Why Capacitive Power Supply Are Bad (electronics educational)
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- เผยแพร่เมื่อ 15 มิ.ย. 2024
- Capacitive Power Supplies are a dirty cheap solution to feed simple low power devices directly from Mains, but the drawbacks are way more than the benefits in many cases.
In this video I'll try to show that with a practical experiment, and why they are bad wasting energy.
In short, lack of isolation, low efficiency and a power factor close to zero should be the main reasons to suggest electronic engineers to avoid this typology of circuit.
In this video I've tested an actual circuit, and described in details how it works and why it is so poor in efficiency and power factor.
Even though they usually are used in small equiplemnts they waste energy and can be a factor when it comes to limiting CO2 emissions. At the moment I am writing this, we do not know whether the antropogenic emissions of CO2 are really an issue in relation to the global climate change, nevertheless increasing the efficiency, and in this case also the safety, of the circuits should be paramount of every electronics engineer.
Educational video in Electronics. - วิทยาศาสตร์และเทคโนโลยี
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I've created a dusk-to-dawn device, which consumes only 8mA and turn on a Triac. It's located inside a plastic box. For this purpose, capacitive power supply is perfect, it's the way to go.
However, I'd never use a capacitive power supply in a open space where someone can touch it. It's very dangerous.
I made a bed side light that uses a caacitive power supply to power a LED, it works well and never gave me any trouble.
cool dude
Very well taught! Good job!
Great video, THANKS!
Amazing explanation .
Best video. Thanks sir
Great video man. I have a timeswitch that has no bridge rectifier at all. It just uses a 20v Zener to rectify. (20v in one direction and nearly zero in the other direction.)
Thank you. Just one zener, well do not show that circuit to Greta Thunberg. :)
Sir, i have made this circuit for the 12v load but starting range is 6.82 v - 12v at 12v its fully operational so after applying the above circuit even with the 12v zener diode the circuit goes to max. Voltage of 6.82 v the voltage at which the loads start and does goes up after that but without load it gives the zener output bolts of 12v plz help!!!
This mans went HAARDDD on capacitors
Liberate a sea of knowledge in a cup of tea.....Great..... Thumbs up
"Sea of knowledge" is a little bit an exaggeration, but thank you.
With or without any load being connected to the output the current of the circuit is constant 23mA,but despite that there are many automation circuits like motion with day night light detectors that this circuit works excellent and these circuits are not accessible so there is no risk of electrocution.
Hi, you should take into into account that more you reduce the R2 resistor 2M2, the better power factor you get. I think you can gain better results with better component value calculation. The second issue is we have to isolate GND connections when we use this topolgy in parallel. Because, the current can find its way from another rectifiers. Anyways, this is a quite good and cheap and robust solution in some points.
Ilhami Kivrak m
1M ohm is enough, right?
thanks a lot good teacher
The c1 capacitor does not store a dangerous charge
I have touched a 310v 0.8 uf capacitor and I barely feel it up both arms
very educative, thnx very much 👍
Glad it was helpful!
Do you have any schematics of power supplies that you could recommend? Thanks.
Alternative schematics? It's hard to give an answer because it depends by the circuit that have to be fed. In general switching power supplies are a good deal, for DIY projects though the simplest, cheapest, cleanest solution (in terms of noise) are the one made with classical transformers and regulators such as 7812 or similar, even though they are not so efficient as SMPS are. Unfortunately I am not a specialist in switching mode power supplies and I cannot give any detailed recommendation about them (for this reason I prefer to buy them :) ).
One important drowback of many low cost SMPS is the inability to start up heavy capacitive loads. I.e. in the lab we had problems with a very well known brand of SMPS that are unable to start up when connected to a capacitive load of just 350 uF.
Claudio.
Excellent explained about power supplies I impressed, thank you Sir. Keep it up..
Best video I've seen so far. But there are still no better alternatives for the size and price which is why it's still used.
When i make it directly on wire the voltage output equal with the voltage on diode zener, but when I make it on handmade circuit print then the voltage output is decrease to 2,5vdc. You can explain? Tks
Hard to say without inspecting the circuit live, try to check the circuit for any error. Low voltage may be due for a wrong zener diode, reversed electrolytic capacitor, or wrong R and C values at the input stage. Also, if you used discrete diodes to make the full bridge rectifier, if one of them is reversed then the output voltage would drop significantly.
Execellent video and the clearest explanation
Thank you
very good presentation. Thanks.
Not useful for any serious loads but useful for power indication leds or powering the coil of a relay switching mains.
Its just a matter of chosing the right capacitor. I have an 10 amp capacitive car battery charger, and 10 amps transformer is much biger, havier, and more expensive than capacitor :)
@@djordjepavlovic5870 10 amps is very high current for capcitor dropper. Are u sure it uses capacitor dropper.
Dear engineer , I have heard when using isolated power supply ( two transformers) we should avoid connecting oscilloscope to the output while this isolated voltage will burn the scope. Am I right ? ( thank you for your detaild explanations)
If there is isolation there is no path the current can take, so no burning can occur. Usually the risk with scopes is the path to ground while attempting to measure mains non-isolated voltage, because the shield of the probe (connected to ground) could short the live wire from mains. If you look at my video about capacitor power supply you'll see that I've arranged te test circuit through two transformers to make an improvised insulating transformer just to avoid that risk.
Anyway always think what path the current may take to work safely. A scheme would be beneficial, may be I will make a video on this topic as soon as I'll recover from a kind of flu.
@@AccidentalScience Thank you so much for fast reply. I'm looking for a video about the risk of blowing up an oscilloscope when measuring voltages on isolated power suply .
I"ll send it as soon as I can find it .
Very well presented, easy to understand and remember. Good job, Sir!
Thank you.
May I ask another question? I'm always having this simple question : In AC circuit we say the polarity is constantly changing. Why we always get the hot wire on only one cable when using a test pencil ? Thank you
The "hot" wire is about your instrument, not the AC circuit. However, AC can be seen relatively to one potential, and that potential could be set to ground in the circuit, that we refer to be at zero potential (this is relative to us as we all are in contact with Earth). Therefore if in one AC circuit one wire is connected to ground by consequence the other wire will be defined to be the "live" one, with a voltage that alternatively goes positive and negative relatively to ground.
For example, in Europe we have power distribution through four wires: the three phases (RST, normatively black wires) that come from the generator at the power station (I'm simplifying) and the Neutral (blue wire) which is connected to ground thus at the same zero potential of PE (Protective Earth, green-yellow wire, which is also ground). For single phase, in your home they carry one of the three phases and the Neutral to provide a single phase power line, thus the black or brown wire that carries the phase is the live wire, the blue is the neutral which is at approximately the same voltage of PE (the typically negligible difference comes from the resistivity of the ground between the two grounded points: N and PE).
@@AccidentalScience That is an awesome answer : clear and concise. I never wondered why the test pencil lit only on one cable, now i understand that the pencil links the live to my body (which is linked to earth) and as neutral is linked (somewhere) to PE, we have a full circuit. Thus, when i touche the live with the test pencil, there is a different in potential and current can flow, but when i touch neutral the circuit is essentially "neutral - pen - body - pe - neutral" so no difference of potential so no current. I'm enlightened and delighted to have understood this. THANKS.
@@nicolaspillot5789 exactly. Glad to be helpful.
What do you think about the case that the power factor is capacitive... once the main power factor of your house is generally inductive, it ends acting as a power factor correction. Am I wrong?
As far as you are paying for real power, it does not matter for you. Industries pay extra fee for apparent power, so they have to compensate. This little capacitor does not compensate so much, maybe it is better for your electricity provider :P
You are right, in the case the load in your house is manly inductive.
Is there ever an advantage to using this dropper instead of a resistive dropper with half wave rectification?
Sorry for the late reply. Actually, despite the low efficiency and distortions, this dropper is better than a pure restistive and half wave rectification.
Hi,
Nice video
Could you give me 5v 350mA circuit using capacitive dropper circuit
350 mah is not possible in this case. Max u can get 100mah
What if you don't use the diode bridge and the rest of the circuit? I only need 8 mA for my DIY application ad that works well. It may be inefficient but its very low cost and does not need extra PCB real-estate.
With no diode bridge your circuit would be powered with alternating current. This is not an endorsement, though. Let apart inefficiency this circuit remains dangerous.
@@AccidentalScience I am only using one rectifier diode (not a bridge). It must be inefficient.
I am using this type of power supply but I am facing power factor reducing problem.The power factor go very bad when I am increasing the value of X capacitor.can I fix this problem? Please help me.
What stand for "X capacitor"? Anyway, the bad power factor is intrinsic of this kind of power supplies so the only possible solution is to change design and choose an other kind of PS, even a very small transformer makes less harm to the power factor, particularly if it is corrected with a capacitor.
I have seen similar power supply in a 1500W electric heater (to power up a small IC that will turn on/off resistance heating coils using relays). Sure, it has poor efficiency, but it's not a problem since it is dissipating thousands of watts at the same time. The whole PCB was in a closed housing, to help with poor isolation.
Yes, there are some cases where this kind of circuit could be an acceptable solution.
Still there are other solutions to this, for example using the voltage drop from a part of the coil with a 7805.
THANKS
Remove transformer stack, R1, and 2M2, and your efficiency will go up significantly. I disagree with the conclusion of your analysis. Diodes can be bought with Vf of ~0.2V. Zener is not needed depending on load.
Thank you for having commented, disagreeing with my conclusions is utterly fine. However some objections: 1. The transformer stack is taken out from the measurement and it is used for safety reasons both to provide isolation from mains and to limit the current. 2. The 2M2 resistor can be removed increasing efficiency at the cost of safety, as already mentioned in the video. 3. R1 (if I remember correctly, I am on a mobile and can't see the circuit rigth now) is required to limit the in rush current in the case the circuit is energized on the peak of the AC mains.
I do agree that a schottky diode would have less Vf, if you can find one that have enough Vr as well, yet the big problem with this kind of circuit is the power factor that is the major source of inefficiency, in particular when the required power is larger than the one used in this demo circuit.
Cheers.
Great video
Thank you!
I'm not convinced, I think it is inefficient because of the other components, so you could make an efficient version of this
Actualy in some.cases capacitive chargers are good litle devices. Using one for manny years to load car bateries. Brought manny dead batteries to life again. Thanks to it wawe form of curent they actualy do a great job on desulfating old lead acid bateries
Well I would *do* *not* recommend doing this thing. Just for the danger.
That said, thank you for comment.
@@AccidentalScience Ofcourse they are dangerous. Buth so they are badly isolated cheep chinese transformers, cables with hair thin wire, and so on.
The facts are:
1. Capacitive voltage dropers are used for decades ( old chargeable lamps and so on)
2. They are simple and cheap
3. No heat
4. Some batteries(lead acid) favour nonlinear current curve. Makes them desulfate.
5. Capacitors can kill you.
6. So can a cola and mentos or a fork or a bicycle :D
Best wishes to all. Be safe, be smart.
@@djordjepavlovic5870 how can it be called inefficient if there is no heat generated ? i tried one such circuit and yes there is no loss to heat at all . the pf loss is not real loss .
@@tolgadabbagh1877 never said that they are inneficient.
@@djordjepavlovic5870 i know , i wrote it to support you .
mostly all led power supplies and also some computer power supplies
Why do you include the zener diode in your measurement? It's got nothing to do with the capacitive-ness of the power supply -- you could just as easily have put a more efficient (and still really cheap) linear voltage regulator in there.
I've shown the typical "dirty cheap" circuit, e.g., the one used in some LED lamps made in China.
Since the diode is part of the circuit, must be measured. I agree that a voltage regulator would have been likely more efficient.
I am going to develop a level detector for liquids, that in my case will be used for a simple control of a submerged pump and alarm/monitoring of a manhole collecting sewage ...you know, disgusting things where a good automation is really welcome ;) Since this device will be always on, I was looking for a very efficient power supply, so I wondered about the efficiency of the capacitive power supply, and I thought to share my findings with this video.
I will show that project in the next videos, however I can anticipate that eventually I found convenient to use a pluggable SMPS recovered from a dismissed video sender.
Claudio.
Excelent video thx
A real Electrical Engineer!
Nice video
Thank you.
I noticed that you're using the unit "Wrms" for the power. This is an erroneous expression. The power is always a mean or average value. So you just write "W". The term RMS tells you about the sequence of calculations (root, mean square) that are done on an infinitive number of momentarely values. This does not apply to the calculation of power.
You are right, I wrote the term "Wrms" to highlight the fact that is derived from the Vrms, but it is not formally correct because it is not the RMS of the power rather the power that come from the squared RMS value of the voltage over the resistance. Thank you for commenting and having spotted this thing that I forgot to clarify in my video.
Very very nice video 🙏💕
Thank you.
Well... A bit too heavy for me but thank you, I had been thinking about building one for a project... Until someone reminded me I could use one of my many power supplies ;)
Its a good power supply for powering low powered non portable items.
What! In the end the solution is actually use commerialised power adaptor?!?!!? HAHAHAHAHA!
I am not sarcastic. I was waiting for the solution and then...I did not expect to hear that. I thought you are going to show how we could DIY a simple power supply which has power factor of near to 1.
I am happy you are so amused for my video :) Yes, you are right about the poor power factor of some wall-warts but at least they have the output that is insulated from mains, and have better efficiency anyway. Furthermore, the purpose of this video was to talk about this kind of circuit to highlight their characteristics, not a DIY video. Cheers.
@@AccidentalScience You are correct about the insulated part. But I dislike the fact that nearly all Chinese products are only 2-prong! Not grounded! According to companies (Dell as well), they say that there is a reason for establishing 2-prong, but no reason stated. Weird indeed.
The only reason I know is 3-prong, the ground can effectively create a ground loop to the circuit making a safe one unsafe. But this reason is invalidated by properly designed and engineered circuits and housing.
Also, grounding really can totally eliminate "electric tingling". This capacitive electrical phenomenon actually renders my precision devices such as GPS unit and camera nearly useless. Thankfully none of them gets fried.
@@realchristopher4334 They have 2 prongs because typically they follow the norm for double insulation (see here for a preview: webstore.iec.ch/preview/info_iec60950-1%7Bed2.0%7Den_d.pdf ).
Being double insulated you can ground the negative. The "electric tingling" as you call it, is a defect that indeed affect several smps for laptops. If grounding the negative causes an increase in positive voltage (spikes when seen at the oscilloscope) or a current goes through the (added) ground wire, then the PSU is severely defective/badly designed and need to be discarded. I think they are not compliant with the normative too, but I have no strong proof of it.
For instance, I noticed that every PSU that came with Acer laptops I had (5 units) were affected by this problem, and one of them fried an AVR MKII programmer while I was reprogramming a unit having an ATmega32 that through a communication line was connected to ground. But because at the time I was the CEO of the company I never had the time to investigate into this problem, even though indeed it would deserve a whole video ...maybe one day :)
@@AccidentalScience Ah. Double insulation. I see the symbol often. Square within square.
According to the article you provided me with, having a device earthed or double insulated or reinforced insulation seems to be an option. I always thought earthed is a necessity in the name of safety and also as a makeshift Faraday shield (as in my case).
I do not have an oscilloscope, unfortunately. I am just another average hobbyist or DIYer.
Hmm. Problem is 3-prong plugs (especially from China and by China, whether it is its Western investors' idea to save cost or deliberately designed that way) have 3 prongs, I dare say almost EVERY ONE of them is only 2 usable prongs. It is because the ground pin is plastic. It is there for the sake of opening up the live and neutral covers. Few I found are 3-prong, the earth pin is metal, but absolutely not wired, it is there for formality sake.
Therefore, what you mentioned about the negative can still be grounded despite of being double insulated, it is not happening. Ground pin is as if a decoration and serves nothing more.
The said "electric tingling" is not limited to only laptop or PSU, in my case. In fact all 2-prong or 3-prong (but only working 2 pins) plugs produce that phenomenon. My laptop is plastic all over so I cannot feel it (I can feel the effect only when I plug in USB cable).
My very old laptop with is very old PSU were the same. I did not know "electrical tingling" is a real problem.
