At 01.19 2012.02.19, you wrote: >Hi Mario >The best discharge capacitors ever are silver mica plate capacitors. They >are not cheap or small but they will fit the bill. I have used then as >pulse dischage capacitors >in ultrasonic avalanche pulse generators producing <5nsec 600v pulses. Thanks, but for a CDI that's overkill. :P > >On Sat, Feb 18, 2012 at 4:44 PM, Electron wrote: > >> At 20.09 2012.02.18, you wrote: >> >> Hello, >> >> I need a >=3D400V >=3D4.7uF pulse capacitor with a dV/dt rating >=3D2= 0V/us. >> >> >> >> I can find them on Mouser, Digikey, etc.. e.g.: >> >> http://www.kemet.com/kemet/web/homepage/kechome.nsf/vapubfiles/F3294_= PH >> >> E426.pdf/$file/F3294_PHE426.pdf >> >> >> >> But they are all too big/bulky!! >> >> >> >> What should I look for? Is there a different technology than >> >> polypropylene, still suitable for >=3D20V/us pulse applications, and = is >> >> not as bulky as those caps? >> >> >> >> Even half the size would already be a big win for me. >> > >> >What you are have found is a capacitor that is rated for continuous >> >connection to 230V mains for use in mains filters or as motor run >> >capacitors and the like, often referred to as X2 rated, or something >> >like that. I don't think you will find anything else that will do what >> >you want. >> > >> >Note also that you don't quote a dI/dt rating - but this will probably >> >be the rating that will bite you in the backside. It is an easy rating >> >to ignore, and will often result in shorted capacitors, a familiar >> >form of failure for anyone that attempted to use the old Philips >> >'lollipop' polycarbonate capacitors in items like capacitor discharge >> >ignition systems. >> >> Yes, it's a CDI. :o I calculated a 50A peak current.. but ignored the >> dI/dt. >> While the dV/dt is the discharge rate of the capacitor (the charge is mu= ch >> slower, and the turn ON time of the SCR doesn't matter in the dV/dt, but >> only the time it takes to discharge into the coil), the dI/dt instead wo= uld >> be linked to the rise time of the SCR going into conduction? >> >> I would never use a polycarbonate capacitor in a CDI.. but I wonder if >> polypropylene is my only practical choice? >> >> I found this alternative to the PHE426 that I've been using so far, it's >> smaller (not by a huge amount, but smaller) and even cheaper: >> >> >>=20 >http://media.digikey.com/PDF/Data%20Sheets/Panasonic%20Capacitors%20PD >Fs/ECWF%28A%29%20Type.pdf >> >> But they don't quote a dV/dt nor a dI/dt.. I wonder if it's suitable for >> my CDI? >> >> With kind regards, >> Mario >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >--=20 >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .