Is this charger safe? - Page 1
Forum section: electronics / beginners

author: Charkel
author_rank: Contributor
timestamp: August 25, 2017, 09:06:11 pm
content: Is this charger to be considered "safe" by an expert? I'm scared of using any generic charger. Please help me understand what I'm looking at here. Just got my first soldering iron for x-mas but haven't used itBut I also need to learn about what good engineering looks like before I can try it myself.Accidentally scratched the cap while opening the case before I knew it was a screw under a sticker... DOH!! Dangerous?

author: madires
author_rank: Super Contributor
timestamp: August 25, 2017, 09:09:02 pm
content: Which charger do you mean? Pictures and schematics would be helpful

author: Charkel
author_rank: Contributor
timestamp: August 25, 2017, 09:17:25 pm
content: Quote from: madires on August 25, 2017, 09:09:02 pmI do not know what you are talking about. There are some mighty fine pictures right there

author: sleemanj
author_rank: Super Contributor
timestamp: August 25, 2017, 09:29:17 pm
content: You are showing components only, a picture is only sometimes worth 1000 words, yours are worth about 2, specifically, "no idea". The only thing that can really be said is it appears to have a fuse so it's at least one step above many.You should go watch some of bigclivedotcom on youtube, he tears down, reverse engineers and evaluates a number of such cheap power supplies.

author: madires
author_rank: Super Contributor
timestamp: August 25, 2017, 09:39:15 pm
content: The back side would be interesting too for checking the clearance between primary and secondary side. I see cheap electrolytics, no X2 filter cap, no MOV, a common mode choke, a SMPSU controller with an opto coupler for feedback, and a LC output filter. It's cheap, but doesn't seem to be nasty.

author: Charkel
author_rank: Contributor
timestamp: August 25, 2017, 09:46:57 pm
content: Quote from: madires on August 25, 2017, 09:39:15 pm

author: wraper
author_rank: Unknown
timestamp: August 25, 2017, 09:53:28 pm
content: Quote from: madires on August 25, 2017, 09:39:15 pmYou normally won't find X2 cap and MOV even in high quality charger of similar power. Common mode choke is already a blessing.This Charger is not bad and seems perfectly safe. Actually I cannot say anything bad about it except electrolytic capacitors of some unknown brand.

author: madires
author_rank: Super Contributor
timestamp: August 25, 2017, 09:56:37 pm
content: The clearance is ok.

author: wraper
author_rank: Unknown
timestamp: August 25, 2017, 10:13:16 pm
content: Quote from: blueskull on August 25, 2017, 09:44:14 pm1. Show a charger with ceramic fuse.2. Nothing to do with reality, you don't need X cap to pass that, modern low power SMPS controllers don't even need a choke to pass EMI test due to very low emissions. From SD6860 datasheetQuoteAnd it even has a ferrite bead on the output.3. There seem to be safety marking on the cap but it's barely visible on the photos.

author: Electro Detective
author_rank: Super Contributor
timestamp: August 25, 2017, 10:36:11 pm
content: Hey Charkel, nice photos and not a bad looking charger compared to a lot of sledge hammer magnets I've seenPLEASE don't be shy typing some details about it, so helpful members here have something to work with

author: TheDane
author_rank: Regular Contributor
timestamp: August 26, 2017, 09:27:08 am
content: The input seems like it is fused, if I think the glass component is in series with the main input.The mains cap is 400v, 105 degrees C, is this a 120v or 230v unit - it should be safe in any case from blowing the cap. Any lightning strike would most likely blow it though, as surge protection is missing.There is a common mode filter in place - it reduces emissions from the switching.The clearance between primary and secondary seems ok, it is hard to judge distance/size from your pics.The output diode is nice and big, so it can most likely stand the current you draw - what is the device ratings?- there seems to be a little bit of output filtering as well. This is good.There seems to be no short circuit protection, and the voltage is fixed - so I recommend getting a regular lab supply to power your new hobby projects.What are you worried about, since you post -?(It is NOT safe if you encapsulate it completely in epoxy and draw lots of continuous power - it will overheat, but since you don't state anything about what you need it for, this is an example of you asking interesting questions, and me answering a hypothetical question. Since I don't know your intentions, it's almost impossible to answer you in full)Experience is experienced, learning is well.. gettingstartedOn a personal note, I wouldn't worry too much about it - if used on low power (rated) consumer electronic items.BTW - there seems to be a broken/cut pcb trace near the top red wire in your pcb view!!!!!Edit - Added: The mains wall input connection seems to be below the PCB as part of the enclosure. You need to take a picture/verify that there is enough clearance between the pins and the PCB, and the soldering job is done well enough, if you need my further advice.A soldered wire onto a pin (wall outlet fixture) can/will loosen over time, and if it shorts to the secondary it is trouble! Mechanical fixture is of utmost importance, especially if used in a rugged environment.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 26, 2017, 09:35:41 am
content: There is no such thing like absolute safety.Yes, the charger appears to be safe enough.

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2017, 09:44:34 am
content: As mentioned above, it's perfectly safe. Note also that it is not a charger, but a DC power supply. It is not designed to directly charge a battery, but power a device with battery charging circuitry built-in.Quote from: wraper on August 25, 2017, 10:13:16 pmThe IC is the SD6830 but I couldn't find the full data sheet, only this:http://www.silan.com.cn/english/product/ProductItemDetail.aspx?id=18&pid=20150315091657635620534364534331&c=Confusingly, there's a microcontroller, with the same part number and Google searches find the data sheet for that.Quote from: TheDane on August 26, 2017, 09:27:08 amThere is short circuit protection. The controller IC has it built-in.

author: TheDane
author_rank: Regular Contributor
timestamp: August 26, 2017, 09:47:47 am
content: Quote from: Hero999 on August 26, 2017, 09:44:34 amThanks, my LCD viewer can't penetrate the epoxy layer of chipsEdit - Added:Chip is on primary side, so does it throttle back - or keep pumping current at its limit ratings, not worrying about output voltage?(no, I have NOT read the datasheet - and I won't)

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2017, 12:36:48 pm
content: Quote from: TheDane on August 26, 2017, 09:47:47 amI couldn't find a data sheet, but if I did, why wouldn't you read at it?I don't know how the current limiting is implemented. The description just says"Various protections: overvoltage, undervoltage, short-circuit, over load and over temperature protections.".

author: oldway
author_rank: Super Contributor
timestamp: August 26, 2017, 01:37:21 pm
content: To be safe, it must comply with class II reforced (EDIT: reinforced) isolation norm and to have been tested at 4250Vdc during 1 minute between input and output.I doubt such a low cost charger has really been tested with high voltage....

