On Monday 07 December 2015 03:24:21 Marcus Bowman wrote: > On 7 Dec 2015, at 03:57, Rafael wrote: > > On 12/06/2015 07:25 PM, Gene Heskett wrote: > >> Greetings all; > >> > >> Before tv's lost their crt's, there was a component in the power > >> inlet circuit that had a very high negative temp coefficient, which > >> was used to create a high voltage drop when it was cold, which in > >> turn forced the first few seconds of its power draw after being > >> turned on, thru the degaussing coils wrapped around the crt in > >> order to demagnetise it. > >> > >> That voltage drop heated it, and it got hot enough to get down to > >> just a couple of ohms, which was not enough to overcome the MOV in > >> series with the coils. This also allowed the tv itself to be > >> soft-started, and it worked so well that it was often the major > >> part failure in the tv for the first 3 or 4 years. > >> > >> About 3 or 4 of those, wired in parallel, would also serve as an > >> inrush limiter when I turn on the power supply for my G0704 mill. > >> But the parts houses we had locally have all evaporated. I just > >> checked a couple surplus places without finding any of those > >> critters. > >> > >> Does anyone have a suggestion as to where a small handfull of these > >> could be sourced? Usually bare, they look like a graphite quarter > >> coin with a lead wire soldered to the middle of a silver plated dot > >> in the middle of each face. Usually slightly thicker than a > >> 'merican quarter. > > > > I think you are looking for NTC (Negative Temperature Coefficient). > > Search brings back numerous links to choose from. However, there are > > better solutions but cost a bit more of course. > > > > Here is an excellent article/solution I found searching for "inrush > > current limiter": > > http://www.edn.com/design/analog/4316203/Simple-and-effective-inrush > >-current-limiter-stops-surges > > > > Circuit is simple enough to implement it on a generic experimental > > board. > > > >> When I was setting up the mill, and building that supply, I had > >> wired up a 4 plex on the wall behind it, putting it by itself on a > >> 20 amp breaker. Turning it on, trips the 20 instantly as the motor > >> supply has a huge amount of microfarads, probably in excess of > >> 80,000 uf, mainly because that was the size of the caps I could > >> source, NOS, locally by the fine old art of horse trading. > > > > One variation of the above circuit could have a resistor/relay on > > the large capacitors side to limit the inrush current then short the > > resistor when they are at 70%+ voltage. > > That's similar to the PSU I built. It uses a pull-in relay (if that's > the right term) which only latches once the supply has come up to > voltage. The inrush current heats a metal-cased resistor and a > thermistor senses the heat. The resistor limits the inrush to the > capacitor. Once it has charged, the relay latches on. It only takes a > second, but its enough to give an effective soft-start. The PSU runs > 79volts at 40 amps, and uses two large toroidal transformers, powering > a pair of steppers off each. The specs are complete overkill. The > start-up current is only the holding torque of the size 42 steppers > when the machine is stationary. The spindle motor is completely > separate and has its own electronics and PSU, so that's not part of > the equation. It only runs 2kW, so is not a problem. Soft-start there > too, and electronic speed control, but a manufacturer-supplied control > circuit. > > Marcus
I did not put any cooling fans in this one, and it also warms up in use, but the major heat source is those 4 toroids that make up the spindle supply. Those are stacks of 2 in the pix at sublink "GO704-pix/inside-of-electronics-box.jpg" So while I am at it, I'll put a line powered rotron style fan in it to move some air around those toroids. The stepper drivers are arranged such that the stepper supply fans, when they come on, are cooled by the outflow from the stepper psu's. Pix of that as it was being built are on my web page. That night light was to serve as a bleeder when it was powered down, but failed I assume while I was doing some rigid tapping as Jon's PWN Servo amplifier is a full 4 quadrant controller, and recovers the energy from the motor when its doing a reversal, driving the normal 126 volts no load voltage up to around 150 as it does the slowdown phase of reversing that 1HP motor. Thats at or slightly above the surge voltage rating of the capacitor bank hidden under the PCB bus bars to the right of the toroids in the above pix. The active link is to GO704-pix, which I thought was in my sig, but its under 'More recent stuff is "here"' on the front page. Now I think I have the link in the sig fixed. I'll revert that in a few days. Pix of that shop-made cyclone dust separator are also there. The entry line going in the top, projects downward to about 3" below the sides tangent entry. Even the fine sand from machining the ebony is caught, very little of it ever making it into the bucket-max to clog its filter. That has already saved me 10x its cost in filters not replaced as I dumped 4 or 5 inches of caught debris out of the cyclones bucket 2 times already, and it currently has about 1/4" of ebony sand in it. See thru buckets would be nice. :) 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/GO704-pix/> ------------------------------------------------------------------------------ Go from Idea to Many App Stores Faster with Intel(R) XDK Give your users amazing mobile app experiences with Intel(R) XDK. Use one codebase in this all-in-one HTML5 development environment. Design, debug & build mobile apps & 2D/3D high-impact games for multiple OSs. http://pubads.g.doubleclick.net/gampad/clk?id=254741911&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
