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 >> >> So, while it draws less than 3 amps with the spindle motor off, and could >> reach 18 if the motor was in a LR state, but it takes a 30 amp breaker >> to withstand the in-rush. If I could find some of these critters, >> building them into that motor supply, I could put the 20 amp breaker >> back in and it wouldn't be quite so ill eagle if an inspector looked it >> over. >> >> Cheers, Gene Heskett >> > > Greetings from the left coast. > > -- > Rafael > > ------------------------------------------------------------------------------ > 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 > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
