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. > > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