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2017, 01:45:48 pm
content: Quote from: oldway on August 26, 2017, 01:37:21 pmIt would surprise me too, especially as such extreme testing is not mandatory.

author: oldway
author_rank: Super Contributor
timestamp: August 26, 2017, 02:01:47 pm
content: Quote from: Hero999 on August 26, 2017, 01:45:48 pmAre you sure of this ?At least in Belgium, it is. (RGIBT - Réglement général des installations basse tension)And all the power supplies manufactured by Cherokee Europe where tested of this manner.

author: madires
author_rank: Super Contributor
timestamp: August 26, 2017, 02:15:25 pm
content: There's no "it's 100% safe". Even if we would enforce compliance testing by independent or federal labs bad vendors would still be able to cheat. For example, the vendor ships good PSUs for testing and later on he ships bad PSUs for profit. You can't expect everyone to buy an isolation tester and to become an electronics expert. The only advice I can give to non-experts is to buy wall warts from well known brands.Just as a side note: If you got a bunch of wall warts in a power strip running 24/7, replace them with a good 12V power brick (>= 90% efficiency) and a bunch of buck converters. That will nearly half the power usage and you don't have to worry about cheap wall warts.

author: oldway
author_rank: Super Contributor
timestamp: August 26, 2017, 02:28:56 pm
content: It seems that a class II (no earthing, reinforced insulation) gear must be tested at high voltage to comply with UL60950-1 § 2.9.4...Unhappely, I only found an extract of UL60950-1....These norms seems not be available for free.....NB: it's not an extreme testing, but a basic and very important safety test

author: TheDane
author_rank: Regular Contributor
timestamp: August 26, 2017, 02:47:12 pm
content: Quote from: TheDane on August 26, 2017, 09:47:47 amTime limitation, simply as that. (And the desire to trawl trough the web, yet again)Today I 'hacked' an old Happauge TV card (HVR-1200) and added an HDMI-AV converter permanently onto it.I also added a 5v power supply module (PCIe bus is 3v3 and 12v), and a diode to avoid reverse power.Cabling, soldering, etc. Now it is time to test it out, and since you asked - I answeredAnd yes, Various protections can mean a lot. Only practical testing can really answer all questions, if there are unknown elements involved - -reverse engineering can be fun, and costly at times.Experience is also experiencing stuff blowing up - having a camera running can provide insights, and/or hit views

author: tronde
author_rank: Frequent Contributor
timestamp: August 26, 2017, 04:17:08 pm
content: Quote from: Charkel on August 25, 2017, 09:06:11 pmSince you appear to be Swedish, you can learn something from this report about USB-chargers published by the Swedish Electrical Safety Board earlier this year.www.elsakerhetsverket.se/globalassets/publikationer/rapporter/elsak-granskning-usbladdare-2017.pdf

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2017, 06:02:54 pm
content: Quote from: oldway on August 26, 2017, 02:01:47 pmNormally a sample needs to be tested, for approval purposes, not every single unit produced. Such a test is also pretty stressful to the insulation, which, unless is ridiculously over-engineered, could be weakened as a result, even if it passes, so the test would actually make the device more hazardous, not safer. I would not feel comfortable using a device which I know has been subjected to this sort of stress test.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 26, 2017, 06:30:56 pm
content: Although this looks reasonable apart from the use of a glass not ceramic fuse it is often the transformer construction that is at fault in these cheap power supplies. The requirement is for 4mm creepage or the alternative is the use of triple insulated wire in either the primary or secondary.The solution is to never trust it and always earth one of the output legs. Certainly do not use this kind of product for powering any experiment that is in contact with body tissue and always use external overcurrent protection on the output even if that is a simple fuse but close rated.If this is going to be your testbench psu you might be better off buying a second hand lab power supply that has a 50hZ transformer (less likely to suffer from skimped construction). Efficiency is not a substitute for safety!

author: oldway
author_rank: Super Contributor
timestamp: August 26, 2017, 09:08:02 pm
content: Quote from: Hero999 on August 26, 2017, 06:02:54 pmThat's not what I have seen as practice in industry....!!!! Safety is not a concern that can be controlled only by sampling...It must be 100% tested...The only thin barrier between mains voltage (230V) and the user is the primary/secondary insulation of the ferrite transformer....Primary and secondary are very close....thats very dangerous.If the test must be repeated, you can only apply a reduced voltage of 80% of the nominal test voltage.

author: oldway
author_rank: Super Contributor
timestamp: August 26, 2017, 09:44:10 pm
content: Quote from: madires on August 25, 2017, 09:39:15 pmI find very interesting that some people are concerned to check only the things they can see, as clearance between primary and secondary side (must be >8mm), data sheet of optocoupler, but forget or even refuse to check the internal clearance/insulation of the transformer.....and the only way to check this is to test the power supply applying the specified voltage (4250Vdc) during 1 minute between primary and secondary sides of the charger.

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2017, 09:53:09 pm
content: Quote from: oldway on August 26, 2017, 09:08:02 pmI disagree. In theory no testing is necessary. If the insulation is so thin, that every product needs to be tested, then the design is marginal and isn't safe to begin with. It should be redesigned so it will comfortably exceed the minimum requirements.Electrical safety can be guaranteed, purely by design. The breakdown voltage of various insulating materials is a well known parameter. All one needs to do is make sure the material is thick enough, sufficiently mechanically robust and large enough creapage and clearances are used throughout the design. In reality it may be necessary to test a small sample of materials/products, to ensure they meet the specifications but 100% testing is not desirable. Any products which have been subjected to the high potential test should be destroyed and not sold to the customer.

author: wraper
author_rank: Unknown
timestamp: August 26, 2017, 11:01:54 pm
content: Quote from: oldway on August 26, 2017, 09:44:10 pmPeople don't forget that (at least me), it's just obvious that it cannot be tested without special equipment. Se mentioning it won't change anything.

author: wraper
author_rank: Unknown
timestamp: August 26, 2017, 11:16:34 pm
content: Quote from: Hero999 on August 26, 2017, 09:53:09 pmPower supplies, optocouplers, transformers are Hi-POT tested individually. You cannot guarantee by design against assembly defects.Good PSU, deadly short due to manufacturing defect:Quote

author: oldway
author_rank: Super Contributor
timestamp: August 27, 2017, 07:15:34 am
content: Quote from: Hero999 on August 26, 2017, 09:53:09 pmFor sure, you have not the least experience in quality control of electricity and power electronics gears to write such a bullshit.Should you be quality control manager, the first customer who will be electrocuted will send you to jail , and for a very long time.For exemple, technical specifications of a SMPS...High pot tested at 4242Vdc 1m between primary and secondary.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 27, 2017, 07:35:04 am
content: And if you saw the way transformers are mass produced (thrown together) in Asia you would understand that the designers intention is completely sacrificed to cut corners so specifying certain types of insulation is useless.As we now live in a deregulated world to encourage trade nothing is tested anymore hence we have corner cutting manufacturing directly in contact with the consumer, it is only a matter of luck that we do not have more serious accidents and of course much goes unreported as the units are simply thrown away if deemed to be faulty.As I said before never trust your life to this kind of mass produced rubbish

author: madires
author_rank: Super Contributor
timestamp: August 27, 2017, 08:03:18 am
content: Quote from: oldway on August 26, 2017, 09:44:10 pmPlease feel free to send the OP a proper isolation testerAnd please see Table 2K of IEC-60950-1 for the clearance. IIRC, it should be 4mm in this case.

