Korad KEL-103 Electronic Load Problems - Page 1
Forum section: electronics / testgear

author: ScottW
author_rank: Contributor
timestamp: February 07, 2020, 02:01:33 am
content: I purchased a Korad KEL-103 Programmable Load in August 2019, after reading several reviews (including one here on EEVhttps://www.eevblog.com/forum/testgear/review-of-the-korad-kel103-programmable-load/msg2276907/#msg2276907).I was initially really happy with it. The front panel and limited GUI made some functions a bit difficult, but I found some Python code to send/receive SCPI over UDP and I was off and running. Seemed really well built, voltage and current measurements were spot on, and it was working great -- especially considering the price was about 50% of anything else I found with comparable capabilities.Then just 3 months later -- it mysteriously quit working. No smoke. :-) It still powered up and still "acted" like it was working, accepting commands and displaying the correct results. But despite what the front panel said was happening -- it never applied any load when activated.The seller agreed to an RMA, and though I had to pay return shipping and wait 5 weeks.... I got the replacement KEL-103 two days ago.But the replacement -- right out of the box -- has a completely different problem: The voltage measurement wrong. When powering the unit with nothing connected (or even with inputs shorted), it initially displays several hundred millivolts, then gradually over about 5 second drops down and stabilizes at 4mV. It never gets to 0V. (My original Kel-103 was spot-on with voltage, showing 0V at power up and very accurate at all voltages).In operation, the error is worse -- always high by at least that 4mV, and up to 25mV depending on the voltage (error scales with voltage measured). But to be honest, the lack of a 0V reading when there's 0V at the terminals is my biggest complaint. The first unit correctly zeroed, and I'd like this one to as well.QUESTION: Has anyone else here with a KEL-103 (or the Tenma / RND clones) seen something like this? Is there any kind of calibration or "zero adjust" function hidden in firmware behind some key sequence? The manual doesn't mention one, but I know some of Korad's power supplies have a calibration feature in their firmware. I am hoping the KEL-103 has something similar.

author: diodak
author_rank: Regular Contributor
timestamp: February 11, 2020, 07:48:53 pm
content: Is the same symptom when you switch to an external voltage measurement (connector on the back of the housing)?

author: ScottW
author_rank: Contributor
timestamp: February 11, 2020, 08:58:47 pm
content: Good question -- I meant to include that info and forgot.Yes, with no load, the measurement is identical whether using the front terminals or the rear "sense" terminals (via the "Shift+CW" keys). Either way, measurement is about 4mV when nothing is connected or terminals shorted. With a load, the front terminals measure a little lower than the back, as would be expected, but both are always high.

author: diodak
author_rank: Regular Contributor
timestamp: February 16, 2020, 05:46:38 pm
content: I wonder about the possibility of calibration. Unfortunately, the STM32 control processor is read-protected, so you can't see which SCPI commands are used for calibration ...I have the TENMA version, but the drift is small and appears immediately after switching on.

author: masterx81
author_rank: Frequent Contributor
timestamp: March 13, 2020, 05:40:22 pm
content: Would be interesting to know the calibration procedure. For the Korad PSU is possible.I'm thinking to buy one of this devices...

author: ceut
author_rank: Regular Contributor
timestamp: April 06, 2020, 11:52:05 pm
content: .Hello,Same problem here: I have just received my Tenma 72-13210 this morning from Farnell, and I have a +4mV +5mV error even when I short the 2 terminals.I have found a hidden boot menu, but I don't understand what it does: press ESC then power ON with ESC pressed: fan will be at 100% and there are strange value on screen without anything on terminals: someone could try and check if values are same than mine?I have tried all buttons and there is only the ESC button which starts with strange behaviour, I have made a photo to show youSo it is really a Zero calibration problemThe production date is 201912 (barcode on the rear).Will see if I return it or not, but don't know what DC load choose afterEdit: Also I have a old software version V4.0, whereas in this video it's V4.1https://youtu.be/2ZzBsZT9Scg?t=167And here the guy seems not to have calibration problem.Someone can upload the V4.1 software? Thanks (only the "72-13210.exe", nothing else)

author: squeakyfeet
author_rank: Newbie
timestamp: April 07, 2020, 03:00:57 am
content: Hi, I bought the Tenma 72-13210 from CPC, which is a UK division of Farnell, a couple weeks ago. The unit correctly shows 0V with no load or with output shorted. The barcode on the back starts 201909.Results from esc+power are 01264 V, 05065 A and 0001 G.

author: ceut
author_rank: Regular Contributor
timestamp: April 07, 2020, 08:56:02 am
content: Quote from: squeakyfeet on April 07, 2020, 03:00:57 amHello,Thank you for your feedback with your working unit.Do you have the 4.1 version of the PC utility (and maybe you can share it)? Thanks youAlso, I have dug into this hidden menu, there are many many group which some strange V/A values (I stopped at 9 G).I think it's really something with calibration but there are so many many values that I give up.I will phone to Farnell this afternoon and see if I could have an exchange or return.Also, in my opinion: may be something with the beginning of corona virus in China, so previous date code are ok (until maybe october), but since november/december date code are not good...If some others could share date code and the drift or not ?

author: masterx81
author_rank: Frequent Contributor
timestamp: April 07, 2020, 11:42:33 am
content: My 202001 powered on, with nothing attached, show 0v.

author: ScottW
author_rank: Contributor
timestamp: April 07, 2020, 04:23:08 pm
content: Quote from: ceut on April 06, 2020, 11:52:05 pmThat is, indeed, the way you enter calibration mode. Calibration didn't solve the problem for me, and the distributor rep told me she tried it on another unit and it made the problem worse. So proceed at own risk. :-) I ended up returning my KEL103 and bought a Rigol DL3021 instead.I am attaching the calibration procedure the US Korad distributor sent me. It is poorly written and confusing -- it is often difficult to tell when it refers to the KEL103 controls versus when it refers to the power supply controls. Also, you need a 100V DC power supply with millivolt resolution and a 6-1/2 digit multimeter. The first (3) steps only need 18V, but you can't save the calibration until ALL steps have been completed and step 4 requires 90V.

author: kahuna0k
author_rank: Regular Contributor
timestamp: April 07, 2020, 06:14:41 pm
content: Quote from: ceut on April 07, 2020, 08:56:02 amMy Korad came with KEL103 assistant v1.2.1 that is not working over the network (because of the broadcast to 255.255.255.255 issue). Could you share your v4.0 software? It is probably much better that this.Thanks!

author: ceut
author_rank: Regular Contributor
timestamp: April 07, 2020, 06:30:00 pm
content: Quote from: ScottW on April 07, 2020, 04:23:08 pmThank you!I think I have understood how it works.So I have only calibrate the low Volt/low Amp parts only, after making photos of all 8 groups to backup the original values.Calibrate with my little DPS5005 + a 20V/3.25A power on it, and a new Keysight U1272A (with calibration certificate of 01/2020, this one is not mine, great DMM).Now on CC mode, it's spot on, at 5V I read 5.0010VBut if I switch between CV/CW/CR: I read 5.007V : about +6mV (that's what I have when nothing on Terminals)If I switch back to CC, again 5.0010V.So I'm pretty sure now this is a hardware problem: I don't know if I try to exchange it or buy another model.Also, on CC mode only on power on: it takes about 5s also to show "0.0000V" with a big jump from "0.0015V" to "0.0000V". The 3 others mode show "0.006V"; all with nothing on terminals.For the Rigol: are you satisfied with it ?

author: ceut
author_rank: Regular Contributor
timestamp: April 07, 2020, 06:36:57 pm
content: Quote from: kahuna0k on April 07, 2020, 06:14:41 pmWarning: the KEL103 is factory onstatic IPat 192.168.1.198 !I have changed it with USB connection and assistant in the Tab "USB debugger", then checked "DHCP" on the right, and "OK" to send it.Then I haved push "Dev Info" to check if DHCP:1After that, I have checked into my router which IP adress the KEL has.

author: kahuna0k
author_rank: Regular Contributor
timestamp: April 07, 2020, 07:12:51 pm
content: Quote from: ceut on April 07, 2020, 06:36:57 pmThanks for the info. I've already written some python code (I attached it to the other KEL103 thread) to be able to control it with SCPI and already set it up to DHCP. I would just like to have a nicer UI that works. The original KEL103 factory assistant doesn't allow you to set the IP of the device, it will always autodiscover it by broadcasting to 255.255.255.255. That's why I'm asking for a different software, in the hope that it will work over the network and let me set the IP and port of the device manually.

author: masterx81
author_rank: Frequent Contributor
timestamp: April 07, 2020, 07:35:49 pm
content: Who not have a 100v 12a psu?1200w is not that bad

author: ScottW
author_rank: Contributor
timestamp: April 07, 2020, 07:48:21 pm
content: Quote from: masterx81 on April 07, 2020, 07:35:49 pmExactly. I sure don't!Fortunately I know someone at a local solar engineering / manufacturing company, and he gave me access to one of their rack-mount supplies that didn't break a sweat going to 100V.

author: ScottW
author_rank: Contributor
timestamp: April 07, 2020, 08:15:03 pm
content: Quote from: ceut on April 07, 2020, 06:30:00 pmMostly. I went with the DL3021A, the 200W model. It was 180% the cost and 100W less power handling compared to the KEL103. Works great, and considerably easier to use due to the display and GUI, has built-in logging to flash drive, communication from python is a bit easier / more reliable since it's full TCPIP (the KEL103 was UDP only). My only big gripe with the DL3021A is that the fan runs constantly, whereas the KEL103 was silent when idle, only turning the fan on when needed.Hard to beat the KEL103 (or similar Tenma) in "bang for the buck". If my original one (which had very accurate voltage readback) had not failed completely, I'd still be happily using it. But when it failed, the replacement had the voltage offset and error, and the distributor was unable to find one in their stock that didn't have the same problem -- with no new stock expected for several months. So in the end, I opted for a refund and bought the Rigol from TEquipment.

author: ceut
author_rank: Regular Contributor
timestamp: April 07, 2020, 08:30:45 pm
content: Quote from: ScottW on April 07, 2020, 08:15:03 pmSo your original one was a super fast no-drift start at 0.0000V like this review ?https://youtu.be/9fe8RnY-Xfw?t=680Then after the exchange you have same problem than mine which is brand new 1-day old (drift then offset).And all your distributor stock have all this problem?So I have no choice exept return it and get refund.. And effectively the Rigol cost too much for meI think I have to wait some months to buy a new one, it's my first "big" DC Load, I have a little RuiDeng LD25 which I like very much (I'm a good RD buyer from their official ali store)

author: ScottW
author_rank: Contributor
timestamp: April 07, 2020, 08:55:49 pm
content: Quote from: ceut on April 07, 2020, 08:30:45 pmCorrect.Quote from: ceut on April 07, 2020, 08:30:45 pmCorrect. The replacement had an offset AND a small additional error that scaled with voltage.Quote from: ceut on April 07, 2020, 08:30:45 pmThat's what the rep told me. She attempted calibration on one, and said it made it worse. Opened / tested several, and all of them had the same issue -- some worse than others -- so her conclusion was they had a "bad batch". They didn't expect any more stock for 3+ months, and I didn't want to wait that long, so opted for a refund.Quote from: ceut on April 07, 2020, 08:30:45 pmIf you're using the front-panel, there's really no good workaround. For programmatic access, I had success "correcting" the raw reading returned from ":MEAS:VOLT?" to remove the offset and additional per-volt error. Here's the routine I was using, with the offset and correction factor that worked for my particular kel103.def kel103VFix(RawV):offset=0.0037factor=0.00015Corrected = (RawV - offset) - (RawV*factor)if Corrected < 0:Corrected=0return round(Corrected,4)

author: squeakyfeet
author_rank: Newbie
timestamp: April 07, 2020, 10:40:02 pm
content: Quote from: ceut on April 07, 2020, 08:56:02 amSorry, only V4.0Quote from: kahuna0k on April 07, 2020, 06:14:41 pmContents of CD:https://www.mediafire.com/file/awfxjzrbbdk1unq/Tenma_72-13210_CD.7z/file

author: ceut
author_rank: Regular Contributor
timestamp: April 08, 2020, 08:06:36 pm
content: For me, I'm waiting my RMA to have my refund.I have found this one that I will buy soon (180W model with the RGB fan):https://fr.aliexpress.com/item/4000478442757.htmlIt doesn't have a case or so, but it has all the fonctionI need, and has a BT connection with .apk and .exe easy to download

author: PavanK
author_rank: Newbie
timestamp: July 17, 2020, 09:08:12 am
content: Hello everyone , I am doing my master thesis on power electronics and in order to test the parameters of the batteries I am suppossed to use RND Kel 103 . I tried to install the software on my laptop but I cannot find the interface where I can write the program. The user manuel is not helpful as it has no info on the setup. Please help me setup the software on the laptop.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 17, 2020, 09:54:40 pm
content: Quote from: ceut on April 08, 2020, 08:06:36 pmThe software does not work well enough to accomplish much that is useful.

author: wernerj
author_rank: Newbie
timestamp: August 12, 2020, 05:04:36 pm
content: Quote from: ScottW on April 07, 2020, 04:23:08 pmI don't think the power supply has to be very precise voltage-wise as all measurements are done when the KEL103 forces the connected supply into CC mode. I DO suspect that the current limit has to be fairly accurate though (if they're using that information during calibration, not sure yet).I had a different issue with a TENMA-branded unit from Farnell, the current sunk was 2mA too high close to zero (but reported as 0) and then gradually it dropped to 4.998A when trying to sink 5.000A. Turns out that the resolution of the unit simply isn't better than ~1mA in the default 30A range. When dropping to the 3A range things behaved a lot better (Shift+CC and set 3A). The current display will change when max current is set to 3A or below, moving the decimal point a step to the left.Also the offsets of the readback changes somewhere around 18.5V (both current and voltage), so the 18V calibration point clearly is at the top of one of the ranges.What's odd is that there doesn't seem to be a way to adjust the readback?I can get reasonable results in the 3A range after calibration (100uA requested results in ~120uA, 1mA results in ~1.010mA and 10mA results in ~10.01mA, 3A results in 2.9998A, but the readback (of the sunk current) clearly changes with input voltage even though the unit does a reasonable job keeping the actual current constant as measured with a 34465A. Are there additional calibration points for readback?

author: rfdes
author_rank: Regular Contributor
timestamp: October 04, 2020, 02:56:28 pm
content: Hi -Ran across this post this morning and was contemplating purchasing one of these units. The last post was in April and from the posting, SRA Soldering claims that the units they had in stock were all problematic. I am curious if anyone is aware whether this was a fluke or if Korad really has a design/mfg problem with this model unit and if so has the problem been resolved. I've sent an email to SRA Soldering and asked the same question. Anyone have any insight as to whether these problems have been resolved?ThanksJim

author: rogersstuart
author_rank: Contributor
timestamp: January 22, 2021, 06:53:36 am
content: Quote from: kahuna0k on April 07, 2020, 06:14:41 pmI was thinking about this earlier today and read a few posts. I had written a C# utility library a while back but it wasn't very useful unless you wanted to write a C# application. All this thing needs is a UDP to TCP server to access it using normal tools. So, I slapped one together today. It will automatically find the KEL103 and start the server. Then you can use something like PyVISA or Keysight Connection Expert to interact with it. Here's the link.https://github.com/rogersstuart/KEL103Driver

author: Helix70
author_rank: Unknown
timestamp: January 25, 2021, 12:54:19 am
content: Can anyone tell me the distance between the binding post centres for this unit? What is the diameter of the posts?

author: rogersstuart
author_rank: Contributor
timestamp: January 26, 2021, 12:32:58 am
content: Quote from: Helix70 on January 25, 2021, 12:54:19 amAbout 30mm. 6mm in diameter.

author: Helix70
author_rank: Unknown
timestamp: January 26, 2021, 12:52:08 am
content: Thanks.

author: elor
author_rank: Contributor
timestamp: August 19, 2021, 12:24:47 am
content: got the Multicomp Pro MP710259 which is basically the same as konard 300w the display stopped workinganyway to get the schematics for those units?

author: diodak
author_rank: Regular Contributor
timestamp: August 19, 2021, 07:12:00 pm
content: And the control via RS232 works or only the lack of displaying parameters?

author: elor
author_rank: Contributor
timestamp: August 19, 2021, 09:49:34 pm
content: dont know i need to find a windows pc for the software installationbut from the way it looks it might just be a cold joint or something the display blink shortly at power offand the jog wheel beeps it is just the display that is not working

author: EHT
author_rank: Frequent Contributor
timestamp: January 26, 2022, 10:42:01 am
content: I'd be grateful for an update from owners of the KEL-103 / Tenma 72-13210 on the verdict after longer ownership. Specifically:Did people experience further faults, if so, has it been possible to fix them, has it been possible to get hold of the service manual?Do the units drift out of calibration (as per the original topic), if so, does the procedure posted above (in PDF) successfully recal them?See alsothis thread