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Need advice on 3 phase converter

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  • metalmole
    replied
    I have used rotary and static converters, I tried a VFD one day......I will never go back to converters, the VFD is so smooth and my machines run much better, I can see it in my parts finishes...
    Here is what you need...

    http://dealerselectric.com/item.asp?...cID=0&scID=165

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  • wmgeorge
    replied
    Get a used 3 phase motor at 2x the motor size at least of the one on your mill. Purchase or build a static convertor or use the suggested heavy push button switch and large Run capacitor to start the above motor and when its running switch in the motor on your mill.

    I built my static convertor years ago from plans published in Home Shop Machinist or the "other" magazine published by Village press. Been working fine for the past 15 years. Run caps can be used in parallel to increase the total capacitance in a circuit.

    Since I was a HVAC tech, I had access to used Run capacitors off broken equipment. Run capacitors are silver or grey covered metal vs the black plastic Start caps which will last about 60 seconds when used instead of the Run caps.

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  • Norman Bain
    replied
    I have been reading the recent threads on VFDs with interest. Target for me is my Kondia mill. I has 3HP main spindle motor but also knee lift motor plus powered X-travel plus coolant motor.

    I do like (feel comforted by) the statements that say if the specs say the VFD is ok for both single and 3-phase input then one can purchase at rated capacity. Certainly 3HP is less expensive than 5HP and I've never felt the mill has been loaded up in a cut.

    Question I still have is, is it as simple as plugging in a VFD to the 3-phase plug of my mill? Will this get everything going in some reliable fashion?

    I think I'd be ok to run the VFD at some solid figure (if figure is the right word; perhaps setting is better) that gave me "normal" 100% speed wise operation of the mill spindle motor (perhaps only changing to slow that motor down when doing some threading or similar) provided it gives me use of the other motors attached.

    Norman

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  • RWO
    replied
    Forget all the phase converter cheer leading and get your self a quality VFD. Do not use the mechanical variable speed mechanism if you want it to last. The advantages of a VFD are overwhelming compared to any kind of phase converter. You have wide range variable speed, dynamic braking, programmable acceleration, soft starting, instantaneous fault protection, overload protection, a tiny box that doesn't make noise and occupies zero floor space, and digital spindle speed read-out.

    My favorite supplier is automationdirect.com. They are a full fledged industrial supplier with everything you need for a professional installation. Their house brand VFD's are reasonably priced and their tech support is top notch. I have 3 VFD's in my shop that I purchased from them. The newest one is 10 years old and all have worked perfectly since new. There are other quality brands out there, but you generally get what you pay for in a new unit.

    RWO

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  • Doozer
    replied
    Hitachi is a Cadillac in my opinion. Hard to beat.
    My last VFD purchase was a Teeco/Westinghouse
    and it is super nice. Enjoy your mill.

    -D

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  • SirLesPatterson
    replied
    To follow up here I ended up with a Hitachi WJ200 VFD and have no regrets. The functionality is impressive, to say the least.

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  • sch
    replied
    Here is a site with "kits" for static phase convertors, which can then be used with a user supplied 3phase motor to make a rotary phase converter. Gives you some idea of how 'simple' these things
    are, but leaves out the box to put stuff in and wiring is up to you. An old computer would do for a box. OTOH no need to experiment with capacitors.... Prices start at $62 and go up.
    Not recommending at all, just for info. They have diagrams. Good deal if you are really sold on the static or RPC idea.
    http://www.wnysupply.com/index.cfm/f...arentcat/25260
    Last edited by sch; 04-08-2014, 02:14 PM.

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  • macona
    replied
    Originally posted by sch View Post
    But the speed control ease of a vector VFD is certainly attractive.
    And dynamic braking too.

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  • SirLesPatterson
    replied
    Thanks for all the info. Pondering.

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  • sch
    replied
    The advice to use a static assumes you have a junk box or access to a junk box with a bunch of start/run caps for motors of various sizes, a suitable metal box to put them in and switches.
    Many HSM used to have these or were associated with industrial facilities that had such or had HVAC friends with such. This is still true for many of us, but less than 20+ years ago. If you buy
    caps, where they used to be $3-5 now they are $10-20, even at Surplus Center. That assumes you know what cap size/voltage you want. A decent static converter has built in relays for
    automatic start and shifting from start to run caps. A rotary converter is a static convertor connected to a 3ph motor at least twice the size of your mill motor and uses the 3ph motor as a
    generator to create a 3ph electrical supply that is then used to run your mill. Again a "surplus" 3ph motor that is a freebie or nominal cost is assumed. If you have to buy and build some
    part of this then, you are way ahead just going with a name brand VFD. A 2hp 220v 1ph input rated quality VFD is in the $180-250 range, depending on source, new.

    If you buy a static convertor it will be at least $100, rotary convertors commercially supplied are $300 and up. Maybe you can rummage around and come up with the parts for free, if so
    then a rotary will certainly do the job. But the speed control ease of a vector VFD is certainly attractive.
    Last edited by sch; 04-07-2014, 09:59 AM.

