Author Topic: Kunkin KP184 electronic load : "fixing" an manufacturer issue (Read 16015 times)

Falkra · « **on:** November 24, 2019, 04:59:26 pm »

Hello,

I bought on may a KP184. It was cheap (170$ delivered) and specs looked good. I'm abolutely no expert, juste a hobbyist, so I use it mainly to check if power supplies are working as they should, or testing power bricks / wall adapters, mainly.
So for what I do, that was a good piece of equipment. Then it got positive (I suppose) and negative reviews.

One concern (apart from the power button on the back side and the front connectors layout) is the following : when you draw current for example from a good and well regulated power supply, for example at one or two amps, the current on the source is not stable. I mean it can jump up to 100 mA (200 mA peak to peak). I didn't notice that at first, and for what I do, it was not a problem.

Then I saw a video from a french youtuber who reviewed it : that's how I noticed my unit also had that problem.
There is an easy fix, that the manufacturer told the youtuber after he mailed them : you just have to remove the 240 (-ish) nF capacitor under R10, and the drawn current on the source unit is now stable. Well, much more than before.
Credits go to that youtuber, not to me, obviously.

The video is here if you understand french : https://youtu.be/NKwUACkCcFs
And the fix starts at 19:00 : https://youtu.be/NKwUACkCcFs?t=1140

So I thought this had to be shared here. I did the fix on my unit, so here are some pictures I took (and I'm not great at taking pictures either).

The unit is really easy to disassemble, you only have to remove the cover (10 screws) :

(click to get better resolution)

Here is the zone :

It is easy to locate :

Done, and that was a tiny capacitor (0603 ?):

I did this with very basic tools, just a tiny soldering iron (no hot air), so if I could do it, you probably also can :

Thanks for having read.

Gregg · « **Reply #1 on:** November 24, 2019, 10:21:03 pm »

Falkra,
Thank you for posting this on the EEVBlog forum; I certainly wouldn't have found this information otherwise. I guess I'll have to take a squizz at my KP184 and see if mine is the same.

Falkra · « **Reply #2 on:** November 25, 2019, 07:49:39 pm »

You're welcome, I'm happy to share this.

JensL · « **Reply #3 on:** January 13, 2020, 06:45:02 pm »

Thanks for the information! I really like the KP184 and I'll have to check if my is affected as well and then fix it.

Falkra · « **Reply #4 on:** January 13, 2020, 07:51:13 pm »

Great ! Let us know, I really saw a difference. Keep the removed component if you have any doubts, but it should be much better.

interflexo · « **Reply #5 on:** April 22, 2020, 10:53:39 am »

KP184 bought in March 2020 and I opened it for inspection. The capacitor was already removed.

Nevertheless the 520mVpp ripple on the 3Vrms voltage drop of the 200mA current flowing on a 15 $\$\Omega\$$ 2W resistor seems too high.

voltlog · « **Reply #6 on:** April 25, 2020, 09:01:54 am »

I’ve recently got my hands on the Kunkin KP184, I did a review and teardown video on the unit and I’ve noticed a few things which are worth mentioning here.

There is an issue with the binding posts having 4.2mm ID which is a problem as most 4mm banana plugs will not ensure a tight fit with these binding posts. This can be easily fixed by replacing the binding posts with another set of M5 binding posts as I’ve shown in this video.
My unit has a VER.04 motherboard which I believe is the latest (had a warranty seal with a date code of Feb 2020), if you would like to check out more info you should watch the teardown video or check this blog post for teardown pictures.
The noise present in the CC mode regulation is still there but appears to be lower when compared to reports from previous revisions of the motherboard. C58 is still installed on the motherboard, it now has a value of 10nF and after removing it the noise is further reduced as I’ve shown in this video.
There is an issue with the blue part of the metal enclosure not being connected to safety earth but that can be easily fixed by scraping some paint away or attaching a secondary ground strap as shown in this video.
Someone reported a supposed bug in tripping the over-power protection which would require the instrument to be cycled on/off to clear. This bug is not present on my unit HW VER.04.
The calibration procedure is somewhat simple and has been linked in PDF format along with additional info in this video. My unit did not need any calibration, as shown in the review video it was within tolerance when compared to my Agilent 34401A.
The mosfets on my unit have a date code of 2009 (P921J) which can mean one of two things: This is some new old stock which Kunkin got their hands on or they are fake mosfets. I have contacted Infineon (former International Rectifier) to see if they would like to discuss this issue further, maybe I can send them the mosfets from my unit for further analysis. An x-ray of these would definitely show any difference from a genuine unit in die size. I will be releasing on update on the subject once I hear back from Infineon.

All things considered this is still the best electronic load one can buy in this budget and by looking at teardowns of previous hardware revision it seems the quality has improved over time and they fixed some of the issues.

interflexo · « **Reply #7 on:** April 25, 2020, 10:21:15 am »

My tested unit has warranty seal dated 16 Nov 2019, PCB VER.03, MOSFETs IRFP250M (P820J) dated from 2008 and no C58 capacitor soldered.

Phildem · « **Reply #8 on:** April 26, 2020, 03:23:44 pm »

Hi, I am the author of the original post on the French YouTube Channel Cyrob.org.
I confirm that removing this capacitor result in a huge reduction of ripple current.
On the new units, the manufacturer changed it by a 10nF, he do not remove it completely.

I think that looking only at the ripple current is not enough, this capacitor is not here for nothing, I haven't tested it yet but I suspect some instability or delay when the load change if it's removed.
10nF is probably the best compromise found by the manufacturer.

Thank a lot for the link on my video and for this nice post.

Have a nice day.

Philippe Demerliac
Cyrob.org

voltlog · « **Reply #9 on:** April 27, 2020, 04:38:08 am »

As Phildem said above, the capacitor is not there for nothing and if it was better all around without the capacitor they would have left it removed in the latest revision, however it's still there and it's a smaller value.
Currently it seems their email address is not reachable:

Quote

<sales@kunkin.cn>: connect to kunkin.cn[60.205.41.196]:25: Connection timed out

Does anyone have another way of contacting them? Maybe they could provide some light to the purpose of that capacitor.

interflexo · « **Reply #10 on:** April 27, 2020, 04:03:16 pm »

Quote from: interflexo on April 25, 2020, 10:21:15 am

My tested unit has warranty seal dated 16 Nov 2019, PCB VER.03, MOSFETs IRFP250M (P820J) dated from 2008 and no C58 capacitor soldered.

I tested a unit bought in 2020 that came without the capacitor installed from factory.

voltlog · « **Reply #11 on:** April 28, 2020, 07:19:42 am »

Please note that date of purchase is not all that relevant as most sellers on ebay and aliexpress are probably selling older stock. A good indicator is the revision of the mainboard and/or the warranty sticker, in my case it is REV.04 with warranty sticker of FEB 2020, as far as I can tell this might be the newest revision Kunkin makes.

Falkra · « **Reply #12 on:** April 29, 2020, 12:24:37 pm »

Thank you.

TSCOLAN · « **Reply #13 on:** April 29, 2020, 12:29:24 pm »

Hi,

In case somebody have the Kunkin KP182, the board is the same, and the fix woks also.

Thomas

ScoobieSnax · « **Reply #14 on:** April 29, 2020, 09:38:56 pm »

Hi,
my kp184 is a VER.01 bought on Ebay in July 19. I had the same ripple current and i applied the cap removing saw in the cyrob (aka PhilDem) video, ripple current is almost gone. Maybe i'll resolder a 10nF later.
But the most annoying with my model is the voltage measurement who stops without reasons (as described in the calibration procedure pdf - page 4). I have the same problem as Voltlog with the kunkin mailbox (Connection timed out), so i can't describe the problem to Kunkin

. I don't even know if there is a solution to solve this problem.
Does anyone have the same bug ?

Thony

Folxs · « **Reply #15 on:** May 25, 2020, 10:12:27 am »

Hi, I have different type of question - can I connect it to PC and log data files of voltage/current in time to later calculations?
If not,do You know any substitution of that? like some digital bench multimeter to count in 1 time current and voltage and save it?
I need to pretty precise measure dicharging characteristics of batteries

HKJ · « **Reply #16 on:** May 25, 2020, 12:39:14 pm »

Quote from: Folxs on May 25, 2020, 10:12:27 am

Hi, I have different type of question - can I connect it to PC and log data files of voltage/current in time to later calculations?
If not,do You know any substitution of that? like some digital bench multimeter to count in 1 time current and voltage and save it?
I need to pretty precise measure dicharging characteristics of batteries

I believe there is some programs that can do it, but it is not included in my program yet: https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/
My program includes some Itech, BK & Maynuo loads and can directly do Ah & Wh calculations.

Folxs · « **Reply #17 on:** May 26, 2020, 07:25:45 pm »

Hmm, but maybe I could use some external benchtop DMM to log current and voltage one time or even more parameters and log it?

HKJ · « **Reply #18 on:** May 26, 2020, 07:32:28 pm »

Quote from: Folxs on May 26, 2020, 07:25:45 pm

Hmm, but maybe I could use some external benchtop DMM to log current and voltage one time or even more parameters and log it?

You can easily do that with the above program and again you can calculate Ah & Wh. It supports both bench and handheld meters, only problem is Brymen where it can only handle one at a time (One Brymen and one or more others works) and only on Windows.

AlexVlc · « **Reply #19 on:** August 14, 2020, 09:55:02 am »

Hi,

It's a noise problem.

I bought this unit in July 2020 (i think is the latest revision) and the problem is not with the load, the problem is that this device have electrical noise with or without load and with or without the capacitor. I think the problem is in the power supply but I don't have time to solve the mistery but maybe someone can look for it.

[ Specified attachment is not available ]

doktor pyta · « **Reply #20 on:** August 16, 2020, 09:29:07 am »

Please describe Your test setup.

P.S. link to a thread related to this subject: https://www.eevblog.com/forum/testgear/an-investigation-about-ripple-current-of-kunkin-kp184/new/#new

HumbleBumble · « **Reply #21 on:** August 29, 2020, 12:28:02 am »

I have rev 5 pcb. There is no cap, its nice to see they are actively updating. Cal card states tested to within 0.1% with Agilent/fluke. It appears accurate with my uncalibrated kit.

Im concerned if the case was grounded and came into contact with the heat sinks. Ive measured both at positive side volt in respect to ground and wonder if they could short.

I may desolder a mosfet and xray and report back.

Faron · « **Reply #22 on:** February 06, 2021, 01:34:00 pm »

Hi everyone!

I need your help. The Varistor (marked VDR1 next to the relais and + terminal) blew up. Sadly the face holding the identification is all charred. Can some of you guys have a look into your unit and tell me which type it is? The part-Number (or at least niminal voltage rating) would be awesome.

I just don't want to fly blind and go with a 150/160V type of random rating.

Thank in advance and best greeting!

patman27 · « **Reply #23 on:** February 07, 2021, 12:49:25 am »

@Faron

You mean this guy?

(o come ye hero and bestow the correct answer)

Faron · « **Reply #24 on:** February 07, 2021, 11:43:57 am »

Hello patman27,

yes, exactly!

I'd be sooo grateful for that Part-ID


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Author Topic: Kunkin KP184 electronic load : "fixing" an manufacturer issue (Read 16015 times)

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