On 2 October 2013 14:55, jrmitchellj . <jrmitche...@gmail.com> wrote: > The relay or contactor you use must be a "break before make" style
The ones I have been using are meant to be, but they are not force-guided to ensure it. > A larger value resistor for bleed off might be in order. > I usually put a very large value resistor across the power supply. You > waste some power, but you always know the supply has been bled off before > poking into it. Do you mean "very large" in the physical sense or the value sense? I have 20,000uF of caps at 300V. For a 100W resistor to be happy steady-state then the minimum resistance it can have is about 1k. That will take 82 seconds to drop the voltage to 5V, which is longer than I would like. I guess I could use a 250W resistor, which is 30s to 5V, or a 1kW resistor, which is 7.5 seconds to 5V. But both seem wasteful, and I am not sure I have the space. (Also quite expensive: http://uk.rs-online.com/web/p/panel-mount-fixed-resistors/7014059/ ) Currently the 50R 100W resistor which is switched-in only when needed takes 5 seconds to drop the voltage to comfortable levels. And it doesn't even get warm in that time. (unless, as has been discovered, the relay that switches it in manages to weld shut and keep it in circuit at the same time as the mains supply is connected) -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60134791&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
