EEVblog #1298 - $70 2000W Power Supply?

[merox]

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).

That 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!".

[D. Head]

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).

That 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!".

I missed that completely, many thanks for you help.

[Neilm]

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.

[thm_w]

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.

Same 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.

[maginnovision]

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.

Same 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.

I had no idea they were popular. Most of the ruideng owners I've seen bought those then searched for better source after.

[johnlsenchak]

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.

That'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 a DC-DC converter

[SuperFungus]

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?

[Kleinstein]

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.

[SuperFungus]

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.

[Kleinstein]

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.

[vince549br]

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.

[mhoekstra 050]

Hi guys,

I just bought this device: the DPM8608-RF

I 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/2Rjre5GXnTh81FZY8
You 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/caLsksMpYfHZzR2r6
When 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.