On 11.01.16 14:00, Gene Heskett wrote: > > I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it > right now that I was going to use once the relays get here. Thats 833 > ohms which would drain it even faster than just the one. And, somewhere > on an undermanned galley in the pacific, is a 250 ohm 250 watt resistor > which would do the bleed-down even faster, and the current peak would be > nominally .5 amps in that case. I can't see that as being capable of > welding a relay contact.
There are alternatives to the electromechanical relay or an SCR/Triac-based SSR, such as opto-coupled FET switches. They switch off, even on DC. In my junkbox I (think I still) have some http://documentation.renesas.com/doc/YOUSYS/document/PN10273EJ02V0DS.pdf With both FETs in parallel, it'll just handle 0.5A, so adding some ohms in series with the bleeder would be wise in this case. There are doubtless beefier units out there by now. Note: If used to switch AC, the FETs need to be used in series, halving the current capacity. That brief technology diversion aside, I'd just go with fixed slow bleeders, I think.¹ (Though a small relay buffered by a big MOSFET would solve all your contact welding concerns, and allow a low value bleeder in the drain circuit. The MOSFET would only switch, obviating your concerns with running one in the linear region. OK, in the last few volts, gate drive would fall off, unless you added a diode to keep charge on the gate.) ¹ Especially given John's suggestion that a split bleeder can serve for voltage equalisation across series capacitors. You're not doing that, instead running the electros at full rated voltage? In the Siemens design labs we were never allowed to design that way. Half of rated was the allowed max, for reliability. I like to stick to 60% for my own stuff, still. Where I'm happier with a switched resistor is as inrush limiter. Erik ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
