Author Topic: An investigation about ripple current of Kunkin KP184  (Read 19295 times)

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Offline KlausF

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Re: An investigation about ripple current of Kunkin KP184
« Reply #25 on: January 07, 2022, 05:56:53 pm »
Can anyone help, please. I am desparately searching for a service manual or at least a schematic of the Kunkin KP184.
 

Offline electr_peter

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Re: An investigation about ripple current of Kunkin KP184
« Reply #26 on: February 02, 2022, 09:15:26 pm »
KP182/KP184 has additional 9th key - there is cutout on front panel (covered with a sticker) and place for a button on display PCB. Does it do anything?
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #27 on: February 17, 2022, 07:15:16 am »
This firmware update is only for KP184 manufactured in 2019, 2020 and 2021, the model of the analog-to-digital conversion chip is AD7799. All actions are at your own peril and risk. If there are no problems, it is not recommended to update the firmware, as the changed location is not necessarily used by the user.
For questions about software bugs you can write to 64908476@qq.com

Someone should post this new firmware file as a downloadable file attachment, so other recent owners of the KP184 could use this too. Would be great, if any future firmware updates would follow this way...
Fortunately there are detailed instructions how to apply the firmware within the .ZIP file and what is needed for this. I made myself a simple rs232 loopback connector and a firmware update "activator" using some parts lying around...
Most modern PCs don't have a built-in RS232 connector any more und therefor have to use an USB->RS232 adapter.
If one is going to apply the firmware update file has to be judged by the individual user, because not everyone uses all features changed or bug-fixed. Unfortunately no info are available about the changes or bug-fixes. Although the built-in microprocessor has lots more of flash memory available this is only used to a small extent. 

@electr_peter
This seems to be reserved for a front mounting placement of the power switch instead of the power switch on the back. At least some have adapted it for this...
« Last Edit: February 19, 2022, 03:23:03 pm by burkm »
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #28 on: February 18, 2022, 10:24:05 pm »
Nice.
Thanks @PaWill68.
Though in my VER:04 KP184 there is no such cap C34, so I hope in VER:04 they have it solved.

Regarding the firmware update, is there any link to see it, download it and any instructions on how to upload/flash it in the KP184 ?

All needed information including the needed flash software is within the .ZIP file containing the new Firmware. Please follow it by the word (pictures are inluded also). Just check, if the RS232 extender does speak to the chip on the KP184 mainboard, or the KP will stay in the firmware-update mode ...
« Last Edit: February 19, 2022, 03:07:36 pm by burkm »
 

Offline electr_peter

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Re: An investigation about ripple current of Kunkin KP184
« Reply #29 on: February 19, 2022, 08:33:39 am »
@burkm, I have added mains switch (wired in series with transformer) on front panel on the bottom right near negative terminal. Additional button position I mentioned above is located between "ON", "->" and "SET" buttons, just left of rotary knob.
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #30 on: February 19, 2022, 03:13:02 pm »
I've held mine up to the light and discovered this "hidden" button position (shadow behind the front panel "mask") you mentioned too, but if it's not supported by the original firmware it won't do anything useful.
Don't have any idea, what it should be used for, may be a "reserve" for some possible extension not known at the time of designing the front panel...
« Last Edit: February 19, 2022, 03:24:29 pm by burkm »
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #31 on: February 19, 2022, 10:35:58 pm »
I checked the Kunkin web site. They got a color model similar to the KP184, the KP184C, which uses an identical front panel and has an additional key at this position (LAST).  This is probably the reason for this empty space...
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #32 on: February 20, 2022, 05:21:54 pm »
Hi, newbie around here. I acquired KP184 in 2020, but really have not used it until recently. As anyone here, I have quickly found out that it exhibits quite a lot of noise on input sockets, even unloaded. Unless I am reading my measurements incorrectly, I see ripple with Pk-Pk value over 1V.  Of course, this "property" defeats the whole purpose of this unit for me as I my intention was to use it benchmark PSU designs, including ripple & noise across their output range. Ergo, I would like to get rid of it, so I did a little bit of digging on my own and I have also evaluated all the tricks users here tried and reported some level of success with it.
In my case, top PCB revision is 004. Firmware has been updated to 20210720A thanks to user who posted the FW in this thread.
Other then FW update, I have tried to remove C58, or C57, played with their values too. I have tried GND wire trick too. I have put low ESR cap in parallel to front panel power rail cap. None of above helped even a bit. The ripple is still there, same levels. With and without front panel and/or fan disconnected - no change.
What I have also realized when scoping across the top PCB that basically ripple with that same signature is present all across the board, on all power rails: +5V, +3V3, +12V,-12V I mean its kind of crazy to see the 0,5V ripple on 3.3V rail, right on STM32 microcontroller pins. Same ripple signature can be also seen on input of 7805, so basically on output of rectifier bridge of 18V AC transformer output (diodes D12, D14, D16, D17). Seeing it basically on these places I am thinking - this can not be all just an induced signal from a digital section, or can it?
Either I am going crazy, or this mess can all be traced back to a transformer.
Can someone please confirm my finding on your unit?
« Last Edit: February 21, 2022, 09:39:40 am by atarian »
 

Offline dophuc

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Re: An investigation about ripple current of Kunkin KP184
« Reply #33 on: February 20, 2022, 06:59:46 pm »
I measured the noise at the KP184 input jack (no load). My Kp184 is the 2020 version, nothing has changed since I bought it.

« Last Edit: February 20, 2022, 07:05:46 pm by dophuc »
 

Offline electr_peter

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Re: An investigation about ripple current of Kunkin KP184
« Reply #34 on: February 20, 2022, 09:06:39 pm »
@atarian, what do you measure when scope probe is on output connector, but DC load is turned-off on the back (but still connected to mains)?
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #35 on: February 21, 2022, 08:43:07 am »
Here are some more grabs. Probe connected onto the VIN+ and VIN- screw terminals on top board this time. Scope set to DC coupling now to be see if any DC voltage is present. Like this, I have seen massive swing down to -3VDC with rise time about 0,8s and drop time about 5s. Just like coil kick back, only there is no coil anywhere as far as I can see? Except for the transformer...
Anyway, here you are:
DC coupling, 1V and 200us /div

« Last Edit: February 21, 2022, 08:46:48 am by atarian »
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #36 on: February 21, 2022, 08:47:40 am »
In greater details:
DC coupling, 200mV and 400ns /div
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #37 on: February 21, 2022, 08:51:40 am »
AC mains switch state change events:
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #38 on: February 21, 2022, 09:24:28 am »
AC output on transformer looks good enough tho. Almost perfect 50Hz sine, no oscillations. Something must have been feeding this 5MHz noise into the 16V DC power rail then. As far as I can see there is only 7805 linear 5V regulator and some SOT23-6 packaging chip hooked up there (U24). I think I have my suspect.

EDIT: U24 seems to be some kind of switched mode power/PWM fan speed controller. With U24 temporarily removed from PCB, all ripple on DC power rails and output is gone.
G.O.N.E.

All I am seeing is just white noise with amplitude of around 15mV (my oscilloscope/probes can not do any better anyway). Naturally, heatsink cooling fan is out of order now and the question is how to hook it up again. Does anyone see any better solution then to move it entirely onto separate board with separate power supply?
Can anyone please identify the chip so that we get at least a datasheet with design recommendations? Maybe Kunkin just fed up something in its implementation.
« Last Edit: February 21, 2022, 09:55:52 am by atarian »
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #39 on: February 21, 2022, 01:00:29 pm »
After all, it will not be that hard task: U24 is simple switching mode regulator with very poor parameters. Yes, it cripples input "by design":
http://aosmd.com/res/data_sheets/AOZ1282CI.pdf

 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #40 on: February 21, 2022, 06:26:29 pm »
To check, if that chip is really responsible for the measured and detected visible noise floor, one should look, if the application notes (spec sheet) for that chip have been observed in detail by the chosen PCB design (layout) and its components.
This will determine, if it really "cripples input by design"
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #41 on: February 21, 2022, 06:29:58 pm »
But there is still another "problem": instability of the electronic load in combination with specific power supplies as determined by some fluctuating output.
Any idea, how to get around it and what has to be done because of this...
 

Offline electr_peter

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Re: An investigation about ripple current of Kunkin KP184
« Reply #42 on: February 21, 2022, 07:18:27 pm »
Noise in DC load can be mitigated if the source is known (mentioned by posters above in KP184 case).

Instability with active DC load can be broadly spitted in few categories:
  • DC supply just cannot handle the load or load changes and goes crazy. DC load is not at fault, any other DC load with same parameters would cause same issue OR
  • DC load just cannot maintain the load and is unstable by design. DC supply is not at fault OR
  • DC supply and DC load in combination become unstable. This is because control loops in DC supply and DC load fight against each other, creating feedback loop with wild oscillating results.
Combination is the most likely cause, as others are easier to solve. Actual strategies to limit instability:
  • from DC load side - do nothing and continue to "maintain" load (most DC loads, including KP184)
  • from DC load side - admit failure, i.e., show that oscillation occurs via "Unregulated load" error message and/or
    turn off DC load
  • manually change DC load and/or DC supply parameters (loop speed) to reduce oscillation capability. Only some DC loads and DC supplies are capable of this
  • modify external circuitry between DC load/DC supply if you have idea what is causing it
In general, Mr Murphy ensures that it is possible to create unfavorable conditions for any DC load. EEVblog has several videos with DC loads oscillating, especially in CR mode.
« Last Edit: February 21, 2022, 07:20:25 pm by electr_peter »
 

Offline atarian

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Re: An investigation about ripple current of Kunkin KP184
« Reply #43 on: February 21, 2022, 07:41:49 pm »
>>To check, if that chip is really responsible for the measured and detected visible noise floor, one should look, if the application notes (spec sheet) for that chip have been observed in detail by the chosen PCB design (layout) and its components.
This will determine, if it really "cripples input by design"

I was referring to their own characteristics published in linked datasheet, namely IN voltage waveforms. And they of course represent best case scenario of flawless implementation "by a book".
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #44 on: February 21, 2022, 08:56:06 pm »
Noise in DC load can be mitigated if the source is known (mentioned by posters above in KP184 case).

Instability with active DC load can be broadly spitted in few categories:
  • DC supply just cannot handle the load or load changes and goes crazy. DC load is not at fault, any other DC load with same parameters would cause same issue OR
  • DC load just cannot maintain the load and is unstable by design. DC supply is not at fault OR
  • DC supply and DC load in combination become unstable. This is because control loops in DC supply and DC load fight against each other, creating feedback loop with wild oscillating results.
Combination is the most likely cause, as others are easier to solve. Actual strategies to limit instability:
  • from DC load side - do nothing and continue to "maintain" load (most DC loads, including KP184)
  • from DC load side - admit failure, i.e., show that oscillation occurs via "Unregulated load" error message and/or
    turn off DC load
  • manually change DC load and/or DC supply parameters (loop speed) to reduce oscillation capability. Only some DC loads and DC supplies are capable of this
  • modify external circuitry between DC load/DC supply if you have idea what is causing it
In general, Mr Murphy ensures that it is possible to create unfavorable conditions for any DC load. EEVblog has several videos with DC loads oscillating, especially in CR mode.

Any idea, what can be done about this ???
I got this same problem in combination KP184 and BK 9174 power supply. The BK 9174 was quite expensive and it goes into overvoltage or overcurrent protection below the range extremes quite often, when this happens...
« Last Edit: February 22, 2022, 01:57:25 pm by burkm »
 

Offline electr_peter

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Re: An investigation about ripple current of Kunkin KP184
« Reply #45 on: February 22, 2022, 07:50:56 am »
Any idea, what can be done about this ???
I got this same problem in combination KP184 and BK 9174 power supply. The BK 9174 was quite expensive and it goes into overvoltage or overcurrent protection below the range extremes, when this happens...
Potential solution requires to know more details. Under what conditions instability occurs? What is the connection setup with leads? Which load mode do you use? Which instrument is turned on first? Can you increase load gradually?
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #46 on: February 23, 2022, 06:46:05 pm »
Friends, there is good news. KUNKIN has released a firmware update:
1) The voltage is read by reading one register, and the voltage value is obtained after smoothing and filtering, so there will be no sawtooth shape. The voltage acquisition rate before smoothing and filtering is 470SPS, and the voltage value after smoothing and filtering, the refresh rate is relatively low, it is 10SPS.
2) Instructions to set the battery discharge mode, half-current discharge is enabled and can be saved

I got a new KP184 a few days ago and it seemed to work just fine (original firmware version was probably the predecessor "2020 something").
After the firmware update (see above) the KP184 was functioning "OK" for several hours, but now, in the midst of a continous 6VDC / 1A load measurement the voltage display (plus the corresponding wattage display) stopped working, just showing now "all zeros", no matter what signal it was currently fed.

I haven't had  any success in finding the cause even after intense searching, although I tried a different (proven) lab power supply from BK Precision I got in my "lab" instead of the Rigol DP832A, different input voltages and amperage profiles, switching voltage sensing from "remote" to "local", a reset to factory default parameters, disconnecting it from the mains, turning it off and on again etc. etc. etc...
Measurement gear connected directly to the output of the power supply are prove of a functional power supply by either unit. Voltages etc. are continously monitored by two Rigol Lab DMMs (6 1/2 and 5 1/2 digits resolution) Everything I could think of to remedy the problem I already tried. I inspected all the PCBs inside the unit without any success and found no hint about any visible cause for the failure. Main board version is "5 (202012)" including the daughter board, display board version is "3". The included test certificate is dated October 20th 2021. Could be a firmware "thing", because your firmware update notes for the new firmware seem to point suspiciously into that direction (=>voltage handling) ?

I don't know, what is going to happen, if I am trying to reinstall the firmware -again- , which is on the KP184 already. Reason: I don't want to be left with a non-functional unit in an incomplete firmware update state, if it's not possible to reinstall the firmware version over the existing one, because i might return the disfunct device. This seems to be my last resort before returning it to the seller...
Otherwise if this is not possible, I would try to reinstall the previous firmware version. Do You have it also ?

If nothing helps, I will contact the seller, being on the verge of returning the KP184, if the problem can't be resolved on my side...

Ps.: Is that new firmware an official release of the manufacturer (Kunkin) or is it "homebrew" ?
If it is "offical" could you check, if an update for that firmware is avilable, may be a "bug fix" ??

« Last Edit: February 26, 2022, 09:26:04 am by burkm »
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #47 on: February 26, 2022, 09:30:23 am »
I tried to message directly the user "PaWill68" several days ago, but he did not respond, neither to the post here nor to my PM message adressing him directly.
Several days have passed since my post dated February 23rd 2022 but no answer from PaWill68 yet... Well...
« Last Edit: March 03, 2022, 09:09:58 pm by burkm »
 

Offline burkm

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Re: An investigation about ripple current of Kunkin KP184
« Reply #48 on: March 10, 2022, 10:32:19 am »
The seller of the KP184 sent me a (free) return label in the meantime.

After a recent clean-up of my (messy  :)) "hobby"-room (inluding moving around and lifting up the KP184 several times) and just before returning my non-functional unit I turned it on "a last time" just to casually check, that everything was as before.
To my surprise the voltage and wattage display seemed to be showing real voltages and wattages again, not just "zeros" as before. Now I'm thinking of a "cold" solder joint, loose connection or something similar etc., which might have caused those problems.
Some have already posted about manufacturing problems in this respect...
I contacted the seller - again - and he gave the permission to open up the sealed unit's case to look after those problems and eventually have them fixed right away. If I will find anything I will report back...
« Last Edit: March 10, 2022, 10:33:52 am by burkm »
 

Offline dirtcooker

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Re: An investigation about ripple current of Kunkin KP184
« Reply #49 on: March 21, 2022, 05:24:02 pm »
In greater details:
DC coupling, 200mV and 400ns /div

I have 2 kp184 units, and can confirm noise coming from it at around 500khz. I purchased this one Oct 2020, and made the following mods: removed C58 (10 nf on v4 motherboard) to reduce instability at 1A current sinking, removed paint under cover screws, applied kapton to rear screws (which are connected to + output), replaced binding posts. old ones > 4mm inside dimension reducing contact with banana plug.
A 10nf cap across the binding posts reduces the noise somewhat. Note that I live in the city, and there is a lot of RF noise from nearby radio stations, unfortunately, which you can see on my scope.
« Last Edit: March 21, 2022, 05:28:02 pm by dirtcooker »
 


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