On Tuesday 12 January 2016 00:37:55 Erik Christiansen wrote: > 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.p >df > > 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.
Yes, 63 volt rated caps, running at 63 volts. They have formed up to such low leakage that without the bleeders, they are still dangerous 2 days after the shut down. No clue how long they will last but I suspect they were a decade+ old when I pulled the 20 some I used out a bushel sized box. Dave was going to make hisself a 10 kw PA amp that would carry the Grateful Dead from his place clear into Ellamore WV, about 5 miles. GD was the star attraction at a charity concert he threw at his place every summer for nearly 25 years while he was working for me at the tv station. It was called, because the stage was across the road from the river, River Rocks. But he's retired, pushing 70 and essentially broke, a small vet pension and SS, but his 40 acres is paid for so he hasn't done the concert in 3 or 4 years. He putters about & keeps busy. I guess that would also describe me. :) > 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 > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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> ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