author: oldway
author_rank: Super Contributor
timestamp: August 27, 2017, 10:53:38 am
content: Quote from: madires on August 27, 2017, 08:03:18 amNot at all. For class II appliances, you must use the reinforced insulation values (R of the table) for peak working voltage of 420V and the clearance is 6.4mm.But this apply only for free air clearance and it can't be apply to circuit board.Here are the PCB's recommanded clearance....To withstand a 4.242Vdv test, clearance should be 12.96mm.That's huge.....this is the reason why air gap's are use instead.For safety, there would be an air gap between primary and secondary circuits.Dave remember this in almost all his teardowns

author: madires
author_rank: Super Contributor
timestamp: August 27, 2017, 11:22:18 am
content: Based on that we would have to trash 95% of all SMPSUs.

author: oldway
author_rank: Super Contributor
timestamp: August 27, 2017, 02:13:59 pm
content: Quote from: madires on August 27, 2017, 11:22:18 amYes, you would have to trash 95% of all SMPS you buy on Ebay for 10 bucks from Chinese sellers....yes, indeed...

author: madires
author_rank: Super Contributor
timestamp: August 27, 2017, 05:09:52 pm
content: ... and also nearly all wall warts which come with gadgets, mobile phones, SOHO routers and what have you.

author: oldway
author_rank: Super Contributor
timestamp: August 27, 2017, 05:29:54 pm
content: Quote from: madires on August 27, 2017, 05:09:52 pmNot all manufacturers are only (qualified ?) hobbyist , some are true and serious professionals....you don't seems to believe this.I worked by Cherokee Europe and even after a repair, the used SMPS had to be High pot tested successfully again before to be delivered to the customer.

author: james_s
author_rank: Super Contributor
timestamp: August 27, 2017, 06:13:01 pm
content: Overall it looks reasonable, but you'd have to disassemble the transformer to really tell, that's the most likely place for a breakdown between primary and secondary to occur.For what it's worth, I've got a bunch of various cheap power bricks like this and they have all been fine. I wouldn't use it to power a medical device or something I was going to use while sitting in a pool or something but for general use I see no reason to be alarmed.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 27, 2017, 07:29:23 pm
content: Quote from: james_s link=topic=94083.msg1289293#msg1289293 date=1503857581but for general use I see no reason to be alarmed.[/quote

author: Zero999
author_rank: Super Contributor
timestamp: August 27, 2017, 07:33:50 pm
content: Quote from: oldway on August 27, 2017, 07:15:34 amYou're talking nonsense. For a start, there's nothing in that data sheet to say that every single device has been tested, just that it can withstand 4242V, from primary to secondary and that the design (not necessarily every single model) has been tested to comply with various safety standards.Safety can be guaranteed by design. There are far more potentially dangerous things, than a mains powered switching regulator, which are engineered to be safe and never tested to the design limits. Take a house for example, the supporting structures in the building, will be designed to hold the maximum nominal load, multiplied by a large safety factor (typically two), but it will never be tested to confirm this. The engineer who designed the building, ensured that it will be strong enough and conform to the relevant building regulations. The same is true for cars, aeroplanes, bridges, etcetera.Testing can be useful to verify a design meets certain requirements (safety being only one of them) but once that's been achieved, it only needs to be done sporadically, to confirm the suppliers and manufacturing process are adequate. It's not necessary or desirable repeat tests, which are potentially dangerous. I certainly wouldn't want to live in a house, which has been tested right up to the design stress limits, that could cause microscopic cracks to form. I'd rather live in a house which has been designed to be safe and not subjected to unnecessary stress.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 27, 2017, 07:55:00 pm
content: Quote from: Hero999 on August 27, 2017, 07:33:50 pmWell IMOP your both right but viewing the matter from opposite ends without much knowledge of what goes on in the middle! In my experience specifying something to an Asian manufacturer is rather different to how things might work in a euro/usa concept, where as in the latter it is assumed the other party to the contract will adhere to the specification throughout the contract in Asia it is seen as an initial requirement that must be met for a few samples but thereafter the manufacturer may at will relax constraints to meet lead time demands or improve profit margins or component supply difficulties. Quite simply eastern and western minds do not think alikeSo as a designer with western manufacturing it is indeed only necessary to test a few examples rigorously and rely upon the manufacturer afterwards for eastern fabs rigorous quality control is necessary to ensure continuing compliance with the contract. Add to this a commodity product and a whole new ballpark opens up that of copying or stealing IP, this is remarkably common and identical designs but badged under different names rapidly appear of course any adherence to the original design requirements are completely ignored as often all that is stolen is a pcb layout and parts list, the transformer being reconstructed (but cost reduced) by reverse engineering (stripping and turn counting). This is the real world of what actually happens, many products like smps landing on consumer laps in the west are 3 or more times removed (copied) from the original design. To imagine any original designer specifications remain in there construction is pure wishful thinking...sorry!!

author: Zero999
author_rank: Super Contributor
timestamp: August 27, 2017, 08:11:04 pm
content: Quote from: fourtytwo42 on August 27, 2017, 07:55:00 pmI see your point. Yes you need to supervise foreign manufactures. Still 100% testing is not required. Spot testing, and inspection, including destructive, should catch contractors cutting corners.Quote from: wraper on August 26, 2017, 11:16:34 pmYes, you can. By design, I mean the whole process, not just the components and laying out the PCB, but the materials and how they're physically put together. The video you've linked to demonstrates this perfectly. Proper design could have avoided this fault. Testing could have made this worse by weakening some marginal components, causing them to fail in the field, which might even be the case here!

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 27, 2017, 08:14:05 pm
content: Sadly I beg to differ, It seems you have limited or no experience of manufacturing!

