Mystery of Chinese Torch Recharging System
This story started when my friend gave me this torch and asked me why this torch stopped glowing. His torch is cheap but has a very bright and strong white LEDs. I decided to recharge it again so I plug it to wall outlet, after 2 hours still the torch can’t be lighted up. Next I opened the torch for troubleshooting purpose.
Inside the torch I found one sealed acid lead battery with a PCB board of charging system and an On/Off switch:
Surprisingly in the PCB I did not find any regulator or any step down transformer to decrease the 220 volt AC to lower voltage to charge the 5 volt battery and it does not have the filter circuit too. If you look at the board there is just 4x 1N4007 diode and one polyester cap that is in series with 220 AC volt. Besides this, it has one red LED that works as indicator and one 1/8 watt 33 ohm resistor to limit the current so that the LED will be protected. Summarize of this circuit-there was no regulation, no filter and no protection in which I think is not a good design and may post danger to the user.
The most important issue that I want to highlight is the manufacturer of this torch, where the 309 volt dc was sent directly to the battery terminal for charging the battery and this voltage is too much and can explode the battery.
That is why this torch is dangerous for the users and I am sure millions of this kind of torch already been distributed to the world because it is cheap and bright but they do not know that it was dangerous to have one.
Conclusions: The only bad component that I found in this torch was a bad battery. This battery suffered the pressure of 309 volts being pumped into it and no longer can be recharged. After I had replaced the battery, the torch works again. However, I have warned my friend not to use this torch due to dangerously recharging system and possible of battery explosion. I have replaced the battery just to make sure is the battery fault.
Note:
A sealed lead acid battery or gel cell is a lead acid battery that has the sulfuric acid electrolyte coagulated (thickened) so it cannot spill out. They are partially sealed, but have vents in case gases are accidentally released for example by overcharging. They can be used for smaller applications where they are turned upside down. They are more expensive than normal lead acid batteries, but they are also safer. They use different chemicals than dry cells, so they are rechargeable –source from Wikipedia.org
This article was prepared for you by Mr Beh from Iran.
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Jayant Gholba
February 15, 2016 at 10:19 pm
I think you measured rectified voltage without battery. The voltage would drop to 4V or so when battery is connected. This drop is due to series cap in series with AC.
beh
February 16, 2016 at 1:14 am
JAYANT
the 309 volt DC directly is going to battery in my case and not have any relation with internal 220 AC
and thanks
beh
February 16, 2016 at 2:13 am
... lower reading by meter after attaching the charger to meter does not mean that the pressure of 309 volt DC is not excite! this reading is just because of the internal resistance of battery that push back the electrons and meter just give incorrect values.
beh
February 16, 2016 at 6:29 pm
... this is another reason that how much the battery is suffering from this high voltages..
Humberto
February 15, 2016 at 11:10 pm
Hi beh, a great discovery. If Battery is supplied contantly with 309 DC volt I suppose it will damage soon. A very dangerous design, that´s why it´s a cheap device. Thank for the article.
beh
February 16, 2016 at 1:20 am
Hi Humerto
yes this is cheap torch and incorrect diagram but unfortunately these kind of device are all around and some times makes problem
thanks for attention
Parasuraman S
February 15, 2016 at 11:17 pm
Yes, Jayant Gholba is correct. I have repaired quite a lot of these lights. The Polyester capacitors are the main culprits. The values such as 105 (1mfd) are used to drop the voltage, along with a high value resistor across it. If you check the voltage without connecting the battery, it will give a wrong reading. Many circuits have a couple of transistors to control the current. The light is a waste of money, as it won't last long because of the failure of these dropping capacitors.
beh
February 16, 2016 at 1:26 am
in my case the polyester cap was good also no transistor found just found a bad diagram .in any case is dangerous torch
Albert van Bemmelen
February 16, 2016 at 12:05 am
Hi Beh, very good of you to point out the danger that these cheap designs can cause. I knew they existed but never had seen one in my repair before. And I read about deadly dangerous USB chargers before. And I even read about someone who got blind just because he accidentally misplaced the battery in his Laser Pen in the wrong direction and so that it exploded. Do not know if that is something that really can happen but I sure won't try it out, especially not now with my new 10Watt Green Laser Pen!
beh
February 16, 2016 at 1:28 am
Hi Albert
thanks for supports.
Robert Calk
February 16, 2016 at 2:40 am
Thanks for the article, Beh. I would refuse to repair a device that I thought could get someone hurt.
beh
February 16, 2016 at 9:42 am
Hi Robert
i repaired this torch just for curiosity that how this torch is working and learn something from others .i gave safety recommendation to my friend about this torch and thanks...beh
Robert Calk
February 16, 2016 at 12:42 pm
That is good. He could wrap the torch with some duct-tape real good and that could help in case the battery ever explodes.
Yogesh Panchal
February 16, 2016 at 4:32 pm
Beh,
I have Repaired rechargeable Mosquito racket say 3 Year Back which have similar design.I have just replaced the bad Battery which last for only six Months with new battery and since then it works fine till the date.Capacitor used is X Rated AC capacitor and is used for dropping the Voltage please refer the link as follows.
http://www.electroschematics.com/5678/capacitor-power-supply/
beh
February 16, 2016 at 11:50 pm
Hi Yogesh
thank you so much of your comment. but please tell me what kind of cap is the x rated AC capacitor?
thanks
beh
Paris Azis
February 18, 2016 at 12:51 am
Please allow me Yogesh. Beh, as X rated A.C capacitors are characterized all these capacitors that are connected in parallel to the utility line. You can usually see them in the first stages of common noise rejection filters in switching PSUs. They are those bulky yellow ones. Of course there are other body-colors used, like the light brown one whcich is very common.
Greetings
beh
February 21, 2016 at 7:56 am
PARIS thanks for info... regards ...beh
beh
February 17, 2016 at 12:25 pm
Yogesh : over this magic cap is written CL 21 225J 250 V i forgot to give this info on article . and is checked good.
Paris Azis
February 18, 2016 at 12:54 am
Beh,
This seems to be a 2,2 microfarad/250V (A.C) capacitor.
beh
February 21, 2016 at 7:50 am
yes it is
Robert Calk
February 22, 2016 at 12:17 am
A 2.2uF(225) should give about 24V 100mA output.
Paris Azis
February 23, 2016 at 3:11 am
This always depends on the input data Robert. If this 2,2 μF cap is connected at 230V/50Hz mains, then for 24 Volts drop it will let 158mA to pass through it. If the same cap is connected at 110V/60Hz mains voltage, then, for the same voltage drop of 24V it will let 89mA to pass through it. These above are the theoretical maximum current values for this cap and for the given voltage drop of 24V at the output circuit.
Paris Azis
February 23, 2016 at 3:23 am
Robert, just for preventing any likely confusion, please read above the word “drop” as “output”…
Paris Azis
February 18, 2016 at 7:55 pm
Hi Yogesh
I also own a similar mosquito racket and I had a similar problem (no battery charging). It has two NiMH AA rechargeable batteries in it, connected in series. Anyway the failure was easy to find and insignificant as well. A cable from the power input plug was just hanging therein after being desoldered. After resoldering it everything was O.K.
This product does not also make use of any battery overcharging protection in its PSU. But at least I could see imprinted in its packaging the instruction “charge the batteries for three hours maximum”…
Greetings
Paris Azis
February 16, 2016 at 4:45 pm
Hello Dears (all)
First of all Happy New Year (please excuse the delay on that)!!
Next, I feel that there is a lot of misunderstanding in this case here. These types of PSUs are quite common and equally quite acceptable within the designers’ community. Especially when it comes to totally isolated circuitry needed to supply current in the mA region (usually below 100mA) this type of PSU is the ideally preferable from most designers as the only drawback the final product has is the inherent danger of someone touching the circuit might hurt him. But this is also of relative value, because as an argument needs much further analysis, not being so simple. As long as the danger to touch anything from the internal circuit is eliminated, there is no good reason for not using this technique for covering almost any low power demand.
Therefore Parasuraman and Jayant are right about this case. It’s not this type of PSU to be blamed. It is the most likely inferior quality of its building materials what should be blamed. Nothing else. Especially regarding the input bipolar capacitor which is “the soul” of the entire circuit.
In my opinion, given that I don’t have the circuit in front of my eyes, the only missing thing from this could be a “charge stop” function.
Anyway, just in order to through the least of the needed light on this topic, please keep in mind that these supplies behave as “constant current” sources rather than “constant voltage” ones. This practically means that under normal conditions (=high component quality) they don’t need a fuse at their input.
Generally speaking and in order to make the already long story short, if anything wrong happens to them (like shorted cap) the inrush current resistor (33Ohms in this case and in general below 100Ohms) blows up and the story is over.
As for their normal operation, they are all based on the frequency dependent impedance of the capacitor they use at their input which shifts the phase of the current against the voltage and this way they perform the necessary voltage drop for the application.
