Thanks for the response Marshall. I've seen a few circuits that use a 555 timer with a power transistor or an SCR on the output to drive an autotransformer that puts out about 20 KV. I was hoping that I could use stuff I had lying around the house for the HV source. I guess I need to break down and buy a neon sign transformer. Do you submerge both of your electrodes or leave a small air gap between one of them and the DW? Any advice is greatly appreciated.
Thank you for your time. Andy Scott Date: Mon, 02 Sep 2002 11:51:23 -0400 From: Marshall Dudley < [email protected]> To: [email protected] Subject: Re: CS>HVAC An auto spark coil would be problematic. First it would be difficult to get the current you need, since they step the voltage up by over 1,000:1 I believe. It would require an amp to generate a milliamp of current on the secondary. Second, the coil is made to operate at high frequencies (that is a rapid rise and fall time). To allow the silver time to aggregate into particles, or move sufficiently away from the electrode before reversal (and it will reverse, even if the waveform is asymetrical unless you put a high voltage diode in the secondary) would require very high voltage. Lets take an example. To make a gallon an hour at 60 htz requires abou 10K volts and about 25 mA of current. With a spark coil, which typically has a 10 microsecond pulse before the leakage inductance shorts it out, it would require 50,000 pulses a second to maintain the same duty cycle. But this would quickly burn the coil out, since it is made for duty cycles of maybe 1/100 of that max. So if we run it at 500 pulses per second, we are running at about 1% duty cycle. The amount of current necessary would need to be about 100 times large for the same production rate. Thus we need about 1.4 Amps of secondary current. With the step up these have, that would require about 3,000 amps on the input. And since the frequency is about 8 times as high, the current needs to be about 8 times as high as well, or about 30,000 amps. Of course if you want to make it at a slower rate, then you could use a lower amperage, of maybe 1 amp, and make a gallon in about 30,000 hours. Now I could be off by a factor of 2, or even an order of magnitude on some of these estimates, but the result would still be the same. I believe it would be impratical. Use a 15 KV neon sign transformer like I do, and it will work fine. Marshall
