Roman, I had the good fortune, in the early 1990's, of consulting with Ralph=20 Kerrigan, the Chief Capacitor Design Engineer with Sprague Electric due to= =20 the quantity of capacitors that I was ordering. I will share a few things=20 that I learned from Mr. Kerrigan. At that time, the high voltage capacitors= =20 manufactured by Sprague were available with either a "foil" conductive=20 material or with a "metalized film" conductive material. Mr. Kerrigan=20 indicated that the "foil" conductive material had a superior reliability=20 for handling "higher currents" while the "metalized film" conductive=20 material had a superior reliability for "voltage transients". The=20 "metalized film" also had a "self healing" characteristic allowing for=20 recovery from minor transient voltage damage. At that time, the Sprague=20 high voltage capacitors were also available with a "polyester" film=20 dielectric material, a "polypropylene" film dielectric material or a "polycarbonate" film=20 dielectric material. The "polypropylene" film was superior to the=20 "polyester" film and cost 150% more than the "polyester" film.. The=20 "polycarbonate" film was superior to the "polypropylene" film and cost 650%= =20 more than the "polyester" film. After weighing all the pros and cons, I=20 decided to go with the "metalized film" conductive material with the=20 "polypropylene" film dielectric material. This combination was available=20 off the shelf in voltage ratings from 400V to 2000V in standard capacitance= =20 values. However, I had to special order because my specification of 1.68uF= =20 was not a standard value. I could have used an off the shelf 1uF and a=20 0.68uF combination, however, that would have doubled the cost and the=20 physical space required. The body of these capacitors was approximately 1"= =20 in diameter and 3" in length. These capacitors had the typical oval=20 geometry, typical white body and typical yellow outer wrap. In quantities=20 of 10,000 the capacitors were $3.90. These capacitors were used to replace= =20 malfunctioning solid state controllers that provided 120 Vac to "Exit=20 Lamps" from a 277 Vac main in all the international airports throughout the= =20 free world! Prior to this project, I didn't know that the typical=20 international airport has 2,000 "Exit Lamps". The capacitors that you have are probably "foil" and "polyester" film which= =20 are fine for non critical applications. You should be able to purchase=20 small quantities of "metalized" "polypropylene" film capacitors from a=20 capacitor manufacturer's distributor and might even acquire "free"=20 engineering samples! It should be noted that a 1,000 V "foil" and "polyester" film capacitor=20 will provide a similar level of reliability as a 630 V "metalized" film and= =20 "polypropylene" film capacitor. This is why I emphasized raising the=20 voltage ratings of the capacitors. The most important thing is that the=20 voltage rating is more than adequate and that the capacitor is not=20 generating heat. The capacitors surface temperature should never be allowed= =20 to reach 75=BAC. The "Exit Lamp" capacitors while enclosed in the lamp=20 fixtures experienced a maximum increase in surface temperature of 3=BAC=20 after 72 hours of continuous operation. I eventually upgraded the "Exit Lamp" design with SIDACs (SYDACs) that were= =20 manufactured by RCA and Motorola at that time. The SIDAC is a very=20 interesting thyristor that has many useful applications. A simple but=20 inaccurate description of the SIDAC would be that it is a two terminal=20 TRIAC (DIAC) that must be activated by the application of a voltage that is= =20 greater than the typical 130 Vac main. Placing a SIDAC in series with a=20 120V lamp on a 120 Vac main will accomplish nothing. However, placing a=20 120V lamp in series with a SIDAC on a 277 Vac main will illuminate the lamp! One last bit of advice and hocus pocus . . . When ever dealing with high=20 voltages, I sincerely think that it is best to be in a Nikola Tesla state=20 of mind! Good luck with the killer volts! Sincerely, Ned Seith Nedtronics 59 3rd Street Gilroy, CA 95020 (408) 842-0858 G O T G A R L I C ? GILROY GARLIC FESTIVAL 2001 STARTS TODAY! At 11:10 PM 7/27/01 +1000, you wrote: >Ned Seith wrote: > > > > Vasile, > > > > Your series capacitance voltage divider circuit has certainly received > > criticism. > > So I hope that I'm not kicking a dead horse. > > While a transformer would definitely be the safest approach for the= typical > > hobbyist, I'm glad to see that there is someone who is willing to be= more > > intimate with the electrons. > > The concept and configuration of your series capacitance voltage divider > > circuit is fine. > > I have designed industrial applications which have provided several amps= of > > current at low voltages from 220 Vac and 277 Vac mains using a series > > capacitor. Industrial equipment and machines frequently use a series > > capacitor instead of a transformer for providing lower voltages. > > A few points: > > I would not add a resistor in series with the capacitor (C9) as this= will > > vary the effective capacitance reactance which is providing the= desirable > > voltage drop and will also dissipate heat. > > I would not add a resistor in parallel to the capacitor (C9) as this= will > > vary the effective capacitance reactance which is providing the= desirable > > voltage drop. This resistor would also dissipate heat. > > I would not be too concerned with the capacitor (C9) remaining charged= as > > the approximate 6 mA current consumption from the voltage regulator will > > quickly discharge the capacitor. UL and TUV stipulate that the voltage > > potential on an unplugged power cord must diminish to 1/3 of the mains > > voltage within 10 seconds. So, If I wanted to increase the rate at which > > the capacitor discharges, I would place a resistor in parallel to (C5)= on > > the low voltage side of the circuit. > > I would want a 1/4 amp fuse between the 220 Vac main and the series > > capacitor (C9). > > I would also want the series capacitor (C9) rated for 800 V to 1000 V. > > If the series capacitor (C9) is getting warm at all, then the voltage > > rating should be increased. > > I would want the diode rectifiers voltage rating increased to 800 V to= 1000 > > V (1N4006, 1N4007) to assure that there is not any brief reverse= conduction > > during the delay of the capacitors charge cycle. > > Otherwise, looks good to me. > > Just a few comments from an old engineer. > > > > Sincerely, > > Ned Seith > > >Hi Ned, I find these type of supplies very interesting, >and have been playing with them for many years. Since >before they were legal. :o) > >I'm really interested in your "several amps" applications, >can you give any more info? Size/cost of the capacitors? >Or custom built capacitors? I've made some medium supplies >with the 630v poly types, pref the blue milspec ones. >They are still going good now after many years. Never >been brave enough to sell one though, just for personal >use in my workshop. > >Do you have any specific tricks for handling current >under-loads or spike conditions? Regulation? Sorry to fire >questions at you. :o) >-Roman > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics