Inverters vs wallwarts...

[Phil Allison]

Jan Panteltje wrote more rubbish:
--------------------------------------------------------

I did some back of the envelope calculation on (well actually I used wcalc)
how much the input elctrolytic in a 12 W (12 V 1 A) wallwart discharges
between mains periods with a bridge (so 10 mS here in 50 Hz land)
IIRC that was about 57 volt ripple! on that tiny cap (usually 4.7 uF / 400 V type).

** So 15% p-p ripple. ( 57/340)
Nothing odd about that.

> No wonder all those electrolytics fail .....

** Bullshit.

> Anybody measured the ripple?

** Why ?

An any case, most plug-pak supplies operate well below their max current ratings.
If electro caps fail early - it is due to internal temp rise only.

Plus the use of cheap as possible parts.



...... Phil

 

[Jan Panteltje]

On a sunny day (Tue, 28 Jun 2022 03:42:04 -0700 (PDT)) it happened Phil
Allison <pallison49@gmail.com> wrote in
<38a7b4bd-81b5-42d3-a9a9-de151a557414n@googlegroups.com>:

Jan Panteltje wrote more rubbish:
--------------------------------------------------------

I did some back of the envelope calculation on (well actually I used wcalc)
how much the input elctrolytic in a 12 W (12 V 1 A) wallwart discharges
between mains periods with a bridge (so 10 mS here in 50 Hz land)
IIRC that was about 57 volt ripple! on that tiny cap (usually 4.7 uF / 400 V type).


** So 15% p-p ripple. ( 57/340)
Nothing odd about that.

Well the same thing is specified from 110 V to 230 V AC
So double the current and the ripple AGAIN when used in a 110V world (ut 60 Hz is 5/6 * 10 mS so that helps.

No wonder all those electrolytics fail .....

** Bullshit.

Do not eat it! Live on a farm?

Anybody measured the ripple?

** Why ?

Why do humming beans exist? Why is water wet?


>An any case, most plug-pak supplies operate well below their max current ratings.

For example the raspberry supplies, when more things are plugged into the USB are maxed out
That is why I have now 2 USB hubs on the Pi4s each has its own supply.

>If electro caps fail early - it is due to internal temp rise only.

The elcos get hot because of the high ripple current creating heat and detoriation of the cap,
creating more heat ... a run-away process.



>Plus the use of cheap as possible parts.

Sure good electrolytics are expensive.
Bigger ones too -

 

[Phil Allison]

Jan Panteltje is a fucking IDIOT wrote:
=============================

** So 15% p-p ripple. ( 57/340)
Nothing odd about that.
Well the same thing is specified from 110 V to 230 V AC
So double the current and the ripple AGAIN when used in a 110V world (ut 60 Hz is 5/6 * 10 mS so that helps.
No wonder all those electrolytics fail .....

** Bullshit.

Do not eat it! Live on a farm?

** Fuck you - imbecile.

Anybody measured the ripple?

** Why ?

Why do humming beans exist?

** So you have no reason at all ? zzzzzzzzz...

An any case, most plug-pak supplies operate well below their max current ratings.

For example ....

** Yawwnnn - more false logic idiocy.

If electro caps fail early - it is due to internal temp rise only.

> The elcos get hot because of the high ripple current creating heat and detoriation of the cap,

** Not at 15% they fucking don\'t - you liar.

Plus the use of cheap as possible parts.

Sure good electrolytics are expensive.

** Yawwnnn - more false logic idiocy.

Scuse me while I vomit.


...... Phil

 

[legg]

On Tue, 28 Jun 2022 08:10:11 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 27 Jun 2022 09:42:08 -0400) it happened legg
legg@nospam.magma.ca> wrote in <mlbjbhp55bpidiekuu6pjjsk607695aths@4ax.com>:

On Sat, 25 Jun 2022 07:32:27 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Thanks for reading,

bob prohaska



I did some passive correction for off-the-shelf 60Hz linears in
the 80s. Best effects achieved using a saturable choke and
quasi-resonant capacitor, over a limited range of power levels
for any specific installation.

The parts are generally impractical for a hobbyist to get
ahold of, though restacking laminations from unvarnished scrap
is possible. Requires good VP Impregnation to silence the
final iteration.

