On Monday 11 January 2016 13:33:22 Bertho Stultiens wrote: > 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. > Probably, I hadn't though it all the way thru.
> > 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. Miss-conception John. Its shorted after the caps are nearly charged. When the final short comes on, the caps are up to 110-teens already, so the remaining charge isn't much. I put an amprobe on the black wire of the AC feed, and its a blond one north of 3 amps when the motor is doing 2500 revs cutting air. > 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. No, I just over estimated the u-f's I'd need for a 1HP motor. The current capacity is there should something short it out, but thats a fault condition, nothing approaching that will ever occur in normal operation even if I should manage to lock the rotor, the servo amp is set for a current limit in the 14.5 amp range, 150% of the motors nameplate draw at full song. The toroids might warm up 30 degrees doing it for 30 minutes, but Jon's driver will survive that. > 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. Rated 410 amps for these 40 amp CCS relays, but that would not be thru the relay contacts ever. With that resistor in circuit for the first 5 or 6 seconds, the max amps is nominally 2.5 rms for the first 1/2 second or so, and tapers to very little as the caps charge. > 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. These are SSR-40DA's, and the spec sheet I'm looking at makes no reference to that, only the maximum "durated" current, which as I read the chinglish translation means 1 cycle duration. I doubt if they'll ever see 10% of that. That doesn't sound appetizing in view of the hard switch the relay would make. So scrub that. > > 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. Well, with better charge-pump-detectors, what I have after adding those dual 5k r's across each cap bank, which is working fairly well, if a second or so slow, right now. Off time back to 40 volts is 4 minutes even, and is down to 7 volts in about 25 minutes. I got tired of resetting the meter because it was timing out and shutting down. It was working, and I had taken measurements and sawed off a 4" piece of white 1.25" PVC that I am going to bore out to about 1.53" for about 3/4" on one end for a tight friction fit on the exhaust snout of the sander, and turn the OD down to around 1.33" for about an inch on the other end, which will serve as the adaptor to hook it up to a vac for dust collection. Where I am right now on these chest lids is a need to be able to run an RO sander wet because it has 2000 grit wet-r-dry paper on it, and dry its plugged and junk in 5 seconds when its being used to level finish preparatory to air brushing a final coat of teak oil on it. To recap, this is working well enough, and with minimumly developed heat that I believe I'll quit trying to build a better mousetrap to do this. Thanks John. Now I'll have spare parts for the next project. :) 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
