Input rectifier cap
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From: Michael A. Terrell on 9 Jun 2010 13:25 Jim Thompson wrote: > > On Wed, 09 Jun 2010 12:27:34 -0400, Hammy <spam(a)spam.com> wrote: > > [snip] > > > >Christ what's it for an industrial egg friar. ;-) > > > [snip] > > "egg friar"? Depends on whether he's wearing his habit, or not ;-) That must be one of those weird European cults. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: Grant on 9 Jun 2010 17:48 On Wed, 09 Jun 2010 12:27:34 -0400, Hammy <spam(a)spam.com> wrote: >On Thu, 10 Jun 2010 01:05:03 +1000, Grant <omg(a)grrr.id.au> wrote: > > >>>There's no way that the commercial SMPS's I've looked at are using the >>>105C rms rateing to select the input cap. Most I've taken apart have >>>either one cap or two in series for a switch doubler including the >>>350W SMPS powering my computer. They must be increasing the rms >>>handling capability of a cap based on a reduced operating temperature >>>then the 105C specified in the datasheet. >> >>A lot of them only want 12 months life -- don't care what happens after >>warranty expires :( > >Mine has been going for 8yrs now. I doubt it could deliver 350W >continuous power. > >I also noticed with mine when cleaning it , it has no Common mode >choke!! This explained why a TV operating off the same line would get >snowy when the PC was on simultaneously. Oddly enough it has all these >regulatory approval stickers and it's a Antec supposedly. > >>>Basso's book mentions a multiplier for determining max rms current for >>>reduced operating temperature. I've looked at several datasheets for >>>caps and haven't seen one. Is there a rule of thumb? Also is there a >>>reasonable estimate for including the converters high frequency rms >>>contribution to the capacitor? >> >>Odd you don't have datasheet numbers for this, it was on datasheets >>I looked at a few weeks ago. Look for a table of multipliers buried >>in the details, the tables are small, perhaps easy to miss? > >Your right it is there. I can double the rms current for 70C ambient. >I always thought the 105C specification was for core temperature not >ambient. I have been grossly derateing my caps! Oh well live and >learn. :-) > >>An example. Recently I worked through ripple current adjusted for >>both temp. and frequency for two different brands of caps and the >>multipliers are a little different. These are 85'C caps. >> >>I built a bank of caps for about 600A ripple current for <45'C, but >>it's down to about 350A at 85'C (~500A at 60), bank is 20 x 10mF/50 >>plus 60 x 4700/50. > >Christ what's it for an industrial egg friar. ;-) A small Splat! (stored energy) welder, only ~25 Ws max. Built for occasional use with the cheapest caps I could find ;) Yet to make the power dump switch, I'm thinking 16 x 75A MOSFETs in parallel might survive the experience, otherwise I could play safe and use a big stud mounted SCR I got in a box here. Grant. > >>First brand is 1.73x < 45'C and 1.5x at 60'C, second is 1.55x <45'C >>and 1.30x at 60'c (both 1.0x at 85'C). >> >>Multipliers for frequency varied more, first is 1.08x for 10kHz, >>second is 1.20x for 10kHz (both 1.0x at 120Hz). >> >>Grant. -- http://bugs.id.au/
From: Phil Allison on 9 Jun 2010 20:52 "Hammy the Halfwit " > > If I calculated a 120Hz, 1.3Arms ripple current for an input rectifier > cap for a flyback, how could I calculate the core temp based on a > given maximum ambient temperature (50C)? ** Look at the data. > I'm interested in using one Panasonic 270uf 105C cap rated at 1.42 > Arms @120Hz. > > http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=EETED2E271BA ** The ripple current data for lower ambients is in the table on page 1 of the pdf - it doubles at 70C . But a 3000 hour life is no good to anyone - so the usual practice is to use the rated rms ripple for 105C and keep the ambient down to no more than 65C. With just a bit of luck, the electro will then outlast the equipment. ..... Phil
From: Phil Allison on 9 Jun 2010 21:01 "MooseFET" > > Things can be extra ugly when you have a mixture of high frequency > and low frequency ripple. Many capacitor makers specify the ripple > current at each. What I usually do is make sure never to exceed the > 100% mark when I add the percentages of each that I have. > > If you add a few ceramics to the design, you can have the ESR and ESL > keep the high frequency stuff mostly out of the big guys. > ** HUH ?????? The impedance of a high voltage ceramic cap is waaaaayy more than an electro at SMPS frequencies. ..... Phil
From: Grant on 9 Jun 2010 21:23
On Wed, 9 Jun 2010 07:41:40 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 9, 9:16 pm, Hammy <s...(a)spam.com> wrote: >> If I calculated a 120Hz, 1.3Arms ripple current for an input rectifier >> cap for a flyback, how could I calculate the core temp based on a >> given maximum ambient temperature (50C)? >> >> I'm interested in using one Panasonic 270uf 105C cap rated at 1.42 >> Arms @120Hz. >> >> http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keyword... >> >> There's no way that the commercial SMPS's I've looked at are using the >> 105C rms rateing to select the input cap. Most I've taken apart have >> either one cap or two in series for a switch doubler including the >> 350W SMPS powering my computer. They must be increasing the rms >> handling capability of a cap based on a reduced operating temperature >> then the 105C specified in the datasheet. >> >> Basso's book mentions a multiplier for determining max rms current for >> reduced operating temperature. I've looked at several datasheets for >> caps and haven't seen one. Is there a rule of thumb? Also is there a >> reasonable estimate for including the converters high frequency rms >> contribution to the capacitor? > >Things can be extra ugly when you have a mixture of high frequency >and low frequency ripple. Many capacitor makers specify the ripple >current at each. What I usually do is make sure never to exceed the >100% mark when I add the percentages of each that I have. > >If you add a few ceramics to the design, you can have the ESR and ESL >keep the high frequency stuff mostly out of the big guys. > >Remember that the heat flows are nearly linear in the case of a >capacitor >on a PCB. The RMS current and the ESR mostly make the heat. You lumping in the tan whatever losses with ESR? Likely be an issue for me soon, so I plan to put temperature probes in a capacitor bank to derate or shutdown at high temperature -- besides, I'm curious... Grant. -- http://bugs.id.au/ |