On Wed, 29 Jun 2022 19:36:21 -0700, jlarkin@highlandsniptechnology.com wrote:>On Wed, 29 Jun 2022 18:14:22 -0400, legg <legg@nospam.magma.ca> wrote: > >>Anyways, wade through it and you may come up with >>something like this: >> >>http://ve3ute.ca/query/Polycarbonate_Current_100KHz_Philips.pdf >> >>It will be different for each dielectric, frequency of operation, >>temperature etc. >> >>RL > >Gosh, real numbers. Thanks. > >I just got this. It's a high voltage half-bridge test board for frying >inductors and film caps. People were doing another proto board so I >hung this on the end as a v-score breakaway. > >https://www.dropbox.com/s/2x8z6yn29ab57xf/Z524_Wing_1.jpg?raw=1One good way of frying film caps is to thermally couple them to hot chokes or power resistors. Like a lot of other parts, they depend on thermal conduction to the PCB. RL
Inverters vs wallwarts
Started by ●June 24, 2022
Reply by ●June 30, 20222022-06-30
Reply by ●June 30, 20222022-06-30
On Thu, 30 Jun 2022 09:25:24 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Clifford Heath wrote: >> On 30/6/22 05:38, Phil Hobbs wrote: >>> Even in an inviscid, incompressible fluid, the equations aren't all >>> that simple.� Forced-air cooling of macroscopic systems runs at some >>> huge and highly variable Reynolds number, depending on where you are. >> >> Pretty sure that Reynolds number cannot be defined for an inviscid >> liquid. But yeah, turbulent flows are difficult however you look at them. > >My point exactly. > >Cheers > >Phil HobbsSure. But is my plate 0.2 k/w, or is it 20 k/w?
Reply by ●June 30, 20222022-06-30
On Thu, 30 Jun 2022 09:51:22 -0400, legg <legg@nospam.magma.ca> wrote:>On Wed, 29 Jun 2022 19:36:21 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>On Wed, 29 Jun 2022 18:14:22 -0400, legg <legg@nospam.magma.ca> wrote: >> >>>Anyways, wade through it and you may come up with >>>something like this: >>> >>>http://ve3ute.ca/query/Polycarbonate_Current_100KHz_Philips.pdf >>> >>>It will be different for each dielectric, frequency of operation, >>>temperature etc. >>> >>>RL >> >>Gosh, real numbers. Thanks. >> >>I just got this. It's a high voltage half-bridge test board for frying >>inductors and film caps. People were doing another proto board so I >>hung this on the end as a v-score breakaway. >> >>https://www.dropbox.com/s/2x8z6yn29ab57xf/Z524_Wing_1.jpg?raw=1 > >One good way of frying film caps is to thermally couple them >to hot chokes or power resistors.That's inelegant. I plan to pump in amps of 250 KHz triangle wave.> >Like a lot of other parts, they depend on thermal conduction >to the PCB.We will have a lot of forced air flow, at least 200 f/m acoss both sides of our plugin boards. That will reduce cap temp rise by at least a factor of 2. Power resistor data sheets sometimes mention power vs air flow. I have seen suggestions of between 2:1 and 10:1 more power with air flow. I'll fire up the board and pump amps into various 4.7u radial film caps, blow some air on them, and measure temps. What else is a boy to do? I should try to evaluate how much cooling we might get through the leads. We could use big power pours on the pins to slurp out some heat. My first guess is that lead cooling will be minor.
