Author Topic: ET5410 Electronic Load mod: add external sense  (Read 1040 times)

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Offline cybermaus

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ET5410 Electronic Load mod: add external sense
« on: September 25, 2020, 06:11:01 am »
Small mod, just mentioning it.

The ET5410 already has small internal sense wires from the board directly connected to the banana lugs, so they were easily intercepted.
I did not even cut them, but instead took out and rerouted the small 2-pin plug on the PCB, and connected those via a slider switch, see photo.
BTW: I forgot to take pictures of the inside, and I do not want to open it yet again, but its simple enough:

The sense wires each go via 2-pin plug a pair of 100K precision resistors (so 200K each) to a TL072 OpAmp with a 30K /4K resistor over it to make it into a voltage scaler;
30K or 4K switched by DPST relay, which is controlled by the range setting of the device, high 150V range presumably choses the 4K.
Alas no reverse polarity protection on the now separate sense wires, I am now wondering if I should have shorted the middle of the 4 100K resistors with a diode. After all, the TL072 can only stand -0.3V


Originally, I had some worry on how the device would respond if there was accidentally no voltage on the sense wires. I worried about software hanging with "divide by zero errors", but it is behaving perfectly:
- CC mode: it does not care, just keep drawing the current, but V and W display go to 0, and back up when reconnect
- CP, CR and CV mode : the device just stops drawing current, but does not hang, Reconnect, and it starts up again.
Even repeatedly switching from internal to external sense seems to not bother the device.

Oh, and while you are in there, put a  felt pad on he support screws of the main heatsink. They protrude a little, and if someone dents the sides, they may make contact to the V+ input.


Comparing to video's of the Kunkin I have seen, I like very much that I can change the CC setting while the load is on.
Also I did not observe any startup instabilities, and the load seems to work properly (on my supplies) down to 0.2V




« Last Edit: September 25, 2020, 06:13:38 am by cybermaus »
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #1 on: September 25, 2020, 11:21:52 am »
Good to see someone having done this successfully - I'm looking at buying the 500V version of this load (or alternatively the similar looking DCL6104A) and doing the same.

Have you got any resistance between the main and sense terminals? A couple of hundred ohms or so would ensure that even if the switch was in the wrong position the supply will still see the voltage at the terminals with minimal error (200/100k = 0.2%) but should still be large compared to wiring resistance if the sense function is used (if the wire is 100 milliohms 0.1/200 = 0.05% error, not sure if that's a completely correct equation but it will be small regardless). Could put a parallel diode to clamp any voltage on said resistor too (in case the main connection goes open) though a polyfuse in series would be advisable as well to protect the diode if high currents are to be used.

Finally, do you have any pictures of the inside of this unit, especially the sense section? Would be interested in seeing them. And have you checked any of the more advanced features (e.g. the Dynamic load) - does it meet or at least let you set it according the datasheet specs (e.g. 1.5A/us slew rate - I recall someone complaining about this being unavailable on this or a similar load)?
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #2 on: September 25, 2020, 12:04:11 pm »
On the resistors, I considered that at first, expected to do so.

However, I  started rethinking this when noticed these were high-precision resistors, and the OpAmp was setup as a voltage divider.
So any additional resistor, or any resistor shunting between main and sense, would bring this voltage divider off balance, and affect precision.

I did some serious thinking on how to make a resistor network or even considered adding a 2nd opamp as voltage buffer.
But between the wanted precision, the fact I could not re-calibrate, and the fact it needs to work over the entire 0-150V, I could not work it out

So I decided to go for the low-tech solution. A DPDT slider switch. And as stated, it works well.
Also, the ET5410 matches my "best" multimeter precisely. Both before and after I added the switch.


On the slew rate specs, I did not test.
But I did at one point use it as a CR to test how some IBGT were working and managed to keep up on the emulated resistor quite well on a 20KHz PMW signal.


