On Friday 07 March 2014 12:29:38 Grant Edwards did opine: > On 2014-03-07, William Ray Wing <w...@mac.com> wrote: > > On Mar 6, 2014, at 8:24 PM, Roy Smith <r...@panix.com> wrote: > >>> I spotted a device on the table of the company calibration office... > >>> > >>> As I recall, it was a 100A capable resistor... 0.10 OHM. > >>> > >>> No idea what it was meant for; big binding posts at one end, and a > >>> slab of sheet steel in a "W" shape (smooth curves, not sharp bends). > >> > >> External shunt for an ammeter? > > > > More likely a dummy load for power supply testing. > > Could be. Back when I was working on PWM controllers for golf cart > and small car motors, we used to use steel coathangers for test loads, > but once they got past orange and more towards yellow, they started to > get too soft. An appropriately dimensioned chunk of sheet steel would > have been ideal. > > > (Normally, ammeter shunts are sized to dissipate as little power as > > possible.) > > I've used chunks of coathanger for that too, but I don't think the > resistance was stable enough over temperature to trust the results at > higher currents.
This is really really offtopic but since its turned into war stories, I recall one time that I needed to test a 5v 200amp supply that there were 2 of in an old NEC Digital Video Effects unit, I looked up the R per 1000' of standard romex in the various gauges & went over the Lowes and bought a 100' roll of of 10/2. Soldered the inside end together after striping and twisting it together, It worked well, but the PSU didn't. Made by HP back when they _thought_ they knew about how to build cement block sized power supplies. The psu went into foldback at about 20 amps. All the bugs were good, nothing running warm. Analyzing backwards in view of the curie point on some ferrite's being below the boiling point of water, I finally came to the conclusion that the ferrite in the output transformer had gone austenitic, eg totally non-magnetic, like it was just so much air, which is what many of those compounds will do if magnetized near saturation when they hit the curie point, and will never recover from. HP of course didn't have the transformer or a replacement supply, but I found some Pioneer's with a suitable rating at M.P.Jones in FL and broke their hands putting a check for 2 of them in them, shipped yesterday. That was in about 1997 & they were still in service when we turned analog tv off June 30, 2008. 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) Genes Web page <http://geneslinuxbox.net:6309/gene> NOTICE: Will pay 100 USD for an HP-4815A defective but complete probe assembly. -- https://mail.python.org/mailman/listinfo/python-list