Reply by ●June 30, 20222022-06-30
jlarkin@highlandsniptechnology.com wrote:> On Thu, 30 Jun 2022 09:25:24 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Clifford Heath wrote: >>> On 30/6/22 05:38, Phil Hobbs wrote: >>>> Even in an inviscid, incompressible fluid, the equations aren't all >>>> that simple. Forced-air cooling of macroscopic systems runs at some >>>> huge and highly variable Reynolds number, depending on where you are. >>> >>> Pretty sure that Reynolds number cannot be defined for an inviscid >>> liquid. But yeah, turbulent flows are difficult however you look at them. >> >> My point exactly.> > Sure. But is my plate 0.2 k/w, or is it 20 k/w? >A zero-order approximation would be to assume that the boundary layer is ~5 mm thick, and the plate behaves like still air of that thickness connected to an infinite heat sink at the outlet temperature. You can compute the outlet temperature using the mass flow rate, heat capacity of air, inlet temperature, and power dissipation. I'd expect things to improve faster than linearly with flow rate, because the boundary layer should thin down as well as the outlet temperature falling. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●June 30, 20222022-06-30
jlarkin@highlandsniptechnology.com wrote:> On Thu, 30 Jun 2022 09:51:22 -0400, legg <legg@nospam.magma.ca> wrote: > >> On Wed, 29 Jun 2022 19:36:21 -0700, jlarkin@highlandsniptechnology.com >> wrote: >> >>> On Wed, 29 Jun 2022 18:14:22 -0400, legg <legg@nospam.magma.ca> wrote: >>> >>>> Anyways, wade through it and you may come up with >>>> something like this: >>>> >>>> http://ve3ute.ca/query/Polycarbonate_Current_100KHz_Philips.pdf >>>> >>>> It will be different for each dielectric, frequency of operation, >>>> temperature etc. >>>> >>>> RL >>> >>> Gosh, real numbers. Thanks. >>> >>> I just got this. It's a high voltage half-bridge test board for frying >>> inductors and film caps. People were doing another proto board so I >>> hung this on the end as a v-score breakaway. >>> >>> https://www.dropbox.com/s/2x8z6yn29ab57xf/Z524_Wing_1.jpg?raw=1 >> >> One good way of frying film caps is to thermally couple them >> to hot chokes or power resistors. > > That's inelegant. I plan to pump in amps of 250 KHz triangle wave. > >> >> Like a lot of other parts, they depend on thermal conduction >> to the PCB. > > We will have a lot of forced air flow, at least 200 f/m acoss both > sides of our plugin boards. That will reduce cap temp rise by at least > a factor of 2. > > Power resistor data sheets sometimes mention power vs air flow. I have > seen suggestions of between 2:1 and 10:1 more power with air flow. > > I'll fire up the board and pump amps into various 4.7u radial film > caps, blow some air on them, and measure temps. What else is a boy to > do? > > I should try to evaluate how much cooling we might get through the > leads. We could use big power pours on the pins to slurp out some > heat. My first guess is that lead cooling will be minor. > > >Film and foil caps work a lot better for that sort of use than metallized-film ones. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●June 30, 20222022-06-30
On Thu, 30 Jun 2022 14:52:03 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>jlarkin@highlandsniptechnology.com wrote: >> On Thu, 30 Jun 2022 09:25:24 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Clifford Heath wrote: >>>> On 30/6/22 05:38, Phil Hobbs wrote: >>>>> Even in an inviscid, incompressible fluid, the equations aren't all >>>>> that simple.� Forced-air cooling of macroscopic systems runs at some >>>>> huge and highly variable Reynolds number, depending on where you are. >>>> >>>> Pretty sure that Reynolds number cannot be defined for an inviscid >>>> liquid. But yeah, turbulent flows are difficult however you look at them. >>> >>> My point exactly. > >> >> Sure. But is my plate 0.2 k/w, or is it 20 k/w? >> > >A zero-order approximation would be to assume that the boundary layer is >~5 mm thick, and the plate behaves like still air of that thickness >connected to an infinite heat sink at the outlet temperature. > >You can compute the outlet temperature using the mass flow rate, heat >capacity of air, inlet temperature, and power dissipation. > >I'd expect things to improve faster than linearly with flow rate, >because the boundary layer should thin down as well as the outlet >temperature falling. > >Cheers > >Phil HobbsOn that basis, with 200 ft/min flowing across both sides of my 4" square plate, I get just around 1 K/W. Sounds optimistic, but I'll try it.
