On Thursday 31 December 2015 13:10:01 Gene Heskett wrote: > On Monday 14 December 2015 14:54:54 Gene Heskett wrote: > > On Sunday 13 December 2015 16:39:16 andy pugh wrote: > > > On 13 December 2015 at 11:01, Gene Heskett <[email protected]> wrote: > > > >> Feed the cap bank through a resistor. > > > >> Use a (cheap $5) solid state relay to bypass that resistor when > > > >> LinuxCNC is turned on. > > > > > > > > I had largely discounted that idea because the first cycle surge > > > > is likely high enough to fuse a 40 amp Crydom. It trips a 20 amp > > > > service breaker instantly when its master switch is closed. That > > > > would also be complicated by needing a high side drive for it. > > > > > > The relay won't see the surge, because what the relay does is > > > bypass the surge absorbing resistor. > > > > > > The relay would go on the AC input side, so you would only need > > > one. > > > > > > You don't need a "high side driver", you need a 5V signal from > > > LinuxCNC. > > > > I got that grokked finally Andy, so I just ordered 4 of them, 40 a, > > 480 volt from MPJones, a tad over a $50 bill by USPS. Now to find a > > pair of uncommitted BoB pins. I'll keep one for a spare, but the > > third one will replace the ice cube I am controlling the vacuum > > cleaner with. I'll use one to switch the line, one to bypass the > > resistor in a few seconds, and one to switch the vacuum. > > > > Cheers, Gene Heskett > > Progress report of sorts. I gave up trying to find the correct baseing > for the 2n2222a's I had so I drove up to Bridgeport and stopped at our > surviving radio shack and made the usual comments about the place > looking like a good place to open a radio shack, heck, even the sign > on the front door looks good. Wandered back to where they had moved > the parts drawers, and lo, and behold even, their zero fill was at > work, so there was a bag of assorted small signal npn transistors > which I transferred to my hand, and over in another drawer was some > IRF511's, so I emptied that divider too, coming home with 2 of those, > all for less than 9 bucks. > > So this morning, I rip out the 2n2222a wireing and bugs, and wire up > the IRF511's (yeah, its 5000x overkill, but that is what Rome had). I > had originally thought I should be using Schottky diodes for the > rectifiers, and I am borderline right, it works as long as the > function generator is making 4.85 volts p-p or more, but drops out at > about 4.7 volts. These things need about +3.75 on the gate to begin to > turn them on. I have 1n914's in there now, si types, but the Schottky > ought to make it work at 4 volts p-p. > > However the teeny psu is making around 36 volts, so the SSR's are > getting 35+ when the p-p is 5 volts or more, and thats above the rated > 32 volt input voltage. So, do I halve the voltage by moving the > tranny lead to only use half its 25.2, or is this within the ratings > of one of these Chinese 40 amp Crydom look-a-likes? > > According to the curves, that would raise the threshold voltage to > turn on by a few millivolts and I'd probably need the Schottky's to > work well. Or I'd have to up the load r on the cF capacitor, currently > 1 megohm now. Shutoff time is a bit quicker than on time. > > I left it running with one of them on, but no loading, and if in an > hour, the red led on the SSR is still on, I believe I'll wire it into > the psu later this afternoon. The hal file is already fixed to run it. > > Cheers, Gene Heskett
Actually as I stood up to go back to the garage, I spotted a box that I knew had one more buck regulator in it, so I put that in and adjusted it for 25 volts. It still works if the p-p is 5.00 volts but starts to fade at 4.9. Next is to wire it to get power when the main switch is turned on, meaning I need to add a neutral to it, NBD. Traffic here is holiday slow, so I guess I'll get to it. Happy New Year everybody! 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> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