Too many coincidences that it is not a coincidence that the plugs or circuits are made such a way. It cannot be every one of them is like that. I think they are meant to fail as quickly as possible to force people to buy new ones. (Sounds like conspiracy. But not a conspiracy when we consider it similar issue to LED. I bet you already know that LED companies overpower their products. This is even true for Chinese knockoff, they use same amount of LED for all claimed wattage but run by different drivers, they can get insanely hot! Only Dubai managed to force Philips to make ultra efficient and possibly never-dying LED by underpowering each LED, they stay cool.)
When I said the negative can be grounded I meant that, should the unit be one with double insulation, you can add an external ground wire safely in some way (maybe changing the power cord and plug). Double insulated equipments MUST have two terminals only, otherwise they won't fit the norms (I am referring to EU-EN norms, I don't know about other places in the world). By "terminal" I mean either prongs and/or side contacts as you may find in Schuko plugs (they are standard EU plugs, look at wikipedia if you are not familiar with them).
Plastic prongs have mere mechanical purpose and can be disregarded the electrical point of view.
About "Electric tingling" I wasn't sure you were using an euphemism to intend a leakage in noise spikes from the switching circuit through capacitive coupling rather than an actual tingling caused by a small flow of electricity through your fingers. So I mentioned both cases, even though they are two very different cases. Sorry if I wasn't clear enough in my previous reply.
If you can actually feel that tingling with your fingers then it is more likely an indication that there is a leakage from the mains, and in that case it can be measured as a current flowing through the ground wire. That situation *could* be dangerous, not to mention that it *could* make your differential circuit breaker to trip. Even some transformer based power supply may show that behaviour which is an indication the insulating material is defective. As long as this current leakage is small it is relatively unharmful, still it could damage other sensitive equipment, and definitely I wouldn't live in comfort with this. That's why I've said the unit should be discarded.
No one of my wall-wart switching power supplies, including laptop ones, apparently sport any leakage from mains. I didn't investigate accurately though. The only exception is those old PSUs from Acer mentioned in the previous reply, where I actually found, with a superficial check, a leakage of spikes from the switching circuit and a very small leakage from mains (some mA can be measured from PSU's negative to ground), not strong enough to be felt with the fingers but enough to fry the AVR programmer.
Also, if you have these units grounded and still feel that tingling then beware that it could be your grounding the problem! I.e., your ground could not be really ground, and maybe get some leakage from neutral or live.
About LEDs, yeah, I am aware of that thing, but that's another topic.
Have a nice day.
This is a video that would benefit from AI Generated voice track. It's amazing how many mispronunciations per minute this video contains
Nnnno AI does add nothing but unnatural feelings. Yes, you are utterly right about mispronouncing. It actually made me laugh after I watched the video today. C'est la vie.
FOOL BRIDGE RECTIFIER⚡⚡
He's like mr bean
*220 VAC IN OK.. TO 18... "NEXT" ...18 TO 220 VAC.. (BUT !! YOU HAVE NO AMP ANYMORE)*
*SO "TO WHAT USE" !!*
*IT IS NOT LIKE "220VAC..10A IN 220VAC...10A OUT" ..!! THINK EVEN NOT "1 AMP" OUT*
*SO ???*
Sorry for the late reply. You need to take into account power. A 220V-18V 20VA transformer roughly can output 1A while absorbing 90mA in input. Reversing the equation gives the same result: 20VA 18V in absorbs 1A and output 90mA at 220V. Indeed the output current is less, because efficiency must be brought into the equation. So suppose the efficiency of each transformer is 80%, the total efficiency of the two coupled transformers will be 64%, so output available power will be reduced at 12.8VA which gives 58mA at 220V vs. 90mA.
1A output means almost 220VA in power, and compensating the power losses, supposing a 90% efficiency (the larger the power, the larger the efficiency), to achieve 1A in output you would need a couple of transformers rated 272VA.
Remark. Edited, reason: typo on output voltage, added further details to achieve 1A output.
*100th comment*
So Why Capacitive Power Supply Are Bad? I watched 9 minutes and you still haven't answered that.
You stopped to watch just at the point where the answer was summarized at around 10:45.
Q rent
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