This has to do with the “cos phi” good old story which needs a lot of space to be analyzed in detail. Anyway, just keep in your mind that you are dealing with a constant current supply PSU when working with them. Of course when they are exposed (under repair) they always remain potentially dangerous.
If you want to investigate the constant current effect of them, just put an amp meter at their input and then don’t hesitate to short out the output, at the DC side, after the rectification. You will be surprised just because the current will stabilize at a maximum magnitude without any other effect. This little magic, along with the fact that there are no heating effects dropping the voltage capacitively instead of resistively is the wonderful characteristic of these tiny but nevertheless marvelous PSUs…
Greetings to all of you
Robert Calk
February 17, 2016 at 6:00 pm
Thanks Paris. I believe you, but I still don't trust it. Murphy's Law dances in my mind...
I took an old mains powered smoke detector apart that worked on a similar circuit.
Paris Azis
February 17, 2016 at 10:56 pm
Don’t be afraid of it Robert and let Murphy keep on dancing! From my experience, there is nothing wrong with it (with the galvanic isolation problem excluded-taken into account). You can trust it as well as it is very reliable. This type of PSU reveals no significant electrical problems (if the capacitor is of known good quality).
As an example, 12 years ago I designed a sunlight sensing lighting-controller along with a PSU like this one here and installed it in our building for controlling the lighting of its yard at night, especially the car parking places. The unit works just fine up to now. I simply chose a first quality cap for it.
My Greetings to you
Robert Calk
February 18, 2016 at 8:41 am
Hi Paris. I guess that circuit would be much cheaper. I'm going to see if I can find a torch or something using a transformer-less circuit like that one, and do some experimenting as you suggested. I will be very careful, of course.
Paris Azis
February 18, 2016 at 7:25 pm
Yes Robert, you are right. It is obviously a much cheaper PSU circuit (and that’s the main reason they are using it extensively in such cases). Nevertheless it’s very reliable if quality caps are used. Especially in its more sophisticated form, including at least a low power zener for stabilization with an electrolytic cap in parallel to it at its output, it would be even better.
Well, given that you have an isolation transformer available in your bench and taking proper care, there is nothing to be afraid of. This circuit is amazingly safe (again if the cap is of good quality and if we exclude the galvanic isolation problem. But this is what finally makes it cheap)!! You will be surprised by shorting its output and seeing that nothing else happens (almost no change in current draw)!
I have repaired many of them, having found the aforesaid zener shorted out, its filtering el cap shorted out but the voltage dropping bipolar cap was intact in most cases! If the design is really good and something wrong happens at its output it doesn’t even blow the inrush current limiting resistor, that small one at its input…
Have a nice time with it anyway. (I am sure you will enjoy it)!
Robert Calk
February 19, 2016 at 11:05 am
Hi Paris,
I have been checking into them with your suggestions and our friends Yogesh and Henrique.
beh
February 16, 2016 at 11:46 pm
Hi Paris
thank you so much of very comprehensive explanations of this psu.
that is why i called this a CHINES MYSTERY RECHARGING SYSTEM and still is a mystery for me.
regards
beh
Paris Azis
February 17, 2016 at 11:10 pm
Well, if it still is a mystery to you dear Beh, the only alternative I have is to publish a detailed article about it dedicated to you! Perhaps I will start immediately gathering the needed info, by the chance of being myself ill because of flu…for a second time this year…Well, this insignificant disease has already killed over a hundred of people in my country so far… No capacitor is that bad!!
Greetings!
peter wang
February 19, 2016 at 9:51 pm
Hi Mr Azis, You are definitely right in saying that this transformerless step down PSU is relatively safe. There is no higher voltage involved than in a common chopper type PSU hot side. The current resistor or bleeder resistor parallel to the AC cap gives safety net should the cap shorts out and drain the stored power in the cap once the circuit is unplugged from the mains. If its limitation of 100mamp can be overcome I think a lot of our gadgets will be priced even lower.
Paris Azis
February 20, 2016 at 1:39 pm
Hi Peter
Judging from your descriptive comment alone, it is obvious to me that you indeed have a complete understanding of this type of PSUs and this is what is needed in order to work with them properly. I am sure you have spent a lot of time in reading relevant texts and playing with them.
Anyway, just be informed that there is no current limitation on them. (Just another reason for me to write a relevant article about them…Robert is already expecting it…And I think I will try it as it is a worthwhile topic).
You can draw any magnitude of current using them. The point is that drawing large currents through them encompasses some serious inherent drawbacks.
