Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 38

Thread: 3-Phase vs Single Phase Equipment

  1. #16
    Quote Originally Posted by Jonathan Jung View Post
    Agree. The motor that caught fire was a US-made Baldor 5hp 22fla, and I was starting it up to 8 times an hour before I was schooled.
    My Oneida 5hp VFD winds up very slowly. It is hard to tell at first if it has started after pushing the start button. I guess that’s why.

  2. #17
    Quote Originally Posted by Michael Zerance View Post
    After your comment, I looked into a 40hp rated rotary phase converter. It's recommended for 50 amps of 3 phase output but it rated at a maximum of 98 amps so it seems like it would work well for my situation. In addition, like you stated, it's significantly less expensive.
    One thing I should point out is that having a three phase dust collector means that the phase converter will be running most of the time. If most of your machines are three phase then it makes sense to just leave it running, but if the converter is needed for only the sander or other occasional loads then you may want to have a single phase dust collector. Rotary convertors are themselves usually started with capacitors, I don't know about Phase Perfect. Capacitor failure is not common, but it does happen. The single phase Baldor motor on my jointer has never popped a cap in 35 years, while I have had failures in my Oneida dust collector, MiniMax bandsaw and rotary converter control panel within the past 10 years.

  3. #18
    Join Date
    Feb 2003
    Location
    Doylestown, PA
    Posts
    6,991
    Quote Originally Posted by Thomas Wilson View Post
    My Oneida 5hp VFD winds up very slowly. It is hard to tell at first if it has started after pushing the start button. I guess that’s why.
    This made me wonder about something. Would a 3 phase motor on a VFD with, say an 7 - 10 second ramp up time generate less total internal heat than an 'instant on' motor? It would be generating heat for a longer period but at lower amps.

  4. #19
    Quote Originally Posted by Malcolm McLeod View Post
    +1. And the bigger the motor, the slower the heat dissipates. We run a lot of 400Hp motors and programmatically limit them to 3 starts/hr; 150Hp :: 5 starts/hr.
    It's worthwhile to point out that this problem is common to both-single phase and three-phase motors. Three-phase motors start up a bit easier than single-phase motors but the difference in the heat generated is not significant.

    I never looked into it, but I would think that a small motor, such as 3-5HP, would heat stabilize fairly quickly.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  5. #20
    Quote Originally Posted by Curt Harms View Post
    This made me wonder about something. Would a 3 phase motor on a VFD with, say an 7 - 10 second ramp up time generate less total internal heat than an 'instant on' motor? It would be generating heat for a longer period but at lower amps.
    As with almost everything, it depends. But, for identical processes, starting conditions, and number of starts per hour, comparing a direct-on-line starter to a VFD with this 7-10sec ramp, a ramped start will generate less heat. The VFD will limit the in-rush current, and the heat generated is proportional to the square of the current (P=i^2*R).

    Yesterday, I tried several ramp times on my 5hp DC, starting it with a 6" duct open.
    Peak amps on start:
    • 20s. accel :: <7 amps;
    • 10s. accel :: ~7.5amps;
    • 5s. accel :: 9amps;
    • 3s. accel :: ~18amps.

    In each case, it settled into steady state running at ~7.8amps. FLA is ~15amps, so clearly not straining the motor.
    ^Very unscientific. Did not measure motor temperature rise - - too lazy.

    I use 240VAC 1-phase input to the VFD, and it converts to 240VAC 3-ph. I used the VFD display to mentally note 3-ph amps, I did not setup an ammeter to capture peak. I have no idea what the H-Y VFD's display refresh rate is, so there is no guarantee that it does in fact 'catch' the real-time highest amp draw. Like I said, unscientific.

    Based on the above, I decided to leave it on 10s accel. since this seems to be the sweet spot where starting amps does not exceed running amps (...previously 20s.).
    Last edited by Malcolm McLeod; 05-23-2022 at 10:30 AM. Reason: formatting and formula for the scientists!

  6. #21
    Join Date
    Dec 2006
    Location
    Toronto Ontario
    Posts
    10,872
    Quote Originally Posted by Curt Harms View Post
    This made me wonder about something. Would a 3 phase motor on a VFD with, say an 7 - 10 second ramp up time generate less total internal heat than an 'instant on' motor? It would be generating heat for a longer period but at lower amps.
    Yes, rotor bar current is related to slip, thereís much less slip with a volts per hertz start than an across the line start.

    If the VFD limits motor current to just slightly above rated, the motor simply runs at normal temperatures

    Regards, Rod

  7. #22
    Air compressors may start many times per hour, but I have never had a compressor motor crap out. Am I just lucky or do mfrs use a better grade of motor?

  8. #23
    Join Date
    Jan 2010
    Location
    Tampa Bay, FL
    Posts
    3,124
    In my similar situation with a 10HP Phase Perfect and a Oneida 5HP dust collector and wide-belt sander, I chose single phase for the Oneida (with it's own separate circuit), and 3-phase for the Wide-Belt from the Phase Perfect to avoid having to upsize the Phase Perfect. I like them being separate.
    - ďItís not that Iím so smart, itís just that I stay with problems longer.Ē Ė Albert Einstein
    - Welcome to Florida. Where the old folks visit their parents

  9. #24
    Quote Originally Posted by Kevin Jenness View Post
    Air compressors may start many times per hour, but I have never had a compressor motor crap out. Am I just lucky or do mfrs use a better grade of motor?
    The engineers know the general duty cycle of a compressor so I expect they specify a motor that will satisfy that duty cycle. That could be a problem if you have to replace one. Normally, the motor regulator will wait until the tank pressure has fallen a certain amount. Then the motor will run until it builds the pressure up. That amount of run time may be sufficient to heat-stabilize the motor. The motor will then sit idle for a while and heat will dissipate from the motor during that time.

