Phil Allison wrote:> ** Even that is NOT an issue. > > Compared to two, good quality, long life electros.I agree, same conclusion on my end. Other parameters are stellar as well. Best regards, Piotr
Film capacitor as power-supply filter
Started by ●October 7, 2019
Reply by ●October 20, 20192019-10-20
Reply by ●October 20, 20192019-10-20
Steve Wilson wrote: ------------------------> jlarkin@highlandsniptechnology.com wrote: > > > Unless a part is very expensive, may as well test it to destruction. >** JL has no empathy for small components. Few EEs do.> Be careful doing that with electrolytics. The process of generating Al2O3 > gives off hydrogen gas: > > 2Al + 3H2O --> Al2O3 + 3H2 (Gas) + 3e > > At high rates this can exceed the capacity of the capacitor to reabsorb and > the hydrogen is released outside the capacitor. If the cap is in an enclosed > space, a dangerous buildup of hydrogen gas can provide the basis for an > explosion. >** Crikey....> A second problem is high current can cause heating which can boil the water > in the electrolyte. The buildup of steam can rupture the case and result in > an explosion. >** Nah - just a cloud of white, smelly mist.> I had the unfortunate experience of an electrolytic explosion once. The cap > was failing but I didn't know about it since the unit was in its case. When > the cap blew, it left a dent in the 1/16 inch lid that clearly outlined the > top of the capacitor. The inside of the unit was a mess of electrolyte and > shredded aluminum foil. >** Seen that once or twice.> This was in the old days when the electrolyte was liquid and would > slosh around when shaken.** Huh ?? Doubt that is true.> But don't underestimate the power > of a steam explosion, and beware of caps that start to get hot.** Of course, that is why all electros have a pressure relief mechanism. The plus lead plug can burst out, there are break away groves in the bottom of radial types and large cans have a plugged hole on top. FYI: One time, despite my strong advice, a customer refused to let me re-cap his 1906s Fender tube amp saying his available funds did not allow for that. Two weeks later, while playing on stage, one of the HV electros puked its insides outside - covering the area around his amp with a thick fog. Folk in the audience thought it was part of the show ... All new electros were fitted the next week, with a promise to me never to doubt my warnings again. ...... Phil
Reply by ●October 20, 20192019-10-20
Phil Allison wrote:> Film caps have plenty of overvoltage capacityCapacity is one thing, its guaranteed specification is another. For example, those: https://www.vishay.com/docs/26015/mkp1848cdclink.pdf can withstand 1.5V_NOM for 10s. This is his 150% stress. One can safely design for this overvoltage, not just rely on some built-in safety margin. If 900V nominal weren't enough, OTOH... Best regards, Piotr
Reply by ●October 20, 20192019-10-20
Bill Sloman wrote:> IIRR Mathcad and Scicad can do it too.Why not Octave (free) or Matlab (better)? It can plot, it can solve differential equations, it can compute FFT... It is may favourite program for magnetics design if FEM-level modelling is not needed. Best regards, Piotr
Reply by ●October 20, 20192019-10-20
Piotr Wyderski wrote: --------------------> Phil Allison wrote: > > > > Film caps have plenty of overvoltage capacity >** Really don't think I wrote that and it sure ain't my opinion. I treat polys with some caution, especially in regards to AC voltage capacity. The data sheets lie, polyester and polycarbonate types blow up. Supply frequency AC kills them, due to internal corona. High frequency AC (say 10kHz ) sets polyester types on fire. You can make a 100nF Green Cap smoke and explode with a 40W bench amplifier and a series inductor of a few mH operating at resonance. Good cheap fun. .... Phil
Reply by ●October 20, 20192019-10-20
On Sat, 19 Oct 2019 20:10:27 -0700, jlarkin wrote:> Unless a part is very expensive, may as well test it to destruction. > > With some parts, the first indication of impending breakdown is failure. > > https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?dl=0 > > https://www.dropbox.com/s/gpc169hj1ilp6xa/photo01x_exploded_resistors.jpg?dl=0 Nowadays you're supposed to warn people before showing distressing images like those, given the number of snowflakes there are these days. If you've been emotionally affected by clicking on the above links, you can find support here: http://www.im-in-crisis.org/ There. That's the proper way. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
Reply by ●October 20, 20192019-10-20
Cursitor Doom wrote: --------------------> > > jlarkin wrote: > > > > Unless a part is very expensive, may as well test it to destruction. > > > > With some parts, the first indication of impending breakdown is failure. > > > > https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?dl=0 > > > > https://www.dropbox.com/s/gpc169hj1ilp6xa/ > photo01x_exploded_resistors.jpg?dl=0 >----------------------------------> > Nowadays you're supposed to warn people before showing distressing images > like those, given the number of snowflakes there are these days. >** OK - that's cute & funny.> If you've been emotionally affected by clicking on the above links, you > can find support here: http://www.im-in-crisis.org/** But that's not a bit funny. .... Phil
Reply by ●October 20, 20192019-10-20
On Sun, 20 Oct 2019 07:44:01 -0000 (UTC), Steve Wilson <no@spam.com> wrote:>jlarkin@highlandsniptechnology.com wrote: > >> Unless a part is very expensive, may as well test it to destruction. > >Be careful doing that with electrolytics. The process of generating Al2O3 >gives off hydrogen gas: > >2Al + 3H2O --> Al2O3 + 3H2 (Gas) + 3e > >At high rates this can exceed the capacity of the capacitor to reabsorb and >the hydrogen is released outside the capacitor. If the cap is in an enclosed >space, a dangerous buildup of hydrogen gas can provide the basis for an >explosion.Conservation of energy says that the explosion won't liberate more joules than I pushed into the cap. None of my bench supplies can deliver explosive amounts of energy in any reasonable time. My cap test used a wonderful old HP 6212A power supply with the current limit set to maybe 10 mA. The cap never got warm. https://www.dropbox.com/s/arbdkg6gocbpd66/HP6212A.JPG?raw=1 I never worry about stuff like that. So far so good. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 20, 20192019-10-20
On Sun, 20 Oct 2019 11:04:51 -0000 (UTC), Cursitor Doom <curd@notformail.com> wrote:>On Sat, 19 Oct 2019 20:10:27 -0700, jlarkin wrote: > >> Unless a part is very expensive, may as well test it to destruction. >> >> With some parts, the first indication of impending breakdown is failure. >> >> https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?dl=0 >> >> https://www.dropbox.com/s/gpc169hj1ilp6xa/ >photo01x_exploded_resistors.jpg?dl=0That resistor pic is actually by Win, but he used my exploder machine.> >Nowadays you're supposed to warn people before showing distressing images >like those, given the number of snowflakes there are these days. > >If you've been emotionally affected by clicking on the above links, you >can find support here: http://www.im-in-crisis.org/Linked to from Im-a-sad-wuss.myomy> >There. That's the proper way.Have a good cry and move on. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 20, 20192019-10-20
On Sun, 20 Oct 2019 08:13:17 -0700, jlarkin wrote:> Conservation of energy says that the explosion won't liberate more > joules than I pushed into the cap. None of my bench supplies can deliver > explosive amounts of energy in any reasonable time.Then just use a car battery. Or better yet a 24V truck battery. :-> -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
