On 01/11/2016 06:01 PM, Gene Heskett wrote: > 1. put a small tranny delivering say 6 volts AC in series with the > resistor and its shorting SSR to encourage that SSR to turn off when the > cap voltage has dropped to 6 volts or less.
How do you connect the 6V AC without it bearing a huge (peak) current? If you have a DC signal in it too, it will feedback into the primary. That is a huge problem. Not to speak of the inductance. > 2. enforce in hal, 2 delay circuits. An on delay long enough for #1 to > have completed its job and the short across the resistor no longer > exists thru that pair of SSR's. Enforcing a software solution is a risk. If the software fails, then you get potentially fried? You'd normally have an electronic interlock to prevent problems. > 3. Time the short enable so its 5 to 10 seconds after the relay has > closed, and time the short disable to take place a second or so before > the relay is de-energized, so that SSR is off by the time the switch of > the resistors position in the circuit takes place. By placing another > timedelay in the relay control, with longer time delays than the > shorting time delay would enforce disconnecting the short whose > timedelay is set for 1 second, so the resistor is switched back into the > circuit well before its transferred to dump the caps duty. The real problem of shorting the resistor are the huge peak currents. You said that you have two 68000uF caps in series, or 34000uF effectively on it, which suggests that you are handling an average DC current somewhere between 30...60A. The current peak from the rectifier, just to maintain that DC current after the cap, is somewhere between 120...240A (estimated) and even higher currents are possible. That will fuse most normal relays. SSRs would probably survive is you get one and stay well below the fusing current (specified in the I^2t parameter) and stay below the peak current rating. However, SSRs do not like to be operated at high peak currents for long periods. > Does anyone have an data on how sensitive these SSR's are to a false > trigger from dv/dt effects applied to the output terminals? They all have that specified in the datasheet. Most large ones are specified at about 500V/us. > Or do I need to use 2 of these relays with a fraction of a second between > them, to assure the line side SSR's have time enough to turn off? At > 60Hz thats 8.3333 milliseconds after drive has been removed, and the > single relay could be faster than that. All TBD when the relays arrive > I guess. They haven't yet. Well, it looks like a very complicated and rather risky setup. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ 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
