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Old 11th April 2011, 01:07 AM   #1
jfitz57 is offline jfitz57  United States
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Default ESL bias supply the GE way

Hey

So I was looking for some computer motherboad capacitors and found a source. Liked what I saw so I looked further. I found 1N4007's for $0.02 each for 100. I'm thinking of making a 25 stage multiplier bias supply run directly from "you ess aaa" mains (120 volts RMS 60 Hz). I made a 6 stage multiplier with 1N4006's and 1n4007's and 0.01uf 630volt caps before and it worked, but the source for those parts sucked.
So I want to know, do you think I should use bigger caps at the bottom of the ladder to stiffen the circuit?

Jim
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Old 11th April 2011, 05:11 AM   #2
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Yes ,the bigger the value of the capacitors you use ,the better the current producing capability. jer

Last edited by geraldfryjr; 11th April 2011 at 05:29 AM.
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Old 11th April 2011, 06:28 AM   #3
godfrey is offline godfrey  South Africa
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Yes, using bigger caps at the bottom of the ladder is more effective. Interestingly, as you add more stages to a conventional multiplier (all caps equal), you eventually reach a point where adding more stages actually decreases the output voltage.

Attached is a text file of notes I made a couple of years ago when I looked into this stuff. Can't remember where I got the info, but maybe it'll help with your calculations / design.

Good luck - Godfrey
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File Type: txt V-mult.txt (1.7 KB, 120 views)
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Old 11th April 2011, 06:40 AM   #4
Calvin is offline Calvin  Germany
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Hi,

25 stages are absolute overkill and won´t give the calculated output voltage of ~8.5kV. The problem beeing that the caps appear in series connection, so their overall capacitance value becomes small and their impedance becomes high. This reduces the current capability of the circuit and the voltage stability under load seriously.
I wouldn´t opt for much more than 5 stages.
I would opt for a galvanic barrier, by using two trannies back-to-back and to achieve a higher voltage level at the multipliers input.
I don´t know the american legislative situation, but in a lot of countries a galvanic coupling of a circuit with the powersupply lines is not allowed and in case of an accident it gives the insurance company a well defined reason not to pay.

jauu
Calvin
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Old 11th April 2011, 09:53 AM   #5
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Originally Posted by jfitz57 View Post
I'm thinking of making (...) bias supply run directly from "you ess aaa" mains (120 volts RMS 60 Hz)
As mentioned by Calvin, this is really not advised: too dangerous. You must use a transformer in all cases.
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Old 11th April 2011, 11:06 AM   #6
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When I look in my own audiostatics (commercial brand) they did make their HV-supply directly run from the mains, so without any transformer at all.
These speakers are pretty aged (though completely refurbished) and possibly audiostatic may use a different aproach these days.
I don't know to what extend this may lead to dangerous situations, to itself or to other equipment. But these hv-supples seem to work very reliable.
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Old 11th April 2011, 11:30 AM   #7
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Two motivations for using a transformer:

Galvanic isolation - Wikipedia, the free encyclopedia

"Galvanic isolation is used in situations where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current between two units sharing a ground conductor. Galvanic isolation is also used for safety considerations, preventing accidental current from reaching the ground (the building floor) through a person's body."
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Old 11th April 2011, 02:32 PM   #8
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Quote:
Originally Posted by godfrey View Post
Attached is a text file of notes I made a couple of years ago when I looked into this stuff. Can't remember where I got the info, but maybe it'll help with your calculations / design.
Perhaps from here:
Experiments: Experiment 15

more in depth theory here:
http://www.blazelabs.com/CWdesign.pdf
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Old 11th April 2011, 07:15 PM   #9
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One way to make a long ladder with smallish capacitors is to increase the frequency. As others pointed out, at 50/60 Hz you can only do so many stages before the ladder voltage doesn't increase anymore. But, if you make a small inverter with two transistors and a small ferrite transformer (or scavenge it from a CCFL inverter), you can get pretty far with 10nF caps...

If you power the inverter from a +24V wall wart, safety is taken care of, too...

Kenneth
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Old 11th April 2011, 09:55 PM   #10
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Thats the method I had used here.


how can test the stator insulation and mylar coating?


Just make sure that recovery time of the diodes is suitable for the frequency that you are driving them them with. jer
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