The actual current phase angle shifted from leading to lagging
over the useful range. Output voltage into the 60Hz capacitive
load was flat-topped, affecting the low-line voltage performance.
The choke/cap combination supported the output difference
during line current reversal.

It\'s no good guessing what the current waveshape is; you\'ve
got to measure it / scope it. Line current transformers are
pretty cheap these days, often included in <$10 wattmeters
from off-shore sources. A scope is useful, but more expensive.

A lot of modern wall-warts are actually PFC compliant, through
the use of dedicated low power integrated controllers. These
employ valley-fill or critical-conduction (FM) off-line switchers
economically, at power levels as low as 5W.

Don\'t guess. Measure. Read specs of devices involved.

Don\'t go overboard. Your UPS output may be more tolerant of peak
loads than you assume, and your loads may be less peaky, simply
due to industry commodity trends and available parts.

RL

Some work on different rectifier and filter/pre-filter circuitry
was published by Richard Redl and Laszlo Balogh ~1995.
Some notes I made in the 80s, on the simplest LC configuration
are also included in this zip file.

In the latter, the effect of series choke saturation at above-
nominal loads is illustrated.

http://ve3ute.ca/query/passive_power_factor_diag.zip

When standards docs start talking about total harmonic distortion
and specs include power factors >95%, you can pretty much rule out
passive approaches. They can be simple, reliable, quiet and
effective in reducing generator and interconnection losses.
. . . which is the OP\'s actual concern.

RL

I did some back of the envelope calculation on (well actually I used wcalc)
how much the input elctrolytic in a 12 W (12 V 1 A) wallwart discharges
between mains periods with a bridge (so 10 mS here in 50 Hz land)
IIRC that was about 57 volt ripple! on that tiny cap (usually 4.7 uF / 400 V type).
No wonder all those electrolytics fail (have repaired many wallwarts here,
BTW I also use floorwarts:
http://panteltje.com/pub/floor_warts_IXIMG_0790.JPG
all that on same UPS too.

Primary cap discharge current between mains peaks:
Given secundary 12 V 1 A and 350 V on primary cap 12 / 350 = 34 mA,
but taking into account efficiency say 50 mA then if cap is 5 uF and t = 10 mS
As Q = C.U = i.t -> U = i.t / C
= (50E-3 * 10E-3) / 5E-6 = 100 V ripple!
50 V ripple for a 10 uF...

4.7 uF 400 V seems to be the normal in those small wallwarts (5 V 1 A), so I have a bunch of those,
and also some big ones for the secondary caps, those often get puffed too.

Maybe I goofed the math, but next time one goes I will scope that ripple
Normally you can visually spot those bad caps because they will all be swollen.

Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

If you convert your delta-voltage into current, you\'ll get a more
meaningful value that can be compared to published ratings.
Higher currents actually occur during the cap charging period and
high peak-to-average current ratios can give punishing rms values
for the same average filter output current.

Electrolytics normally have a predicted life some orders of
magnitude shorter than most other components - and they are the
main non-moving parts that determine of predicted MTBF in
commercial products running off the AC line, through a rectified
filter.

There have been eras where bad mfr formulations, misapplication
of product and simple bad design made early mortality abnormally
evident.

RL

 

[Phil Allison]

legg wrote:
================

** Learn to trim - asshole.

Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

** You just made that mad crap up.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Electrolytics normally have a predicted life some orders of
magnitude shorter than most other components

** Then in practice often outlast the lot.
The one exception being vacuum tubes.



...... Phil

 

[server]

On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Thanks for reading,

bob prohaska

You could scope the input current. It may not peak as high as you have
estimated.



--

Anybody can count to one.

- Robert Widlar

 

[Phil Allison]

bob prohaska wrote:
================

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

** A well chosen choke will do that, but not by much.

> If anybody\'s been through this exercise I\'d be grateful for guidance.

** PFC corrected SMPSs were invented for this job.
Doubt if you will find such in wall warts.



....... Phil

 

[Phil Allison]

On Saturday, June 25, 2022 at 12:15:48 PM UTC+10, jla...@highlandsniptechnology.com wrote:

On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska
b...@www.zefox.net> wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Thanks for reading,

bob prohaska


You could scope the input current. It may not peak as high as you have
estimated.

** Yeah, it more like 20 to 25% .

With 50Hz power, 100Hz current pulses are about 2mS duration.



...... Phil

 

[Don Y]

On 6/24/2022 7:10 PM, bob prohaska wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

What are the *final* load voltages? E.g., a more efficient
design may skip the mains voltage and convert direct to
your actual load voltages E.g., I run a straight 48VDC supply
instead of UPS->mains->48VDC -- because my loads are 48VDC powered.
You might be able to just power your loads directly off a well
chosen battery voltage (and simply *charge* it from the mains)

 

[server]

On Fri, 24 Jun 2022 19:52:53 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

On Saturday, June 25, 2022 at 12:15:48 PM UTC+10, jla...@highlandsniptechnology.com wrote:
On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska
b...@www.zefox.net> wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Thanks for reading,

bob prohaska


You could scope the input current. It may not peak as high as you have
estimated.

** Yeah, it more like 20 to 25% .

With 50Hz power, 100Hz current pulses are about 2mS duration.



..... Phil

Big supplies are now required to be PFC, namely not pull big current
spikes. Small warts may be exempt.

Even with a simple rectifier front-end, the top of a sine wave is
pretty soft. And it wouldn\'t shock me if some people skimp on caps.

It\'s not hard to measure. Or just plug it into the converter and not
worry. An 800 watt converter probably won\'t notice a 40 watt wart.



--

Anybody can count to one.

- Robert Widlar

 

[legg]

On Tue, 28 Jun 2022 13:37:59 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

legg wrote:
================

** Learn to trim - asshole.


Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

If you stick one next to a vacuum tube, it\'s received radiated that
dominates part temperature, and voltage stress of the app that
dominates.

** You just made that mad crap up.

If you\'ve ever calculated mtbf under Mil Hdbk 217, or Belcore,
you\'d be aware of dominating life factors.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Current forces self-rise due the part\'s ESR and limited
body surface area, (unless you stick it next to a hot radiator).
The actual relevant temperature is measured on the component\'s
body.

Electrolytics normally have a predicted life some orders of
magnitude shorter than most other components

** Then in practice often outlast the lot.
The one exception being vacuum tubes.

Given a reliable heater and low vibration, tube life is
roughly related to the temperature of the glass envelope.

http://ve3ute.ca/2000a.html

..... Phil

RL

 

[Jasen Betts]

On 2022-06-25, bob prohaska <bp@www.zefox.net> wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

Yes but only a little, the current phase angle is typically only
about 20 degrees leading so a line reactor will not help much. Most
of the power factor comes from crest factor rather than cos(phi).

It will work better if you put a bridge rectifier before the inductor.
(because now you can use a larger inductor), but now you\'ll have to
figure out which wall warts actually need AC, and only connect the
DC-capable ones.

--
Jasen.

 

[Phil Allison]

legg wrote:
----------------------

** Dear Mr legg.

Kindly go stick your fat stupid head up a dead bear\'s arse .
YOU are so dumb, make pig ignorance look like genius.

Fuck you and fuck off.
You ASD fucked cunt.



...... Phil

 

[Jan Panteltje]

On a sunny day (Sat, 25 Jun 2022 02:10:59 -0000 (UTC)) it happened bob
prohaska <bp@www.zefox.net> wrote in <t95qrj$r99$1@dont-email.me>:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching power
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That\'s well within the continuous power rating of the inverter, which
is 800 watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average
load by putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Thanks for reading,

bob prohaska

Interesting question, my cheap UPS seems to put out a square wave
I wondered if the flat tops are actually not better for the wall warts
as the charging part is longer than with a sine wave top...
Been working now fine for a year or so with this thing,
comes in almost every day these days with mains company fiddling,..
flashing light bulbs sometimes here too.
To backup for longer times I have a pure sine wave 2 kW converter and a 250 Ah lifepo4 battery..
So I can keep watching sat TV or even cook food.
More than 10 wallwarts on that UPS now, some Raspberry Pi, some USB hubs, some cameras., also
security recorder, monitors... .. audio amp... 4 TB harddisks...
I would personally not bother with a a series inductor...

