EEVblog #1284 - How Bad Product Design Kills The Environment

[TerminalJack505]

So far as I understand it, all of the current that flows through the capacitor has to be burned off (by the load, Zener, in-line resistor, rectifier, etc.) so that is energy lost.

This is a particularly bad circuit so far as efficiency is concerned.  The smoke detector will need--in the worst case--the current to drive the Piezo element in the event of a fire.  It will likely need around 10mA to sample for smoke every 10 seconds, or so.  All other times it is likely burning no more than 1mA.  They likely draw 50mA of current from the battery during a low battery test but--unless their circuit is incorrectly designed--that should come exclusively from the battery and never from mains.

[gf]

The capacitor drop supply is just not good for something that usually needs low power, but sometimes needs much more.

Unfortunately a zener is a shunt regulator. On the other hand this design can provide about 70mA when needed. Would be interesting how much current it needs when crying, an how long it is supposed to cry at minimum. Would a low-current series regulator + supercap suffice?

[EEVblog]

What is the failure rate of the crappy solution "they" have used compared to the ones you showed, could that be a reason they went with it?

Bordering on nothing in it really with a zener vs a HV regulator. I guarantee it's because of cost.

[EEVblog]

I think a point that is missed is that the I2R losses aren't extending to the grid.  They probably aren't even getting to the pole pig.  They are getting to the nearest traditional electric motor (non-inverter-driven), where the capacitive reactance is a benefit and any harmonics are being absorbed.
modulation.

How are the harmonics being absorbed by the motor?
The harmonics need matching harmonics in the voltage waveform in order to be compensated, if that's not the case then the harmonics will contribute I²R losses right up the delivery system until they are filtered out.
This is why non-linear loads are a huge problem and standards like 61000-3-2 and EnergyStar exist.
https://en.wikipedia.org/wiki/IEC_61000-3-2
and why harmonic filters like this exist:
https://www.nhp.com.au/files/editor_upload/File/Brochures/Power-Quality/NSCHAFFC.pdf

[EEVblog]

The capacitor drop supply is just not good for something that usually needs low power, but sometimes needs much more.

Unfortunately a zener is a shunt regulator. On the other hand this design can provide about 70mA when needed. Would be interesting how much current it needs when crying, an how long it is supposed to cry at minimum. Would a low-current series regulator + supercap suffice?

That's in the video, I measured 15mA peak current from the 9V battery.

[EEVblog]

So far as I understand it, all of the current that flows through the capacitor has to be burned off (by the load, Zener, in-line resistor, rectifier, etc.) so that is energy lost.

Yes, zener regulators are the traditional "worst case design", which is why they have gone the way of the dodo, unless you want to save a couple of cents.

This is a particularly bad circuit so far as efficiency is concerned.  The smoke detector will need--in the worst case--the current to drive the Piezo element in the event of a fire.  It will likely need around 10mA to sample for smoke every 10 seconds, or so.  All other times it is likely burning no more than 1mA.  They likely draw 50mA of current from the battery during a low battery test but--unless their circuit is incorrectly designed--that should come exclusively from the battery and never from mains.

Again, this is in the video.
The measured current draw is 50uA maximum during standby and 15mA max during sounding.

[TerminalJack505]

The capacitor drop supply is just not good for something that usually needs low power, but sometimes needs much more.

Unfortunately a zener is a shunt regulator. On the other hand this design can provide about 70mA when needed. Would be interesting how much current it needs when crying, an how long it is supposed to cry at minimum. Would a low-current series regulator + supercap suffice?

I worked on a wireless smoke detector for the US/Canada market and I seem to remember that the minimum time the battery needed to support the sounder was 15 minutes.  Which is to say that the low-battery indication needed to factor this in.  Once smoke is detected and the sounder goes off, it won't stop sounding until either 1) the user intervenes, 2) smoke is no longer detected, or 3) the battery gives out.

[coppice]

So far as I understand it, all of the current that flows through the capacitor has to be burned off (by the load, Zener, in-line resistor, rectifier, etc.) so that is energy lost.

Yes, zener regulators are the traditional "worst case design", which is why they have gone the way of the dodo, unless you want to save a couple of cents.

Zener regulation is also valuable when you want a low cost regulator that clamps - e.g. when your design needs to deal with high EMI conditions, and energy can get in post regulator. An LDO won't stop the Vcc rising dangerously, but a zener will.

[gf]

At
This is why non-linear loads are a huge problem and standards like 61000-3-2 exist.

And not to forget millions of LED lamps w/o PFC...

[EEVblog]

So please enlighten us with a real calculation including a good estimate of the actual grid losses. Hint: if small devices with low PF are deemed a problem then they would be subject to regulations regarding power factor.

Just because they didn't bother to do <75W devices in EN61000-3-2 and EnergyStar doesn't mean it doesn't matter. The entire point of the video is to consider this in product design.
If it's a problem at 75W for a single device, why shouldn't it be a problem with 75 devices of 1W each (localised EMC excluded).

Small correction: It's 75W (or 100W) input power, so that includes device efficiency. So if your widget takes 37.5W real power, but it's only 50% efficient, then it falls under the regulation for power factor and harmonic content.

[thm_w]

Unfortunately a zener is a shunt regulator. On the other hand this design can provide about 70mA when needed. Would be interesting how much current it needs when crying, an how long it is supposed to cry at minimum. Would a low-current series regulator + supercap suffice?

70mA capable makes sense:
- 15mA peak as Dave stated, add 2x for safety factor, then add another 2x for degradation of the capacitor over time (10yr).
Big clive has seen a number of these capacitors where they have degraded to the point of not being able to supply enough current.

[EEVblog]

Zener regulation is also valuable when you want a low cost regulator that clamps - e.g. when your design needs to deal with high EMI conditions, and energy can get in post regulator. An LDO won't stop the Vcc rising dangerously, but a zener will.

Good point, but still it's ultimately a cost driven choice at the expense of efficiency. Has been since the 1970's.

[EEVblog]

Unfortunately a zener is a shunt regulator. On the other hand this design can provide about 70mA when needed. Would be interesting how much current it needs when crying, an how long it is supposed to cry at minimum. Would a low-current series regulator + supercap suffice?

70mA capable makes sense:
- 15mA peak as Dave stated, add 2x for safety factor, then add another 2x for degradation of the capacitor over time (10yr).
Big clive has seen a number of these capacitors where they have degraded to the point of not being able to supply enough current.

The better quality more expensive design is much lower than the 79mA in the cheapo though.
For capacitor degradation, if you halve the capacitance you halve the current, so that could be a thing.

[dcac]

You may find this “cheap” capacitor dropper circuit in almost any product where there’s a MCU controller board and just some LED indicators or i.e. a LCD display that only require a low current DC supply.

While you (perhaps) can debate how much power losses it really is resulting in, in my experience it is also a quite high failure rate design. And when they fail the product has still often been working but just intermittently, not exactly the behavior you’d want in a smoke alarm.

I've only worked with battery powered smoke alarms and they will warn also for the battery running low and needs changing, but in those mains powered smoke alarms - will they also warn if the dropper capacitor is about to fail, or any other failure from the mains circuit?

[langwadt]

So please enlighten us with a real calculation including a good estimate of the actual grid losses. Hint: if small devices with low PF are deemed a problem then they would be subject to regulations regarding power factor.

Just because they didn't bother to do <75W devices in EN61000-3-2 and EnergyStar doesn't mean it doesn't matter. The entire point of the video is to consider this in product design.
If it's a problem at 75W for a single device, why shouldn't it be a problem with 75 devices of 1W each (localised EMC excluded).

Small correction: It's 75W (or 100W) input power, so that includes device efficiency. So if your widget takes 37.5W real power, but it's only 50% efficient, then it falls under the regulation for power factor and harmonic content.

afaiu there is a minium required efficiency for wall warts and such in that power range of ~85%

[TerminalJack505]

Now that I think about it--if Aussie detectors are the same as US/Canada detectors--the detector will check for smoke while the Piezo sounder is going, so that is likely the worst-case so far as current draw goes.  I'm guessing that would be about 25mA.

[EEVblog]

Now that I think about it--if Aussie detectors are the same as US/Canada detectors--the detector will check for smoke while the Piezo sounder is going, so that is likely the worst-case so far as current draw goes.  I'm guessing that would be about 25mA.

No, the detector only draws 50uA maximum when checking, it's practically nothing. This is why a 9V battery lasts for a couple of years, and they can get 10 years lithium ones.

[EEVblog]

but in those mains powered smoke alarms - will they also warn if the dropper capacitor is about to fail, or any other failure from the mains circuit?

Just the usual low battery indicator, which could be low battery, or mains cap failure reducing the zener current and ultimately voltage.
https://datasheetspdf.com/pdf/1082256/Allegro/5366/1
But in theory I could imagine a scenario where the cap has failed but the zener just has enough voltage to not trip the low battery warning, but then doesn't have enough current in order to maintain the voltage during the alert, so the alarm never goes off.

[EEVblog]

I imagine the rest is power that simply flows in and out of the capacitor, the joules that enter end flowing back into the grid and dilute into the other zillion grid loads that are in parallel. Similar to what a grid tied solar inverter does, only that this one pulls half a cycle and injects it back during the other half. If so, the net load to the grid would be ~= zero, except for the losses in 100R and the zeners. No?

No, the 80mA is real current that will have I²R losses in the transmission system until it is compensated for (lead/lag and harmonic). If you have say 5 in your home at 80mA a pop that's 0.4A that must be delivered from the grid infrastructure.
The lead/lag compensated part can be done locally at your home with other leading phase device, but the harmonic content usually cannot, so it will go back down the grid resulting in losses until it's filtered out.

[richnormand]

Enjoyed the video Dave, thanks.
No reason to put up with inordinate power usage when solutions exist, even if they initially cost a few cents more.
The idea of "built to a cost" and "cheap as possible" from mains power for safety equipment that should be reliable made me think of this pic.

[EEVblog]

Enjoyed the video Dave, thanks.
No reason to put up with inordinate power usage when solutions exist, even if they initially cost a few cents more.
The idea of "built to a cost" and "cheap as possible" from mains power for safety equipment that should be reliable made me think of this pic.

Can't get that sort of energy readily from a 9V battery!

[TerminalJack505]

Now that I think about it--if Aussie detectors are the same as US/Canada detectors--the detector will check for smoke while the Piezo sounder is going, so that is likely the worst-case so far as current draw goes.  I'm guessing that would be about 25mA.

No, the detector only draws 50uA maximum when checking, it's practically nothing. This is why a 9V battery lasts for a couple of years, and they can get 10 years lithium ones.

I'll have to re-watch the video to see what technology your detector uses.  The one I worked on used photoelectric technology for smoke detection which consisted of an (ultraviolet?) LED and phototransistor.  So both the detection chamber LED as well as the "sampling indicator" LED (as seen by the user) would have to be powered when the sample is done.

Disclaimer: I only worked on the embedded code for the wireless transceiver so I don't claim to be an expert in smoke detector technology.

[EEVblog]

Bonus screenshot:
(Attachment Link)

Turns out all that funny business is not coming from the product consumption, and with a moments thought that is obvious, more investigation required, likely a proby thing.
A pure R-C-Zener circuit should not create that mid frequency stuff, just the front and back porches.

Well this is strange. Using my AIM current probe I get the exact same waveform. And if I bypass the power monitor for mains input I also get the same waveform.
More investigation required...

Double strange - Exactly the same result using my Micsig portable scope with either my HV probe and sense resistor or my AIM current probe.
So everything is completely isolated.

I can't see how a shunt zener regulator can produce this? I can only imagine it's some sort of harmonic resonance thing happening because of the sudden high slew waveform rise.

[EEVblog]

It has to be some sort of mains system resonance caused by the harmonic distortion. If so, brilliant example of the problems harmonic power factor can cause.
Need to find another way that it doesn't resonate somehow though

[EEVblog]

My next hunch is resonance with a PFC capacitor bank inside the building. I might go to the old lab in another building and try again. Worth a shot.
And BTW, those wiggles are not random, that waveform above is an average, they are completely consistent across scopes and probing.