Electric Motor Phase Shift Explained

Electric Motor Phase Shift Explained


another quick motor update so there was
there were some questions about the motor and the capacitors and things like
that and I did a little brief exclamation about how the capacitor adds
a phase shift to the starting windings and what I have set up here is my oscilloscope
and I have it hooked up to the motor and I’m going to show on the
oscilloscope what the phase shift is and how you can calculate exactly how many
degrees of lead or lag that you have and from that you can actually adjust your
capacitor to get it so it’s perfect at 90 degrees if you want and I already
have the motor all hooked up with with two channels and one channel is the
voltage on the incoming voltage and that which would be the run winding when it’s
running and the other is hooked up to the starting winding so it will take a
snapshot of the starting winding as it starts and show us that against the
running of the motor or the run winding all right I’m gonna plug it in there we
go that’s a little bit better zoomed in now
what we have here are the two sinusoidal wave’s of the motor
the one in the middle here I have said actually I have them set at both the 200
volts range right and that one in the middle here is the run winding as the
motor is running here the A over here is marked by a this
one and was the start sinusoidal wave and you can see how they’re not in line with one another out there that here
this is rising voltage the peak and on down and then drop it down here you Now here our
AC here is 60 cycles and then here the peak of this one here there’s the
peak and undoubted peak so that’s one one cycle right and it all matters it’s all a point of
reference if you use the running winding waveform as a reference then the starting
winding lagged then it lags the run winding and then some people will say it
leads well if you use this that then they’ll say the running current is
leading the starting current so if you use the start winding as a reference
then yes the other current leads the the thing is is the difference in
phase angle between the two waves and we can move the there’s these dashed lines
here you’ll see these you should be able to see these dash lines so you’ll see
these dashed lines here and those are cursor lines and I’m going to adjust
them a little bit here because what we want to do is we want to measure the
difference in time yeah like I said this is 60 cycles both waves are 60 cycles
and the time difference between the cycles is what we need to check now this
meter will give us that right here is its dT it’s the differential time
between the two cursors and I’m going to on both of the rising waveforms
okay so the rising wave form of the rising way from the tide difference from
a zero point two zero point here so let’s we’re going to adjust this cursor
I’m adjusting this cursor over at zero voltage where it crosses the zero
voltage point and then I’m gonna adjust the other cursor this one here to cross
at this waveform right there that’s comes up to be
5.2 5.0 milliseconds
between the two okay now we can do a quick little calculation to determine
that that phase shift angle between them so we’ll do a little math so we know
it’s 60 cycles and I don’t have it set right here most change here for
frequency and right here the frequency is fifty nine point nine eight sixty
point zero one it’s at 60 cycles for all intent purposes so go back here to the
scope so a 1 over 60 will give me how many
microseconds coming milliseconds it is anyway 16.6 milliseconds
so that’s a really is 0.016 now it’s 300
the generator whose jiménez generating this it’s 360 degrees there – there for
one cycle okay so 360 degrees 16.6 milliseconds and that
equals vehicles 21.6 a degrees per millisecond
well our time difference between the two is five milliseconds so five times
twenty one point six eight because 108 degrees
so that’s our that’s our face our phase-shift angle is 180 degrees
pretty simple and by changing your capacitance you can adjust that so that
the current here the voltage or the current here is not lagging as much or
you might want to like more it all depends on what you want to do here
would what we’d want to reduce it a little bit so you can change your
capacitance to adjust that 108 that’s right in the ballpark it’s it’s good I’m
not going to change but anyway that this gives you a nice
representation to see what’s happening and stuff I could change the scales here you know you can you can see where how
to do something more look the same but by changing your scales to what you can
do is you can actually get a more accurate number if you want in there and
you know move your cursor and we could zoom in basically we zooming in I’m
gonna zoom in I might be able to get a little more
accurate number yeah 5.12 you know it’s gonna change 5.2
milliseconds so it makes it a five-point to makes it a 112 degrees you know you
know or you can even change our scales and get the waveform so there’s steeper you know where they where they cross and
then you’re gonna just your cursors maybe a little bit still where a 5.12
there so it’s close enough for what we’re doing we’re doing a demonstrating
here okay that’s how the motor why the motor
starts and how they held this type of system works alright I hope that
everybody helps everybody else II have an idea with what’s happening with their
motor it’s a pretty good unit i I’ve had this one really quite a long time but
it’s an older unit it’s a Fluke 95 scope here but it works and works good
battery’s going to get a long time ago and now I hear what ideas might hit the
auto set button here and it kind of sets up both up and you can see that phase
shift between the two so there all right so I hope that I helped
somebody and kind of a cool thing to see and what catch will catch you next one

28 Replies to “Electric Motor Phase Shift Explained”

  1. Most interesting. It is always interesting how the capacitors can change the phase shift. I know there is a lot of this when a person is making a rotary phase converter and trying to get all three of the three phase amperage draws the same. You said 108 degrees was in the ballpark.
    On starting a single phase capacitor start motor. Is there a certain degrees of phase shift one needs to make the motor start most efficient? Thanks, Tom

  2. The representation shows to me that you have 2 phases of a 3 phase waveform. It would seem to me that is exactly what you want in a single phase motor boost started by a capacitor and a rpm switch.

  3. I was drinking my morning cup of coffee.
    Clicked on your channel.
    Instantly I was back to my engineering college days!!
    AC/DC Analysis…
    Will there be a Quiz ???
    πŸ™‚
    p.s. I use the same Fluke Scopemeter….just a newer Model…..Batteries are still available…

  4. Now you've gone and done it! Who cares about speeds and feeds when you have phase angles and voltage probes! I see you now with your best white lab coat complete with pocket protector explaining inductive reactance as the ways on your machines rust slowly in the background.

  5. It looks like the run winding and start winding are physically mounted in the stator 90 degrees apart… If that observation is correct, the ideal electrical phase shift for that motor would be 90 degrees. +/- 20% seems like a valid tolerance to me.

  6. Great demo of what's happening with the electrical. I don't have an oscilloscope, so I use thumb rules for my capacitor choices, if I can't read the start cap info. If I get a medium start, with correct voltage and amps, with no overheating, then I'm good. Haven't burned one up yet. I do like the info you get from the scope.

  7. very old motor you turn on the motor then press the start button until the motor is near run speed when you take your finger off start it settles down

  8. I really liked this segment on the motor restoration an excellent presentation. I don't have a good knowledge of this subject, but your explanation of it makes good sense and is very understandable to someone like me with very little knowledge on the subject. Thanks for sharing.now I know what out of phase means and how to adjust.Have a blessed day!
    Watching in Alabama

  9. Thanks Randy I was able to understand what was going on and put everything in perspective. Which is not always the case with electricity

  10. Question. Would there be a situation where you don't want maximum staring torque? For example to give you a softer start and less strain on some mechanical part?

  11. Whoaaaaa Rando, my brain nearly overheated on this one. Regardless, I will risk what grey matter I have left and will continue to watch your videos as they are enlightening, informative, educational and entertaining. Your a true renaissance man.

  12. Nice demo about showing phases on practical app… πŸ™‚πŸ‘
    Just a little hint I use here, to avoid hunting focus on the camera, find the manual focus adjust and set it on the main subject, then, you avoid the hunting problem…. πŸ˜‰

  13. If you go to the cursor menu and turn on phase A-B, then turn on marker for phase. It will calculate it for you. You dont need the markers but it helps to confirm you are in the correct spots for measurements.

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