Inverters vs wallwarts

On a sunny day (Sun, 26 Jun 2022 10:27:49 -0400) it happened legg snipped-for-privacy@nospam.magma.ca> wrote in snipped-for-privacy@4ax.com:

Yes, and most of the wallwarts I have have a big input voltage range like 110 to 230 V AC.

That gives the UPC some time to come in in case of 230V :-)

legg wrote: =============== Phil Allison

** The man said " square wave " - over and over.

** Not a *square wave* any more.

..... Phil

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.

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

Look at the plug-in output voltage inverter-fed versus line-fed. If no difference, then no issue. Look at the inverter RMS output with and without a bunch of plug-ins. If no difference then no issue.

They just lifted the same technology used in inverter generators. If it coasts through what you call a momentary outage then it wasn't an outage. The price is pretty good but then again 1200 Watt is not really that much. Are you mining bitcoins or something? What in the world kind of computer setup requires 1200W these days...

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

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:

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?

Jan Panteltje wrote more rubbish:

--------------------------------------------------------

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

** 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

On a sunny day (Tue, 28 Jun 2022 03:42:04 -0700 (PDT)) it happened Phil Allison snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:

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.

Do not eat it! Live on a farm?

Why do humming beans exist? Why is water wet?

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.

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

Sure good electrolytics are expensive. Bigger ones too -:)

Jan Panteltje is a f****ng IDIOT wrote: =============================

** Fuck you - imbecile.

** So you have no reason at all ? zzzzzzzzz... ** Yawwnnn - more false logic idiocy.

** Not at 15% they f****ng don't - you liar. ** Yawwnnn - more false logic idiocy.

Scuse me while I vomit.

..... Phil

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

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

** Learn to trim - asshole.

** You just made that mad crap up. Temp is the single determining factor on expected life. Almost always the local ambient completely dominates. ** Then in practice often outlast the lot. The one exception being vacuum tubes.

..... Phil

Hmmm, _maybe_ I get your point. The input capacitors never discharge, so dv/dt is zero. Thus, no inrush peak after startup.

Dammit. Didn't need a sine inverter at all..... It's on the bench now, waiting for the battery to arrive.

Thanks for posting!

bob prohaska

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.

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

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.

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

RL

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

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.

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.

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!

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.

There was a bit of a fad in the '90s for people to publish various semi-empirical papers on fan cooling, but that sort of died out.

You can compute the thermodynamic limit, obviously, because you know the inlet temperature, the air mass, the maximum component temperature, and the heat dissipated, but most heat sink systems don't get anywhere near it.

Cheers

Phil Hobbs

The stress factors for measured voltage current and temperature are a fair indication of design integrity. Designs can be 'bad' for other reasons entirely.

It's always been difficult determining film cap ratings. The dielectric losses usually have a positive temp co above 50C and the parts themselves can have some of the lowest part body temperature limits in the deck.

Part construction and materials quality, though largely the product of automation, can vary. Not many other parts are dependent on a coat of paint for env integrity.

Keep in mind that self-healing construction can mask a considerable defect level. You've probably pulled simple film decoupling caps out who's capacitance measured almost nothing compared to their original mfred values, due to repeated intervening self-healing processes.

Philips published good information on polycarbonate, polyester and polypropylene parts, when they were still in the business of using them. Check their 'Components and Materials Part 15' prior to 1990. I don't think there's been much improvement on that. Siemens tended to be more spotty. CDE did some mil stuff that must have been backed up by something more than body temperature rise. Polycarbonate development has lost some steam due to issues with flammability.

There were film caps in most early fluorescent bulb replacements, besides the usual HV electrolytic. At that temperature, it was a toss-up which failed first.

Pulse-rated products get more attention to their reliability and ratings. If your part doesn't provide sufficient data, chances are it's a misapplication waiting to happen. Pulse steepness dV/dT (~peak current) is dependent on both the process characteristic voltage AND the part body size, so that the amps/uF can actually reduce with an increase in leadspacing.

PPK and polyphenylene sulphide are potential rivals in some applications, with slightly higher temperature limits, but I don't recall anyone providing tabular or graphical data.

Can't imagine where my notes could be on that stuff. Today, even the binder labels are illegible. Probably need a different kind of 'specs'. RL