 

[John Doe]

Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:

bob prohaska wrote:

I\'m setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw is only
about 40 watts measured with a Kill-A-Watt, but all the associated
wallwarts use capacitive-input switching power supplies. That means
they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%, meaning
that the average 40 watts is really 400 watts 10% of the time. That\'s
well within the continuous power rating of the inverter, which is 800
watts, so it\'s likely the setup will work as it is.

The question is: Can the peak load be made closer to the average load by
putting an inductor in the AC line feeding the wallwarts?

If anybody\'s been through this exercise I\'d be grateful for guidance.

Interesting question, my cheap UPS seems to put out a square wave I
wondered if the flat tops are actually not better for the wall warts as
the charging part is longer than with a sine wave top... Been working
now fine for a year or so with this thing, comes in almost every day
these days with mains company fiddling,.. flashing light bulbs sometimes
here too. To backup for longer times I have a pure sine wave 2 kW
converter and a 250 Ah lifepo4 battery.. So I can keep watching sat TV
or even cook food. More than 10 wallwarts on that UPS now, some
Raspberry Pi, some USB hubs, some cameras., also security recorder,
monitors... .. audio amp... 4 TB harddisks... I would personally not
bother with a a series inductor...

For a personal computer only... I use a Tripp-Lite LC1200. No battery at
all. I don\'t recall the last time we had a power failure that lasted more
than an moment. But there has been flickering. The line conditioner works
great for momentary outages, no messing with a battery.

Of course that doesn\'t suit everybody.

 

[Phil Allison]

Jan Panteltje wrote:
------------------------------------

Interesting question, my cheap UPS seems to put out a square wave

** So when rectified is pure DC.

> I wondered if the flat tops are actually not better for the wall warts

** See above.


....... Phil

 

[server]

On Wed, 29 Jun 2022 08:23:22 -0400, legg <legg@nospam.magma.ca> wrote:

On Tue, 28 Jun 2022 13:37:59 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

legg wrote:
================

** Learn to trim - asshole.


Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

If you stick one next to a vacuum tube, it\'s received radiated that
dominates part temperature, and voltage stress of the app that
dominates.

** You just made that mad crap up.

If you\'ve ever calculated mtbf under Mil Hdbk 217, or Belcore,
you\'d be aware of dominating life factors.

Belcore has no derating factor for bad design. That often dominates
MTBF.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Current forces self-rise due the part\'s ESR and limited
body surface area, (unless you stick it next to a hot radiator).
The actual relevant temperature is measured on the component\'s
body.

We are designing a fancy switching power supply and need a 20 uF cap
that can handle several amps RMS, a 250 KHz triangle from a
half-bridge and an inductor. We are thinking about using four 4.7 uF
radial-leaded film caps in parallel.

We have samples of several types on order. I plan to set up a test rig
and push amps of triangle into them and see how hot they get. May as
well snoop the waveform across each cap while I do that.

Film cap data sheets are typically not much help. They might spec a
few sinewave loss tangents and maybe allowable voltage vs frequency,
but rarely spec ESR or ESL or any thermals. We have to measure all
that.

 

[Fred Bloggs]

On Wednesday, June 29, 2022 at 10:20:07 AM UTC-4, jla...@highlandsniptechnology.com wrote:

On Wed, 29 Jun 2022 08:23:22 -0400, legg <le...@nospam.magma.ca> wrote:

On Tue, 28 Jun 2022 13:37:59 -0700 (PDT), Phil Allison
palli...@gmail.com> wrote:

legg wrote:
================

** Learn to trim - asshole.


Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

If you stick one next to a vacuum tube, it\'s received radiated that
dominates part temperature, and voltage stress of the app that
dominates.

** You just made that mad crap up.

If you\'ve ever calculated mtbf under Mil Hdbk 217, or Belcore,
you\'d be aware of dominating life factors.
Belcore has no derating factor for bad design. That often dominates
MTBF.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Current forces self-rise due the part\'s ESR and limited
body surface area, (unless you stick it next to a hot radiator).
The actual relevant temperature is measured on the component\'s
body.
We are designing a fancy switching power supply and need a 20 uF cap
that can handle several amps RMS, a 250 KHz triangle from a
half-bridge and an inductor. We are thinking about using four 4.7 uF
radial-leaded film caps in parallel.

