On Monday 07 December 2015 11:13:45 andy pugh wrote: > On 7 December 2015 at 15:53, Jon Elson <el...@pico-systems.com> wrote: > > I would just get some vitreous enamel resistors. They are > > not that expensive, even new. > > Or higher-power lower-resistance for a faster discharge. > http://www2.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtual >keyTHS50560RJ > > As the capacitance and voltage rise you get to the point that the > bleed-of resistor becomes an electric heater, but I think you may be > below that point. > > My mill has 6600uF at 300V, and I wanted a 10 second discharge > That means a 500R resistor, > A 500R resistor permanently across a 300V bus dissipates 180W. And > that's a pretty big resistor. Which is why, in my case, I decided to > only switch-in the resistor at power-off. > > With less capacitance, and lower voltage, the power requirement falls > rapidly. (with the square of V). > > 120V and 3300uF comes out at a far more reasonable 14W with a 1K > resistor
I have nominally 63 volts and nearly 100k u-f to discharge. I have a similar getup on the lathe at slightly lower total voltage (107) & quite a bit less u-f, and its about 15 minutes to screwdriver safe. 3 or 4 minutes until the bulb is dark. This may need the switched load if you want to work in it without going in and re-boreing an empty coffee cup & refilling it for a time killer. :) Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Some mill pix are at: Genes Web page <http://geneslinuxbox.net:6309/gene/GO704-pix> ------------------------------------------------------------------------------ Go from Idea to Many App Stores Faster with Intel(R) XDK Give your users amazing mobile app experiences with Intel(R) XDK. Use one codebase in this all-in-one HTML5 development environment. Design, debug & build mobile apps & 2D/3D high-impact games for multiple OSs. http://pubads.g.doubleclick.net/gampad/clk?id=254741911&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