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 27, 2017, 09:12:30 pm
content: Quote from: fourtytwo42 on August 27, 2017, 07:35:04 amYou could argue that if you don't fully test all the electrical equipment yourself, you are trusting your life to it. A faulty USB charger can quite easily burn your house down, with you in it. You trust the equipment around you every day.

author: Zero999
author_rank: Super Contributor
timestamp: August 27, 2017, 09:51:20 pm
content: Quote from: Mr. Scram on August 27, 2017, 09:12:30 pmIndeed, the same thing could be said about anything. There's such thing as due diligence. If you can prove, you've designed it properly and you've got paperwork from the manufacturer, stating they've followed your instructions to the letter, to meet the specification, then you've gone as far as you can. If there's a manufacturing defect, which causes a safety issue, then you've done all you can. The blame then falls on the manufacturer for not building it to specification.In practise, most companies don't even make their own power supplies any more. They use subcontractors. I doubt Apple or any other company, tests their PSUs made by a third party.Why is it that as soon as the issue of electrical safety is raised some people seem to lose all perspective? They'll happily live in buildings, drive cars and take flights in planes, which haven't been 100% stress tested, to the design requirements, yet they mandate the same for a mundane, comparatively low risk, switched mode power supply?

author: wraper
author_rank: Unknown
timestamp: August 27, 2017, 10:19:42 pm
content: Quote from: Hero999 on August 27, 2017, 08:11:04 pmHi pot testing does not weaken insulation if it was good in the first place. While under high voltage, leakage current is measured, if it exceeds (tiny) specified value, device does not pass. If the insulation was weakened during test, it would not pass test in the first place. I don't know for sure if that PSU was Hi-POT tested, likely it was and during test insulation was good enough to withstand it. But then it could drop, and wire could move a little bit over damaged insulation area. There was no fault in the design itself, reinforced multiplayer insulation was mechanically damaged during production. BTW I was myself in the factory where they Hi-POT test their devices where high voltage is present. Haven't you ever seen hi-pot stickers?

author: Zero999
author_rank: Super Contributor
timestamp: August 27, 2017, 10:30:46 pm
content: Quote from: wraper on August 27, 2017, 10:19:42 pmYes. I've seen hi-pot stickers and have never seen the point. It won't stop marginal devices from slipping through or show up poor manufacturing. Only disassembly and visual inspection can do that. Yes, you're right, it shouldn't damage the insulation, as long as the test voltage isn't too high (much lower than the withstand voltage) and hasn't been applied for too long.I disagree with you about the construction of the transformer. There isn't enough insulation, where the windings pass near one another and it appears too much force has been used when it was wound. Very shoddy.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 27, 2017, 10:52:39 pm
content: Please guys, remember that we're here to help Charkel. I don't feel he is benefiting much from this discussion. It seems pretty clear some products are tested to their design specifications, but that others are not. The discussion which are tested in what way and why seems more suited for another thread.

author: wraper
author_rank: Unknown
timestamp: August 27, 2017, 11:32:15 pm
content: Quote from: Hero999 on August 27, 2017, 10:30:46 pmThe point is to indicate that test was passed. Therefore no untested device may accidentally slip further.QuoteVisual inspection will happily pass most of the faults, it's only good for finding the most obvious defects. It's really obvious you never dealt with actual production. And you cannot inspect inside the parts (where most of the faults happen), and you won't be able to see imperfections in insulation anyway. Exactly Hi-POT test is what weeds out marginal devices. Withstand voltage meanswithstanddon't confuse that with breakdown voltage.QuoteWire used in secondary winding had reinforced insulation by itself. Basically you could wind primary winding directly on top of it, and it would be just fine. The issue was that a big piece of that insulation was missing because of mechanical damage.EDIT: Something like thishttp://www.totoku.com/products/cables/tiw/post-2.php, additional insulation between windings is not required at all.

author: oldway
author_rank: Super Contributor
timestamp: August 28, 2017, 06:10:36 am
content: "High voltage test (also called hipot or HV test worldwide) has by far the highest priority among all of the electrical safety tests.This test of the dielectric strength ismandatoryas it is part of the requirements of all national standards (e.g. VDE and UL) and international standards (e.g. EN and IEC).The often used term insulation test or insulation measurement is wrong in this context as a real, ohmic resistance is measured with the direct voltage in this case. In contrast, the high voltage test is carried out with both direct and alternating current. The result of this test is a leakage current, flowing between live parts and the metallic casing. Devices of protection class I always come with a metal casing, whereas the casing of the devices of protection class II must be replaced by a metallic contour during the test. In reality, the high voltage test is a geometric distance measurement in the DUT (Device Under Test): If the DUT withstands a certain voltage without flashover, an appropriate minimum distance between the metal casing and electrical components in the device is ensured. Thus, the term withstand voltage is also plausible again."https://www.spselectronic.com/en/products/high-voltage/

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 08:25:55 am
content: Quote from: oldway on August 28, 2017, 06:10:36 amI've done more research and I stand corrected. The regulations mandate some high voltage testing. I had confused the withstand voltage and breakdown voltage.Quote from: wraper on August 27, 2017, 11:32:15 pmI meant spot checks, involving destructive visual inspection.QuoteYes, I confused withstand with breakdown voltage.QuoteMechanical damaged, caused by poor manufacturing process. If the winding machine was incorrectly set, there will be other devices with a similar fault and the high voltage withstand test might not have revealed it.

author: oldway
author_rank: Super Contributor
timestamp: August 28, 2017, 10:05:06 am
content: I think you were influenced by the multimeters, which is why you wrote that you felt that a device undergoing a high voltage test could no longer be sold to the customer.For electrical appliances and power electronics, the standards are different and this has nothing to do with multimeters.There are several classes of isolation, I refer you to Wikipedia for more explanations.https://en.wikipedia.org/wiki/Appliance_classesChargers and power supplies belong to Class II double insulation.Since the secondary is not grounded, the safety of the user depends only on the quality of the insulation between primary and secondary.This safety is guaranteed by an Hi-Pot test.The test conditions are difficult to find on the Internet because the standards are protected by Copyright and are not free available on the Internet .... Moreover, these standards are complicated and difficult to interpret correctly.As far as I can remember, the test voltage applied for Class I equipment is 1500Vrms in 50 or 60Hz or 2121Vdc and 3000Veff 50 or 60Hz or 4240Vdc for Class II.The test time is normally 1 min. But can be reduced to minimum 1s. (It should not be possible to make a test of 1 min. duration in mass producted appliances.)It is intended that the voltage should be applied gradually. (ramp).This test is fundamental and it is the only guarantee of safety for the user against the risks of electrocution.It should be remembered that in Europe, many distribution networks have a 230V ground-phase voltage and the risks are high.Is this test actually done at the factory?There is no guarantee and no way to verify it.So you can only trust in the well known brands.Any no-brand or unknown brand, or fake gear is therefore not safe.To answer Charkel, no, this charger is not safe

author: madires
author_rank: Super Contributor
timestamp: August 28, 2017, 10:52:27 am
content: I'd like to suggest that you take three randomly choosen wall warts apart. As the family's repair shop I see what's under the cover with all the fancy certification labels. Paper doesn't blush. And I'm talking about typical consumer electronics from more or less known vendors, and not about cheap crap bought directly from China.

author: wraper
author_rank: Unknown
timestamp: August 28, 2017, 12:11:23 pm
content: Quote from: Hero999 on August 28, 2017, 08:25:55 amSuch fault may happen to one in 100 000 transformers and destructive inspection of sampled devices won't reveal anything wrong. The good thing with Hi-pot test is that 100% of devices are tested and may reveal rare issue with production process.

