On Thursday 04 September 2014 12:08:45 John Kasunich did opine And Gene did reply: > On Thu, Sep 4, 2014, at 11:15 AM, Gene Heskett wrote: > > pieces of wood to hold a pair of huge 15k uf, 60 volt Sangamo > > capacitors in a power supply I'm building for the lathe motor > > > > I don't trust the 140 > > volt surge ratings of the smaller 100 volt caps > > With this > > transformer, those 100 volt caps have a no signal voltage of 113 > > volts. > > > > I'll put 7 watt night light lamps > > across them for charge equality and power down bleeders. > > Be very carefull using light bulbs as balancing resistors. They have a > resistance vs temperature curve that can bite you. You can get in a > situation where one bulb has a bit less voltage across it than the > other. The one with less voltage dissipates less power, it cools down > and the other one heats up. Its resistance drops and the other one > increased. That results in even less voltage across the cool bulb, and > more across the hot bulb. The cool one gets even cooler. Depending > on the exact characteristics of the bulbs and the total applied > voltage, you can wind up with a 2:1 or bigger difference in voltage. > > I would dig in my scrap boxes for real resistors if I was you.
You're absolutely right John. But 99.99% of my resistors are puny power, 1/4 watt and less. And because the time related failure of bulk carbon in that resistor range, related to folks commonly exceeding the rated voltage, regardless of the wattage being plumb safe, they will not be carbon. So I'll have to find a pair of 10 watt wirewound's in the 5k-10k range. I hate to admit it, but you headed me off at the pass on that one, and I needed it. Might even have to go raid the old NTSC tx site. The shack of course has nothing remotely close, so I got a 10 pack of 5k 10 watters that will burn about 1.5 watts each from PartsExpress. Along with half a pound of the new 4% silver, lead free solder since my spools of 15 year old GC 3% silver lead/tin are just about ~30~. So it will be 3 or 4 days, in the meantime I can finish the mountings for the big 15k uf x 60 WV Sangamo's. Gotta figure out a way to put some pressure on the mount caps, s/b fun since they made from MDF. Thanks John. 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> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
