ET5410 Electronic Load CC+CV and CR+CV modes, what do they do?

[cybermaus]

So I got this ET5410 Electronic load, and the CC/CV/CP/CR modes are quite clear to me, and they work well.
Or well enough for hobbyist like me, no more messing with hot power resistors and incandescent light bulbs as load.

But what do these combi modes CC+CV and CC+CR do?
I found this description:

"The CC+CV mode is to prevent the source to be measured from being damaged by overcurrent discharge. In this mode, when the source cannot output the current set by the load, it will automatically switch from CC to CV mode."

But.. that does not make sense.
If the source cannot supply the CC, it goes to CV? HOW? to clamp the voltage, it needs to draw current.
And indeed, that is what it does. For as much as I can observe, the CC+CV modes works pretty much the same as the CV mode

Of course, I could simply claim its a cheap china device, but really, not knowing how it is supposed to work makes it a little to easy to talk trash.



What am I missing? What is the "normal"  use case and behavior for a combi CC+CV mode on such devices in general?
(And same for CC+CR mode, though probably when the penny drops for CC+CV it will also for CC+CR)

Thanks

[cybermaus]

bump.. no-one?

[tautech]

bump.. no-one?

Typed a reply yesterday but chickened out. 

I think CC+CV description is lost in translation when instead it maybe should mean CC with an end V so to not damage a battery by over discharging it.
Defpom recently did a video on a 9V rechargeable testing its stated capacity where he set an end voltage.
This might give some clues to these modes:

[cybermaus]

Thanks

Interesting idea. Somewhat true.

It has a separate "Battery"  mode for that. With 3 separate cutoff voltages. So I can say: draw CC down to 1.3V, then draw slightly less CC down to 1.2V then even less down to 1.1V, and then stop and display Wh and mAh. So pretty sophisticated test, but that is that other " Battery"  mode. Not the CC+CV.


But still, your suggestion is interesting, because if I interpret "CC+CV"  as "Constant Current *down* to Cutoff Voltage"  it does work like that. It keeps drawing the CC till I go -down- past the voltage, and then stops drawing current.
But there is no mAh or Wh readout, and also the measurement is still on.


So is that what it is supposed to do. What is the real word usage of it. Not battery test (with no Ah counter). Brown-out protection testing?
It is what it seems to do, but what is the use for it?


More intuitive would have seemed in upward motion: Keep CC till I go -up- till the voltage, then increate current to clamp voltage, like the true CV mode.
But that is not what it does.

[TurboTom]

I don't think it stops drawing current when it reaches the CV limit. It probably keeps on reducing the current drain as much as necessary to keep the preset voltage. In case of a battery, this means, it will eventually end at zero current with the battery completely drained of all charge right to the CV limit voltage.

But consider checking a power supply with a fold-back current limit (that is, if the load can cope with the negative resistance inherent with these PSU protection schemes without starting to oscillate). This would actually make good sense to characterize such a power supply.

[cybermaus]

Well, I tested that too, and no. In any way I can test, the CC+CV acts the same as just CV. Other then I have to set a current, it just keeps the voltage constant, on either side of the current I set, moving up or down. I even hooked up through a power resistor, to make sure the "stability" of the power supply would not allow for varying voltage without extreme on/off current.

(some irony here, bought a Load to stop messing with power resistors; am messing with power resistors to figure out the Load....)

Anyway, I decided I am not going to let the mystery mode "CC+CV" or " CR+CV" become an issue. Modes CC/CV/CP/CR work. As does the "battery" mode.
And if this forum does not have an immediate and well traveled use for any such labeled mode, then its probably not something very important. Let it go.

[H.O]

Obviously the implementation may be different or the mode might simply not work on ET5410 but here's the description for CC+CV for the GW-Instek PEL3000:

When CC+CV mode is enabled, the unit will act as constant current load after
the input voltage is greater than the user-defined CV level.
At the CV level, the unit works as a constant voltage load.
This mode effectively creates a voltage ceiling before the unit operates in CC mode.

