Judging by teardowns, which cheap PSUs are better - "Korads", UNI-T, PeakTech? - Page 1
Forum section: electronics / testgear

author: midix
author_rank: Contributor
timestamp: June 17, 2021, 11:58:50 am
content: I'm looking for a hobby-level 0-30V 5A PSU for working with Arduinos, Raspberry & clones, small motors, LED strips etc., and also occasional laptop repairs & experiments.In my local shops, the low-budget options are mostly UNI-T UTP3315TFL, UTP3315TFL-II, UTP1305, and those well-known Korad clones (from a company named RND) - 320-KD3005D and variations.I managed to find teardown videos for both UNI-T and Korads, but I'm not experienced enough to judge the quality in comparison:https://youtu.be/g94mpom2Ahs(Dave's famous Korad teardown)https://youtu.be/yjcoc74NBDw?t=202UNI-T UTP3315TFL-IIhttps://youtu.be/qjOIns3mwO8?t=409UTP1306SNo teardowns for UTP1305So, what would you suggest, which ones seem to be a better build with more reliable components (especially the main power circuits & transistors)?I have read about Korad issues here on the forum, but not much info about UNI-T.Maybe it is better to have a Korad clone with known issues and recipes for fixing them instead of UNI-T with unknown pitfalls. On the other hand, UNI-T seems to be a somewhat known brand and they might have more responsibility about their products, unlike that "RND".

author: masterx81
author_rank: Frequent Contributor
timestamp: June 17, 2021, 03:52:13 pm
content: RND are rebranded Korad, not clone. I have ka3305p and kel103, and they work as they should. The UI is awful

author: midix
author_rank: Contributor
timestamp: June 19, 2021, 05:09:23 pm
content: The pricing is somewhat confusing, when trying to judge the quality.For example, when looking at models with about the same specs (30V 5A) UNI-T models are 50% more expensive than RND, and PeakTech are 50% more expensive than UNI-T.The question boils down to this - is it worth paying more for a UNI-T or PeakTech with a hope of getting better quality components (better cooling, more power reserve, better OV and OC protection), or are they the same as those Korads/RNDs and I would be overpaying for the brand relabeling and maybe nicer packaging and warranty?

author: radiolistener
author_rank: Super Contributor
timestamp: June 19, 2021, 06:20:45 pm
content: I vote for KORAD, because UNI-T has less features and cheaper circuit

author: midix
author_rank: Contributor
timestamp: June 19, 2021, 06:35:11 pm
content: I just found a PeakTech 6070 in a local shop.Seems a nice PSU, but almost twice the price of 320-KA3005D. Not sure, if it's actually so much better than Korad - haven't found any solid reviews and teardowns. Of course, it's Chinese-built OEM, and some cheapest PeakTechs are known to be pretty bad.There's one simple test video where a person claims 6070 has very little ripple, and also demonstrates that it has enough precision for current limiting to light a LED without burning it. I've seen complaints about cheaper PSUs that immediately burn LEDs when trying to use them without a resistor. Not that I would do that, but still, that might be indicative of the quality and precision of 6070. So yeah, maybe I should go for 6070 instead of 320-KA3005D.

author: masterx81
author_rank: Frequent Contributor
timestamp: June 19, 2021, 09:13:41 pm
content: 6070 seem a nice unit, linear, 500uv ripple, it seem also fanless. I not know how a fully linear supply can dissipate 150w of power without a fan. Maybe have an smps pre-regularor before the linear stage?

author: kcbrown
author_rank: Frequent Contributor
timestamp: June 19, 2021, 10:01:48 pm
content: Quote from: midix on June 19, 2021, 06:35:11 pmThe KA-3005D does this without any issues. I used a red LED and set the PSU to 5V and 50 mA. Hooked it up and enabled the output. The LED lit up nicely without any problem whatsoever. Same for yellow, green, and blue LEDs.I should note that the supply will still output enough current to light up the LED even when you set the current to zero. For the red LED, I measured this to be about 36 uA. So "zero" current isn't really zero. Of course, turning off the output really does cut the power to the LED.

author: midix
author_rank: Contributor
timestamp: June 19, 2021, 11:43:43 pm
content: Quote from: masterx81 on June 19, 2021, 09:13:41 pmJudging from photos, it has a beefy heatsink at the back. Not sure if that's adequate though.In the worst case, it's always possible to mount a fan on it, and it might be a better solution than those small fans and heatsinks inside other PSUs.Still, it would be great to find somebody who can peek inside a 6070 and tell if it's worth the 2x price of 320-KA3005D.Another good signal - while there are only 21 reviews on Amazon about this model since 2018, still there are no significant negative reviews. The worst complaint I've found is about transformer buzz and illogical button arrangement for 2 output device. So, this gives some hope there are no massive known issues with the device. It's also good that it does not have any rotary elements that usually wear out with time. I guess, I'll go with 6070 then.

author: radiolistener
author_rank: Super Contributor
timestamp: June 21, 2021, 02:29:15 am
content: Quote from: midix on June 19, 2021, 06:35:11 pmSuch issue can happens due to a small electrolyte capacitor for additional ripple filtering on the output terminals. If you set too high voltage, the charge of this capacitor can damage the LED. As I know almost all PSU on the marked have such capacitor on the output terminals.

author: kcbrown
author_rank: Frequent Contributor
timestamp: June 21, 2021, 03:02:01 am
content: Quote from: radiolistener on June 21, 2021, 02:29:15 amJust in case the Korad might be susceptible to this, I cranked the voltage up to 30V and retried the experiment. Same results as before: the LED lit up as expected without issues.So it appears that the Korad passes this particular test with flying colors.

author: masterx81
author_rank: Frequent Contributor
timestamp: June 21, 2021, 07:41:09 am
content: On the korad units there is a capacitance. If you connect the led and after you power on the output, the constant current will work as it should (no spikes also with a short circuit, 100% safe). But if you connect the led while the output is already powered (let say 30v, 0.02a) it will burn (due to output capacitance that slow down the constant current control)

author: edigi
author_rank: Regular Contributor
timestamp: June 21, 2021, 07:59:37 am
content: Quote from: masterx81 on June 19, 2021, 09:13:41 pmNo. The way how they do it (in most of this kind of cheap PSUs) is that the transformer has many secondary windings and they switch between them with relays. In my PSU they switch every 4 volts. This can reduce the power dissipation need to around to 5A*5-7V that can be passively cooled already.This has also its disadvantage though, especially if it's used in a way that relays have to be switched a lot as it can wear them out. For example constant current mode can mean a lot of switching.A few points that was important for me when selecting PSU:- Output switch, so that adjustment is possible without unplugging the powered electronics/no immediate power after switch on- Constant current mode but sometimes it's good to have also overcurrent switch off mode (some SMPS have only this)- Low noise (switching mode PSU vendors prefer to specify only RMS but Peak-to-Peak is very good to know)- Quick reaction to load change (and load not much impacting output voltage)I ended up not one type but multiple types. The SMPS that I have has lots of power (10A) and many features in a small form factor but it required modding to get the noise even below 5mV RMS/100mV Pk-Pk. It has also slow reaction time for load change. The linear PSU that I have does not have a very good interface (but at least it has output switch) so that fine/course setting may require extra iterations and has the relay switching issue (that can impact durability) but it has very low noise that is actually hard to measure.I've never had a PSU with a push button only interface and my concern with that when slow increase of voltage or current is used to check the impact it's probably slow to do with such interface.My most preferred interface (have not seen in this kind of cheap PSUs) that fine control is without limits (so that there is no endpoint with fine control where you cannot go any further). With rotary encoder it would be easy to do but still not used.

author: masterx81
author_rank: Frequent Contributor
timestamp: June 21, 2021, 08:27:52 am
content: Korad's have also some taps on the secondary, and a quite good heatsink, but it get quite hot, enough to need a fan.