If you hit “capacitive PSUs” or “transformerless PSUs” in youtube you’ll get mad with what is going on there. The tragedy is that most of the people using real monsters there do not realize or better said they don’t have the slightest idea about the magnitude of the danger they expose their own lives and this is a nightmare to me… So, for the time being just keep in mind that all engineers in the world prefer to draw current through coils (i.e tranformers) and not through capacitors as the certainty for them to short out (especially in the case of high currents and high voltages) is always present.
If you know the basics about small induction motors (i.e. for ventilation fans) then you know that they usually make use of an auxiliary winding along with a capacitor in series connected to it. This circuit shifts the phase of the current within the motor in order for it to reach and maintain its nominal speed in a fast and steady way. Well, this capacitor (called the “running capacitor”), although it’s always chosen with great care for withstanding such an important task, it usually fails over time, whereas the coils of the motor are still intact…
Thanks for the comment and your support.
Robert Calk
February 20, 2016 at 2:50 am
Hi Paris,
I would enjoy reading your article on the power supplies very much. Excellent idea!
Paris Azis
February 20, 2016 at 1:56 pm
Hi Robert
Although this task (of writing a relevant article) suits better the capabilities of our friend Gerald Musy who is far superior than me in that field, I think I will try it. Just give me some time to prepare it. This needs at least a minimum of mathematics in order to be understood but don’t get freaked about that. I will try to make a “hands on” presentation in an as much as possible manner.
Greetings
Robert Calk
February 20, 2016 at 3:51 pm
Hi Paris,
I won't get freaked by the math. I have the new book," The Art
of Electronics - Third Edition", that is chocked full of math.
I have confidence that you will do an excellent job. Take your
time.
Paris Azis
February 21, 2016 at 4:00 pm
O.K Robert. I prepare this article as soon as possible. Thank you for your understanding.
beh
February 21, 2016 at 7:47 am
Hi Pris
tanks for your efforts to clear this strange looking psu for me
i wished you to get better and get ride of these bad viruses and start to write your article about this AMAZING charger ( high voltage with very low amperage} hope to that date
i want to recommend that just wash your nose and your face with enough water several time in day and mechanically destroy the viruses this is the last way for remedy from in flu with no cost and medicine and good luck..beh
Paris Azis
February 21, 2016 at 4:29 pm
Hi Beh
At a first glance it is strange looking indeed, but once its secrets get deciphered it automatically loses its mystery and becomes a trivial matter (as usually happens in life).
Thank you for your recommendations about that flu. This is what I ordinarily do when this kind of illness appears. Washing especially the hands many times within the day is of utmost importance in such cases indeed. I also avoid taking medicines for flu, but although I did the same currently, hearing the every-day news about it, I admit that it scared me this time. Over a hundred people lost their lives because of its mutated virus and this is a relatively large number. Anyway, thank you for your advice. As for the article, just stay here giving me time to prepare it…
Paris Azis
February 22, 2016 at 2:50 am
You are always welcome Beh. This circuit that looks strange for the time being will lose its mystery after deciphering its secrets and will become a trivial matter thereafter!
Thank you for your wish and recommendations about confronting the flu issue as well. I always take care of having my hands clean all the time, especially when being ill of flu. This is important in such cases indeed.
Henrique J. G. Ulbrich
February 17, 2016 at 12:28 am
Dear Paris, undoubtedly you put the things in their due place. Thanks for the comprehensive explanation. It doesn't get any better. In addition, the link http://www.electroschematics.com/5678/capacitor-power-supply/ suggested by Yogesh Panchal (thanks too) closes the issue.
Paris Azis
February 18, 2016 at 7:38 pm
Hi Henrique
Thank you for your kind words. I also visited the site suggested by Yogesh (thank you too Yogesh). It really provides valuable additional information on the topic.
My Greetings to you!
beh
February 22, 2016 at 11:30 am
Hi Paris
yes .also wash your hands several time during the day. but the viruses are living in your nose and your face wash them off by water .hope to see you soon healthy again.
beh
Paris Azis
February 23, 2016 at 2:33 am
Thanks again Beh, I already feel much better.
Greetings
beh
February 23, 2016 at 6:26 pm
PARIS: thanks gods you feel better.
Yogesh Panchal
February 22, 2016 at 9:52 pm
Paris,
Thanks for detailed explanation.
Paris Azis
February 23, 2016 at 2:32 am
You are welcome Yogesh.
Greetings
bamixfernan
January 30, 2018 at 1:05 am
the mystery is the resistor connected under the capacitor take a look of it,.. thats the reason why it drops 5v dc without regulator. (y)