Note that when the source voltage is less than the CV level, no current will flow due to a very high impedance.

[cybermaus]

Thanks. So that would mean CV is Cutoff Voltage (or maybe "Cut-in Voltage, depending if you go up or down), rather then Constant Voltage.
And I can see some use for it. It was in fact what I originally envisioned.

But alas. It is not how the device is behaving. Below the set CV, there is no current (that part fits) but above the CV, there is no limit to the current, and current is so high it clamps to the set CV. Which asimply means the entire thing behaves like a normal singlular CV.


Probably the GW-instek behavior is what it is supposed to do, but it is simply broken.
I did in parallel also asked manufacturer for help and/or firmware update, but am somewhere between non understanding (Chinglish) and not wanting to understand (hiding behind Chinglish). And I am not even asking for money back, the normal modes are way to useful. Just a firmware update....

[H.O]

Here's another explaination from the PEL-3000E "brochure".
I have to admit I don't quite understand what the mean or what to expect if I'd try it (I don't have a PEL-3000E BTW and my Maynuo doesn't have +CV mode).

+CV mode can be selected under CC, CR or CP mode.
When +CV mode function is turned on and electronic load sinks more current than the maximum current of power supply under test, electronic load will automatically switch to CV mode. It is because that the current sunk is the maximum current of power device. Therefore, power supply will switch to CC mode and PEL-3000E will switch to CV mode to limit electronic load from sinking the total current of power supply so as to prevent power supply under test from damaging.  Electronic load will cease operation once the voltage of DUT is lower than the set voltage under +CV mode.

I mean, how can the load possibly sink MORE current than the maximum current of the power supply under test?
Do they mean that when the load TRIES to sink more current than the supply can deliver the supply under test switches to CC mode, the supplies output voltage drops and when the voltage at the load input (or remote sense) gets belowe the +CV limit the load input is disabled?

[cybermaus]

So manufacturer send me a small video. It seems they specifically setup a test and videotaped it for my benefit.
So they went up in my respect, any suggestion they were purposely trying to not understand me is a falsehood.
Following their example, my 6 month old device behaves the same as their current one.

So what do they say, and what does the video show?

They say: "once the device hits CV mode, it stays in CV mode"
(that is pretty much the only thing they write)

It shows:

• Load set to 15V-2A, with Supply set to 18V it draws 2A (so CC is indeed active).
• Going down on V, at 15V current drops to 0A (CV becomes active)
• Going back up above 15V, current goes way past the set 2A to clamp voltage (continued CV mode)

Together with @H.O 's description of the PEL-3000E, re-interpreting the original ET5410 description, it is supposed to be the same protection mode. Protecting the DUT power supply from hanging on in a "brown-out" situation. Stop drawing power and stay in the minimum viable voltage.

Makes some sense, but I believe it is then in error to -stay- in CV even as the DUT recovers.
It means a small transient current spike, or DUT being slow to react to startup, would trigger CV, after which it would stay in CV and draw maximum current.
Now, maybe the DUT can supply the current, it is then holding the voltage after all, but it means this transient effectively canceled the whole set CC, so why bother setting it in the first place.

Which is also hinted at by @H.O first description of the PEL-3000E: "this mode effectively creates a voltage ceiling before the unit operates in CC mode" 
Talking about ceiling rather then floor hints it would also go with upward voltage. So likely the PEL-3000E goes back to CC after the voltage rises again.
It would be nice if someone with said device could test this.


Anyway. As mentioned, I keep on this just for the fun of it, will even argue this back to manufacturer, ideally after someone with a PEL-3000E confirms.
But I am not bothered too much by it. With the simple modes working as I intuitively expect, its a pretty good device anyway.

[Tjuurko]

Makes some sense, but I believe it is then in error to -stay- in CV even as the DUT recovers.

DC electronic load Maynuo M9812 has exactly the same behavior.

[cybermaus]

Really? Thanks for the test.
I guess is supposed to be like that than.

