Korad KD3005D bench supply power on spike - Page 1
Forum section: electronics / testgear

author: vikisonline
author_rank: Contributor
timestamp: March 12, 2021, 08:49:55 pm
content: Hello,I just bought a chinese bench supply. It wasnt cheap at about $140 bucks.The power off spikes are about +/- 10V usually, sometimes more.Otherwise it seems like a decently performing supply.I could return this and grab a real name one for twice as much. Mostly will be used with Arduino and related circuits.Is this acceptable for that?https://youtu.be/A9F_jTEThfc

author: ataradov
author_rank: Super Contributor
timestamp: March 12, 2021, 10:16:54 pm
content: Try the same with a higher load. A few mA should be sufficient.And also, untangle your scope probes and power supply wires.

author: vikisonline
author_rank: Contributor
timestamp: March 12, 2021, 11:30:59 pm
content: Untangled wires. Put a 1 watt resistor on it.Up to 3.3v 200mah the spike was still there mostly.At 5v and 300mah the spike was almost gone, but still present.The amplitude of the spikes remained the same through all this, just the duration and number of cycles was reduced.

author: ataradov
author_rank: Super Contributor
timestamp: March 12, 2021, 11:42:09 pm
content: Then it is not great. I would not use this for anything sensitive. But I also would not use a power supply with analog knobs.I use Korad KA3005D and it has clean ramps on power up and on power down. I can highly recommend this power supply, even though it is about 2 times as expensive.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 12:04:40 am
content: Seems like the KA3005D shouldn't be much more than the KD3005D (and maybe less depending on where you purchase them). If you can return the KD go for the KA. Not sure what your options are where you are located but if buying from SRA Solder or through Amazon is feasible you should be in good shape.https://sra-solder.com/korad-ka3005d-precision-variable-adjustable-30v-5a-dc-linear-power-supply-digital-regulated-lab-grade

author: CDN_Torsten
author_rank: Regular Contributor
timestamp: March 13, 2021, 12:43:26 am
content: Make sure you are not picking up the collapsing magnetic field of the transformer. This can get coupled to the scope leads.Things to try:Move the power supply away from the scope and all circuitry. If this reduces or changes the amplitude of the 'spike' then there is a good chance the you are measuring an induced signal.Try disconnecting one of the leads from the power supply (the positive for example). Do you still get a spike?

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 12:46:50 am
content: Magnetic field is what I was thinking when I suggested to untangle the wires. It may be actually a good idea to short the scope ground to the tip and don't even connect it to the power supply. The ground wire loop may pick up the field.

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 01:10:12 am
content: Quote from: Electro Fan on March 13, 2021, 12:04:40 amAgree, just return it and buy normal KORAD KA3005D, its price about 80 USD, but it don't have such issues and have digital control with encoder and pretty precise.

author: vikisonline
author_rank: Contributor
timestamp: March 13, 2021, 03:06:50 am
content: Hmm could this really be just the collapsing field?I moved the scope and supply to separate wall outlets on separate circuits.I placed them as far from each other as the leads will allow me to.I get this on my scope now.Notice I have no leads connected to channel two, but the spikes line up with the noise on channel one. HmmmEdit.I have negative of the supply attached to the ground lead of the scope, and the probe is attached to the positive side of the resistor if that matters.

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 03:09:50 am
content: Floating channels could easily pickup noise from other channels. What about the shorted probe disconnected from the power supply entirely?

author: vikisonline
author_rank: Contributor
timestamp: March 13, 2021, 04:55:25 am
content: When I disconnect the leads from the supply it doesnt show up. Looks like the KA programmable model has the same issue from posts on this forum.I think I'll just live with this and keep it in mind. Nothing else in this price range anyway.Curious how some of the more expensive rigols behave in this regard.

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 04:57:24 am
content: I just looked at the programmable one and it has clean output on 200 mA load at 3.3 V and 5 V. I can't exclude that it may have problems on other settings.

author: techneut
author_rank: Regular Contributor
timestamp: March 13, 2021, 08:02:54 am
content: With the KA3005 you normaly switch on and off the output, not the whole supply. The switching of the transformer gives also spikes on the mains and ground.

author: vikisonline
author_rank: Contributor
timestamp: March 13, 2021, 05:18:56 pm
content: Ah yes I see it now. No idea why they didn't put two power buttons on this one....Well Im returning this one and getting that one. Looks like amazon pooched me anyway. For the amazon price of the KD3005 I can get the KA3005 on digikey.I hate returning things but alas, this makes sense.Thanks!

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 08:23:02 pm
content: Quote from: ataradov on March 13, 2021, 03:09:50 amNo. Oscilloscope has high impedance input, so when connector is open (and there is no noise source close to the connector), it will be the same silent as properly terminated connector.For example open connector is used during self calibration procedure. Because open connector have minimum noise on the input.Most of all, these noises are leaking through mains lines or ground loops. My oscilloscope also sensitive to high noises on the mains (from home equipment with SMPS) and can see similar noise when both input connectors are open or terminated.

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 08:51:32 pm
content: Hm... just tested my KORAD KA3005D, it also has some spike at power On/Off (see the first screenshot).I connected PSU to oscilloscope with a BNC cable and banana-BNC adapter on PSU side.Tried to connect just a ground, but the spike don't appears in such case.The peak voltage is about 5 V (no load).When I use output On/Off button it works ok, with no spike (see the second screenshot).

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 09:01:00 pm
content: Yes, there are spikes when you power on/off though a physical button. Which I guess is still bad if you keep the powered device attached when you power on/off the power supply. Not ideal at all.No spikes when powered on/off via a soft button.But also, it looks like those spikes happen when you rapidly power cycle. If you let it sit for a while in the off state, they are much smaller.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: March 13, 2021, 09:09:05 pm
content: Got one of each, and are a little puzzled by the price you paid but maybe it raised over the years.were like half of that, 5 years back and that was even the P-model with computer interface.Got the KA3003P and I got the KD3005P.the KA3003P was from China and the KD3005P from Europe.(likely also why is had inverted sockets)Video and gallery of my two older Korad unitshttps://imgur.com/gallery/B7ZOQ3JI use them for laser diodes, but dont recall massive spikes when I checked them, though don't use the clunking on-off switch, mostly the knob or the PC software that do have all the bells and whistle and have the on/off buttons build in, same with automatic power raising over time, also recalled you could use KA-software on the KD-model, but since you have the KD3005D model, no PC interface on D variant with all the PC controls..Minor cons with both, I recall the KD3005P (likely EU unit) had a temperature control-fan and which I did not believe that KA model had, but maybe Im wrong on that, or is has changed since,.One huge annoyance on the KD3005P variant was the lack of an on/off output feature.. though you can hold in the knob button for some time and it will turn off the output to a certain extent' but my plan was to do something as crazy as read the manualas I was confident that I missed something and the interface is not as intuitive as one could hope with these two knobs and time-based push features, and something as fundamental as controlling the freaking output should IMO be a straight forward on any bench PSU..I do recall holding in the knob for some time did got the output to turn off, or something like this, but it wasn't a dedicated on-off output approach, more like a lock..With PC and high current NUBM05,06,07,08 Nichia diodeshttps://imgur.com/a/jna30xhFor me it was an cheap way to get a liniar PSU able to peak at above 5.1A by daisy-chain them.If you just cycle the output by pushing and then holding one of the knobs and don't use the main switch, I reckon you don't get the same spikes, and have you read the manual (so I don't have to) arent there a dedicated approach to turn on and off the output on the KD-series?I also tend to use one of these DIY cables that i refitted with a cheap China-switch where I cleaned the touchpads to make sure I got clean connection and to make sure I got full control of the output when dealing with fragile expensive laserdiodes in the more exotic wavelengths.But its usually a lot in intervals I use mine, so if they are any good in regards to other alternatives anno 2021.. really cant say.. useally periods in wintertime I work on electronics, and in lack of a dedicated lab/bench it needs to be portable and they do weigh around 4.3kg (5.1A) and 3.7kg. (3.1A)https://imgur.com/a/7LKjZ9d

author: tautech
author_rank: Super Contributor
timestamp: March 13, 2021, 10:10:27 pm
content: Quote from: radiolistener on March 13, 2021, 08:51:32 pmDoes it default to output OFF when connecting the mains ?

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 10:11:48 pm
content: Yes, it does. The spikes appear on the output even when the software mode is Off.Same with physical power off. Spikes appear even if SW move was Off.

author: tautech
author_rank: Super Contributor
timestamp: March 13, 2021, 10:15:41 pm
content: Quote from: ataradov on March 13, 2021, 10:11:48 pmSwitch arcing is probably the cause then. Some suppression of the spikes is likely possible.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 10:29:18 pm
content: About 7 year old Korad KA3005P....Connected Korad output terminals to scope with banana to alligator clip leads to regular Rigol 10x probe.Set for 5V 4mA max. Results as seen in the photos.Also tried with 1k resistor - also no spikes.Also tried with Korad set for 5V 0mA - also no spikes.

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 10:29:20 pm
content: Quote from: tautech on March 13, 2021, 10:15:41 pmyes, it looks like switch arcing issue, because each time there is random pulse pattern - sometimes just 1-2 small pulses and sometimes a lot of pulses.How to reduce it? May be high voltage capacitor + resistor in series across the power switchQuote from: Electro Fan on March 13, 2021, 10:29:18 pmWe're talking about the spike which happens when you press a power switch (a hardware switch for mains voltage).

author: tautech
author_rank: Super Contributor
timestamp: March 13, 2021, 10:39:01 pm
content: Quote from: radiolistener on March 13, 2021, 10:29:20 pmDo these have a mains X-Y cap input filter network ?

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 10:49:32 pm
content: Quote from: tautech on March 13, 2021, 10:39:01 pmNo (actually I didn't verified it inside, just tested it with DMM for capacitance).Capacitance Neutral-Ground and Ground-Phase both are below 100 pF

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 10:59:22 pm
content: Just for the heck of it....Korad connected to Rigol scope as follows: BNC cable from scope via a BNC to banana adapter to alligator clips on leads connected with normal banana plugs at Korad output terminals.Scope set for 50 ohms, 1X, 2V, 0A. Note scope is set for 20mv/Div.

author: nctnico
author_rank: Super Contributor
timestamp: March 13, 2021, 11:00:55 pm
content: Quote from: ataradov on March 13, 2021, 09:01:00 pmThese spikes are not on the load but induced in the leads of the oscilloscope. If you put a low value resistor across the oscilloscope input (and switch the probe to 1:1 mode) they are gone. As Electro fan just demonstrated

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 11:12:05 pm
content: Quote from: Electro Fan on March 13, 2021, 10:59:22 pmDo not touch enable output button. Just press POWER ON/OFF switch.Set single trigger mode on oscilloscope and press POWER ON button.All leds and fan on PSU should be off (no mains) before pressing POWER ON switch.Quote from: nctnico on March 13, 2021, 11:00:55 pmNo. There is no oscilloscope probe, I used RG58 cable with BNC connectors and BNC-bannana adapter on PSU side.When I touch a ground only to oscilloscope BNC, there is no spike.Here is 50 Ω pass-through dummy load placed on oscilloscope side. This is a pattern at power off.As you can see, the pulse still present. Just a little smaller - about 2 V peak-to-peak (about 10 mW).

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 11:14:52 pm
content: One more....Korad connected to Rigol scope as follows: BNC cable from scope via a BNC to banana adapter to alligator clips on leads connected with normal banana plugs at Korad output terminals.Scope set for 1M ohms, 1X, 2V, 0A. Note scope is set for 1V/Div.

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 11:15:38 pm
content: Note the time scale. You won't see them at 100 or 200 ms/div.And also, any tests with soft on/off button are irrelevant. We know the output is clean in this case.

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 11:18:35 pm
content: Quote from: Electro Fan on March 13, 2021, 11:14:52 pmYou're doing wrong measurement. Do not touch ON/OFF button. ON/OFF button should be always in OFF stateUse POWER ON/OFF button instead of ON/OFF button!

author: tautech
author_rank: Super Contributor
timestamp: March 13, 2021, 11:22:25 pm
content: Quote from: radiolistener on March 13, 2021, 10:49:32 pmWith mains switch ON or OFF ?It needs be ON of course to be able to measure any X-Y network beyond the switch.

author: radiolistener
author_rank: Super Contributor
timestamp: March 13, 2021, 11:33:53 pm
content: Quote from: tautech on March 13, 2021, 11:22:25 pmFor both states. There is no difference, just no capacitors.

author: tautech
author_rank: Super Contributor
timestamp: March 13, 2021, 11:37:42 pm
content: Quote from: radiolistener on March 13, 2021, 11:33:53 pmWell there you go then. If this is proved true who, what corporation gets away without a mains suppression network in their products in this day and age ?

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 11:44:55 pm
content: Quote from: radiolistener on March 13, 2021, 11:18:35 pmI did, in each set of photos you can see what happens when the Ouput button is used AND when the Power button is used.Obviously, when the Power button is first turned on the Output button is in the off state - so that isn't too exciting. Butyou can see in the photos when the Power button was turned off with the Output button in the on state. Let me know if that isn't clear and we can discuss further or I can take some other photos if you would like.fwiw, after using a KA3005P for over 7 years and a KA3005D more recently, I'm not ready to say they are going to replace Keysight et al power supplies in commercial labs but the KA's are reasonably accurate, reliable, and enjoyable to operate. I think it makes more sense to go for the KA's than the KD's for the better UI including the separate Output button. I think if we listed all the new test equipment that could be purchased new for about $100 the Korad KA3005D would have to be near the top of the list for overall good value.Below a repost of one of the images showing the Power Button Turning Off with the Output Button On.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2021, 11:49:40 pm
content: Just to put this to bed, here is an image of the Power Button turning on (with the Output Button off).

author: ataradov
author_rank: Super Contributor
timestamp: March 13, 2021, 11:53:45 pm
content: Why are you keep looking at 100 ms time scale? The spikes are a few us long.You need to try harder, they are there. Your unit is not special.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: March 14, 2021, 12:40:46 am
content: Tried with my KD3005P with one of these chin crocodile to BNC and just single capture while turning on and off with the KD3005P AC switch.the start is with 1v out and the latter part is with 0v.

author: nctnico
author_rank: Super Contributor
timestamp: March 14, 2021, 01:14:09 am
content: Quote from: ataradov on March 13, 2021, 11:53:45 pmAnd a tell-tale sign that you are looking at an 'EMC' effect. The control loop in a PSU isn't fast enough to produce spikes in the us region (and if you look closer at the screen you'll see the actual pulses are in nanosecond territory). A power supply misbehaving is in the milli-second time scale.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 14, 2021, 03:26:30 am
content: Quote from: ataradov on March 13, 2021, 11:53:45 pmataradov, I chose the timebase setting to show the knees of the curves. And when I look around at 5us I don't see any spikes. Not trying to hide anything or prove anything - just showing what I see. So, I'm not sure what you are looking/asking for. Please let me know what power supply, load, and scope setup and capture parameters you are looking for and I'm happy to give those a try.Quote from: nctnico on March 14, 2021, 01:14:09 amI think this (what nctnico is saying, if I understand correctly), is the case. We can look at the power supply or we can look at other environmental effects. Seems like the power supply is performing properly but if I'm not understanding and missing something please let me know.Edit: ataradov was right, I needed to try harder. Events found and captured... will post shortly.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 14, 2021, 04:03:23 am
content: Ok, found a couple events when looking at 1us/Div. This was with the 10x probe at 1Mohm connected to the alligator clips of the banana leads with the KA3005P set for 1V, 1mA. These were using the Power Button to turn the power supply on, and the Power Button to turn the power supply off (when the Output Button was still on). Happy to try other combinations now that I'm looking in the right neighborhood.I now have various other combinations to try......

author: radiolistener
author_rank: Super Contributor
timestamp: March 14, 2021, 04:06:06 am
content: Quote from: Electro Fan on March 14, 2021, 03:26:30 amCan you show 1 uS/div scale for POWER-ON sequence?Also, could you please check if your KORAD has Y-capacitors on the mains?Quote from: nctnico on March 14, 2021, 01:14:09 amPSU noise from a dynamic LED indication can be found in the nanosecond time scaleQuote from: tautech on March 13, 2021, 11:37:42 pmJust inspected inside, there is no Y-capacitors. The mains connector is connected to the transformer through the power switch. Ground is connected to the shell.I found there are two blue capacitors between ground (shell) and + and - output terminals.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 14, 2021, 04:52:12 am
content: Ok, the plot thickens.I remembered Dave did a video with a BNC to probe connector so I gave that a try with the same 1V, 1mA settings I had in the post above.In general, I think the better connection minimized the severity of the spikes. I ran about a dozen power cycle tests. Some of the results might vary based on how long I left the power on or off - not sure. Perhaps most interestingly, when I set the trigger to just above the 1V signal level there were no spikes to trigger the 1V signal. On the other hand, there are still spikes when I turn the Power Button off. You can see they vary across the three samples attached below - might be random or it might be related to how long (several seconds here or there) between power ons and power offs.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 14, 2021, 05:05:05 am
content: Quote from: radiolistener on March 14, 2021, 04:06:06 amLooks like you found what you were looking for on the inside... thanks for sharing the findings.I ran the 1us/Div Power-On sequence. Nothing happens at Power Button Power On and with the Output Button Power On the signal triggers cleanly (no spikes).

author: Electro Fan
author_rank: Super Contributor
timestamp: March 14, 2021, 05:35:51 am
content: I'd like to think it's persistence more than OCD.I have a theory that the turn off spikes might be influenced by how the Power Button operates during Power Off (ie, how fast it is making/losing contact inside the switch). I guess the good news is that if the spikes don't occur at 1) Power Button On, 2) Output Button On, and 3) Output Button Off, then the only trick is to get a DUT disconnected after the Output Button is off and before the Power Button goes off.

author: vikisonline
author_rank: Contributor
timestamp: March 17, 2021, 12:54:28 am
content: Well sent back the KD3005D. Got the KA3005D...Well the KD had about a +/-20mV ripple/noise on the line from the set voltage.Well looks like the KA I got has +/-100mV from the set voltage.GAH!Im tempted to send this back too and get a sigilent. I was really hoping this would behave exactly like the KD but with the soft power button to avoid the crazy spikes.Though to be honest Im also at the point where Im willing to break down and attempt to live with it. I don't think this is high enough to cause issues with anything I will be doing. Though a far cry from the KD unit I had,and a very far cry from the manufacturer claimed 2mV....this was at 2v and 0.143 amps drawnAs expected no spikes with the soft button.

author: radiolistener
author_rank: Super Contributor
timestamp: March 17, 2021, 01:28:31 am
content: Quote from: vikisonline on March 17, 2021, 12:54:28 amthis is strange. Most of all this is error of your DMM.My KORAD KA3005D has error about 0.01 V or even better, depends on the voltage.KORAD KA3005D has a calibration mode, so you can calibrate it, if you have precise DMM.

author: ataradov
author_rank: Super Contributor
timestamp: March 17, 2021, 01:31:26 am
content: 100 mV is a peak to peak noise. I checked my unit and there is a periodic ringing as shown on the second capture. It is about the same amplitude on open terminals, and goes down a bit with load, but still present at loads of ~200 mA. I don't have anything to quickly create higher load.

author: radiolistener
author_rank: Super Contributor
timestamp: March 17, 2021, 01:44:18 am
content: my KA3005D also have some noise pulses, most of all it come from a dynamic LED indication or a fan PWM. But their average power is very low. And actually KA3005D noise power below 1 MHz is even better than complete linear PSU HY1505D.Since KA3005D noise power is very low, I don't catch any issue with it. It's even hard to catch this noise with a receiver.For example here is comparison of the noise between KA3005D and HY1505D taken with a radio receiver.You can see PSU power-on sequence on the screenshots.As you can see, KA3005D has some noise peak at about 600 Hz, but the power of this noise is below -80 dB and even better than 50 Hz leak (mains). Which is better than fully linear PSU HY1505D. Also overal noise floor for KA3005D is much better.If you're not obsessed with extreme ultra low noise, it doesn't affect you. For ultra low noise circuit you can buy another fully linear PSU without digital circuits inside (such as digital control or digital display).

author: Electro Fan
author_rank: Super Contributor
timestamp: March 17, 2021, 05:27:00 am
content: Maybe try with 20M bandwidth limit - I think ripple specs generally assume a bandwidth limit.If I set the Korad for 2V and up to 4mA but with no load I get about about 2mVRMS.I think to measure ripple you have to have a pretty good probe technique/connection and you you need to be sure you aren't in a noisy environment.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 17, 2021, 05:33:48 am
content: Another at 200msEdit: added adapter image

author: Electro Fan
author_rank: Super Contributor
timestamp: March 17, 2021, 05:48:27 am
content: Article mentioning bandwidth limit.https://www.eetimes.com/power-tip-6-accurately-measuring-power-supply-ripple/#I think Dave did a video on measuring ripple that also cited the use of a bw limit for measuring ripple.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 17, 2021, 06:03:22 am
content: This article that also talks about using a bandwidth limit to measure ripple gives examples at 1us.https://www.digikey.de/Web%20Export/Supplier%20Content/Excelsys_633/PDF/excelsys-measuring-ripple-noise.pdfAt 1us the Korad is under 1mVRMS and averages about 3.5mV pk-pk.

author: vikisonline
author_rank: Contributor
timestamp: March 20, 2021, 05:22:59 am
content: Your trigger is way in the band though, try moving it further out and see if you see occasional spikes

author: Electro Fan
author_rank: Super Contributor
timestamp: March 20, 2021, 08:35:59 am
content: Quote from: vikisonline on March 20, 2021, 05:22:59 amHere are two more, both with the trigger at 14.9mV; one was 1us the other was 200ms (should be plenty of time to find ripple).The ripple was a little higher than previously - my guess is something (other test equipment, computers, lights, air conditioning, who knows what) was off last time and was on this time. Let me know if you want something else tested.At around $100 per power supply for the KA3005D model I think it's possible that there might be some unit to unit variation and it's possible that some units will be defective or out of spec but I think Korad is generally likely to meet or come pretty close it's specs most of the time. If you buy from a reputable seller hopefully you can return it if it doesn't meet specs.Regarding ripple measurements I think some keys are 1. measuring with a very good connection (preferably with a probe to BNC adapter), 2. use a 20MHz bandwidth setting, and 3. be careful to distinguish between PS ripple and environment noise.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 20, 2021, 08:48:33 am
content: After the several minutes it took to post above I looked again and saw the ripple was reduced somewhat. My guess is something nearby shut off in the meantime. I'm pretty sure that at somewhere around 1 to 3mVRMS it's possible that something starts acting like an antenna and that a variety of things can be transmitters.

author: xani
author_rank: Frequent Contributor
timestamp: March 21, 2021, 03:48:16 pm
content: Quote from: Electro Fan on March 20, 2021, 08:35:59 amMy KA3005D-3S had 12V rated fans powered by 24V. I only noticed when they died after few years of occasional uses. But power is clean without spikes...

author: vikisonline
author_rank: Contributor
timestamp: March 23, 2021, 09:03:19 pm
content: Yea unit to unit variation might be my guess. But for the price Im happy with it. I didn't get as lucky as some others but this will do for now.Thanks for running those tests.

author: vikisonline
author_rank: Contributor
timestamp: March 23, 2021, 09:05:02 pm
content: Quote from: xani on March 21, 2021, 03:48:16 pmHA. That is one of the good things about mine. Even on full power (30v 5A setting drawing 1 amp) the fan in mine is quieter than my rigol scope... Go figure.From others I heard it would be horribly loud but I guess I got lucky with that part.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: March 26, 2021, 12:34:21 am
content: Aint these temperature-controlled to an extent that the fan will turn off with no load? been a few revisions.so a given fan-noise on a KA-unit, like almost a decade back, can vary quite a bit from a buyer purchasing one today.Got the KA3003-P model and the KD3005-P model.. the KA3003P were from China and the KD3005P from Europe (purchased 4 to 5 years back).Took a look inside #17 (KA3003-P model) to put my unit ino perspective with the unit Dave got' but I do recall my KD-5A model was more silent than my KA-3A model.but the very early models like 9 years back, had some challenges, like Dave is pointing out here, but were fixed very soon after by Korad, and made these Korad-PSUs to be some of the most popular lowbudget linear PSU's for the hobbyist's--and the follow-up after Korad changed it...https://youtu.be/_HrvuHSywms?t=137Here is a fan noise-display of my KD3005P with a full 5.1A load on a Nichia-laser diode peeking around 6.3w. .

author: Electro Fan
author_rank: Super Contributor
timestamp: March 26, 2021, 12:52:10 am
content: Quote from: vikisonline on March 23, 2021, 09:05:02 pmIf you want to see what the power supply really can do on the ripple measurement I think it's best to test using one of these:https://app.caltestelectronics.com/product-list/product-page/view/CT3655/They come in different sizes - just make sure to get one that will fit the oscilloscope probe you are using.https://www.farnell.com/cad/2702874.pdfThis 3.5mm adapter fits a Rigol RP3300A. Some of the older Tektronix probes I think require a slightly larger adapter.Edit: you need one of these too, of coursehttps://www.pomonaelectronics.com/products/adapters/bnc-f-double-stacking-banana-plug