Edit: Oh, and as to a very low resistance like you state (100 ohm. Which would make the OpAmp 30K/230K turn into 30K/230K1 so only 0.04%
Yes, but. if I would cross over my lines, I'd have the full voltage over 100 Ohm, theoretically 150V and thus 225W, practically for me 24V so 6W
The resistor would evaporate. So rejected low ohm. And high ohm would as mentioned, would affect measurement.
« Last Edit: September 25, 2020, 12:52:46 pm by cybermaus »
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #3 on: September 25, 2020, 01:12:50 pm »
Edit: Oh, and as to a very low resistance like you state (100 ohm. Which would make the OpAmp 30K/230K turn into 30K/230K1 so only 0.04%
Yes, but. if I would cross over my lines, I'd have the full voltage over 100 Ohm, theoretically 150V and thus 225W, practically for me 24V so 6W
The resistor would evaporate. So rejected low ohm. And high ohm would as mentioned, would affect measurement.
Yes this is indeed an issue, which is why I suggested a diode clamp and a polyfuse - unfortunately this is extra complication so fair enough if you'd prefer just to rely on remembering to have the switch correct.

The main issue here is the fact that the voltage and current range is so high - a power supply with sense may only supply say 5A or 30V - this can be covered either with a low value resistor (bypassed by a diode) or a higher value resistor with no diode (accepting a moderate accuracy loss if the sense switch is on but no sense leads connected). 150V/30A is trickier though, a resistor big enough in value to not smoke would cause major inaccuracy if the switch was in the wrong position, while a clamp diode would need to also deal with a big power dissipation if a lot of current were drawn.

I might have a quick look at how the itech supplies do it as I've got one handy at work (hopefully it's obvious).

Thanks for the IGBT testing info - if it handles 20kHz OK that's better than expected! Did you take any pics btw when doing the mod?
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #4 on: September 25, 2020, 01:36:05 pm »
Well, yeah. Though the rate cannot be adjusted (I did search for that) but was better than I expected.
20KHz worked, though I did see a little slow responce in the square wave. If I remember, at 10KHz the resulting wave was pretty much square, on about 3 Amps.
But this is in no way precise measureing


Anyway, I would just go with the slider switch.
Only, as stated, next time I open it, I will add a reverse protection diode, in the middle of the 4 100K resistors.
So it is 2x 100K away from input, no need for a fuse. And also still 2x 100K away from OpAmp, so reverse leakage current has less impact.


Edit: Simulation shows I should just add a 2n4148  as protection  completely on the inside, directly between + and - of OpAmp. While it is closer to the OpAmp, the voltage over there is so low, leakage is in the pA range (in simulation) so that it would not affect the measurement. Where is in the middle of the 2 100k resistors, it gets actual double digit voltages, and leakage does affect outcome (only a little, but more).

« Last Edit: September 25, 2020, 08:18:52 pm by cybermaus »
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #5 on: September 25, 2020, 08:10:30 pm »
So I checked the Itech load and it uses a relay to switch to the sense inputs - you have to enable it in a menu then use the terminals on the back.
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #6 on: September 25, 2020, 09:04:01 pm »
Some testing showed that in dynamic CC mode the ET5410 has a highest slew of 4Amp in 10mS. So 0.4A/ms
Which is so out of whack with the specs (1.5A/uS) that I wonder if I am doing something wrong
Am I misinterpreting how this slew rate works?

The difference with the previous mentioned 20KHz was, this was where the CR mode responded to an external AGBT switching, whereas here it is the load itself that drives in a dynamic mode: 10ms .1Amp, 10ms 7 Amp

Or maybe my power supply is the limit.
I will test more tomorrow.
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #7 on: September 26, 2020, 07:28:16 am »
@Hydron: So, on your question regarding transient rise times.


So I did some more testing, and either I do not understand how it is supposed to be measured, or this ET5410 is not what you want when you value dynamic testing.
I mean, it works well for what I bought if for, and the price is right. So I should probably not let this get to me. But the dynamic testing seems to be lacking.


Dynamic CC Continuous:
- Basically works (if we ignore specs)
- Settable resolution is fixed 5-digit ms, so 1ms to 60.000ms. Not in μs like the spec say. And certainly not 50μs to 3600s
- Best rise time I got is about 1A/ms in part of the slope, and 0.3A/ms in the overall 5Amp rise (see screens 1, 2, 3)
- Then again, I find the advertised 1.5/μs very fast. Are those kind of figures normal?

