How to fry a KORAD in less than a second... SALVAGED! - Page 1
Forum section: electronics / testgear

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 08:45:46 am
content: Hi,May was not my month...This is a textbook example of stupidity.I just received a KORAD power supply from USA and I was so excited to test it that I forgotto switch it to 220V from 110V....I switched it on, it made a loud hum and in less than a second, boom. That was it.I opened it and the only thing I could find was a mark on the plastic cover of the transformer.Do you think that I fried the primary? I cannot see any other protection like a fuse or something.And I asked the seller twice if the transformer was 220V or 240V. He could have switched it to220V since he knew that it was shipping to Europe. It is totally my fault, but...Definitely no mains protection for the KORAD. Watch out!What do you think, is there any hope?Please help!Thank you.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: May 27, 2013, 08:53:05 am
content: I wouldn't try salvaging the transformer. But since you opened the PSU, I'm not sure if you can return the unit under warranty. Failing that, if you can find out what the secondary(ies) are, you could always replace the transformer. I'd also buy a fuse and put it on the positive input side of the transformer.

author: AlfBaz
author_rank: Super Contributor
timestamp: May 27, 2013, 08:55:56 am
content: Lets hope the core saturated and you didn't get twice the output voltage. You may have damaged components hanging off the secondary

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 08:57:25 am
content: So do you think that the primary is dead? How can I test it?Is the mark on the yellow cover the burned part?

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 09:19:17 am
content: Correction. In the manual it says that it has fuses.Are these on the photo?

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2013, 09:26:09 am
content: Sorry to hear of your disaster.In all similar cases that I have worked on the transformer is a write-off.

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 09:33:24 am
content: They are actually the legs of some beefy transistor that are glued from below on the heatsink.Ok, I found the fuse... Its on the outside of the box near the mains plug. Its blacker than black...Good thing they had included a replacement fuse with it.I replaced the fuse and it works! That was close! +1 for KORADThe panel works ok. Lets hope that the output works ok as well.I will do some measurements.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2013, 09:51:58 am
content: Please be very careful here......If that damage to the transformer outer insulation is a result of this accident, you will likely have windings in there that have suffered enamel insulation damage. Such damage can lead to a shorted turn situation in the transformer primary and a burn-out of the winding.I strongly suggest you do not use this unit whilst you are not present to smell any overheating that may take place.If the damage to the covering of the transformer is just from the manufacturing rather than the accident, you will be OK.

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 09:59:01 am
content: Survived !Basic functions seem to work.Voltage range accurate down to both decimals!I also connected a small LED without a resistor and I was able to control the current properly.(I haven't measured the current accuracy yet)I would definitely change the fan because its noisy and it resonates.Why they always choose the worst fans I really don't know!Lets hope that everything else is fine as well.Thanks.Aurora, thank you for the advice. Is there a way to check that? The yellow cover does not seemburnt or have any black traces whatsoever. How can I find out?

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 27, 2013, 10:06:48 am
content: Hmm - I have to agree with Aurora. The transformer is now at best suspect - there may be interwinding shorts, the isolation may have been comprimised, the secondary components may have been stressed. OR - you may have got lucky.What is that nick in the transformer outer insulation? Any signs of blackening (or any burnt smells) around there? That outer insultation damage may just be careless handling during assembly, prior to your efforts!Set the power supply up on a low (say 25% of full rating) load for a few hours WHILE YOU ARE ABOUT, and see how it performs. The transformer should get comfy warm (but not hot) to the touch. Tere should be no burning smells. Double check for very high impedance between the transformer secondary and primary windings, and between the primary winding and ground.The core probably did saturate when subject to the overvoltage, and that would see the primary current rise quite spectaculalry, even on no secondary load. The primary fuse then did its job.If, as you say, the fuse took just a second to blow, chances are that the transformer wont have heated much in that time, but the instrument needs to prove itself to you before you should trust it.Chalk it up to experience!

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 10:28:52 am
content: Hi LawrenceW,I will check it again this afternoon. I am trying to find what load to use.Primary winding and ground should have a very large impedance?Thank you.

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 10:55:03 am
content: Do you think its a good idea to carefully remove part of the yellow cover to seewhat going on in the coil and then replace it with some electrical tape?If there is some minor damage it will show up, correct?

author: Psi
author_rank: Super Contributor
timestamp: May 27, 2013, 11:15:04 am
content: Yeah, pry the yellow insulation back a little and have a look underneath itIf that damage was from a short i would expect charred insulation or discoloration around the area.If i had to guess i would say that was impact damage during assembly and unrelated to the short.But even if the damage is unrelated it could still be dangerous.Another idea, give it a good sniff, burnt transformers are quite obvious.

author: digsys
author_rank: Unknown
timestamp: May 27, 2013, 11:21:31 am
content: That nick in the Transformer doesn't look like a failed turn or thermal fuse result. The Transformer looks like a proper spec'd one as well,especially if it was made in USA. If so, it would easily take 2X I/P voltage, and put up with the saturation for a while. Something on thesecondary took the brunt, hence the fuse blowing it's guts. When you say "boom" .. was it "boom" or a "SPLAT" sound? Important.Fuses can make a terrible splat / flash sound when they go off, which is normal. MY primary concern is the Input filter cap. Did that goway over it's Voltage rating? I wouldn't open the Transformer up at this stage. IF you can borrow a megger, unplug the secondarywindings and check it at 500V P-S and P-F/S-F. You may have been lucky. A proper designed unit that has 110-220V switch is usuallytested for what you did. Trust me ... thousands / millions have done that over the years :-)

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 11:33:15 am
content: It made a splat actually. Nothing loud. They only loud noise was the buzzing until it failed.Less than a second. It does not smell like anything is burning. It has the typical smell of anewly powered electronics unit. The large capacitors look ok. I might test them with theLCR meter, after I discharge them...When I switch it on, it makes a little 'dong' sound but not all the times. If I switch it off andon fast it will not make it. Although its a typical high voltage transformer sound I am not sureif its normal for this one.So do you think I should leave the insulation as it is?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 27, 2013, 11:45:58 am
content: SeriouslyAssuming they are rated correctly, how is the transformer going to fail before a fuse?

author: eevblogfan
author_rank: Frequent Contributor
timestamp: May 27, 2013, 11:52:30 am
content: Heyless then a sec is okay , you may need X4 the voltage ( resulting into current ) in order to manage to burn the enameld coil , trust me , no worrieshave fun with your new PS !

author: digsys
author_rank: Unknown
timestamp: May 27, 2013, 11:53:46 am
content: Quote from: hggThat's definitely a fuse pop then. OKQuote from: hggSound OK as well. Primary was under stress for a short while. Our transformers have to take ~500V before breakdown.Quote from: hggSounds good so far.Quote from: hggOdd sounds when you switch on are "normal". Inrush currents can be quite high. Nothing "unusual" here.Quote from: hggWell, here is where you have to make the choice, as you have a few different opinions in replies.I* would say leave it alone. You "may" accidentally do damage for no reason. I'd keep an eye on it, maybe see if it heats up a lot aftera lot of use. Another GOOD test is to check the mains AC current with no load .. but be CAREFUL ! Don't do it if you don't feelconfident with AC mains. Excitation current should be ~10-20mA .. 50mA I'd start to worry. Otherwise, you can have it tested.What city do you live in?

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 12:02:01 pm
content: eevblogfanthat's encouraging. I hope it survived.digsys, I live in Athens. We have 230V AC. Plugged in with no load, consumes 16 Watts.20 Watts when I turn the dial to 30V. (It also makes some clicking sounds which are therelays changing to different scales I suppose.

author: digsys
author_rank: Unknown
timestamp: May 27, 2013, 12:02:12 pm
content: Quote from: HackedFridgeMagnetSeeing as it was made in USA, it's a fair guess it was rated correctly. P/Supply failures in this country (from China mainly) are one ofthe BIGGEST causes of house fires. Just because there's a fuse, if the Input components can handle it, there won't be an issue.I'd still keep an eye on it.

author: digsys
author_rank: Unknown
timestamp: May 27, 2013, 12:08:13 pm
content: Quote from: hgg~70mA with secondary connected seems fine. The test should be run without the secondary plugged in. Is it a plug you can easily unclip?Quote from: hggYEP. A common and effective design to reduce heat.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 27, 2013, 12:13:27 pm
content: QuoteI was just talking about the transformer, surely the fuse would be rated to blow before the transformer would overheat from excess current.So if the fuse was rated correctly and inline to the transformer then the transformer should be fine.On the other hand, the rest of parts could suffer catastrophically from over voltage.

author: Psi
author_rank: Super Contributor
timestamp: May 27, 2013, 12:41:17 pm
content: I wouldn't leave it on while you're away from it until its had a good number of hours run-in and everything seems fine.Just to be safe

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 12:45:16 pm
content: All the connector clips inside are glued...I am trying to find a 4A load in order to test the temperature of the transformer with anIR meter.

author: digsys
author_rank: Unknown
timestamp: May 27, 2013, 12:47:35 pm
content: Quote from: HackedFridgeMagnetCompletely agree with what you're saying. Not seeing the unit or knowing what standards it was built to, it's all conjecture.If the regulator part fails, from O/V, it should be quite an easy fix. I'd check the excitation current though (no SEC).

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 01:41:55 pm
content: Here is a photo of the blown fuse...and one of the power supply.They have actually fixed the 5 memory display with 4 memory buttons thing...The old M5 led indicator is now a Lock indicator.It has an autosave memory function now. You just select the memory, adjust V/C and itwill be autosaved.They should replace the Off/On buttonthat switches the output on with a transparentone that lights up red. Much better than having to look to the right for the little Out ledindicator that is exactly the same with all the other indicators...The annoying crrrr/beep is still there. At least you can disable it.I am definitely changing the fan!

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 27, 2013, 01:57:02 pm
content: Quote from: hgg on May 27, 2013, 01:41:55 pmI think this was already there, if I remember correctly Dave complained about it in the review. I also think it is not very handy, if I set a memory to 12V I'd like it to stay there even if I adjust the output, unless when pressing the 'save' button of course or long pressing the memory button.

author: hgg
author_rank: Frequent Contributor
timestamp: May 27, 2013, 02:11:15 pm
content: Its handy if you pretend that you have 3 memory slots...I've connected the power supply to an old laptop that needs 2.5A to work and until nowthe temperature of the transformer is 28 degrees Celsius and the temperature of the airblowing out is 35 degrees Celsius. Room temperature is 25 degrees. Looks ok I think.This thing is loud though! 60 dbC from 39 dbC.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 27, 2013, 03:09:06 pm
content: Yup, that's a blown fuse! It was on the PRIMARY side, right?I agree that the fuse did its job. One second, even at double the rated voltage, isn't going to fry a transformer that badly. During that second, the secondary voltage would have been much higher than spec, but not double - the transformer saturated before then, cuasing the current to rise.Switch-on clunks are nothing to worry about. For the first few mains cycles, the transformer is trying to deliver into the low impedance discharged smoothing cap. There is alway a current spike, then.I am thinking you got away with this one. None of the readings you've mentioned look out of whack, to me.Not sure where the thinking that your Korad transformer might be US-built came from? This will be Chinese, I would bet on it.

author: Salas
author_rank: Frequent Contributor
timestamp: May 28, 2013, 06:04:02 am
content: Quote from: hgg on May 27, 2013, 01:41:55 pmMy TENMA 3A variety from Element 14 UK is at the hands of a friend who bought another 2 for himself and he is happy but the fan rattle. He will hand me mine at a point when visiting and I would like like to know your progress with the fan. The way he describes it its a rattle when low rev, maybe just elastic grommets is the answer?

author: Salas
author_rank: Frequent Contributor
timestamp: May 28, 2013, 12:46:31 pm
content: Quote from: hgg on May 27, 2013, 01:41:55 pmIs it easy to change the led color for the particular indicator?

author: hgg
author_rank: Frequent Contributor
timestamp: May 28, 2013, 01:09:24 pm
content: Its the fan. It rattles at low speed because its an excellent quality Chinese one...Sleeve bearings and you can almost remove the blades if you pull them. That much they move.The rattling stops at high speeds.I just replaced it with a relatively silent one I had. The Be Quite! SilentWings Pure 80mmRifle bearings instead of sleeve. Its much better now especially at low speeds. I will bereplacing that with the Sharkoon Silent Eagle 2000rpm 80mm which is much better with fluidbearings and completely inaudible at low speeds. The sound level now decreased from 60dbCto 50dbC with the same load.The transformer temperature now raised from 28 to 33 degrees and the temperature of theairflow from 35 to 46 degrees with a load of 2.8Amps after half an hour of use.I don't know if these values are normal... Ambient temperature 25 degrees Celsius.(The previous measurements though were taken with a 2Amp load)The manual says that the fan speed is temperature controlled. Clearly it isn't. The fan speedchanges immediately after any load change and now that the temperature is higher it does notspeed up the fan any more. (the fan can go even faster)SalasI just closed it... When I will replace the fan again I will have a look.If we can find a similar size rubber button that is somewhat transparent, it would be easyto light it up I think.

author: Salas
author_rank: Frequent Contributor
timestamp: May 28, 2013, 01:18:42 pm
content: Thanks. I will be looking for a better fan than elastic mounts then.

author: digsys
author_rank: Unknown
timestamp: May 28, 2013, 02:12:40 pm
content: Quote from: hggFor a linear design at that current, those temperatures are FINE. Part of Transformer design is Temp rise at rated load.It's all part of the size / weight / cost calculations. All our design programs default to 50oC normal, ~70oC at max ambient.

author: hgg
author_rank: Frequent Contributor
timestamp: May 28, 2013, 03:53:11 pm
content: Good news then! Success with the fan replacement.I couldn't resist and I stretched the yellow transformer cover to see if that was the damage causedby the mistake I made. I cannot see any coils. Is this an outer protective layer? Any ideas?free uploaderOk, this one is for Dave.They erased this chip as well and they did not bother cleaning the board ...This time though you can see one letter and one number. The letter should be an 'N' and the number '2'.What can it be ?picture hostIs this how you make a common ground...?screen shot captureGenerally I did not like what I saw. Very bad assembly of the parts. The front panel cover and oneboard were missing 2 screws each! Luckily I had some. The rotary encoder board is kept in placeby accident... If you look at the photo the screws are just holding the board in place and some orthe board receptors are already broken. So be careful with the rotary selector...image hosting no sign upFinally the indicator LEDs are not standard LEDs but some kind of cubic ones.Its difficult to light up the off/on button because its not transparent and its part of a membranewith other buttons.Does anybody know if I can find a blue or white LED of the same type?Maybe brighter.image hosting imageshackI think this is the last time I am buying a Chinese product...Ok, maybe the Rigol DS2102 oscilloscopeThanks.

author: don.r
author_rank: Frequent Contributor
timestamp: May 28, 2013, 04:38:39 pm
content: Quote from: hgg on May 28, 2013, 03:53:11 pmLOL! Just about everything is Chinese these days! You just have to be careful which is easier said than done. When it comes to PSUs, I buy local and old (i.e., proven, repairable, and Western built) but now that I no longer fiddle for a living, I don't really need programability.

author: hgg
author_rank: Frequent Contributor
timestamp: May 28, 2013, 04:44:01 pm
content: Yeh, I know.... This is bad.At least there are some manufacturers that have better quality and specification standards.You have to know which is which...

author: hgg
author_rank: Frequent Contributor
timestamp: May 28, 2013, 04:59:22 pm
content: Do you think that this is a compatible LED replacement?http://www.alibaba.com/product-gs/218633272/5x_5_mm_square_super_bright.htmlIt looks like they used one like this and they wrapped around some black tape.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 28, 2013, 10:25:51 pm
content: Quotesorry but I seriously doubt that statement.

author: Mike Warren
author_rank: Unknown
timestamp: May 29, 2013, 03:10:38 am
content: Quote from: hgg on May 28, 2013, 04:59:22 pmI just fitted a 5mm round yellow one I had lying around. I ground the top flat so it was the same height and fitted a small piece of heatshrink around it.

author: Salas
author_rank: Frequent Contributor
timestamp: May 29, 2013, 04:43:51 am
content: Now that one is eye catching enough the output is active. Success.

author: hgg
author_rank: Frequent Contributor
timestamp: May 29, 2013, 04:50:08 am
content: Nice job!I might do something similar.

author: hgg
author_rank: Frequent Contributor
timestamp: May 29, 2013, 07:10:48 am
content: Just did it.I replaced it with a white LED I had. I filed it down to 7mm with flat top and put some electrical tapearound it. They indeed used heatshrink.Way better now!image ruThe original LED was a red 5x5x7mm

author: Salas
author_rank: Frequent Contributor
timestamp: May 29, 2013, 08:24:32 am
content: Looks nice.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 29, 2013, 08:27:01 am
content: I have a hunch Korad has some smart people. I think the problem is that they might only partially know what the market requirements are. I'm betting they don't know or expect that more than a handful of their customers look inside their products to see how clean the boards are or if holes in the boards are cracked around the edges, etc. My guess is if they are reading this forum and decide that the users here are representative of the market that they will find ways to make adjustments as they build more units. Or they might decide that users here are not representative of the market but that as early customers the users here might be thought leaders that influence the decisions of later customers. Either way, I don't think it's an ability thing, I think it's decisions and actions based on input and priorities. Some of the changes desired here probably wouldn't cost them much and might even reduce their costs. Other changes might raise their cost and therefore their prices. All in all, when you look at the quality (moderate?) and the functionality (better than moderate) for the price (about $105 in the U.S.) it's not all that far off being a very good value.Along these lines, I think if the users here take a reasonably constructive/thoughtful tone this could turn out to be a site where product managers from companies like Korad and GW Instek (to name a couple) might not only lurk but potentially engage - which would give us something I think a lot of us might enjoy - the ability to influence some future product direction.

author: Salas
author_rank: Frequent Contributor
timestamp: May 29, 2013, 08:33:39 am
content: Win-Win game.

author: Salas
author_rank: Frequent Contributor
timestamp: June 12, 2013, 09:44:09 pm
content: This is the TENMA 72-10480 variant. It has a 3A labeled transformer and 31V/3.1A CV/CC set limits. Its fan has the low RPM rattle and the high RPM turbine effect but its not much annoying. Sounds quieter than in some videos or descriptions about the 5A KORAD.In my unit the transformer moves in its shell. Not properly clamped in it. As a result, a chassis floor ridge developed, probably during transport.The voltage indication is spot on when the current indication is almost there by 5mA less on average. Even closer to CC set limit when measuring a current loop to a load than what self displaying. Ref to a Fluke 87V.It overshoots half a volt for ~6ms in most settings when hitting the output On button. Here are some pics. A couple of 2.2mF/63V Rubycon MXR 105C capacitors can be seen amongst other parts.

author: TRIO_Smartcal
author_rank: Contributor
timestamp: June 12, 2013, 10:36:25 pm
content: Quote from: hgg on May 27, 2013, 01:41:55 pmChanging the fan will not fix the noise. The fan speed is variable depending on load. I suspect it is driven by PWM. I haven't checked. Listen to the fan when the supply is delivering near its full power. the annoying "rattle" goes away.I reckon what you hear at no or light load is caused by the way they drive it. I haven't the time to check.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 12, 2013, 10:43:43 pm
content: Hey charlsQuoteI think you shall consider the following :I am no way near to be a "transormers expert " - But I think that rattle related to either poor core material - or not enough windings on primary ( is that related to the flux capacity of the core ? )

author: TRIO_Smartcal
author_rank: Contributor
timestamp: June 12, 2013, 10:45:52 pm
content: Quote from: hgg on May 27, 2013, 12:45:16 pmFor a load to test this supply, here's an idea. Watch at 4:57 onwards.Just don't burn you or your desk! Sunglasses aren't a bad idea either

author: TRIO_Smartcal
author_rank: Contributor
timestamp: June 12, 2013, 11:07:46 pm
content: Quote from: eevblogfan on June 12, 2013, 10:43:43 pmI'm referring to the fan noise not the transformer. We pulled 18 of these apart when we modified our stock after the first batch kept blowing up. We found no issues with the transformer physical or electrical. We even took some pictures of it under full load with a thermal camera. It was OK.The fan on every power supply has an slightly annoying noise under no load idle conditions. This is what folks are referring too. Personally I am convinced this is caused by the way they drive it.Also if you have a look at this video after about 5 minutes into the video you will hear the fan speed increase immediately with increased load. I don't think it is a thermal response. The change in fan speed is too rapid. I think it is directly related to the current drawn. Anyway I'm now curious and if I get time I will investigate further.

author: hgg
author_rank: Frequent Contributor
timestamp: June 13, 2013, 08:24:45 am
content: In the case of my Korad, it has a buzzing and a rattling sound...The rattling was definitely from a bad quality fan. I replaced it and its gone.The buzzing is from the transformer. I am not sure if you can eliminate that.It also has a 200mV overshoot.

author: TRIO_Smartcal
author_rank: Contributor
timestamp: June 13, 2013, 09:47:03 am
content: Sounds like you got one from the batch made on Friday afternoon at 4pm !!

author: Salas
author_rank: Frequent Contributor
timestamp: October 29, 2013, 07:28:04 pm
content: Quote from: hgg on June 13, 2013, 08:24:45 amI just changed the fan in mine too, and yes, the rattling is totally gone. The chassis itself can amplify the low RPM resonances to some buzz if the screws that hold the fan to it are not properly tensioned. Same care goes to when tightening up the cover screws themselves. Some trial and error for relative tensions in a quiet room will do the trick.

author: poorchava
author_rank: Super Contributor
timestamp: October 30, 2013, 02:27:43 pm
content: QuoteThis might be Nuvoton chiphttp://www.nuvoton.com/hq/enu/pages/default.aspx. That "curvy" 'n' looks liek the last letter in Nuvoton logo.

author: mos6502
author_rank: Frequent Contributor
timestamp: October 30, 2013, 03:15:49 pm
content: So why does the voltage look like a staircase? Glitch in the program?The DAC is driven by those 595 shift registers. So maybe they clock in the data without turning off the latch enable first?Looks like an error an amateur programmer would make.

author: kfitch42
author_rank: Frequent Contributor
timestamp: October 30, 2013, 05:10:40 pm
content: How big are the staircase steps? Most scopes have 8-bit ADCs. Lets say for example that you managed to just barely fit this signal within the range of the scope. Chances are if it can measure +12.5V, it can also measure a similar negative voltage. So our range is from -12.5 to +12.5 ... or 25V total swing. To fit that on an 8 bit ADC that gives roughly 100mV per step of the ADC. That actually looks close to what you are seeing, about 5ish steps within a 500mV division.So, you might be seeing an artifact of the limited precision of the scope instead of what is actually happening on the power supply.

author: Salas
author_rank: Frequent Contributor
timestamp: October 30, 2013, 06:07:30 pm
content: This one is in Hi Res mode if it will help your observations by any chance.

author: hgg
author_rank: Frequent Contributor
timestamp: December 01, 2013, 08:55:04 am
content: Hi,Just a quick question about the Korad and the OCP function.Please have a look at the small clip below:When I try to switch on the output with a low limit current setting, it takes a while and thevoltage indicator counts fast up to to specified voltage. The lower the current limit, the longerit takes to switch on. If I enable the OCP function though, it will not switch on! The current/voltagecombination has to be more than a constant value in order to switch on. Looks like it is drawingmore current than the limit in order to switch on. There is no load connected at the output.With a setting of 5V, 50mA and OCP will cannot switch on the output...Is this normal? (it is for a chinese product...)Does anybody else has the same problem or just me?Thanks!

author: hgg
author_rank: Frequent Contributor
timestamp: December 01, 2013, 04:29:04 pm
content: Anybody with a Korad to try it out ??

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 01, 2013, 08:17:10 pm
content: Quote from: hgg on December 01, 2013, 08:55:04 amThat makes sense, it has to charge the output capacitor(s) so the less current there is available the longer it will take.QuoteSadly enough that makes sense too for the same reason, there is no current limit on charging the output caps. I wonder how it could be solved, you don't want the OCP ignored when you switch the supply on. I guess just don't connect anything to the output and disable the OCP, then switch it on and when the output voltage shows the correct value turn on the OCP and connect your device to the output.

author: hgg
author_rank: Frequent Contributor
timestamp: December 01, 2013, 09:49:19 pm
content: Hi, I see. I thought that there might some kind of problem with it...They should have made a simple circuit that waits for the output capacitors to charge and thenswitch on the output. I don't know if that is common with other power supplies but it looks likea design fault to me.

author: Electro Fan
author_rank: Super Contributor
timestamp: December 02, 2013, 12:35:16 am
content: Quote from: hgg on December 01, 2013, 04:29:04 pmWith 5V and 50mA plus OCP turned on the Korad output does not want to turn on. (With OVP turned on the Korad output does turn on; with neither OCP or OVP turned on, the Korad output does turn on.)- What were the power supply settings that were used above to do the rise time measurements? 10V, 12V? What current setting? Thanks

author: hgg
author_rank: Frequent Contributor
timestamp: December 02, 2013, 06:57:07 am
content: Same, 5V, 50mA, OCP. (If you mean the one in the video clip, 5V, 1mA lowest setting with OCP)So, its a common theme...

author: Electro Fan
author_rank: Super Contributor
timestamp: December 02, 2013, 07:18:13 am
content: I was trying to determine the Power Supply voltage and amperage settings in Salas' post #46 .... Thx

author: Electro Fan
author_rank: Super Contributor
timestamp: December 02, 2013, 08:05:17 am
content: I tried to duplicate the rise time test done earlier by Salas. It looked like those tests were done by turning on the Output at 12V, but I wasn't sure what the amperage setting was in Salas' test. I turned on the Output at 12V at various current settings on the Korad Power Supply: 4A, 2A, 1A, 0.5A and 0.25A and measured the Rise Time (and also the Voltage using the Peak to Peak, Amplitude, and Maximum measurements).

author: pickle9000
author_rank: Super Contributor
timestamp: February 13, 2014, 03:08:33 am
content: Has anyone checked the overshoot at 3.3 and 5 volts?

author: Mike Warren
author_rank: Unknown
timestamp: February 13, 2014, 03:27:45 am
content: Quote from: pickle9000 on February 13, 2014, 03:08:33 amI just made some quick tests.

author: pickle9000
author_rank: Super Contributor
timestamp: February 13, 2014, 05:27:26 am
content: Has anyone drawn out the power output board?Sorry I don't have one of the and I did have a look around and couldn't find any diagrams.I haven't heard of any complaints once the voltage stabilizes is that correct?It would also be interesting to see if there is any spiking if you change a voltage while the output is on.

author: commongrounder
author_rank: Frequent Contributor
timestamp: February 13, 2014, 03:30:06 pm
content: There is some investigating going on in the thread "Korad KA3005P power supply faulty/repair" (Sorry. Still figuring out how to embed links in this forum). pomonabill221 has reverse engineered a partial schematic (available in that thread) and is spending some time sorting out the overshoot issue.

author: pomonabill221
author_rank: Frequent Contributor
timestamp: February 13, 2014, 07:35:33 pm
content: Here is the link to the thread where I posted my schematics as pdfs.https://www.eevblog.com/forum/testgear/korad-ka3005p-power-supply-calibration/Scroll down to reply #32Remember... these are hand drawn and partial. It may be a little confusing to follow so if you have questions, feel free to ask and I will try and answer them.

author: pickle9000
author_rank: Super Contributor
timestamp: February 13, 2014, 08:06:31 pm
content: Wow, good timing thanks I just walked in.

author: hgg
author_rank: Frequent Contributor
timestamp: March 30, 2014, 11:35:20 am
content: Hi,I have been using this power supply many months now and I have to say that I quite like it.Only the fact that you can calibrate it so easily, makes it awesome.The only thing that I don't like is the following: When you press the Voltage/Current buttonto set a new value, you only have 5 seconds until you make your next change. So if you areworking on something were you need to change the voltage frequently, you have to press theVoltage/Current button all the time...Is there a way to increase that delay?Thanks.