On Tuesday 03 May 2016 08:46:07 andy pugh wrote: > On 3 May 2016 at 13:37, Gene Heskett <ghesk...@wdtv.com> wrote: > >> And does the "fail to turn off" problem description include not > >> turning off ever again, even when removed from the circuit and from > >> all power? > > > > Generally yes, its an avalanche mode failure that shorts the > > switching junction. > > I am not 100% clear on the source of this dv/dt. Is it simply the > result of turning on the main contactor, with the SSR turned off, when > the mains supply is in a high part of the sine wave?
I've not been able to confirm that as a destructive turn on. Looking at your circuit, the 620 seems too high so its instant surge heating may be quite destructive over many cycles of power up, I have a 50 at 200 watt wirewound there. But I also have a bit of a di/dt limiter in the form of some large toroid power transformers that are series-paralleled to get the dc I desired. With a purely capacitative load, the di/dt would be limited mainly by the powerline impedance. If suitable chokes could be had to make a choke input filter, thats what I would do as its output voltage regulation is quite a bit better than a purely capacitative design. But suitable chokes are lotsa bucks even on the surplus market these days. A suitably current rated "filament" transformer could be used if the primary winding could be cut away as its voltage output when using the filament winding as a choke could easily top a couple thousand volts leading to a short circuit failure. Then most of the inductance would go away. Unfortunately, most of those are wound with the high voltage primary winding laid on the bobbin first. Winding your own on a good sized ferrite core could be done if you can find a core with high enough magnetic saturation so it doesn't saturate at the expected current, keeping in mind that if it does saturate, you have effectively an air cored inductance. That isn't a desirable thing, and its exactly why you cannot use a vga sweep speed CRT monitor on an old computer that outputs pal or ntsc sweep speeds. That doubles the effective on time of the sweep transformers drive, the core saturates and everything between it and the power source goes by-by by letting out all the smoke and breaking the mirrors that makes all this stuff work. 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