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  • J Tiers
    replied
    The derate is a serious consideration.... Still....

    The causes are two-fold. First, the diode rating... That is fairly easy to fix, for the manufacturer of the power module, but many modules still use smaller diodes. Second, the ripple current rating of the capacitors must be suitable for single phase.


    Drives are going two different directions these days.

    1) low power drives may be rated for single phase, with larger filter capacitors, both to hold up voltage, AND to carry the high ripple currents (charge and discharge current) inherent to single phase input. BUT they may not be also....

    2) Drives of all sizes are being designed with minimal filtering, often just a medium sized film capacitor of perhaps 50 uF. The film caps are now much cheaper than they used to be, and also are smaller. 50uF at 400V is about the size of 2 or 3 pocket-sized matchboxes. That size capacitor may be rated for 40+ amps of ripple current. The design is possible because 3 phase voltage never drops below 86% of peak (single phase voltage drops to zero twice per cycle).

    Obviously, if you have a smaller drive with a proper single phase rating, you are OK.

    However, the film capacitor will not hold up voltage, even if it can take the ripple current. You won't get a good output from the drive, and it will probably fault on low bus voltage.

    For a drive with regular capacitors but no single phase rating, the life may be short if you draw rated power, because the capacitors will fail from overheating. They will probably open the pressure vents and leak corrosive electrolyte onto the innards of the drive.

    Read the specs before purchase.

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  • macona
    replied
    With most drives you are good for about a 10% range outside their specced range, in the case of most Japanese drives, the rated range is usually 200 to 240v. +/-10% on that gives you down to 180v input so you would have to get the bus voltage down to that point. Even with not-so-great buss filtering you will probably not drop below that level on most drives. Possibly some real old ones.

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  • PStechPaul
    replied
    I think the main reason why VFDs are rated at lower power on single phase is the size of the DC bus link capacitors and ripple. For single phase, especially at lower line voltages (208V), there must be enough capacitance to hold the voltage above the cutout point (usually 200V). The peak rectified DC voltage from a 220 VAC supply is about 310 VDC, and 2HP is about 1500W or 4.8 amps. There is about 5 mSec between peaks where the voltage drops below 200V, so what is needed is 1500W * 5mSec = 7.5 Watt-Seconds (Joules). The necessary capacitance is about

    C = 2*7.5/250^2 = 240 uF

    A 3HP VFD that I recently tried to repair/salvage had 2300 uF of 400V capacitors, so that is more than enough to work on single phase (which was how it was being used, and rated).

    In that case, the power limit may depend more on the power factor of the VFD and the line current on the 220 VAC supply. For 2HP, the current for a perfect 1.0 PF would be 6.8A, but it could easily be two or three times that at full load.
    Last edited by PStechPaul; 04-07-2014, 01:45 AM. Reason: PF limitation

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  • macona
    replied
    Originally posted by Rich Carlstedt View Post
    Keep in mind that to use a VFD , you need to upsize it 50 % , so a 3HP unit is needed unless it specifically says for single phase input.
    No, no, no, NO! This is a myth that keeps getting propagated and it is only true in a specific circumstance, that being the VFD was designed for 3 phase input only. Almost all sub 5hp VFDs are now made for single or three phase input and will run motors up to their rated capacity with no derating. And even then a lot of VFDs are rated to run down to less than 200v @ 50hz for Japanese mains operation so the chances of you getting an under voltage condition under full load are very slim. I run a lot of "3 phase only" drives and have never had an undervolt error.

    Patterson, do yourself a favor and just buy a good Hitachi, Toshiba, Cerus (LG), or one of the many other name brand drives and you will be happy.


    Edit, argh. Didn't read that right. Doh.

    But the part after my stupidity still stands.
    Last edited by macona; 04-06-2014, 11:35 PM.

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  • Richard King
    replied
    First of all I have never done this, just heard how to do it. Back in the old days my Dad ran his shop with a 3 phase motor. In the area of MPLS that didn't have 3 phase yet.
    He would said to double the HP, so go out and look for a 4 or 5 HP motor. Run the 2 single phase wires in and connect it to 1 & 7 & 1 lead of the 3 phase motor to it. Then 2 & 8 of single phase to another 3 phase wire and wire then 3 & 9 of the 1 phase together with the other 3 phase motor lead. Then hook 4,5,6 Together by themselves Tape them up good. He had 2 switches one on the single phase and another on the 3 phase going out. He started it s simple with a lawn mower rope. The 3 phase motor has a 4" pulley on it and he cut a notch to put the knot at the end of the rope into. He would wrap the rope around the pulley flip on the single phase and pull the rope and then flip on the other switch and away they went. Call up some scrap dealers or look on CL and get a used one. Some guys hook up a 110 v motor on it to turn the pulley, I suppose it is a lot safer too. Rich

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