Dynamic CC Pulse:
- Basically does not work. When I turn on or off, the current turns on or off. I am unable to get a pulse out of this
- Rise time is slightly better though when turning on, about 5A/ms, but with overshoot (see screens 4)

Dynamic CC Trigger:
- I think it works. The manual trigger swaps between level A and level B, and thus the  durations have no meaning
- Trigger can be "Auto, Manual, External"  which hints that the cut-off ribbon cable near the back has a trigger in it.
- Rise time is same as Continuous.


Thinking about this, one thought I had is that the rise time is slow, because it is limited.
Maybe there is a settable 1A/ms default somewhere. But if so, I cannot find it.

Another thought is, this is rebrand with (bad) custom firmware. The fixed 5-digit milli-second duration setting, instead of 50μs to 3600s hints at this.
So maybe this is a re-branded OEM and East Tester only makes front panel and new firmware, and they messed up on the firmware but publish the original device's specs.
After all, between the Kunkin, East tester, DingChen, too many nearly similar form factor devices hit the market at the same time.


Images
Sorry for the photos, could not find a FAT formatted USB stick.
Yellow = measured with current clamp probe; Blue = measured with 0.1Ohm shunt


Next up I will redo my IGBT testing, see if my memories on the 20KHz were correct.
But the wheater is good outside, so not now....
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #8 on: September 26, 2020, 01:54:09 pm »
Thanks a lot for the measurements. I would also not use the dynamic mode very often (probably occasionally for testing power supply transient response), but it seemed to be a point of difference between the EastTester and the other similar options. The reviews most people do are based around CC, CV and battery testing rather than looking much at dynamic performance.

As the specs are just lies anyway I'll probably buy based on availability and price instead, or pay the extra for a KEL103 (which has sense inputs built in, a front panel switch unlike the Kunkin, and an ethernet connection). Still good to have options suitable for most hobbyists available for reasonable prices though, unlike a few years ago when Itech was the "cheap" brand.

As for screen capture, there are some python scripts etc available to grab shots via ethernet if that helps you (photos also work though).
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #9 on: September 26, 2020, 07:29:56 pm »
One feature I do like a lot. And I did not know it was a feature until I say on a Kunkin teardown that it could not do it:
You can change the CC/CR, while it is already active. So while drawing 5 amp, you can walk up or down.

I do that a lot. From the Kunkin video I was let to believe you need to stop the load, change the setting, start the load.
That alone would make me chose for this East Tester instead of Kinkin all over again, had I need for another one.
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #10 on: September 26, 2020, 07:47:56 pm »
Agreed, after I heard about that issue with the Kunkin I was never going to buy one regardless of price difference.

Edit: ...and the above is wrong, read it elsewhere too but must have been user error or something! I've just checked a video and the guy is adjusting it live.
« Last Edit: September 26, 2020, 10:05:28 pm by Hydron »
 

Offline aristarchus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #11 on: September 26, 2020, 08:27:22 pm »
That is the problem with those that do reviews and do not even know how to operate the device under review.. thus their videos give wrong impressions to viewers.
Got a KP184 and honestly I believe there is nothing to beat its VFM and the more I see other similar loads the more I appreciate it.
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #12 on: September 26, 2020, 09:02:52 pm »
@aristarchus
Sorry, I am not quite sure how to interpret your remark.

Anyway, I did do the IGBT test again.
So Load is set as a 4 Ohm resistor, and a MOSFET is drawing current through it, driven by a 20KHz PWM signal.

And indeed, it is doing pretty well emulating this resistor. Maybe it is because it does not need to react, just stable keep its internals set to the emulated 4 ohm, regardless of the PWM state.
But initially when I tested this, I wondered this sort of setup would work, and it does. Even at 20KHz it shows a fairly square amp use.
Note how the amp does jump from 0Ampt to almost 3 Amp (12V over 4 Ohm) but the load display calculates the average current

Yellow is current drawn. (almost 3 Amp peak))
Blue is voltage over MOSFET, connected to Load Negative (12V then open).
 

