Kungber Bench PS Tear Down Images - As Requested - Page 1
Forum section: electronics / testgear

author: DW1961
author_rank: Frequent Contributor
timestamp: May 19, 2021, 04:18:05 am
content: Here you go. Any comments especially welcome:Edit: 06/02/21, just noticed they do list ripple:Constant Voltage State Voltage stability≤0.1%±3mV Low Voltage:0.2~0.3%±3mV Load stability≤0.5%±3mV Ripple noise≤30mVrmsConstant Current State Current stability≤0.2%±3mA Load stability≤0.2%±3mV Ripple noise≤20mArmsLink:https://www.amazon.com/gp/product/B0923LXSM7[ Specified attachment is not available ]

author: DW1961
author_rank: Frequent Contributor
timestamp: May 19, 2021, 04:34:36 am
content: It's not like the stuff you guys posted on the other thread. It's a metal shell that screws together with 6 screws. the plastic face plate is secured to the front by 3 of those screws that also attach the cover. It's not like molded plastic shell that is specifically molded for the electronics, like the HP that was posted, and other high end PSUs. I wasn't really impressed with the build quality of the face plate/housing. I mean, it will work, probably forever, but it's not like a molded case specifically made for the PSU. The internals looked nicely laid out and the CB soldering attachments were nice.Let me know what else I can do and I'll post it.No, I don't have a scope to test the power in puts out, sadly.If any of you live in Sacramento, CA (USA) or area, and have a scope, and you would like to test it, let me know.

author: beanflying
author_rank: Super Contributor
timestamp: May 19, 2021, 04:34:46 am
content: Well it is earthed at leastAlso a handful of what looks like Y class Capacitors so better than some already.On the Earthing front some (me included) will dislike soldered ring terminals and also snip the Earth out of the cable tie and tie the Active and Neutral with a new one. The Sharp kink on the Earth copper combined with the solder isn't a good thing in terms of stress so reduce it. Better thing would be to replace the ring terminal with a crimped one and make sure there is a shakeproof washer under the screwhead (not clear if there is one).What was alluded to in your 'should I buy thread' by one of the later responders was to also check with your DMM if there is an AC coupling from the Earth to the DC Ground terminal. While I would hope you are ok with this one there have been plenty of examples where the DC Ground is referenced to mains and can be dangerously high. This can fry both humans and electronics. So Test it using your DMM on AC and with the supply turned on measure Earth to DC Ground.

author: xavier60
author_rank: Super Contributor
timestamp: May 19, 2021, 06:54:12 am
content: What's the part numbers on U18 and U19?

author: DW1961
author_rank: Frequent Contributor
timestamp: May 20, 2021, 08:08:06 pm
content: Quote from: beanflying on May 19, 2021, 04:34:46 amI'd like to make those changes. Before I begin I'll upload images to make sure I understand what you are saying.As far as testing the earth to DC ground, I want t make DAMN sure I have clarification as to what parts you are referencing inside the PS. I think I get it, but I want to make sure.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 20, 2021, 08:15:11 pm
content: This is a real noob question, but when I connect the PSU to a load, it gives me a reading of watts and amps. Given that the unit is accurate, if that going to be the same amp reading would get testing amperage with a DMM?

author: tautech
author_rank: Super Contributor
timestamp: May 21, 2021, 01:51:43 am
content: Quote from: DW1961 on May 20, 2021, 08:15:11 pmWhy wouldn't it be ?Obviously this PSU has an internal current shunt in series with the output and if the Vset takes its reference from the load side of the shunt it should track fairly close irrespective of the load.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 21, 2021, 02:17:55 am
content: Quote from: tautech on May 21, 2021, 01:51:43 amI remember back when I was using a DMM test total AMPs for custom LED strips I was making for my computer. I would plug in the LEDs power brick, then connect the DMM to that and yadda yadda. So, I did it, but it was a pain. Then I saw the bench PSU and they had amp readouts, so that's when I really wanted one.So, anyway, I was just wondering if they would be as accurate as a DMM, at least to 2 decimal places. I didn't test it yet with a DMM hooked up to it, but I did calculate the average amps per 5050 SMDs, which is .01875 amps @ 12V, per SMD. It was dead on. Pretty awesome. I'm excited about it.I am not excited about how the face plate is mounted. The bottom kinda clicked into place, but the sides and top have one screw each side, which is from the cover. The screws do go through the steel sides of the cover, but face plate screw holes are plastic. I don't like that. They should have threaded inserts in the plastic.

author: beanflying
author_rank: Super Contributor
timestamp: May 21, 2021, 02:18:58 am
content: Quote from: DW1961 on May 20, 2021, 08:08:06 pmIn your case as the Earth is on the front panel si it's simple and safe. DMM set to maybe 200V AC to start. One probe on the Earth and one on the DC Ground. Check it and if it is flicking up or down by a volt or two drop the range to say 20V AC and re test and so on down the range.We ran into this with the Feeltech Frequency generators and found the isolation was complete crap and the ground was floating at 80-90V. If by comparison as I just did boot up my 'Siglent' to keep Tautech happyI get about 40mV AC. While I was at it quick check of my Agilent 6632B Power supply was under 0.1V AC. This is sort of where you want to be in terms of numbers and not 10's of volts.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 22, 2021, 05:12:53 am
content: Quote from: beanflying on May 21, 2021, 02:18:58 amWell, bad news. At first I measured the current with my Amazon DMM. It only has two settings, 200 and 600V, but on the 200V setting, it will measure down to 0.1V. It measured between 000.1 and 000.0. I then plugged in my Unity DMM and it measured 35V. So I used another DMM and it also measured 35V. So I got the Amazon DMM specifications out and it said it will measure down to .1V at 50-60Hz. I then stuck it into a 120V 60hz outlet and it measured 121V and so did the other two DMMs. So, I have no idea why the Amazon DMM isn't showing the same voltage as the two other DMMs. But 35V I guess is pretty shitty.Just to be clear, this is with the power supply AC on and the power to the DC side enabled also. It has the ability to power on, but not supply power to the DC circuitry. You can se in the images there are two power buttons. Again, I tested it with the entire unit energized.I'll contact the vendor and let them know. We'll see what they say.

author: radiolistener
author_rank: Super Contributor
timestamp: May 22, 2021, 05:49:42 am
content: Quote from: DW1961 on May 22, 2021, 05:12:53 amdifference can be strong indication that the output has significant ripple and pulses. Different DMM have different filters.That's switching mode power supply....

author: Kleinstein
author_rank: Super Contributor
timestamp: May 22, 2021, 11:57:03 am
content: The supply is resonably isolated from ground and mains. So when measuring the AC voltage relative to ground one has a very high impedance voltage source to measure. Different DMMs can be quite different in the input impedance in the AC ranges. Some are close to 10 or 11 Mohms and some are more like 1 M Ohms. So the different readings are likely just because of different impedance of the meters.The residual voltage is likely due to the EMI suppression capacitors from both sides of mains to the ground at the output side. With 2 equal caps this would be halve the main voltage (some 60 V). The meters read less, as the impedance of the parasitic voltage seeems to be about as higher as the impedance of the meter - so reading only half of the open circuit voltage. One could test this effect by using the 2 meters in series. Instead of some 30 and 35 V I would expect something like 20 and 24 V for the 2 meters.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 22, 2021, 08:03:33 pm
content: Quote from: Kleinstein on May 22, 2021, 11:57:03 amThanks for that explanation.One of the meters show no voltage, or almost no voltage. Should I use the meters that read 30-35V or one that shows 35V and one that shows .1 volts?Also, what does this mean? Is the PSU faulty or badly engineered? Or, without the suppression caps, would be seeing very low voltage?

author: beanflying
author_rank: Super Contributor
timestamp: May 23, 2021, 01:52:19 am
content: Not faulty for a start far more likely by design which is what Kleinstein alluded to. What you are looking at is ripple on top of the DC voltage similar to this below.In your case what you are likely getting is something with more large spikes in part due to it being a switching supply. You might want to have a look at this thread just for some mixed random images of noisehttps://www.eevblog.com/forum/chat/show-me-your-psu-noise/Drop a load on it now preferably resistive (so a Fat Resistor, light globe or LED string) and retest it and see how it goes under load with the same tests.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 23, 2021, 06:48:15 pm
content: Quote from: beanflying on May 23, 2021, 01:52:19 amI got 43V now under a very light load 0.2A.

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 23, 2021, 11:58:49 pm
content: Although they do play a big role in getting some of the measurable unwanted AC on the secondary side I don't think the EMI suppression capacitors are the only cause.(In any case I wouldn't say that DC ground is "referenced" to mains if it isn't ground referenced.)The transformer itself has parasitic capacitance between primary and secondary, the switching frequency also has some effect on the amount of stray AC on the secondary side, under load there will be more ringing in the transformer which can also affect the amount of AC capacitively coupled through the transformer.While it's nice to know what amount of mains leaked AC to expect on the secondary, the more relevant measurement for user safety is the amount of leakage current available.For component safety, if you're using MOS components in the wrong conditions even 35V will be enough to fry them.In most cases it's probably wiser to permanently tie the negative or common output terminal to ground on SMPS lab supplies.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 24, 2021, 01:57:53 am
content: Quote from: shakalnokturn on May 23, 2021, 11:58:49 pmSo what does this mean for the power supply discussed here?

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 24, 2021, 04:06:22 pm
content: Not much... Just probably wiser to tie negative output and ground together either internally or externally with something permanent.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 24, 2021, 05:00:27 pm
content: Quote from: shakalnokturn on May 24, 2021, 04:06:22 pmCan't you just do that manually? Also, if it were permanent, it wouldn't be floating and the benefits of a floating PSU would be lost?I'm just wondering if anyone found anything questionable in the pictures, or would like some more detailed images for the unit? That is, did anyone see anything that was alarming, or anything that was positive (like the Y caps). For instance, how would I test it for EMI, or is it already acceptably protected?Does it get a pass from the community?

author: beanflying
author_rank: Super Contributor
timestamp: May 25, 2021, 01:42:08 am
content: Without a scope to have more of a look at the actual noise we are like you taking a bit of a stab in the gloom.Back before I got a few decent Linear supplies I was things like a PC ATX or my 0-15V 60A Manson as a raw source then I had made a couple of small Linear 78xx based convertors for powering anything delicate but fed from the SMPS. So much as it is probably not needed just for the safety of those sorts of devices in your place I would make something similar and feed it off this supply. These days maybe even look at some low drop out Regs over the 78xx series.There are some options to reduce that floating voltage a bit and they were discussed buried in the Feeltech mega thread (bound to be others if you search) so you might like to have a read before and after this and also and in particular the Keysight link in the posthttps://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1344167/#msg1344167

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 03:13:25 am
content: Quote from: beanflying on May 25, 2021, 01:42:08 amIs the floating voltage on this unit bad or could cause problems?

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 25, 2021, 08:40:12 am
content: Quote from: DW1961 on May 24, 2021, 05:00:27 pmQuote from: DW1961 on May 24, 2021, 05:00:27 pmIf it's permanent the floating output is lost, sure you can do it manually.It all depends on your typical usage. I just wouldn't trust myself to leave it floating because usually a SMPS isn't floating enough for me.It isn't a criticism of this PS, but more a general "be aware of what you're using"...I mentioned MOS previously because one of my last traps was using a "floating" SMPS for a quick and dirty Gate drive to beefy MOS transistors used to discharge beefy capacitors into circuit breakers to simulate and scope short-circuit opening.I killed a couple of transistors before understanding that when replacing the circuit breaker touching the MOS Drain wire I was putting the "floating" SMPS to ground through the Gate...Considering something "floating" is not that simple, ideally you'd consider what impedance it's floating at and breakdown voltage. If I want something floating I go for a SMPS behind a isolation transformer or a linear PS.Quote from: DW1961 on May 24, 2021, 05:00:27 pmNothing awful for me other than the earthing that could be a bit better as others have mentioned.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 05:59:52 pm
content: Quote from: shakalnokturn on May 25, 2021, 08:40:12 amYou mean the wire angles and the soldered wire vs crimped?

author: DW1961
author_rank: Frequent Contributor
timestamp: June 03, 2021, 04:00:41 am
content: I just noticed they listed they ripple on this unit:Constant Voltage State Voltage stability≤0.1%±3mV Low Voltage:0.2~0.3%±3mV Load stability≤0.5%±3mV Ripple noise≤30mVrmsConstant Current State Current stability≤0.2%±3mA Load stability≤0.2%±3mV Ripple noise≤20mArms

author: beanflying
author_rank: Super Contributor
timestamp: June 23, 2021, 02:13:37 am
content: Well a few weeks later and I had a cheapo "Wanptek' branded 120V 3A power supply arrive with a powerful inner coreThis job is fine with some ripple and noise as it will just be powering a hot wire cutter.Interesting having a compare it along with yours are either the same or a close cousin mainboard and likely front display board (different orientation). Similar slightly suspect Earthing connections but at a quick first look somewhere close.I will clear the bench and fire up some proper testing over the next day or two including a look at ripple/noise and loaded and unloaded.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 23, 2021, 04:47:45 am
content: Quote from: beanflying on June 23, 2021, 02:13:37 am100V? Seriously? Wow. Kinda cool.I would check with the local FBI to see if carrying around a power supply that has a small nuclear device in it is actually legal. On the upside, you shouldn't even need to ever plug it in. In fact, you cold start your own power company with it.Kidding a side, how much was that? Looking forward to you scoping it.Found it on Amazon:https://www.amazon.com/Wanptek-DC-Power-Supply/dp/B08F7HFNK2?th=1

author: beanflying
author_rank: Super Contributor
timestamp: June 23, 2021, 06:10:38 am
content: I will admit I might have 'massaged' their marketing picture a littleI got mine via AilExpress with the Wanptek badge for a bit less than @med6753 got a Kungber branded one via Amazon USA ($90USD)https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3592146/#msg3592146

author: TurboTom
author_rank: Super Contributor
timestamp: June 23, 2021, 07:34:13 am
content: Shame that none of these entry level switchers include a proper PFC, which makes them illegal to be sold in many countries "officially". IMO, this is also a clear indication for their general level of sophistication and quality (or rather lack thereof)... Yet, for many applications these "El Cheapos" are quite useful.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 23, 2021, 05:59:23 pm
content: Quote from: TurboTom on June 23, 2021, 07:34:13 amWhy do you say none of them use PFC? Even cheapo computer power supplies have PFC circuits. Even really nice computer power supplies are less than 80 bucks, and incorporate PFC circuits. Corsair makes some really clean PSU and they all have PFC circuits--they'd have to in order to run PCs (although before PSU became really clean, about 2010 or so, we were running computers on those noisy, nasty, dirty early computer PSUs, and having little failures with the equipment--lol). I did have one let go and take out the entire rig, motherboard, drives, RAM everything. But that was back around 1999. And, only one that I knew of among all of my computer building friends).I was just wondering why you said the PSUs here don't use PFC?

author: DW1961
author_rank: Frequent Contributor
timestamp: June 23, 2021, 06:00:46 pm
content: Quote from: beanflying on June 23, 2021, 06:10:38 amI'm really interested in your tests. When are you gig to test it?

author: DW1961
author_rank: Frequent Contributor
timestamp: June 25, 2021, 05:37:21 pm
content: Quote from: TurboTom on June 23, 2021, 07:34:13 amI contacted Kungber and asked if they used TC and they said, "No." Isn't that a really cheap circuit to include? If so, why not just add it?

author: beanflying
author_rank: Super Contributor
timestamp: June 26, 2021, 02:26:14 am
content: Quote from: DW1961 on June 25, 2021, 05:37:21 pmhttps://en.wikipedia.org/wiki/MuntzingWhen you chase the price down to what the Chinese manufacturers think we want at the expense of increased reliability and features then we get what we deserve. In a recent mid life crisis (I have had three now and am working on a 4th) I was importing Kites from Europe, the USA and China. When I raised concerns over samples from China the reply was all to often along the lines of 'it is to make it cheaper' or 'it doesn't matter they are only for beginners'. When you turn around and then ask for a particular spec or tweak and buy sufficient quantity that same flawed design for 20-30% more got brought up to a European or USA made standard and was still way under those costs. The question really needs to be would we as consumers pay that 20-30% more to random company X in China for features?Re testing for mine I fished out some spare 250resistors and I will temporarily re task two more out of another box and strap them onto some heatsinks. 6 in parallel for circa 40across 120V and 3A and for short bursts will handle full power of the supply.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: June 26, 2021, 04:56:09 am
content: Quote from: DW1961 on May 25, 2021, 03:13:25 amconnect a 1 meg ohm resistor between the negative output (black) terminal and the ground (green) terminal. now measure the voltage across this resistor. calculate the current with I=V/R. report back both the (very small) voltage you measure, as well as the (even smaller) current calculated.cheers,rob :-)

author: TurboTom
author_rank: Super Contributor
timestamp: June 26, 2021, 08:40:51 am
content: Quote from: DW1961 on June 25, 2021, 05:37:21 pmAn active PFC adds at least one more HV power semiconductor, a fast power rectifier (with asscociated heat sinking provisions for those two components), a power inductor, a controller IC and miscellaneous passives to the BOM. Since the gadget will work perfectly well without that complication, albeit with a much higher crest factor and thus feeding considerable current noise/harmonics back into the mains, the disadvantages of the missing PFC don't get directly obvious to the individual user as long as the the electricity provider can cope with the situation.But the shift from analog PSUs in all kinds of devices to switch-mode technology during the past three decades exacerbated the situation up to a point that all of the components of the electricity supply chain had been pushed to the limit. Thus the legislation nowadays requires (new) electrical appliances above a certain power consumption to have to be equipped with a PFC to be legal in most countries. And that's why (practically) all of today's PC and laptop power supplies are equipped with such a circuitry. But especially the low-end, "hobby-grade" switch mode power supply manufactures do without this complication - see the "Muntzing" approach mentioned by @beanflying.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 26, 2021, 07:01:30 pm
content: Quote from: TurboTom on June 26, 2021, 08:40:51 amVery interesting, Tom. Thanks for that information.

author: Tekjive
author_rank: Contributor
timestamp: February 17, 2022, 03:09:47 am
content: So I just bought this unit, worked great and stable and accurate the last week, goto use it today, recall mem1 @ 12v/2a, play some, goto turn off active power (rubber on/off button) and it doesn’t respond, I press it a few times and nothing, I power down, unplug and replying and power up and still the buttons will not respond. I open it up to take a look and see there’s 2 wires clipped from the larger front panel harness and soldered to the main ground, which is not done in the pics on the 1st post. Any idea why this is done or why the front panel has stopped responding? Any help would be great, ty.https://imgur.com/a/aYlOO4XIt’s actually the Main Earth GRD and V- lines from the panel, seems the main chip on the daughter front board, TM1640, must have gone bad ...out of nowhere ...joy.https://imgur.com/a/BThXhtAThat’s just the LED Drive control circuit ...lol, updating post as I find info ...just at a loss :/Well, after completely disassembling the front, checking all solder connection, reattaching the Main GRD and V- to harness, and giving it a good thump for a good measure ...lol, it’s working again. I’m assuming something is loose somewhere in the front panel, if it happens again I’ll reflow everything, if anyone knows what IC controls the front buttons I’d appreciate the look out.

author: DW1961
author_rank: Frequent Contributor
timestamp: February 17, 2022, 06:09:31 pm
content: Quote from: Tekjive on February 17, 2022, 03:09:47 amI'd just return it! Some units are going to be lemons.