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3 phase grinders....why?

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  • 3 phase grinders....why?

    Hi

    I noticed while reading the manual for my new Mazzer Mini that some grinders are available in 3 phase.

    Why bother?

    Sure you get more torque but 900 watts is 900 watts 3 phase or 1 phase. At least thats what my electrician tutor told us.

    Im guessing the 3 phase motor would have a heavier duty cycle i.e. able to run for a longer period before over heating and less time the motor would need to rest/cool down before using again.

    One added bonus is that a dishonest employee couldnt pinch it and expect it to run at home.

    You could always swap 2 phases making it run backwards and un-grind you beans

    lol

  • #2
    Re: 3 phase grinders....why?

    Wheres Mal?

    Maybe this site can help you/us out:
    http://www.3phasepower.org/

    Quote from there:
    A 3 phase induction motor has a simple design, inherently high starting torque, and high efficiency. Such motors are applied in industry for 3 phase pumps, fans, blowers, compressors, conveyor drives, and many other types of motor-driven equipment. A 3 phase motor is more compact and less costly than a 1-phase motor of the same voltage class and rating.

    I would have a guess and say more reliable (high start torque with no cap and high efficiency equals less heat).

    Also found this on Wiki:
    Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.

    Maybe reducing vibrations would help with an even grind? Probably just a bit of a wank?

    Comment


    • #3
      Re: 3 phase grinders....why?

      That was pretty much my guess.

      No brushes to wear out either.

      You could get really funky and put a star/delta motor starter on it and have extreme starting torque. Now thats a real blokes grinder.

      It would grind just about anything

      Comment


      • #4
        Re: 3 phase grinders....why?

        Originally posted by 3012160A1111060F04110A13630 link=1245977100/0#0 date=1245977100
        One added bonus is that a dishonest employee couldnt pinch it and expect it to run at home.
        Until we renovated the house and put in a new board, we used to have 3 phase at home.

        Comment


        • #5
          Re: 3 phase grinders....why?

          "There is always 1 in every family ....... 2 in mine actually" Zazzoo

          Comment


          • #6
            Re: 3 phase grinders....why?

            Yep,

            Its all about Total Cost of Ownership....

            More economical to buy,
            More economical to run,
            More torque available, therefore lower HP(KW) ratings may be suitable,
            Simpler design so less to go wrong translates into very long service life,
            Smaller footprint for equivalent output rating.

            Ideal therefore, in a commercial environment 8-)

            Mal.

            Comment


            • #7
              Re: 3 phase grinders....why?

              lol
              I knew it would be one of those questions id basically answer myself wit prompting from those in the know

              Still a star delta starter would be the most awesome in cosmic grinding power.

              thanks
              Guys

              Comment


              • #8
                Re: 3 phase grinders....why?

                Originally posted by 0022263A2121363F34213A23530 link=1245977100/2#2 date=1245978990
                You could get really funky and put a star/delta motor starter on it and have extreme starting torque. Now thats a real blokes grinder.
                Nothing new! I opened up an old Ditting Industrial grinder that stood about 5 ft that was Star/delta. No need even for the throughput of something like a 3 phase Robur. Though at work, putting 11kg in 8/9hrs through a single phase Robur you can feel the collar getting warm during the peaks.

                Like Mal said - ideal for a commercial environment.

                Comment


                • #9
                  Re: 3 phase grinders....why?

                  Originally posted by 0725213D2626313833263D24540 link=1245977100/2#2 date=1245978990
                  You could get really funky and put a star/delta motor starter on it and have extreme starting torque. Now thats a real blokes grinder.
                  Gday SG,
                  a star-delta starter actually reduces the start up torque, so in fact it would be a reverse situation of what youve mentioned.
                  A real blokes grinder would have a DOL (Direct On Line) starter 8-).
                  Heres a link to some info about star delta starters.
                  http://wiki.answers.com/Q/What_are_t..._delta_starter

                  Comment


                  • #10
                    Re: 3 phase grinders....why?

                    Originally posted by 2F0C15061A630 link=1245977100/8#8 date=1246348246
                    a star-delta starter actually reduces the start up torque, so in fact it would be a reverse situation of what youve mentioned.
                    Um Lovey not quite true. I use to wire these things for a living a long time ago granted. In star you get 1/3 of the Torque that you get in delta.

                    First start is delta then switches to star on run. ie start sequence is Delta then Star



                    Delta with max current, max torque and is generally used to get LARGE 3 phase induction motors started usually if they have to start under full load.

                    Starting such motors started in star doesnt provide enough torque to get it moving and it stalls causing the motor to over heat and burn out.

                    Leaving the motor connected in delta causes(if I remember right ) excessive current draw due to the low resistance (Back EMF is a component in that too) and again excessive heat. You also have to use larger wires to feed the thing too. I think power factor correction is an issue too but Im real hazy on that now.