[H.O]

First of all, thank you for bringing to my attention that my Maynuo DOES have this +CV mode.

I had a quick play and I think the idea is this:
You're testing a 12V power supply capable of delivering 1A. As soon as the supplies output current reaches the limit the output voltage will start to drop - no surprise there.
In normal CC mode the load can basically short out the supply completely, bringing its output voltage very close to 0V - which might not be good for the supply.

If you instead activate +CV mode and set the +CV limit to 10V the load will actually switch from CC mode to CV mode when the input voltage reaches 10V effectively preventing the load from TRYING to pull more current than the supply can deliver without the voltage getting lower than 10V.

But yeah, once it's went from CC mode to CV mode it'll stay there until the input is cycled off/on.

[cybermaus]

Yeah, after all these posts that's sort of my current thinking as well.

But it means that if your PSU/DUT is somewhat slow to respond to you turning on the load; Like maybe it needs to step up its switching frequency, or needs to step up a tab in the transformer, it may temporary drop just below the voltage, and then recover. But by now, it is in CV mode, and will *pull* to the CV *with all its might*. Which seems counter productive to the idea of protection of the DUT.

I manage to do this by setting the CC+CV to just where my PSU has a clickover to the next internal transformer tap. When I turn on the Load, I hear the PSU click, and then see current rise to the maximim because load went to CV


I feel the same protection would be granted better if the thing would not stick to the CV mode, but would return to CC when the voltage rises again.

Of course, if it does not stick to CV, it would not really be Constant Voltage. Maybe it would better be a CC+MV (minimal voltage) or LLV (Lower Limit Voltage) or even CV, but now meaning "Cut-off Voltage".

I even imagine the latter *could* have been the original meaning from some engineer somewhere in the past, but people got confused and are now just copying each other products...

[Tjuurko]

In fact, there are three possible variants of these modes.
[ Specified attachment is not available ]
The latter does not implement the CV mode.
CC+CV mode is suitable for full battery discharge.

[cybermaus]

I think you are absolutely correct. But was I not saying the same? It would not be called "Constant Voltage"
You call it "??"  and I am fine with that. But would it be be more useable?

I think it would work equally well (or better) to "protect against brown-out" as listed in the manuals.
And would work equally well be used to deplete batteries to a set level (though there is a dedicated mode for that, that also counts Ah and Wh)

BTW, small update to your picture to clarify on that the direction of delta-V matters.
I tried to graph it in 3D with dV as 3rd axis, but it did not make it more clear, just more incomprehensible.

[TurboTom]

A battery could be problematic in that mode: Consider a _very_ cold LiIon / LiPO4 battery, thus with a high source resistance. It cannot supply the CC dialed in and voltage drops below CV setting. Due to the current flowing, the battery heats up and its resistance drops. The current skyrockets while the load clamps the voltage. This can easily result in a dangerous situation (thermal runaway of the battery and possibly a risk of fire).

So be careful with CC+CV mode and batteries...

[cybermaus]

@TurboTom: Noted. That is an extra argument why CC+CV is not a good mode? Why it should return to CC?
Surely there must be a valid scenario for this, but I cannot get my head around it.

In more positive news: I found how to set the 3rd scenario, the one I wanted.
The one labeled ?? by Tjuurko or CC+MV (minimal voltage) by myself earlier.

And I think it is a a normal setting on most loads: Voff and Von.
Or at least, I seen it referred in some video's

My Load has settings Von and Voff, that apply to all the normal modes CC/CR/CP
- Von : start drawing current once voltage rises above this (as well as above Voff)
- Voff : stop drawing current once the voltage sinks below this

If I set Von lower or same as Voff, I get exactly the 3rd scenario.
More intentional of course is to set Von a little higher then Voff, to introduce a hysteresis

Which was fine for what I originally tried to do as well: Only start drawing current once I reach a minimal voltage.
And -never ignore Iset- and just go to max-out on the current (which is where CC+CV surprised me because I approached CV from the bottom up)

Graph and video below.
Sets to start using CC at 12V and stop below 11V