    I have heard problems about compressor motors running continuously, because of a break in a line, and having a motor failure. Based on that, it would seem that the idle time is important to limit heat buildup. Of course, compressors are often put in enclosures because of the noise. Running continuously, the enclosure gets hot and the ambient may get too hot to keep the motor within safe temperature limits.

    I really wonder about the specification of four starts per hour on a dust collector. I sure start mine (only 2HP) many times an hour and never even considered that I might have a problem.

    Mike
    Last edited by Mike Henderson; 05-23-2022 at 2:40 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  10. #25
    Quote Originally Posted by Kevin Jenness View Post
    ... Am I just lucky or do mfrs use a better grade of motor?
    Certainly one; probably both.

    You will see 'compressor duty' motors offered. They are built for higher torque output than a comparable 'standard' motor to deal with the high starting torque load of a recip compressor.

    This is way off base for the OP, but LOTS of factors at play on a compressor: cast iron/aluminum, recip vs screw, # of cylinders (recip), duty cycle, flow vs dischg pressure, motor:compressor belt ratio (if any), unloader valve function, air temperature/humidity/altitude ....to name just a few - - in addition to Mr. Henderson's list. Most 'shop' compressors use ODP motors, rather than TEFC. Not a motor designer, but I've always heard ODP motors cool a bit better, all other things being equal.

    You can probably max out 1 or even 2 of these factors on any given motor driven system. Safely. For awhile. But not forever. All design is a compromise. You get what you pay for. Etc., etc.

    As for starts/hr, you can certainly exceed the recommended limits (sometimes) and never have any issue. I just wouldn't do it all the time, every time: DC's - let 'em run (w/ gates closed) between operations when you know you will use it again (let the fan do its job); Air compressors- if it's running all the time, you might consider slowing down on that Taj Mahal spray paint job; was that 2Hp Harbor Freight really built to run a 100psi/600CFM jack hammer? - maybe consider a bigger unit, even if a rental.

    Temperatures? At work, I have operated on the theory that if I can't put my hand on a motor, then I probably did something wrong in the control logic. Or I need to find a way to blame the process design folks.

  11. #26
    Quote Originally Posted by Michael Zerance View Post
    ....
    Is there any benefit of going with the 3-phase in this situation?
    I've been replying to replies, but to address your question from my perspective - it would depend on future plans - mostly involving horsepower. If planning for additional equipment over 5Hp, I'd probably find a way to get proper 3-ph power feed(s). 5Hp or less and I'd use the available 1-ph, or add a VFD - mostly for the phase conversion - if tool was already equipped w/ a 3-ph motor.

    I'd be worried I'd be forever upgrading my 3-ph feeder....every time I added a tool. Or, I'd buy too big a PP (for instance) and then never need/use the capacity.

  12. #27
    Join Date
    Feb 2003
    Location
    Lafayette, IN
    Posts
    4,457
    Quote Originally Posted by Mike Henderson View Post
    The engineers know the general duty cycle of a compressor so I expect they specify a motor that will satisfy that duty cycle. That could be a problem if you have to replace one. Normally, the motor regulator will wait until the tank pressure has fallen a certain amount. Then the motor will run until it builds the pressure up. That amount of run time may be sufficient to heat-stabilize the motor. The motor will then sit idle for a while and heat will dissipate from the motor during that time.

    I have heard problems about compressor motors running continuously, because of a break in a line, and having a motor failure. Based on that, it would seem that the idle time is important to limit heat buildup. Of course, compressors are often put in enclosures because of the noise. Running continuously, the enclosure gets hot and the ambient may get too hot to keep the motor within safe temperature limits.

    I really wonder about the specification of four starts per hour on a dust collector. I sure start mine (only 2HP) many times an hour and never even considered that I might have a problem.

    Mike
    At work, I have a large Champion compressor running a pneumatic HVAC control system. It’s got two 3ph, 208V, 3-HP motors, (two separate belt-driven compressors as well) with a controller that alternates running them, but will kick on the second motor if pressure drops too low. One time, one of the pressure switches welded itself closed. My co-worker discovered the one motor running away—on fire. Both motors have since been replaced, and the contactors connected to the controller have been upgraded with contactors that have a connected overload module.
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


  13. #28
    Join Date
    Feb 2003
    Location
    Doylestown, PA
    Posts
    6,991
    Quote Originally Posted by Rod Sheridan View Post
    Yes, rotor bar current is related to slip, there’s much less slip with a volts per hertz start than an across the line start.

    If the VFD limits motor current to just slightly above rated, the motor simply runs at normal temperatures

    Regards, Rod
    Thanks Rod. This would be something to keep in mind for frequent start relatively high load applications - like a dust collector. Then I think about single phase table saws. They sometimes get started multiple times per hour but we seldom hear of motor failures on them. I imagine that virtually no starting load has something to do with it.

  14. #29
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    7,416
    Another thing to consider is ambient temperature. Not a big concern in a woods shop unless you live in the west and have a motor in the attic. My attic under roofdeck can easily get to 125-135F on a summer day when it is only 100 outside.
    Bill D.

  15. #30
    Join Date
    Jan 2008
    Location
    Whidbey Island, WA
    Posts
    158
    With at least American Rotary it's possible to add HP to the RPC by adding another idler. At least that's what they told me.
    Timberlight Designs

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •