Help I bought a Empire turntable for 115V 60Hz in a 240v50Hz country - diyAudio
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Old 2nd June 2010, 05:01 PM   #1
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Default Help I bought a Empire turntable for 115V 60Hz in a 240v50Hz country

The Papst Assuenlaufer motors of the Empire are 60Hz speed regulated. So how do I produce the required frequency?

Buy a car battery, a charger and a true sine inverter ?

Are there any less bulky, cheaper solutions? Help!!
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Old 2nd June 2010, 06:25 PM   #2
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Even that isn't a good solution, as most inverters are not frequency stable. I would first get a step down transformer to bring the power down to about 100V (with consideration for the lower frequency). Then change the diameter of the motor pulley - it's too small for 50 Hz. (I assume this is either belt or idler driven, not direct drive.)

Measure the pulley with a micrometer and make a sleeve for it that is as close as you can get to 6/5 the diameter. You will now have a working setup, but with two down sides - the torque will be lower due to the lower mains supply, and you will get a bit more wow and flutter if your sleeve isn't perfectly true to the rotational center.
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Old 2nd June 2010, 07:29 PM   #3
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Hm, That might work. It is a belt drive.
I might be able to get a custom pulley turned at work. By talking nice to the mechanic.

As far as torque and power at 50Hz I need to enlist the enlightened ones here at the forum. I donīt understand how you arrive at 100v instead of 115V

Here is another way of solving the problem, by Mark Kelly, but I can not find any schematic.
ClariSonus - Clear and enjoyable sound Mark Kelly on Empire Motor Project, part 1
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Old 2nd June 2010, 10:17 PM   #4
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Mark Kelly's solution requires a 60 Hz oscillator, again with the stability issues I mentioned.

The reason I suggest 100V rather than 115V is that, due to the lower frequency, you might be flirting with core saturation. Reducing the voltage to 100 will avoid that. Of course you could try it at 115 if you monitor the line current carefully but at least be aware of the potential problem. The flux density is proportional, sort of, to the excitation voltage and inversely proportional to the excitation frequency. If you lower one you must lower the other to maintain flux density.
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Old 3rd June 2010, 08:40 AM   #5
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I agree with the 100 volts, 60Hz motors often take a big surge and start abnormally fast when run on 50Hz at their nominal voltage. Papst motors often have phase splitting caps, if so the value should be increased by about 20 percent, this will increase the torque though generally these motors are torquier at 50Hz anyway. Torque is unlikely to be a problem although you will need more with the larger mptor pulley. Some one who has access to Empire spares may already have a 50Hz pulley.
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Old 3rd June 2010, 09:49 PM   #6
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I fitted an OL dc motor to mine.

Click the image to open in full size.

Click the image to open in full size.
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Old 3rd June 2010, 10:32 PM   #7
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What's an OL dc motor?
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Old 3rd June 2010, 11:00 PM   #8
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Quote:
Originally Posted by bob91343 View Post
What's an OL dc motor?
Origin Live.
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Old 4th June 2010, 06:50 AM   #9
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If you want an accurate 50 Hz voltage the best way is to start with an xtal oscullator driving a PLL synthesizer chip to generate a supermultiple of 50 Hz, say 50Hz*256. Then use this signal to drive a counter which accesses a sinewave look-up table. The lookup table drives a D/A converter and a low voltage amplifier capable of producing 10-20 VRMS. All that needs to be done then is use a stepdown transformer wired bakcwards to get the desired voltage. This approach is stable to the tolerance of the cxtal, typically a few hundred PPM. Most of the functions I have described above are available in an integrated device, so the parts count need not be that high.
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Old 4th June 2010, 07:09 AM   #10
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Here is a simpler way to achieve the same goal: using a counter, divide an xtal frequency down to yield a 50 Hz square wave and then low pass filter it to remove the upper harmonics. I have implemented this approach using a 3-pole Sallen-Key lowpass filter; it yielded <5% THD on the sine wave. The amplitude tolerance will be limited by the Vdd tolerance (assuming rail-rail CMOS output swing on the counter).
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