                    This is of course unless my Poly Tech (Tafe) tutors were wrong and old text books were wrong. Im sure there are newer better ways to do it now tho but Star delta is or was cheap, effective and easy to wire.

                    below snipped from the web site supplied by Lovey.

                    "If there is insufficient torque produced by the motor in STAR, there is no way to accelerate the load to full speed without switching to delta and causing those severe current and torque transients. These must be allowed-for in the design of the motor and its starting system if they are to have an economic useful life."

                    In short more current more torque delta.

                    The reason it isnt known as a "Delta -Star Starter" is because its harder to say when drunk than "She sells sea shells......." and drunk electricians arent a pretty sight at the best of times especially when trying are trying to explain what they had been doing all day.

                    Oh and DOL start is the same as leaving it in star or delta depending on how you have wired the motor.

                    I suspect that the 3 phase motor used in grinders would permanently wired in star and would be virtually impossible to actually set up a star delta starter, without getting it rewound.

                    Comment


                    • #11
                      Re: 3 phase grinders....why?

                      Originally posted by 5E7C78647F7F68616A7F647D0D0 link=1245977100/9#9 date=1246351470
                      Originally posted by 2F0C15061A630 link=1245977100/8#8 date=1246348246
                      a star-delta starter actually reduces the start up torque, so in fact it would be a reverse situation of what youve mentioned.
                      Um Lovey not quite true. I use to wire these things for a living a long time ago granted.
                      Same here, quite a long time ago for me actually  .

                      In star you get 1/3 of the Torque that you get in delta.
                      Which is what I alluded to in my reply to you, ie that there is less torque when the motor is in star configuration.

                      First start is delta then switches to star on run. ie start sequence is Delta then Star.
                      Im happy to stand corrected, but Ive never heard of a delta-star starter. It doesnt make sense to me to have the motor starting in delta (with max current and torque), then switching over to star (less current and torque), you may as well have a DOL starter. It also goes against what is listed in the image that you attached.

                      Delta with max current, max torque and is generally used to get LARGE 3 phase induction motors started usually if they have to start under full load.
                      Starting such motors started in star doesnt provide enough torque to get it moving and it stalls causing the motor to over heat and burn out.
                      I dont think that star-delta starters are suitable for motors being started at full load. There are newer and better starting options, like soft starters, but Ill leave that to the engineers  .

                      Oh and DOL start is the same as leaving it in star or delta depending on how you have wired the motor.
                      I suspect that the 3 phase motor used in grinders would permanently wired in star and would be virtually impossible to actually set up a star delta starter, without getting it rewound.
                      To have a motor wired for a star-delta starter, you need a motor with 6 connection posts. From memory (hazy) most motors only have 3 connection posts, and they are wired in delta permanently, ie there is no star point in the connection box.
                      Again, Im happy to stand corrected on these points, but it was good to get the electrons flowing through the old brain again  .

                      Comment


                      • #12
                        Re: 3 phase grinders....why?

                        The actual Torque relationship between a Star connected motor and a Delta connected one is that of "1/[ch8730]3*[ch8710]T" or 0.577 times the Torque/Current in Delta configuration. The inverse is 1.73 times the Torque/Current in Star configuration (neglecting phase relationships).

                        I cant see the point of a Delta/Star Starter either and have never seen one utilised after nearly four decades as an electrical engineer working in heavy industry and mining. The most common method utilised for starting large motors on-load is via a Wound Rotor Motor with a Variable Resistance Starter and can be found throughout the above spheres of industry. VF Drives are more commonly used where a controllable variable output is desired from the device being driven.... Pump, Conveyor, Feeder for example and not for restricting start-up current. Soft Starters have their place too of course and are most frequently found where large motors are installed at the end of very long power cable runs, so as to avoid excessive Voltage Drop at the terminal end of such a run during a motor start.

                        Cheers,
                        Mal.

                        Comment


                        • #13
                          Re: 3 phase grinders....why?

                          Originally posted by 6A47434F422E0 link=1245977100/11#11 date=1246438437
                          "1/[ch8730]3*[ch8710]T"
                          Lordy Mal - I havent even seen some of these symbols before, let alone understand them! Dont worry about trying to explain them to me though. My brain goes to spaghetti whenever I see something like this. ;D

                          Comment


                          • #14
                            Re: 3 phase grinders....why?

                            Originally posted by 476A6E626F030 link=1245977100/11#11 date=1246438437
                            "1/[ch8730]3*[ch8710]T" or 0.577 times
                            Yeah thats what I was gonna say, I just didnt feel like it :-?

                            Comment


                            • #15
                              Re: 3 phase grinders....why?

                              Originally posted by 7F52565A573B0 link=1245977100/11#11 date=1246438437
                              1/[ch8730]3*[ch8710]T" or 0.577 times the Torque
                              Dont most machines use a Motor Start Capacitor to get things started while things are at load and when its up to speed the motor takes over

                              A mechanical explanation of this is a car starter motor

                              Hope I am right #~^+= simple ? :

                              KK

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