Input rectifier cap
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From: MooseFET on 9 Jun 2010 22:24 On Jun 10, 9:23 am, Grant <o...(a)grrr.id.au> wrote: > On Wed, 9 Jun 2010 07:41:40 -0700 (PDT), MooseFET <kensm...(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... Yes the ESR I am referring to is the one with the ideal capacitor in series with a resistor. > > Grant. > --http://bugs.id.au/
From: Hammy on 10 Jun 2010 14:00 On Thu, 10 Jun 2010 11:23:04 +1000, Grant <omg(a)grrr.id.au> wrote: >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. CORNELL DUBILIER has some Java calculators for calculateing lifetime based on ambient temp and ripple current. Its here for anyone who wants to try it. http://www.cde.com/calc/ The site seems a bit slow mainly when useing firefox. Has anyone else noticed CDE is slow. Here is an application note on how they calculate the values and how to use the tool. http://www.digikey.com/Web%20Export/Supplier%20Content/CDE_338/PDF/CDE_SelectingCaps.pdf I plugged in my ripple both 1.3Arms @ 120Hz and 0.8Arms @100kHz, for an inferior capacitor then the panasonic. The results were 0.44W dissapation, Avg core temp 63C Expected life hours 84,000 hr's!! In a max ambient of 50C, reasonable its only a 50W flyback no major heatsources and I'm mounting a small fan in the enclosure.
From: Joerg on 11 Jun 2010 12:02 Hammy wrote: > On Thu, 10 Jun 2010 11:23:04 +1000, Grant <omg(a)grrr.id.au> wrote: > > >> 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. > > > CORNELL DUBILIER has some Java calculators for calculateing lifetime > based on ambient temp and ripple current. Its here for anyone who > wants to try it. > > http://www.cde.com/calc/ > > The site seems a bit slow mainly when useing firefox. Has anyone else > noticed CDE is slow. > It isn't too slow here on Firefox. But the applets won't work even though I did enable Java and all that for this site :-( [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Grant on 11 Jun 2010 17:26 On Fri, 11 Jun 2010 09:02:07 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Hammy wrote: >> On Thu, 10 Jun 2010 11:23:04 +1000, Grant <omg(a)grrr.id.au> wrote: >> >> >>> 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. >> >> >> CORNELL DUBILIER has some Java calculators for calculateing lifetime >> based on ambient temp and ripple current. Its here for anyone who >> wants to try it. >> >> http://www.cde.com/calc/ >> >> The site seems a bit slow mainly when useing firefox. Has anyone else >> noticed CDE is slow. >> > >It isn't too slow here on Firefox. But the applets won't work even >though I did enable Java and all that for this site :-( Same here :( Download + reinstalled Java JRE for it too, no joy. Unless it wants the full Java development kit installed, I lost interest... Grant. -- http://bugs.id.au/
From: Hammy on 11 Jun 2010 18:27
On Sat, 12 Jun 2010 07:26:11 +1000, Grant <omg(a)grrr.id.au> wrote: >On Fri, 11 Jun 2010 09:02:07 -0700, Joerg <invalid(a)invalid.invalid> wrote: > >>Hammy wrote: >>> On Thu, 10 Jun 2010 11:23:04 +1000, Grant <omg(a)grrr.id.au> wrote: >>> >>> >>>> 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. >>> >>> >>> CORNELL DUBILIER has some Java calculators for calculateing lifetime >>> based on ambient temp and ripple current. Its here for anyone who >>> wants to try it. >>> >>> http://www.cde.com/calc/ >>> >>> The site seems a bit slow mainly when useing firefox. Has anyone else >>> noticed CDE is slow. >>> >> >>It isn't too slow here on Firefox. But the applets won't work even >>though I did enable Java and all that for this site :-( > >Same here :( Download + reinstalled Java JRE for it too, no joy. > >Unless it wants the full Java development kit installed, I lost interest... > >Grant. Yea I should have mentioned it doesn't work with Fire Fox. It does work with IE...... I know Blah :-) I found it handy even if I'm not using the caps they have loaded in the tool it gives you an idea quickly on any similar cap. Or if you couldn't be bothered the application note shows how they make the calculations and you can just do it up in Math CAD or excel. I have noticed the site doesn't seem Fire Fox friendly, even downloading data sheets is problematic. They claim the site is FF compatable. I'm sure they did rigorous testing after all CDE is a huge multimillion $ corporation. So the only logical conclusion is we are doing something wrong;-) |