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DIY 4 Phase Sinewave Generator for Turntable Motor Drive
DIY 4 Phase Sinewave Generator for Turntable Motor Drive
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Old 11th November 2018, 05:10 PM   #721
hpasternack is offline hpasternack
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Join Date: Sep 2002
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Good point; I didn't think of that. Hopefully under steady-state conditions the power dissipation will be much lower than the rated value and heat won't be an issue.

Hmmm. The bottom of the pod is an inch of solid lead so it might absorb some heat but again it's inside the plastic housing and isn't in contact with the motor housing so it's unclear how much that would help. If it's a problem I can make an aluminum top cover.

It was always my grand plan to have a house with a machine shop in the basement. Instead I have no basement, no machine shop, and I make things on the kitchen table, LOL.

Edit: Looks like an option is Front Panel Express which will do a cover for about $45.

Last edited by hpasternack; 11th November 2018 at 05:14 PM.
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Old 11th November 2018, 05:31 PM   #722
Pyramid is offline Pyramid  United States
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The starting voltage for the motor was determined for rated power (12W); if run at that level for extended periods, the motor case temp will exceed 140F. The SG4 has the capability to reduce the voltage after initial start up and the recommended levels will reduce the power to ~9W IIRC. With a metal housing the temp should stabilize ~110-115F; not sure what they will be with a non-metallic case. The motor will certainly run at higher temps (AA recommends to keep the case temp below 175F), but it becomes a balancing act of temp vs torque (power). Anything you can do to get the heat off the motor will make the balancing act easier.
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Old 11th November 2018, 05:56 PM   #723
carlthess40 is offline carlthess40  United States
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Is there anyway to add a very small fan blade at the bottom of the motor? And drill some slots or holes in the case for air flow?
One way is to glue a small shaft at the bottom of the motor to use as a bearing and
Install the small fan blade onto that and run it using the magnetic field of the motor to spin the fan blade ? Crazy? Yes/no
Just thinking outside the box
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Old 11th November 2018, 08:43 PM   #724
hpasternack is offline hpasternack
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Well, it's up and running and works fine. Thanks, Phoenix.

After playing two albums the motor isn't warm at all (I can touch the mounting flange through the hole in the top cover). I don't think heat is going to be a problem. A fan is definitely not needed and if heat did become an issue passive heat sinking ought to be more than adequate.

One thing I notice is the amplifier is causing some hum in the speakers. Unplugging the motor cable and turning off the SG4 doesn't make a difference. I assume putting everything in a shielded enclosure will help.
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Old 11th November 2018, 08:49 PM   #725
vgeorge is offline vgeorge  Greece
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DIY 4 Phase Sinewave Generator for Turntable Motor Drive
I would advise to also ground the motor with the amp enclosure.
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Old 11th November 2018, 08:55 PM   #726
hpasternack is offline hpasternack
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Quote:
Originally Posted by Pyramid View Post
The starting voltage for the motor was determined for rated power (12W); if run at that level for extended periods, the motor case temp will exceed 140F. The SG4 has the capability to reduce the voltage after initial start up and the recommended levels will reduce the power to ~9W IIRC. With a metal housing the temp should stabilize ~110-115F; not sure what they will be with a non-metallic case. The motor will certainly run at higher temps (AA recommends to keep the case temp below 175F), but it becomes a balancing act of temp vs torque (power). Anything you can do to get the heat off the motor will make the balancing act easier.
Forgive me if I misunderstand but I was under the impression that motor power dissipation is a function of mechanical load as well as supply voltage. Once the platter is spun up the power to maintain rotation is minimal and so the winding current should drop significantly due to back EMF opposing the supply voltage.

Anyway, as I said so far the motor is running quite cool. I'll keep an eye on it.
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Old 11th November 2018, 09:43 PM   #727
Pyramid is offline Pyramid  United States
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Quote:
Originally Posted by hpasternack View Post
Forgive me if I misunderstand but I was under the impression that motor power dissipation is a function of mechanical load as well as supply voltage. Once the platter is spun up the power to maintain rotation is minimal and so the winding current should drop significantly due to back EMF opposing the supply voltage.

Anyway, as I said so far the motor is running quite cool. I'll keep an eye on it.
The amount of torque the motor delivers is a function of the load and will affect the angle between the rotating field and the magnetic rotor; at no load, the field and rotor are aligned, and maximum torque is produced when the rotor is 90 behind the field. The available torque will remain nearly constant. The electrical power consumption of the motor changes very little with load, until the motor stalls. The power consumption is a function of the winding resistance and the back EMF; the faster the motor spins, the higher the back EMF, the higher the apparent impedance and the higher the drive voltage needed to maintain constant power. If the motor stalls at high RPM, the back EMF disappears and the current draw (now equal to supply voltage/winding resistance) could be enough to reset the wall wart.

I noticed that you have 2 power supplies: one for the MA-3D and one for the SG4. You can power the SG4 using the 2 unused outputs on the MA-3D (marked 12V and Gnd) so you only need one wall wart.

Beautiful table BTW.
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Old 11th November 2018, 11:31 PM   #728
hpasternack is offline hpasternack
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I measured the current in one of the motor leads. It's about 90mA with no load and increases to about 180mA when driving the platter. So three times 3.2V times 180mA is about 1.7W. Of course, some of that power is coming out as mechanical work and the motor isn't a purely resistive load so the actual dissipation will be lower, maybe a watt? It seems like it should be ok.

Thanks for the compliment on the turntable. If you're not familiar, the parts came from the original Teres group buy, maybe fifteen years ago. The plinth is Corian and baltic birch with lead shot inside.

I need to put the motor drive in a box and get some proper drive belts. I also have one of the SDP/SI flat belt pulleys so want to give that a try. The dental floss works but the grip on the pulley isn't great.

Oh, about the wall warts. I forgot to buy another barrel connector when I was at the electronics store yesterday. I didn't want to sacrifice the cord on the small power supply so for now I am using both wall warts.
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Last edited by hpasternack; 11th November 2018 at 11:41 PM.
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