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 04:40:30 pm
content: Quote from: wraper on August 28, 2017, 12:11:23 pmOr you might have 100 000 transformers, with shoddy winding like that, but only a few of them are bad enough to fail the high voltage test. Many of the others will fail in the field. The test shouldn't be relied up on to catch all faults.

author: oldway
author_rank: Super Contributor
timestamp: August 28, 2017, 08:21:46 pm
content: This test of the dielectric strengh is part of the requirements of all national standards (e.g. VDE and UL) and international standards (e.g. EN and IEC), it is mandatory and there is nothing to discuss about utility of these standarts.It is like a law .....You must obey or you will have serious troubles....This is the way a quality control works....you must comply with the standarts....nothing more.Do you think you are more clever than the people how make these standarts ?.

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 10:40:49 pm
content: Quote from: oldway on August 28, 2017, 08:21:46 pmI've already told you I've changed my position on that. Yes I agree, it's law but that doesn't mean it's perfect.QuoteNo!Standards are just the bare minimum.Electrical tests will not catch all faults and relying on them alone, will only lull one into a false sense of security. There are plenty of faults which will not cause the device to fail the test, yet still cause catastrophic failure later on. We might have seen an example of this here. It's possible that the transformer passed the high voltage test with flying colours, then after some rough handling the insulation chafed, causing a short from the primary to secondary. No electrical tests will pick up on this kind of thing. I still blame poor manufacturing, test or no test.QuoteI'm smarter than some of them, but not as smart as others.

author: Audioguru
author_rank: Super Contributor
timestamp: August 28, 2017, 11:48:07 pm
content: Many electrical "standard tests" are done then a passing design is certified to be safe.My electrical utility gave away compact fluorescent light bulbs for free for people to try then replace all the power-robbing incandescent light bulbs so that the utility will not need to build additional very expensive generating stations. But many of the new bulbs dripped burning plastic. The Chinese no-name-brand manufacturer never had the bulbs certified to be safe, instead they stole a certification number from a competitor and put that number on all their faulty bulbs. They were all recalled and replaced with name-brand certified and safe bulbs.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 29, 2017, 05:18:06 pm
content: Quote from: oldway on August 28, 2017, 08:21:46 pmI used to think that standards and certifications meant thorough inspections and qualification. Boy, was I wrong. Thinking quality control is the same as complying with standards is setting yourself up for failure. You just make life easier on yourself by being compliant, but generally much more is needed to do it right.

author: oldway
author_rank: Super Contributor
timestamp: August 30, 2017, 07:07:35 am
content: It seems that you did not understand what I meant.When I say "you must comply with the standarts .... nothing more.", I mean that we do not have to discuss these standarts, nor seek to know whether they should be applied or not, whether they are valid or not, just apply them,

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 30, 2017, 02:12:49 pm
content: Quote from: oldway on August 30, 2017, 07:07:35 amI understood, but I don't agree. Understanding why you do something is a huge boon.

author: oldway
author_rank: Super Contributor
timestamp: August 30, 2017, 07:04:45 pm
content: Quote from: Mr. Scram on August 30, 2017, 02:12:49 pmThis kind of discussion has nothing to do with the topic.The question is simple,"Is this charger safe ?" the answer is also simple...NO...The high pot test is mandatory and it is the fundamental test to ensure safety.Has the charger passed the higt pot test?Probably not.Is it safe? NO .... final point.

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 08:55:26 am
content: Quote from: oldway on August 30, 2017, 07:04:45 pmWe don't know whether it has been high voltage tested or not and even if it hasn't, it still might be safe.Quote from: Mr. Scram on August 30, 2017, 02:12:49 pmIt's also vital to understand the limitations of the test, in order to design a safe product, otherwise one is just designing something to pass a test, not be safe. The same is true with car emissions tests.

author: oldway
author_rank: Super Contributor
timestamp: August 31, 2017, 11:30:17 am
content: QuoteSafety is not a lottery...Your security conception is completely false ... and you continue in your mistakes.Not long ago, you said that the Hi Pot tests were not mandatory and now you claim that a device can be considered as safe even if it has not passed the hi pot test ....No at all, if a device has not passed the mandatory tests, it is not safe even if nobody has been electrocuted .... We must not confuse safety with Russian roulette.QuoteAbsolutely non senseIf insulation passed a High Pot test of 4240Vdc, we can be sure that it is safe and that there is no risk of insulation failure between primary and secondary with only 230Vac (325Vpeak).

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 02:22:26 pm
content: Quote from: oldway on August 31, 2017, 11:30:17 amI didn't say it's safe, just that you can't be certain it isn't safe. Was a learner driver unsafe the morning before they passed their driving test? Passing the test is just a legal requirement. I agree, there's a sound reason for the test, but it doesn't make it perfect.QuoteI see your point. I don't blame you for erring on the side of caution and believing something is not safe, until tested, but I'm certain I take bigger risks in every day life, than using a switched mode power supply, which might not have been tested, so it wouldn't bother me personally. Everyone has a different idea of what level of risk they're prepared to take. At least now the original poster, if they're still here, has some idea of the level of risk they might be taking.QuoteNo. Passing the test, just means it can withstand that voltage at that point in time. It doesn't mean it's of mechanically sound construction and will continue to do so, in the future, or under all operating conditions. Suppose the insulation isn't adequately rated to withstand the nominal operating temperature, due to a bad design, or a faulty batch of tape? The power supply may pass the high potential test, when cold, but when it heats up, the insulation would melt, potentially shorting the primary winding to the secondary.You still fail to understand the limits of the high potential test and that it's not perfect. There are plenty of other possible reasons why the device may pass a certain test in the laboratory, then fail it later. This is why it took a lot to convince me, that the high potential test, is a legal requirement in the first place. It may be a legal requirement but that doesn't mean it will prove the device is safe.

author: madires
author_rank: Super Contributor
timestamp: August 31, 2017, 03:38:43 pm
content: Just a simple question: how many consumers got a Hi Pot tester, know how to use it and test every device? Based on the arguments stated several times we would have to assume that any device is unsafe until proven by a Hi Pot test. The reality is that consumers have to trust fancy certification labels and laws. And we've all seen wall warts with nasty surprises despite several certification labels printed on the enclosure. In theory every wall wart should be Hi Pot tested, in reality they aren't. And it's also reality that we have far more fatal traffic accidents than fatalities caused by poor wall warts.

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 05:23:05 pm
content: Quote from: madires on August 31, 2017, 03:38:43 pmI agree. In this case, it would certainly pass non-destructive visual inspection. It seems to be of sound mechanical construction, with adequate creepage and clearances on the PCB. It has a common mode choke, a Y-capacitor and a ferrite bead. All indicative of a fair effort at both safety and EMC compliance.No special equipment is necessary to test that it's safe. All that's needed is a multimeter and a 10k resistor. Plug the PSU in to the mains, connect a 10k resistor between one of the the output conductors (either + or -) and mains earth and measure the voltage across the resistor. The maximum allowable current is 0.25mA, which means the voltage across the resistor should be below 2.5V. Check both + and - conductors, on AC and DC ranges. If the resistor gets hot or the voltage is higher than 2.5V, then you have a dangerous power supply, which shouldn't be used.

author: oldway
author_rank: Super Contributor
timestamp: August 31, 2017, 06:05:09 pm
content: How can you compare a technical problem (a hi pot test) and an human problem (an unsafe driver learner) .... nothing to do ... comparing apples and pears is wrong and a proof of lack of rigor of reasoning.Is a test perfect? no, but it is considered sufficient ...Is it really?It is not up to us to decide ...... but standarts have scope of law for the quality control and it is mandatory to respect them.Anyone who does not respect them becomes criminally responsible in the event of an accident, at least in Europe.Something is not safe until it is prooven that it is safe and not the opposite!You play with the lives of other people, comparison with car accidents is not acceptable ....In Europe, the principle of accepting a victim on 5000 or 10,000 chargers sold is not acceptable (it seems that in China, yes) .... There can not be victims, not one!All European countries have a penal code that punishes with jail assaults and killings, even through negligence (not carrying out the imposed tests is a negligence)The hypotheses of melted insulation and others are absurd ..... The hig pot test is not the only test imposed by the standarts ..... if there was a fault such as transformer would heat to the point of melting the insulation, the first fault would be the short circuit between coils and layers, which would cause to blow up the Mosfet and the input fuse.QuoteNo sense .... how can you ensure that the insulation resists transient network overvoltages without doing a Hi-Pot test?

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 06:39:37 pm
content: Quote from: oldway on August 31, 2017, 06:05:09 pmNo, the test alone is not sufficient. It's just something which must be done because the law says so.QuoteI agree, which is why one shouldn't rely on these tests as the only way to ensure the product is safe.Quote from: oldway on August 31, 2017, 06:05:09 pmMelted insulation is a possibility and the fuse could be on the neutral line, if it has a crappy non-polarised EU plug. The PSU would go dead and possibly the user too. Melted insulation was just an example. There are other possibilities: a weak coil former, crappy soldering, poor PCB mechanical support and an unearthed metal enclosure. The tests can't catch everything and will certainly not detect poor/unsafe design/manufacturing. The tests should supplement existing quality assurance measures. They're not a replacement and cannot guarantee the design is safe.QuoteYes, it won't test for a transient over voltage but it's "good enough" in a domestic situation and it passes all the basic visual inspection criteria: creapage, clearances, build quality etc. It certainly reduces the level of risk further. I think we forget the scope of this thread is, assisting someone to determine whether their switched mode power supply is safe, not compliance testing in a factory.

author: oldway
author_rank: Super Contributor
timestamp: August 31, 2017, 08:06:29 pm
content: Quote from: Hero999 on August 31, 2017, 06:39:37 pmHi Pot is not the only test to check if the product is safe, I have said this several times...but it has by far the highest priority among all of the electrical safety tests.Quote from: Hero999 on August 31, 2017, 06:39:37 pmIf the power supply stop to work, temperature stop increasing and will not be high enough to melt thicker and reforced insulation between primary and secondary.Quote from: Hero999 on August 31, 2017, 06:39:37 pmEvery switched mode supply must pass the High Pot test.Class I power supplies (with earthed secondary) must pass the High Pot test at 2120Vdc between primary and (earthed ) secondary, class II (dubbel insulation) power supplies must pass the test with 4240Vdc....for power supplies with secondary not earthed, this test is absolutely essential for the safety of the user !!!This test must be executed at the factory.The problem is that, with no name or unknown name products, there is no way to be sure that this test has really been made or not....For this reason, all brands fake or no name must be considered as not safe, you buy and use it at your own risks.Don't risk your life, buy good quality products from a well known brand, not crap devices as this charger.

author: oldway
author_rank: Super Contributor
timestamp: August 31, 2017, 08:19:20 pm
content: Quote from: blueskull on August 31, 2017, 07:46:10 pmIf , as you said, all parts and pcb are safety rated, the transformer is High Pot tested, there is no necessity to High Pot test the entire PSU....but you speak about OEM factory , not really the kind of factory who manufactured this piece of crap you see on the pictures of this topic....You can be sure nothing is certified, the components are of lowest quality and cost possible, the transformer has never been High Pot tested.....It can't be safe.....It only don't kill many people because not every electric chock kill you and because we have a 30mA earth fault current circuit breaker.

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 08:31:05 pm
content: Quote from: oldway on August 31, 2017, 08:06:29 pmClass II appliances can have a metal case you know!Appliances should still remain safe, even if they're no longer functional, so a failure of the insulation due to overheating, will still leave the device in an unsafe state. Whether it's functional or not, is immaterial.Insulating materials can be mechanically weak and brittle, yet still hold off the required voltage, until subject to vibration or heat. Weak solder joints can break, allowing loose wires/components to come into contact with things they shouldn't. If the enclosure isn't adequately fastened together, it can come apart, leaving the user exposed to live parts.Electrical tests will not catch any of the above! Please don't imply they can.Quote from: blueskull on August 31, 2017, 07:46:10 pmThanks, that makes much more sense.Quote from: oldway on August 31, 2017, 08:19:20 pmHow do you know this is the case with the original poster's SMPS? All they posted was a picture of a PCB. It might have gone through all the necessary tests or it might not have. Just because something has a marking to say it's been tested, it doesn't mean it has. Brand isn't always a reliable indicator these days.There are different levels of risk. Forget the law for a second. The original poster is not getting this power supply mas produced. They just want to be 99% sure it won't kill them. By looking at the inside and doing a visual inspection, they've already lowered the risk somewhat. A basic electrical test, such as the one I mentioned above, would lower the risk further, even though it may not be stringent enough to satisfy the legal requirements.

author: oldway
author_rank: Super Contributor
timestamp: August 31, 2017, 09:54:17 pm
content: QuoteYes indeed, class II (double insulation) does not require a safety connection to electrical earth (ground) of metal case, if any. Safety is usually achieved by having at least two layers of insulating material between live parts and the user, or by using reinforced insulation.With reinforced insulation is choosed, no need of earth connection of the metal case.Hi Pot is a test made on NEW or REPAIRED devices, it is a punctual test, not a safety warranty against abuses as transformers used in humid and salty atmosphere, transformers that have fallen,....In normal use that meets the manufacturer's technical specifications, there can be no degradation of the insulation, except normal ones due to aging.You are inventing something stupid that borders on ridicule.QuoteNot possible, there is a physical separation (distance) between the primary and the secondary circuits...If it would come in contact with "things they shouldn't", it could only be "things" of the same circuit, not a safety concern.QuoteAnd the user will turn on the open device because he has not noticed that the device falls apart...you are kidding ?QuoteLowest tecnology possible, low quality components and PCB, no marking on transformer, no brand on PCB (RXZ does not seems to be any brand)....QuoteWe will never agree because your point of view is that of an amateur who knows nothing about quality control and who treats safety with lightness and unconsciousness, whereas I has been quality control manager (actually retired).Sorry, but in a quality control department, a person like you has no place. More or less does not exist in quality control...It pass or it fails.....

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2017, 10:36:05 pm
content: Quote from: oldway on August 31, 2017, 09:54:17 pmIt happens, I've seen it before and have had to repair a device, because the PCB support wasn't strong enough to stop live parts from touching the case, just because you've not seen it, it doesn't mean it never happens.QuoteYes, it happens. This is why we have portable appliance testing in the UK.QuoteThen by that logic 99% of consumer grade power supplies aren't safe. Throw away your phone charger now!QuoteOh dear, you're one of those people who's so indoctrinated with procedure, they blindly follow it, without actually understanding its limitations or applying any critical thinking whatsoever: monkey see, monkey do. Clearly there's no point in attempting to have a rational discussion.

author: wraper
author_rank: Unknown
timestamp: August 31, 2017, 10:52:17 pm
content: Quote from: oldway on August 31, 2017, 09:54:17 pmIt's not even remotely lowest technology possible. Not that many PSUs have 2 layer PCBs to start with, and FR4 as such is not that common in PSUs. Secondly this PCB have SMT components with soldering of decent quality, which already puts it above most of the cheap PSUs.For example, monitor PSU/inverter made by Delta, which is no way to be called a dodgy company. 1 layer, phenolic PCB. Technology used is on around the same level.

author: oldway
author_rank: Super Contributor
timestamp: September 01, 2017, 07:47:44 am
content: Then by that logic 99% ofcrap no name brand (or fake)consumer grade power supplies aren't safe. Throw away your phone charger now!....yes, indeed, it is a very serious problem of safety.The tests must be carried out at factory....there is no way to control if these tests are really carried out or not.If some accident happen, there is also no recourse to justice against the firm established in PRC.So the only way to guarantee safety is to buy a product from a reputable and known firm.The example given by Wraper is interesting because 2 well-known companies are responsible for the safety of the power supply:1) Delta which is a known firm.2) the manufacturer of the monitor.In case of an accident, these two known firms can be prosecuted as well as their legal representatives in Europe.In the case of a no-name brand, it is impossible to locate it, these types of firms open and close in one hour and the owners disappear into nature

author: oldway
author_rank: Super Contributor
timestamp: September 01, 2017, 08:21:55 am
content: There is also another reason why one can not trust unknown brand products made in China.It is the safety concern that is totally different in China from that in Europe.Here is an extract from an answer that Blueskull had posted on this subject.https://www.eevblog.com/forum/chat/incredible-lack-of-safety/Reply #14 on: July 16, 2017, 04:41:52 PM"....BTW, in China it's allowed to put a price on human lives unless the possibility of death is very high (which makes it murder). If the expectancy of life loss cost is lower than the cost to prevent this, then no bosses will install extra safety systems. In fact, workers don't essentially hate this practice since should something happens, the settlement can be well higher than his or her lifetime income, which can change their family's fate. I've read news that Chinese workers intentionally pinch their fingers into machines to get thousands, tens of thousands or even hundreds of thousands of CNY worth of settlement."

author: wraper
author_rank: Unknown
timestamp: September 01, 2017, 08:22:56 am
content: Quote from: blueskull on September 01, 2017, 08:05:50 amBTW it's not illegal to sell because that PSU is certainly below 75W. What self oscillation topology? It has proper PWM controller. Self oscillation topology is long gone in the past or used in the most cheap and crappy Chinese chargers of low power. And nobody uses synchronous rectifier at such PSUs.Quote88% efficiency at full load, are you gone mad? It's a requirement for 80 Plus Gold certified PSU. And yes that board is old.

author: wraper
author_rank: Unknown
timestamp: September 01, 2017, 08:44:32 am
content: It's used in 22" TV, should be around 40W max power consumption. I measured power consumption of my 30" CCFL backlit DELLs in the past (long gone now). IIRC it was around 130w at max brightness.

author: madires
author_rank: Super Contributor
timestamp: September 01, 2017, 10:58:40 am
content: Quote from: Hero999 on August 31, 2017, 10:36:05 pmTunnel vision with a green "Pass" and a red "Fail". A green "Pass" only states that the device passed the test and we assume the device is safe to use. But that's only an assumption tagged with some probability. If your mains got spikes up to 5kV your "safe" wall wart, hi pot tested with 4kV, isn't safe anymore despite the fancy certification label and proper QA. I doubt anyone is checking for the worst case of a direct hit by a lightning strike.

author: Zero999
author_rank: Super Contributor
timestamp: September 01, 2017, 11:22:49 am
content: Quote from: madires on September 01, 2017, 10:58:40 amYes, also note that the test just demonstrates that it can withstand that voltage under laboratory conditions. It doesn't prove that the design is safe, i.e. mechanical construction, the creapage and clearances are sufficient for the pollution degree rating. The manufacturing facility might be considerably cleaner and less polluted, than the conditions in the field. That's something which needs to be verified by design.QuoteI agree, if you're struck by lightning, there are far more serious things to worry about, than getting a shock off a dodgy wall wart!

author: oldway
author_rank: Super Contributor
timestamp: September 01, 2017, 12:40:08 pm
content: Standards set reasonable limits that ensure a high level of safety.These limits are sufficiently high to leave a good margin of error and to compensate for problems due to the aging of the insulation.But the High Pot tests do not protect users against falling meteorites or bullshit like taking your charger with you in your bath or in the shower .

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: September 01, 2017, 12:59:00 pm
content: As regards safety of small SMPS wall warts, Big Clive has done some teardowns on YT. While you can see easily enough if there are adequate clearances on the PCB, the thing that's not so easy to determine is if there is adequate insulation on the transformer leads where they go into the windings.Since the inner winding much cross the outer one to reach its terminals, if all it has as this point is varnish then it's not very safe. Most do have a sleeve though. It's the ones that don't which are potential death traps.A split bobbin is of course much better, but rare on budget items.Bear in mind the switching input may have 400v or more on it, so potentially more dangerous from a shock hazard POV than straight mains.Since finding out typically means breaking the transformer apart, only feasible to examine sacrificially on a one-per-batch basis.

author: Gyro
author_rank: Super Contributor
timestamp: September 01, 2017, 01:43:20 pm
content: Unfortunately split bobbin transformers don't work well in an smps due to the high leakage inductance at their switching frequency.The closest approach was a side by side interleaved winding transformer used by Pace in their Set Top Boxes. They did have good physical barrier but the interconnections involved looked like a spider's web. I always felt they were far too susceptible to physical damage compared to the standard SMPS style. They were cheap to manufacture (in the UK) however.Photo attached.P.S. I always felt far more comfortable with closely specified transformers from the far-east with triple insulated wire, regular sample teardown inspection and 100% hipot testing.

author: wraper
author_rank: Unknown
timestamp: September 01, 2017, 02:11:31 pm
content: Quote from: IanMacdonald on September 01, 2017, 12:59:00 pmSplit bobbin takes additional size and is horrible for efficiency and load regulation.

author: fourtytwo42
author_rank: Super Contributor
timestamp: September 01, 2017, 05:46:44 pm
content: It is really good this subject is still going strong, perhaps I feel a little sorry for the OP who must be totally confused by now BUT it's great to see people actually seriously thinking about the safety of stuff many peeps take for granted. I do feel that equipment intended for a testbench scenario as the OP indicated should have extra safety levels, after all it's bad enough risking bangs and smoke from ones prototypes under test but you don't want the test gear doing it and even more so you want the test gear to behave properly irrespective of what your prototype does!I noticed the comments here about split bobbin, an excellent way of achieving the creepage requirement and used in many smallish 50hZ transformers BUT it is also becoming used in smps to deliberately increase the leakage inductance for resonant designs, yes I agree the voltage regulation of the transformer is worse as a result of the high leakage but the feedback loop takes care of that. You will see many consumer items using split bobbin now as resonant smps designs increases efficiency (reduce cost).Hopefully the more this discussion continues the more people will become aware of real safety issues and why they should distrust lots of mass produced products! There is no serious regulation anymore, look at Grenfell tower!! Where were the building regulations and inspectors, ineffectual and none.

author: oldway
author_rank: Super Contributor
timestamp: September 04, 2017, 05:12:06 pm
content: It seems to me that this subject has had a very important influence on many forum members concerning the safety of these crap chargers and cheap wall wart.It was amazing that everyone was very concerned about the safety of multimeters, whereas a switching power supply or a charger can be much more dangerous than a multimeter.Those who have read this topic have realized that there is a serious safety problem when using a device with no name or an unknown name.Indeed, safety is guaranteed by factory tests, especially the hipot, but what guarantee are there that these tests are actually performed or not?When it comes to renowned firms, there are third-party controls that check the compliance of the tests.But this is not the case for small Chinese firms that try to manufacture these devices at the lowest price, with unskilled labor and without means or technical skills.A rented location, a few dozen tables, chairs and soldering irons are enough to open an charger and wall warts industry ....And you entrust your lives to them?Never trust these cheap chargers and SMPS ....A good quality device is indeed a little more expensive, but it's worth it

author: madires
author_rank: Super Contributor
timestamp: September 04, 2017, 05:43:51 pm
content: Please tell that all the vendors who package their devices together with a cheap crappy wall warts. I can't remember any consumer electronics with a SMPSU from Delta/Mean Well/etc. in the box. Only unknown Chinese SMPSU vendors.

author: oldway
author_rank: Super Contributor
timestamp: September 04, 2017, 06:10:28 pm
content: Quote from: madires on September 04, 2017, 05:43:51 pmThey will reply that they know nothing about electricity or electronics and that you can buy a better wall wart if you want.On the other hand, you who have enough knowledge and information in the field of electricity or electronics, you are responsible because you know that it is dangerous.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 06, 2017, 02:43:53 am
content: Quote from: oldway on September 04, 2017, 05:12:06 pmBefore, it has been discussed that you trust your life to what you apparently consider unproven devices every day, no matter how stringent or paranoid you actually are. I don't see how repeating the same point of view over and over is going to change much, other than simply wearing people with other views down.Yes, it is good to be aware of safety. Yes, it is good to be aware that very cheap products might yield very real dangers. But no, you're in no way capable of checking everything you use and depend on in such a way that you're not entrusting your life to total strangers with, quite likely, very different opinions about safety and danger. Even aircraft have crashed due to mechanics being complacent and doing stupid things, like using the wrong bolts. Those aircraft more often than not have all the appropriate stamps, ticks and signatures when they take off. Buying a more expensive ticket isn't going to save you.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: September 06, 2017, 06:38:11 am
content: Well, I agree that these cheap SMPS are a concern, particularly as the collector/drain voltage on a flyback converter can easily be double the mains voltage, so you are talking about something that's potentiallymore dangerousthan touching a live mains supply.With multimeters, I think it's the usual issue with safety certifications: We start with an uncontrolled situation that is downright hazardous, we go through the stage where that has effectively been fixed but don't stop there. Instead, the certification requirements continue to ramp-up into the realm of micromanagement where insane levels of protection are required, levels which would only have any relevance to a tiny proportion of uses for the instrument.It's this inability to find a sensible balance that's the real problem with all kinds of bureaucracy and red tape.

author: oldway
author_rank: Super Contributor
timestamp: September 06, 2017, 09:56:17 am
content: QuoteIncorrect comparison: if you pay more, the risk is the same as you are traveling on the same plane.With a charger or a wall wart, if you pay more, you have a safer and better quality device tested according to standards.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 06, 2017, 04:51:35 pm
content: Quote from: oldway on September 06, 2017, 09:56:17 amIt's a correct comparison, I'm afraid, as there is more than one aircraft operated by more than one operator or crew. Not that it matters, because even the most well regarded airlines, flying the aircraft models with near perfect safety records and all the requisite stamps, ticks and signatures have come hurtling down due to dumb luck, human stupidity, a basic oversight or a combination of the three.You will need to trust your life to strangers and some of them, if not most, have different standards from yours. I understand that when your life was spent being a safety inspector, you'd like to believe otherwise, but there's no such thing as being sure in life. There's sure enough and that's about it.

author: oldway
author_rank: Super Contributor
timestamp: September 07, 2017, 07:41:38 am
content: An accident is seldom the consequence of a single defect, it is, in most cases, the consequence of a series of errors or faults, both material and human.To minimize the risks, all possible faults must be remedied.For chargers and wall warts, it is essential to ensure that the conditions of double insulation standards are guaranteed by a hipot test.It is clear that there is no guarantee that this test is actually performed, except by the seriousness and reputation of the manufacturer.Most insulation faults go unnoticed because they do not result in a fatal accident.Indeed, mostly that's the accumulation of several factors which lead to a fatal outcome.But we have to act on each of these factors and not neglect anything to reduce the risks, it is the principle of safety