We have samples of several types on order. I plan to set up a test rig
and push amps of triangle into them and see how hot they get. May as
well snoop the waveform across each cap while I do that.

Film cap data sheets are typically not much help. They might spec a
few sinewave loss tangents and maybe allowable voltage vs frequency,
but rarely spec ESR or ESL or any thermals. We have to measure all
that.

These people don\'t figure current into life expectancy, only voltage and temperature.
https://www.cde.com/resources/technical-papers/filmAPPguide.pdf

 

[server]

On Wed, 29 Jun 2022 08:18:39 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Wednesday, June 29, 2022 at 10:20:07 AM UTC-4, jla...@highlandsniptechnology.com wrote:
On Wed, 29 Jun 2022 08:23:22 -0400, legg <le...@nospam.magma.ca> wrote:

On Tue, 28 Jun 2022 13:37:59 -0700 (PDT), Phil Allison
palli...@gmail.com> wrote:

legg wrote:
================

** Learn to trim - asshole.


Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).

If you stick one next to a vacuum tube, it\'s received radiated that
dominates part temperature, and voltage stress of the app that
dominates.

** You just made that mad crap up.

If you\'ve ever calculated mtbf under Mil Hdbk 217, or Belcore,
you\'d be aware of dominating life factors.
Belcore has no derating factor for bad design. That often dominates
MTBF.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Current forces self-rise due the part\'s ESR and limited
body surface area, (unless you stick it next to a hot radiator).
The actual relevant temperature is measured on the component\'s
body.
We are designing a fancy switching power supply and need a 20 uF cap
that can handle several amps RMS, a 250 KHz triangle from a
half-bridge and an inductor. We are thinking about using four 4.7 uF
radial-leaded film caps in parallel.

We have samples of several types on order. I plan to set up a test rig
and push amps of triangle into them and see how hot they get. May as
well snoop the waveform across each cap while I do that.

Film cap data sheets are typically not much help. They might spec a
few sinewave loss tangents and maybe allowable voltage vs frequency,
but rarely spec ESR or ESL or any thermals. We have to measure all
that.

These people don\'t figure current into life expectancy, only voltage and temperature.
https://www.cde.com/resources/technical-papers/filmAPPguide.pdf

That\'s interesting but, typically, qualitative and theoretical. I\'ll
have to test actual caps.

We will have a lot of air flow too, which will increase allowable RMS
current and needs to be quantified too. We should orient and space the
caps to take advantage of the air cooling. This ain\'t simple.

It\'s distressing, in electronics data sheets and literature, how
seldom you find actual numbers. I recently bought a book about
electronic cooling, but it\'s packed with equations and theory, with
not a single worked-out case of blowing air over a flat plate. There
is an equation, but it\'s a nightmare.

If I had a 6\" square of 0.062 thick aluminum, and blasted 200 f/m of
air along both sides, what would theta be? I\'ll have to measure that.

And what would the temp rise be of my 4.7u film caps, in degc/watt, in
still air and with air flow? Gotta measure that too.

 

[whit3rd]

On Tuesday, June 28, 2022 at 1:38:06 PM UTC-7, palli...@gmail.com wrote:

legg wrote:
================

** Learn to trim - asshole.

Anybody measured the ripple?

Electrolytic life is rms current dependent, among other things (like
temperature).
** You just made that mad crap up.

Temp is the single determining factor on expected life.
Almost always the local ambient completely dominates.

Electrolytics normally have a predicted life some orders of
magnitude shorter than most other components

** Then in practice often outlast the lot.
The one exception being vacuum tubes.

Electrolytic capacitors are active-chemistry devices; temperature affects the
seals that hold the reagents in place, and either internal heat or ambient temperature
will cause aging, irrespective of electrical stress. High ripple voltage is associated
with processes that cause i nternal foils to become fractured.

Vacuum tubes are also active-chemistry devices; usually become gassy due to slow
diffusion of contaminants. There\'s better chemcal integrity available in solid state devices
as far as aging is concerned. Batteries exemplify the worst chemical integrity in the business...
you always want to check the dates on those!