Offline Hydron

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Re: ET5410 Electronic Load mod: add external sense
« Reply #13 on: September 26, 2020, 10:17:09 pm »
That is the problem with those that do reviews and do not even know how to operate the device under review.. thus their videos give wrong impressions to viewers.
Got a KP184 and honestly I believe there is nothing to beat its VFM and the more I see other similar loads the more I appreciate it.
I assume you mean value for money by VFM?
And yes, it does appear that you can adjust it live, I read somewhere else on the forums (can't remember where) that there were issues adjusting it live but I found a video disproving that - apologies.
If the Kunkin was the only <$250 load then I would get one for sure, however it looks like there are others that are more user friendly and I'm happy to pay a bit more for a nicer UI and a power switch on the front rather than on the back next to LIVE screw heads (i.e. safety modifications required before use).
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #14 on: September 27, 2020, 04:54:48 am »
.. next to LIVE screw heads (i.e. safety modifications required before use).

Well, I did check that, not a problem on the East Tester, and also the heatsink is further away from the back plate so you have to go really go in there to even touch the heatsink with a DMM probe.
There are some internal screws at the side of the heatsink though, that potentially touch the sides if they dent. So I did put some felt pads on those.
 

Offline Wintel

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Re: ET5410 Electronic Load mod: add external sense
« Reply #15 on: September 28, 2020, 09:42:03 pm »
Anyway, I did do the IGBT test again.
So Load is set as a 4 Ohm resistor, and a MOSFET is drawing current through it, driven by a 20KHz PWM signal.

And indeed, it is doing pretty well emulating this resistor. Maybe it is because it does not need to react, just stable keep its internals set to the emulated 4 ohm, regardless of the PWM state.
But initially when I tested this, I wondered this sort of setup would work, and it does. Even at 20KHz it shows a fairly square amp use.
Note how the amp does jump from 0Ampt to almost 3 Amp (12V over 4 Ohm) but the load display calculates the average current

Yellow is current drawn. (almost 3 Amp peak))
Blue is voltage over MOSFET, connected to Load Negative (12V then open).
cybermaus, have you try to test the Battery Discharge feature and set to CR "Constant Resistance", ie. connect a battery and set the Battery Discharge feature CR to 5 Ohm or 10 Ohm,  Does it work ?

Because many users report that Battery Test doesn't work with CR, when selected constant resistance nothing happened, only when constant current was selected did it start to discharge.
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #16 on: September 29, 2020, 08:25:43 am »
cybermaus, have you try to test the Battery Discharge feature and set to CR "Constant Resistance", ie. connect a battery and set the Battery Discharge feature CR to 5 Ohm or 10 Ohm,  Does it work ?

Because many users report that Battery Test doesn't work with CR, when selected constant resistance nothing happened, only when constant current was selected did it start to discharge.

I checked, and indeed, I am not able to get the CR submode of the Battery test to work. CC works OK, but CR does not.
I tried several cutoff voltages and resistance values, but it just is stuck to about 7~8mA. And no, this was not the value still set for the unused CC mode, those were set way higher.

So it seems this really is a failure of the device.
 

Offline Wintel

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Re: ET5410 Electronic Load mod: add external sense
« Reply #17 on: September 29, 2020, 10:40:38 am »
cybermaus, have you try to test the Battery Discharge feature and set to CR "Constant Resistance", ie. connect a battery and set the Battery Discharge feature CR to 5 Ohm or 10 Ohm,  Does it work ?

Because many users report that Battery Test doesn't work with CR, when selected constant resistance nothing happened, only when constant current was selected did it start to discharge.

I checked, and indeed, I am not able to get the CR submode of the Battery test to work. CC works OK, but CR does not.
I tried several cutoff voltages and resistance values, but it just is stuck to about 7~8mA. And no, this was not the value still set for the unused CC mode, those were set way higher.

So it seems this really is a failure of the device.

What is the hardware and firmware version of the ET5410?
 

Offline cybermaus

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Re: ET5410 Electronic Load mod: add external sense
« Reply #18 on: September 29, 2020, 01:43:21 pm »
Purchased January 2020
Software: V1.0.1942.024
Hardware: V1.10.1946.002
 
 

Offline Wintel

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Re: ET5410 Electronic Load mod: add external sense
« Reply #19 on: September 29, 2020, 03:20:06 pm »
Purchased January 2020
Software: V1.0.1942.024
Hardware: V1.10.1946.002

Maybe there is a bug of firmware, or will be fixed after firmware update (maybe?!)

Is there any new firmware for ET5410?
 


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