EEVblog #1298 - $70 2000W Power Supply? - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2020, 05:44:24 am
content: A look at the $70 Juntek 2000W power supply with wireless display.Also the 3000W model, but does it have a problem?https://s.click.aliexpress.com/e/_dZVpwTI

author: Kleinstein
author_rank: Super Contributor
timestamp: April 06, 2020, 08:37:10 am
content: The constant power mode is likely mainly an issue with the electronic load. It start oscillating when the supply hit the CC limit.For a pure switched mode regulator those oscillations are not so bad. Still it is some endurance testing for the CC/CV transitions. The supplies that don't like this are linear ones with a relay for transformer tap switching.The reset of the higher power module is likely due to the input side power supply hitting the CC limit. So a drop in the input and thus a reset from there. Can't blame the regulator module for that - maybe except for an explanation in the manual for this probably not so uncommon situation.The output ripple is really a little high, but this is kind of expected. The output side caps are relatively small for 20 A.The 50 mV may be no load or a lower power version from the line. The higher power model may be better, as it may be a dual phase regulator - this at least would make sense with 2 equal power inductors and 2 power mosfets.For the output loss, in a conventional buck converter the loss to a large part depends on the current, not so much the voltage level. So 20 V in an 5 V 20 A out is actually already causing quite a fraction of the maximum losses. 100 V in and 95 V out at 20 A would likely have less loss - it would be essentially the FET on nearly all the time.The remote control unit looks really nice.

author: jeremy
author_rank: Super Contributor
timestamp: April 06, 2020, 09:35:37 am
content: Anyone else not seeing this video appear on YT?

author: EEVblog
author_rank: Unknown
timestamp: April 07, 2020, 02:36:04 am
content: Quote from: jeremy on April 06, 2020, 09:35:37 amIt's been reuploaded, it's more betterer.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: April 07, 2020, 04:27:59 am
content: DaveWouldn't those units be (Buck) "DC-DC converters" instead of calling them switch mode power supplies ?

author: maukka
author_rank: Unknown
timestamp: April 07, 2020, 04:58:32 am
content: Quote from: EEVblog on April 07, 2020, 02:36:04 amI see you did an overlay on the pro mille issue I commented on

author: r0d3z1
author_rank: Regular Contributor
timestamp: April 07, 2020, 06:38:09 am
content: Quote from: johnlsenchak on April 07, 2020, 04:27:59 amindeed I initially thought it was an AC/DC

author: maginnovision
author_rank: Super Contributor
timestamp: April 07, 2020, 07:11:20 am
content: I'd love for you to get a scope of theirs to look at.I still don't know why individuals would want these. If you have a power supply that can feed this, assuming it's not a battery, then why would you not just use that as your supply. If you are using batteries as the supply I can see where these might be more useful as long as you don't mind the ripple.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: April 07, 2020, 07:29:19 am
content: Anyone notice that the microcontroller is marked "STM32F" on the first line of text? This appears to be a telltale that they're not genuine ST devices, and probably a relabelled CKS32 clone. At the mentioned pricing, would not be too surprising - anything to save some pennies.See the thread on fake STM32 chips in the Microcontrollers section of the forum:https://www.eevblog.com/forum/microcontrollers/cheap-bluepill-very-likely-it-has-fake-stm32-right/

author: filssavi
author_rank: Frequent Contributor
timestamp: April 07, 2020, 07:48:01 am
content: The only way that unit is dissipating 160W is very briefly and while on fire, the heatsink while it seems to have a fair mass of aluminium has way to little fin surface, just as a wild guess I would say 50W dissipation is already quite optimistic with that puny fan (now with a proper delta 15krpm fan that might be different). Also since most of the heat will be dissipated in the single switching transistor, only part of the heatsink will be effective at cooling (even if low thermal resistance is a thing in metals too) cutting down the surface area even furtherTo put it into perspective a mid to high end CPU cooler will be capable of dissipating 160W from a single point source, however their design is much different, they have a ton more surface area and use heatpipes to evenly distribute the heat to all the fins

author: maginnovision
author_rank: Super Contributor
timestamp: April 07, 2020, 08:51:12 am
content: Quote from: filssavi on April 07, 2020, 07:48:01 amDave was definitely being nice. Like Dave though I'd be hard pressed to be able to sink(or source) the kind of current that'd be required to actually test it. My biggest power supply is 800W and if I put all of my supplies together, due to a voltage limit on a bunch of them, I'd only be able to supply roughly 55A @ 32V which is only 1760W on the input side. Probably enough to catch it on fire if I found a decent load though which would be the second problem although probably easier to solve. I guess the easiest supply side solution would be a decent 48V(or 2 in series) battery but what about a load? The simplest solution would probably be a decent inverter and just run some AC stuff with it.

author: D. Head
author_rank: Contributor
timestamp: April 07, 2020, 09:03:00 am
content: What do you mean by "NOTE the PSU integrated!"?Isn't that allway the case, for scopes that the PSU is build in the device (execpt for the Tektronix TPS).

author: firewalker
author_rank: Super Contributor
timestamp: April 07, 2020, 09:38:47 am
content: The 5 volts on the communication port is probably for the optocouplers for the isolation.So is it JUN-TEK or JUNK-TEK?Alexander.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 07, 2020, 09:45:40 am
content: For the worst case power loss one does not need the maximum power. The worst sould be somewhere with maximum current, but only some 50-70% of the maximum output voltage.I would consider some water heater / cocking stove / electric grill (no electronic) / toaster / iron as a load. Some radiators also work. One may have to put a few in parallel.It looks like the 5 V are together with the com port - maybe an interface to a remote control unit. This is actually not a bad idea, maybe just missing documentation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 07, 2020, 09:59:11 am
content: I wonder if they're even current mode controlled.Wonder what the common mode (input to output) noise is. As bad as the output, or worse?Wonder how long they last at full power. Guarantee it's not continuous, but it might be usable at a hefty derating.Guessing the TO-220 at the end of the heatsink is the temp sensor. Didn't get a good look at it. Rather silly they didn't bolt it down, eh?Oddly enough, I made a module with similar ratings last year; custom job for a custom product. A bit higher max input voltage, two phase interleaved, and much smaller (and more efficient). Digital control too (but not from an MCU, just an ADC/DAC onboard). If anyone's interested I can provide contact info; the client might be interested in selling standalone modules.Tim

author: langwadt
author_rank: Super Contributor
timestamp: April 07, 2020, 10:40:31 am
content: is that a fix for a ripped off track at ~16:44 ?

author: Psi
author_rank: Super Contributor
timestamp: April 07, 2020, 01:02:53 pm
content: I reckon the chip marking removal was a service provided by the PCBA factory.I think they put the boards back into the depanelization router stage after reflow and created a tool path to remove the tops of the chips. Looks like a goto x,y and plunge Z mm down/up then move to next x/y.A PCBA factory already has all the tooling and equipment for doing that.Also the size of the markings on the ICs matches the size of router bit you might find in a depanelization router machine.Would also explain why it's only the SMT chips and not the TH ones.

author: Nystemy
author_rank: Contributor
timestamp: April 07, 2020, 01:55:50 pm
content: I myself wouldn't refer to these as power supplies. Since that term tends to indicate that it runs off mains voltages.Though, regardless of the price of these units, they clearly lack adequate output filtering.Whacking in a pair of large caps do cut down on the ripple a bit, but doesn't really do much against the noise.Though, the 3KW unit has two large inductors in it, two transistors, and two diode packages.And the traces seems to indicate that it uses a dual phase converter in it. This would dramatically cut down on the ripple, and lessen the EMI just a bit.Not to mention also make the power supply a little bit more responsive towards transients, not to mention increase efficiency at the higher end just a bit. (if they run 180 degrees out of phase with each other.)Though, a good lab power supply should have a pass transistor for the output. A linear regulator one might say.Then we can filter out all the noise much more efficiently before passing it through the transistor to drop another few mV before sending it out to the load. Though, this obviously adds to the cost of the device.So, next time, can we see some actual power supplies?

author: filssavi
author_rank: Frequent Contributor
timestamp: April 07, 2020, 02:31:36 pm
content: Quote from: Nystemy on April 07, 2020, 01:55:50 pmWhen we are talking regular signal electronics you can’t have a linear supply, however when the power is high unless you have a very specific need, and you are willing to pay dozens of k$ (I have seen a 30 kW class A linear power amplifier/function generator/four quadrant power supply)Moreover Switching mode power supplies can be as low noise as linear supplies, when designed correctly, however you will not find that in a el cheapo unit from AliExpress

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 07, 2020, 02:48:40 pm
content: A lowpass filter will be cheaper, more efficient and more effective than a linear pass regulator.I don't get why people fantasize about those things...Tim

author: Nystemy
author_rank: Contributor
timestamp: April 07, 2020, 02:56:28 pm
content: A linear pass transistor on the actual output allows us to correctly go into current limit without worrying about output capacitance to the same degree.It can also help cutting off the last bit of noise, but that is honestly a secondary concern most of the time.A low pass filter most often also brings along a bunch of output capacitance. Depending on the load, this might not matter, but in cases where it does matter, the transistor is the better solution.

author: Nystemy
author_rank: Contributor
timestamp: April 07, 2020, 03:00:24 pm
content: A weren't talking about linear supplies, nor class A amplifiers.I just stated that you can have a transistor on the output to do final regulation. Ie, cut out both noise and ripple, and ensure proper constant current behavior.We can still have a switch mode solution providing the actual power.And the transistor is a superior solution when it comes to constant current applications.But if voltage is all one needs, a good old low pass filter is usually sufficient.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 07, 2020, 03:29:09 pm
content: I should've written "post regulator" to be more specific.Yes, fast response current limiting is one useful feature.Even with "capacitor multiplier" style circuits, it's difficult to get extreme attenuation, and impossible at high frequencies where device gain is low and parasitics are dominant. Common mode noise is completely unaddressed. Whereas a passive filter, just keep tacking on stages and shielding until it's done. (Yes, you can stack linear stages as well, but that degrades efficiency proportionally.)A couple years ago I made a low voltage, multiple output module with <= 0.1mV output noise, from 1MHz to well over 100MHz (noise <1MHz was specified differently). Easy enough with a modest switching frequency, a few stages of filtering, and good layout. Single board, no shields needed. Probably, to do better, shielding would be mandatory.Linear circuits can still be attractive around extreme corner cases, like where a passive filter would be too bulky, the efficiency hit is unimportant, and attenuation at relatively low frequencies is required. There are also active power filter circuits, mostly for low frequencies because again, device/loop gain is degraded at high frequency.Tim

author: Nystemy
author_rank: Contributor
timestamp: April 07, 2020, 03:55:20 pm
content: Yes, low pass filtering should still be there. Passive filters are usually superior at higher frequencies, especially if we want to handle a fair bit of power.The pass transistor would mostly be there on the final output, it could handle the low frequency filtering like taking out ripple.The higher frequencies will most likely be out of reach for it.Though, I wouldn't drive the transistor as a capacitance multiplier, that seems honestly a bit crude.Since then we wouldn't be able to easily control the output current.Another advantage of using a pass transistor in this fashion is that we can more quickly react to load changes if we have remote voltage sensing. Since we can characterize the resistance over the power cables, and take that into consideration. Ensuring that the voltage dropped by the pass transistor under no load is roughly equal to the voltage drop of the cables under full load. Meaning that we don't need to rapidly force the low pass filtering and bulk capacitance supplying power to the pass transistor to shift up in voltage to handle the higher load.Ie, a lab bench power supply just becomes better with a pass transistor on the output. Though we still will need actual filtering before it. The transistor is there to regulate and filter out the ripple. So we don't need large passive filters for the low frequency stuff.

author: Muny
author_rank: Contributor
timestamp: April 07, 2020, 04:11:59 pm
content: I posted this as a comment on the YouTube video, but I doubt it'll be seen; copying here:The weirdness you were having seems like it could be from the voltage drop across your input wires. You have your main supply set to 20V, but the voltage that ends up at the input is likely less than the minimum rated input voltage of 20V. And I doubt it's very stable near the low end of its probably-immodest input rating. How about re-doing some of your tests, but feeding it say 30V or more from your supply?

author: merox
author_rank: Regular Contributor
timestamp: April 07, 2020, 05:05:32 pm
content: Quote from: D. Head on April 07, 2020, 09:03:00 amThat scope does not just function as a scope but also as a power supply. Look right under the screen on the left hand side - there are two jacks. Also it says on the screenshot in the video: "Select accessory: ... 30V2A output DC power supply". That's whats ment by "NOTE the PSU integrated!".

author: D. Head
author_rank: Contributor
timestamp: April 07, 2020, 05:57:41 pm
content: Quote from: merox on April 07, 2020, 05:05:32 pmI missed that completely, many thanks for you help.

author: Neilm
author_rank: Super Contributor
timestamp: April 07, 2020, 08:22:34 pm
content: There could be a sensor under the heaksink. I have designed units in the past where we could get a small pocket milled in the heatsink. This was designed to sit a on a small SMD temperature sensor and measured the temperature quite nicely.

author: thm_w
author_rank: Super Contributor
timestamp: April 07, 2020, 09:00:07 pm
content: Quote from: maginnovision on April 07, 2020, 07:11:20 amSame reason why lots of people use the RuiDeng supplies. You might have one or two powerful 48V surplus server supplies, now you can use those to power this buck converter and get a variable output with current limit, for very low cost.

author: maginnovision
author_rank: Super Contributor
timestamp: April 07, 2020, 10:09:55 pm
content: Quote from: thm_w on April 07, 2020, 09:00:07 pmI had no idea they were popular. Most of the ruideng owners I've seen bought those then searched for better source after.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: April 07, 2020, 10:34:27 pm
content: Quote from: Nystemy on April 07, 2020, 01:55:50 pmThat's how I look at them they don't run on mains voltage and take raw bulk direct current and produce a well regulated DC output at a high wattage In other-wards like I already stated they are more of aDC-DC converter

author: SuperFungus
author_rank: Contributor
timestamp: April 08, 2020, 02:14:22 am
content: Seems like Dave glossed over the CH340 inside the control unit. I wonder what features are exposed over the USB UART?Also, I'm not tracking why he was saying his active load was attempting to put a short across the output capacitance of the supply. I must be missing something, but it seems to me that regardless of how the load was set up (CV, CC, CP) the only thing that could push the control loop to try to pull more current would be if the output voltage on the capacitors increased when the input supply was removed... I wonder if the issue is energy from those massive inductors unintentionally making it's way to the output on an uncontrolled shutdown?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 08, 2020, 10:09:59 am
content: The constant power mode in most electronic loads is implemented very poorly: usually using the digital reading of the voltage and than adjusting the current as needed. This work OK if the power source is stable, but it goes bad once the supply hits the current limit. So with the oscillation in constant power mode it usually the electronic load to blame, not the supply.The energy stored in the choke is not that large - it is about what you get as ripple when dumped into the output capacitor.

author: SuperFungus
author_rank: Contributor
timestamp: April 08, 2020, 12:52:00 pm
content: I'm not trying to be obtuse, but I'm still not tracking.If the the load is programming a current (perhaps poorly) why is it all of a sudden going to pull unregulated current unless the voltage presented to the load changes quickly (which the large capacitor prevents!)? Put another way, if the load is not in a current overload condition before the brown out why is it in one after? It's connected to the same capacitors at the same voltage!I'm not sure I agree with the comment about the energy in the inductor either, but thinking about in terms of the ripple does seem helpful. Yes, there must be a volt-second balance on the inductor cycle to cycle which would be an amount of energy similar to the ripple. But in many buck typologies, the full DC current is carried by the inductor as well, which could be a significant amount of energy separate from this ripple.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 08, 2020, 03:02:17 pm
content: For the electronic load the feedback in constant power mode is often too slow and also sometimes unstable: When the supply chances to CC mode increasing the load current will reduce the power and thus call for even more power. For the electronic load it is not so easy to control the power, when the source resistance changes, and it changes a lot, from near zero in CV mode to near infinite (mainly the capacitor) in CC mode. Once the source source impedance is hight the simple feedback goes the wrong way.Once the supply is in CC mode the voltage will drop, until the load detects some lower limit / brown out and turn off. Than the voltage will rise again and part of the current is used to charge up the output capacitance. Chances are the load can turn on again before the supply is back all the way and than trigger the CC mode again.When too close to the edge the transients from turn on may be enough to trigger the CC limit, or at least cause a drop in the voltage that than calls for too much current.For the ripple to inductor energy, there is some extra current directly from the source and the current may not reach zero. So the energy can be somewhat larger (maybe a factor of 2 or 3), but it is still order of magnitude.

author: vince549br
author_rank: Newbie
timestamp: May 09, 2020, 10:25:39 pm
content: I just got a Minleaf LW-K3010D PS from Banggood.0 - 30 V 0 - 10 A.Three problems. The PC board was not mounted on one side, this let the board move and then the heat sinks contacted the case causing sparks. The heat sinks were at mains voltage because of all things the power cord had the line and neutral swapped. Any one getting one of these be very careful.The case was poorly grounded.I put a lock washer under the screws of the case, mounted the PC board properly, and discarded the power cord. I've sent the manufacture a note and also given feedback to BangGood with images.

author: mhoekstra 050
author_rank: Newbie
timestamp: December 19, 2020, 08:02:37 am
content: Hi guys,I just bought this device: the DPM8608-RFI was wondering if you other owners have the same problems like me:When turning on the device, the output is always short-circuited for a few seconds, during the boot-process (when the fan runs for a few seconds).With the "Fast-speed discharging" function enabled, the output is short-circuited in the idle state (output off) continually.This does not happen when the "Fast-speed discharging" function is disabled.Only when the output is switched on (press OK), the output gives power like you would expect and there is no short circuit of course.In both cases the charger is supplied by an external power supply and is switched on.Secondly there are extremely high inrush currents on the input and output.It happens when connecting the charger to a power supply in the input side, when the power-switch is in the on-state. Also the device reboots every 2 seconds when the power supply is connected from a powerless state, and the power-switch was already in the on-state.It also happens when connecting a battery to the output.Please watch my videos as proof, by clicking on the following links:1. "Fast-speed discharging" function enabled: https://photos.app.goo.gl/2Rjre5GXnTh81FZY8You see a 18650 battery connected to the output of the device. I connected a little motor as a reference to visualize the short-circuit. When I turn on the device in de idle-state (no power on output), you see the motor turning, because it is fed by the battery in the closed loop. This is because the output is short-circuited.2. "Fast-speed discharging" function disabled: https://photos.app.goo.gl/caLsksMpYfHZzR2r6When powering on the deice, the motor is running for a few seconds and is fed by the battery in the closed loop. Again, this is because the output is short-circuited.