 and an earth.
      That's reasonable evidence for a star/delta starting arrangement and the number of contactors points that way too.

      When a motor is intended to be run on dual votages it's usually marked. Mainland Europe uses 240V three phase, whilst the UK uses 415 (240V times root 3). A 415/240V motor can of course be used with a star/delta starter on 240V.

      Sometime though, even when a motor is dual voltage, it's not always marked with both. I had an Avon CNC mill with a 415V nameplate on the motor, but once in the terminal box I could see it was six terminal and wired in star, so a conversion to 240V was just a few moments work.
      Paul Compton
      www.morini-mania.co.uk
      http://www.youtube.com/user/EVguru

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      • #33
        i wonder what lines/breakers you have in the uk on single phase. here i couldt make them install larger than 16 amps (1.5 mm2 wire).

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        • #34
          Originally posted by dian View Post
          i wonder what lines/breakers you have in the uk on single phase. here i couldt make them install larger than 16 amps (1.5 mm2 wire).
          UK mains wiring is *different* from the rest of the EU, at least: breakers up to 40A are common, for electric showers and other instant water heaters individually wired back to the "consumer unit" with the breakers and RCD, usually under the stairs or in the garage.

          General household power sockets are connected in "ring mains" which loop through a set of sockets (e.g. a ring for the kitchen, another for the ground floor living rooms etc.) with both ends of the cables connected to the breaker / consumer unit. The breaker is a 32A on 1.5mm or 2.5mm cable, idea is that the current is shared between the two directions around the ring. It works well, and was specified after WW2 when the UK needed to build a lot of replacements for bombed homes and copper costs were significant.
          Single loads (the heating system, often freezers etc.) may be spur wired to their own breaker to isolate them from other faults (kettle tripping a breaker, letting the Xmas food defrost in the freezer, followed by a pipe freezing because the heating isn't working and leaking into the consumer unit from upstairs and really making Xmas an enjoyable, really traditional event with open fires, candlelight, misery and hunger, for instance...)

          The other big difference is that anything that plugs in to a ring-main power socket (ignoring phone chargers etc.) must be fitted with a fuse *in the plug* to protect the cable between plug and equipment from overheating / fire if the equipment faults - the fuses are rated 3A, 5A, 7A, 10A and 13A (hence the male connector's known as a "13 Amp plug") but Joe Public always fits the 13A and waits for the equipment to start smoking... The socket outlets now have to be switched (double-pole, so line and neutral disconnect) but old unswitched sockets are still in use in older houses.

          I understand that the rest of Europe uses "spur" wiring where each socket is connected directly to a breaker which is sized for the cable's carrying capacity? Correct me if I'm wrong? (If so, Dian could have asked for heavier cable (e.g. 4mm, 10mm) and a higher-current breaker, assuming that's allowed in Swiss law?

          Anything unusual (e.g. huge VFDs, rotary convertors and huge welders) in the UK is usually spur connected via a sub-unit with the required breakers (40A type-D, for instance - the "type-D" indicates that it has a slower response than types B and C to allow high start currents) and often with IEC mains plugs and sockets (IEC 60309, not the little 10A on the back of your PC!).

          The UK has the "Wiring Regulations", which are considered law when installing and modifying electrical installations - e.g. there are tables of cable sizes Vs current and distance as a maximum voltage drop under load is one of the legal requirements, it gets moderately difficult to work out whether you need e.g. a 4mm, 7mm or 10mm cable for a 40A shower without measuring the cable run - and in the home almost any work now needs to be done by an approved electrician and certified compliant or inspected and certified on completion but it makes work for electricians, and the certification process is there trying to make sure they don't work "off the record" and that they pay their taxes

          I hope that helps, rather than confuses!

          Dave H. (the other one)
          Last edited by Hopefuldave; 12-19-2016, 05:47 AM.
          Rules are for the obedience of fools, and the guidance of wise men.

          Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

          Comment


          • #35
            Dave,

            would love to know more about your VFD hack ( at the risk of diverting the thread! )

            PS is it you that runs a Holbrook?

            all the best


            Alan
            West Sussex UK

            Comment


            • #36
              Yep, a Model C No 13, nice piece of kit With some quirks...

              Its disadvantage is the 3-speed, 3-phase, 415v-only motor - I wanted to keep the "Holbrook Experience" so retained the 3-speed switching (between VFD and motor...) and use the speed-switch interlock (when pulled from the detent in each speed) switch to shut off the VFD output, "dec and brake*" stop mode with a long deceleration (10 sec.) when the interlock's operated for speed change, short deceleration (0.2 sec.) when it isn't to allow VFD braking, start mode is "fly and boost" which will match up to a rotating motor or ramp up from 0Hz with a current/torque boost to get it moving. The ABB can (and mine does) use one digital input to select acceleration / deceleration rates, which allows the interlock switch to have a bit of control...

              The hack's pretty simple with one proviso: It needs to be a VFD with two banks of reservoir capacitors, normally it'll be two banks of two, with the capacitors wired in series, two bleed resistors (one for each bank). I use an old ABB ACS-301-4P9, which is rated 5HP and derated it (I think) to power my 3HP motor.

              Instead of taking the 240v Neutral to the 3-phase bridge rectifier as normal, take it to the connection between the two banks of caps (I put a 4BA brass bolt through a newly-drilled hole in the board, bolted it tight then soldered it on the track (under) side, then used a ring terminal onto the bolt on the component side).

              The Line connection can go to all three of the phase inputs to give the diodes in the bridge an easier life, this should give an unloaded voltage of about 340v across each bank of caps, so a total reservoir voltage of about 680v DC - a bit arbitrary, perhaps, but sufficiently close to make the VFD run a 415v motor! Capacitor life IS shortened though, as the ripple current's far higher

              Here's a Crap-O-CAD that sort of illustrates the hack:

              [IMG][/IMG]

              Hope this helps, rather than confuses!

              Dave H. (the other one)

              * Braking resistor required! I took values from a similar (newer) VFD, after I came round from the faint over ABB's price I ordered what I needed from some gents in China for less than a twentieth of ABB's price...
              Rules are for the obedience of fools, and the guidance of wise men.

              Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

              Comment


              • #37
                Ok got the motor wired in delta and with a few tweaks to the VFD its running beautifully. 30 amp C rated trips seem fine. With a thirty second ramp the VFD isn't pulling more than 6 amps on startup and settling to about 5.5 when running.

                I was relieved because when I bought the VFD I thought the motor was 5hp and its actually 7.5.

                Have adjusted the clutches and brake on the DSG and it all seems good.

                Thanks for all your help people

                Al

                Comment


                • #38
                  Originally posted by EVguru View Post
                  The motor will be 415V in DELTA and 720V in Y/Star. The 720V configuration is not for running off that high a voltage, but is instead used on 415V for soft starting. I've seen quite a few motors like this and often the higher voltage is not marked, presumably because it's not intended that the motor be 'run' at that voltage.

                  The VFD is a 415V input/output model that has been modified.

                  The DC bus capacitors may already have been arranged as two lower voltage units in series. Making a connection between the incoming neutral and the mid point of the capacitors creates a voltage doubler circuit (as used to be common in PC power supplies that had the slide switch for 120/240V operation). You now have a DC bus voltage more than high enough to generate three output phases at 415v.
                  Spot on

                  Thank you

                  Comment


                  • #39
                    For those that may not have come across this, http://static.schneider-electric.us/...0140CT9201.pdf, I have had it bookmarked it for some time now, it covers just about all configurations of motor control, including DC.,
                    The symbols used also show N.A. as well as EU style of schematic and symbols.
                    The only one thing I have issue with is the use of a contactor O.L. on the N or return side of the circuit, this used to be a practice but is now frowned on in modern installations due to safety issues.
                    It also shows the universal colour code used on sensors conductors.
                    Max.

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