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In Reply to: RE: Finally! Automatic Speed Control... posted by John Elison on January 12, 2017 at 21:03:21
That looks like a great upgrade. How many other TT mfr's use 3-phase motors....? I keep coming up with one; SME.I am curious about the type of 3-phase motor you have. For instance is it a true synchronous motor that locks onto the frequency? Or is it another type, like a shaded pole motor, that, while being influenced by the power frequency, can slip at its poles when the physical load gets high enough?
Is it a flywheel (ausenlauffer) motor like some of the Papst motors where the rotor is external?
Stuff like that.
-Steve
Edits: 01/14/17Follow Ups:
Hi Steve,To be honest, I know very little about electric motors. All I can tell you is that this motor is quite substantial. It spins up my Sota's 15-lb platter in just a few seconds. Sota's platter has a fairly high moment-of-inertia because much of its mass is concentrated in a lead ring around it periphery.
The motor is a 12-watt brush-less DC motor operating from 24-VAC 3-phase sinusoidal power, which eliminates cogging completely. It has approximately twice the torque of a 10-watt Hurst AC synchronous motor and its RPM is governed by frequency. The Condor controller has a soft start function that ramps up frequency to full speed in about 2-seconds. As a result, there is absolutely no noise at startup and also no noise when running at full speed. After reaching full speed the Condor reduces voltage slightly for quieter operation, if that's even possible since it's totally silent to begin with. I get stable readings from the RoadRunner in about 12-seconds after startup, but I think the RoadRunner takes about that long to stabilize as a result of its averaging algorithm. This 3-phase system is designed to operate turntables with massive platters and it works exceptionally well with my Sota Millennia Vacuum turntable.
Best regards,
John Elison
Edits: 01/14/17
"The motor is a 12-watt brush-less DC motor operating from 24-VAC 3-phase sinusoidal power, which eliminates cogging completely. It has approximately twice the torque of a 10-watt Hurst AC synchronous motor and its RPM is governed by frequency. The Condor controller has a soft start function that ramps up frequency to full speed in about 2-seconds. As a result, there is absolutely no noise at startup and also no noise when running at full speed. After reaching full speed the Condor reduces voltage slightly for quieter operation, if that's even possible since it's totally silent to begin with. I get stable readings from the RoadRunner in about 12-seconds after startup, but I think the RoadRunner takes about that long to stabilize as a result of its averaging algorithm. This 3-phase system is designed to operate turntables with massive platters and it works exceptionally well with my Sota Millennia Vacuum turntable."
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I presume that it is the motor controller that locks onto the power frequency. DC motors tend to be voltage dependent. Other words, in a DC motor, more DC volts equals more rpm and fewer DC volts means fewer rpm. In the essence of all this a motor controller for a DC motor could be as simple as a voltage regulator.I'm not at all certain how AC 3-phase power and DC ouput come together on this. (except through an AC to DC conversion within the power supply) but I'll be happy to leave those details to its designer who has already proven himself highly competent in power supplies and motor speed regulation. Ergo, I take it on faith in its designer.
In any case it sounds as though that setup would have worked very well on a Teres.
thanks for this info John. Very interesting stuff.
-Steve
Edits: 01/15/17 01/15/17
As I stated earlier, I really don't know much about electric motors, but from what little knowledge I've gleaned recently, it seems that brushless DC motors are actually AC motors in the sense that without brushes and a commutator, the motor controller must switch polarity to the motor coils in order to make it run. Therefore, the motor controller is essentially providing AC power to the motor instead of DC power. Usually, the AC power takes the form of a square wave or trapezoidal waveform, but in this particular case the stationary coils are receiving true 3-phase sinusoidal power in order to eliminate cogging. In other words, the motor coils are connected in either a Y-configuration or a delta configuration. Therefore, the Condor motor controller converts DC to AC instead of the reverse as you suggest because the Condor is powered by a 24-volt DC wall-wart power supply and must generate 3-phase AC power to send to the motor.
Best regards,
John Elison
ouch. AC becomes DC then it becomes AC again. But we call it DC becuz...uh, it likes AC going into 3 phases but then it synchronises its whatzits to the quartz crystal oscillator .... and stuff.
ok that's beyond me. Like I said early, I'll trust in the designer's ability to do this. I do recall using the 'brushed' DC motors I had on my Teres that could run either off a wall-wart that converted AC to DC, or straight off a 12 volt battery (sized about like a large motorcycle would use). But obviously this little piece of tech you have is quite different.
Pretty cool, though.
-Steve
If you think about it, the commutator and brushes are there to transform DC into AC so the motor can run. You need an alternating magnetic field otherwise the motor won't turn. Consequently, aren't all electric motors really AC motors?I've never studied electric motors and I'm just guessing. Perhaps I'm wrong! ;-)
Best regards,
John Elison
Edits: 01/16/17
Yes. That seems likely.....and I suppose to all those who have actually studied electrical motors it should seem like one of the fundamentals. I guess a little reading up on what makes electric motors work would be useful.
thanks,
-Steve
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