Low Freq. Capacitor Charger
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From: Jeff Niles on 24 May 2010 02:32 I need to build a circuit that will charge a 100uF capacitor to 240V with a _10 Hz_ pulse, and then have the cap hold the charge for at least 24 hours. The purpose is to establish a static field via a pair of plate electrodes connected in parallel with the cap. I am thinking of an LM555 feeding a 10% duty cycle pulse to an 8R:1K miniature audio transformer, or two of the latter with output sides wired in series to increase voltage. The cap would be connected across this, and isolated from the charging circuit with a switch after charging. Can anyone please any suggestions or improvements regarding this type of circuit? Also, what would be the best type of cap to use? Thank you, Jeff Niles
From: John Devereux on 24 May 2010 03:22 jellniles(a)optolux.com (Jeff Niles) writes: > I need to build a circuit that will charge a 100uF capacitor to 240V > with a _10 Hz_ pulse, and then have the cap hold the charge for at > least 24 hours. The purpose is to establish a static field via a pair > of plate electrodes connected in parallel with the cap. "Static" == "DC" so what *exactly* do you mean by a "10 Hz" pulse? What voltage waveform do you want to appear on the capacitor? > I am thinking of an LM555 feeding a 10% duty cycle pulse to an 8R:1K > miniature audio transformer, or two of the latter with output sides > wired in series to increase voltage. The cap would be connected across > this, and isolated from the charging circuit with a switch after > charging. > > Can anyone please any suggestions or improvements regarding this type > of circuit? If you just want to end up with a charged capacitor you probably want a flyback convertor circuit. > Also, what would be the best type of cap to use? This is a dangerous circuit. Defibrillators work both ways you know... -- John Devereux
From: mike on 24 May 2010 04:52 Jeff Niles wrote: > I need to build a circuit that will charge a 100uF capacitor to 240V > with a _10 Hz_ pulse, and then have the cap hold the charge for at > least 24 hours. The purpose is to establish a static field via a pair > of plate electrodes connected in parallel with the cap. > > I am thinking of an LM555 feeding a 10% duty cycle pulse to an 8R:1K > miniature audio transformer, or two of the latter with output sides > wired in series to increase voltage. The cap would be connected across > this, and isolated from the charging circuit with a switch after > charging. > > Can anyone please any suggestions or improvements regarding this type > of circuit? > > Also, what would be the best type of cap to use? > > Thank you, > > Jeff Niles > > Before you build the supply, you should do some math. Do you care how accurate the initial voltage? What's your definition of "Hold the charge for at least 24 hours?" If you're content to have a third of the voltage after 24 hours, that's one time constant. 86400 seconds / 100uF --> 864 MegOhms of equivalent leakage resistance. Even if you ignore the leakage in the cap and the surrounding circuit, depending on the environment surrounding your plate electrodes, you might find that difficult to obtain. If you need more than a third left, you need proportionally higher equivalent leakage resistance. Look into the technology used for radiation dosimeters. As for the power supply... Last I checked, places that develop pictures from disposable cameras got paid 22-cents for each used camera they returned to the factory for refurbishing. My local Walgreens sold me 10 of them for $3. The flash power unit is just about what you need. mike
From: Jeff Niles on 24 May 2010 08:57 On Mon, 24 May 2010 08:22:08 +0100, John Devereux <john(a)devereux.me.uk> wrote: >jellniles(a)optolux.com (Jeff Niles) writes: > >> I need to build a circuit that will charge a 100uF capacitor to 240V >> with a _10 Hz_ pulse, and then have the cap hold the charge for at >> least 24 hours. The purpose is to establish a static field via a pair >> of plate electrodes connected in parallel with the cap. > >"Static" == "DC" so what *exactly* do you mean by a "10 Hz" pulse? > Sorry, if I did not explain this fully. The 10Hz charging circuit would be disconnected from the cap after charging, thereby leaving the isolated cap holding a static charge. Jeff Niles
From: Jeff Niles on 24 May 2010 09:05
On Mon, 24 May 2010 01:52:55 -0700, mike <spamme0(a)go.com> wrote: >If you need more than a third left, you need proportionally higher >equivalent leakage resistance. > The charge circuit will be disconnected from the cap after charging, thereby leaving the cap fully isolated. I was also planning to use a low leakage variety, if they are available at 250V rating. Given this, what would be the longest interval I could expect before the cap discharges by half? >As for the power supply... >Last I checked, places that develop pictures from disposable cameras got >paid 22-cents for each used camera they returned to the factory for >refurbishing. For this application, it must be charged with the 10Hz oscillator as described in my OP. It's part of an experiment. Thank you for your reply, Jeff Niles |