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PostPosted: 17 Jan 2015, 22:47 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
My friend Dave was running his 240V (mains) TT with a 12V car battery and a 240V inverter. He claims that all the 100 and 200Hz harmonics on the mains (Australian mains is 50hz) cause the light weight synchronous AC TT motors to chatter and shake. The inverter is a pure sine wave and generates a pure 50Hz 240V signal.

The 12V car battery could be replaced with a 12V regulated source and not effect the pure sine wave being generated. But I don't want to use an inverter. So I came up with an isolation system which uses two step down trannies one backwards. 240->24->240V. Use an RFI\EMI filter first and even a DC blocker before that. But as Dave pointed out this may not stop harmonics passing through. One thing the inverter will do is provide a regulated 240V but voltage regulation is not required.

The second design passes the lower 24V through a couple of 9mH Xover iron chokes. The idea is this should dropout higher harmonics. Also a few small X2 caps to reduce higher frequencies. I just plucked the choke and cap values out of the air. Can anyone suggest correct values for the chokes and caps. The idea is to only allow 50hz and lower through.
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PostPosted: 17 Jan 2015, 23:29 
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At 24V, you don't need x2/y1 safety caps... that's the glory of low voltage.

You'll also need higher current inductors than for 240V.

Other than that, looks like a sound idea! :D

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PostPosted: 17 Jan 2015, 23:42 
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The chokes only handle 24V. They are probably rated 100V and are wound with very heavy copper wire. I get X2 cheap from where I work.

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PostPosted: 18 Jan 2015, 22:48 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I'm not to fond of either circuit but like the second circuit better. One thing you have not addressed is phase shifting. With all the reactive components you might well end up with a non-sinusoidal wave. The commercial power filter / conditioner / voltage stabilizer devices (like the APC H1500 I have) have all sorts of guts to clean the power, maintain the voltage and particularly insure purity of the output. For the small amount of power you require I believe that the existing circuit might be better than the filters. This type of application has become somewhat common at shows I have recently been to. Take the raw AC and convert it to DC and then regenerate the AC. It is used even in budget TTs like Pro-ject when you use one of their "speed boxes". It has an advantage that you can adjust the frequency a bit in case the turntable is slow or fast. .......Me, I use a DC direct drive TT (with a modified DUAL EDS 1000 motor and controller) that doesn't care what comes in as it converts it to DC and regulates it. Serious over design from 40 years ago. I vote for sticking with the existing way provided that the inverter puts out clean sine waves.

Good listening
Bruce

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PostPosted: 19 Jan 2015, 00:05 
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I have a feeling inverters put hash back on the line and into the atmosphere. The tranni idea does none of these.

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