On Thursday, April 07, 2011 10:27:37 AM Erik Christiansen did opine: > On Thu, Apr 07, 2011 at 08:10:55AM -0400, gene heskett wrote: > > An additional thought comes to mind when using them for something like > > my A3877 based xylotex setup, an extended time at low voltage is not > > recommended as it causes more heat in the A3977's than the normal > > voltage, so its possible it could actually increase the 'turnon' > > failure rate of such devices if its too slow to warm up. > > Gene, you're beginning to convince me there's no such thing as a free > lunch, and I'd be just as well off going back to my MOSFET idea, which > leaves a fat (low value) power resistor in series for enough mains > cycles to charge the capacitor bank, then shunt it with about 5 > milliohms of drain resistance. (In addition to your favourite source, I > have a tube of 'em waiting to serve man and country. And what's in the > junkbox is kinda prone to being designed in.) > > Since we only need enough resistance to limit a whacking great inrush > current, that'll bring up the supply for the control electronics within > a few mains cycles. I think we'd take a few breaths before starting the > gcode program and firing up the motors. If the MOSFET is hard on within > a few hundred milliseconds, then I'd hope stuff like your A3977's would > be fine, especially since they'd be idling at the time. > > I think drives have to provide their own current limiting once we have > lift-off. (And they generally do.) > > Erik
Well, I'm probably playing chicken little here when I mentioned it as I suspect even the NTC will allow the output of my supply to exceed the 12 volt minimum for the A3977's within one full cycle of the powerline, or 16.33333 milliseconds. If I had a problem with the inrush I'd consider them, but a simple little alps mini-switch has been working as its power switch for a good 3 or 4 years now. Mounted in a shack mini project box right in the line cord. Like you, whats in my junkbox tends to be what gets designed in. ;-) -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) <http://tinyurl.com/ddg5bz> <http://www.cantrip.org/gatto.html> Q: How many mathematicians does it take to screw in a light bulb? A: One. He gives it to six Californians, thereby reducing the problem to the earlier joke. ------------------------------------------------------------------------------ Xperia(TM) PLAY It's a major breakthrough. An authentic gaming smartphone on the nation's most reliable network. And it wants your games. http://p.sf.net/sfu/verizon-sfdev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
