Help with Siglent SDL1xxx Electronic Load New DCR Mode

[mbarszcz]

Today I checked for a firmware update on my Siglent SDL1020X-E and saw that there was an update from Siglent that added a "DCR Mode".  After fighting with different USB drives for an hour until I found one that the electronic load liked, I finally got the new firmware installed.

Despite reading the terrible instructions, I still can't figure out how to use it or how it is supposed to work.  The manual can be found here: https://tm-co.co.jp/wp/wp-content/uploads/2022/10/SDL1000X_UserManual_E02A.pdf instructions for DCR mode are on page 57.

Chapter 2 Function and Features SIGLENT
SDL1000X User Manual 47
DCR Mode
DCR function, which can test the internal resistance of the battery.
Operating Steps
In the "Battery" testing interface, press the mode function key to select
"DCR" and enter the DCR testing interface.
Set the time_ 1 and Time_ 2. Current_ 1 and Current_ 2. After set "ON", the
test can be conducted. After two periods of operation, it will automatically stop
and a prompt will pop up on the test completion screen.
The graph shown on the screen allows users to clearly understand the
relationship between Time_1 and Time_2 and Current_1 and Current_2. The
waveform in the graph does not change with the test result. The test result is
updated in the 'DCR' item on the screen, and when the next test is performed,
the last test result is updated to keep the 'LAST' value.

What values should I be using for all 4 of these to measure the internal resistance of an 18650 for example?  It seems that they can be completely arbitrary.  It seems something like 10 seconds at 1A and then 10 seconds at 2A might be reasonable 

No matter what I put in for time 1 though, it only ever seems to last for 1 second.  The total length of the test seems to be 1 second for time_1 and then however long time_2 is set for.  Maybe I just don't understand what the electronic load is doing.

Anyone else have an SDL1020X-E that has used this feature?

[TheDefpom]

DCR doesn’t stand for DC Resitance, it stands for DisCharge Rate.

The battery mode is used to discharge a battery using a specified current so that the battery capacity can be determined.

EDIT: This is wrong, the update added a new feature back in 2023 which I had not noticed.

[mbarszcz]

I'm not so sure that's correct.  This was added as a new feature and the unit could always measure the capacity of the battery in constant current, constant power, or constant resistance mode.  Plus in DCR mode it has an Ohms readout. 

[tautech]

https://www.youtube.com/shorts/1RuZ9lI0fHI?feature=share

[mbarszcz]

https://www.youtube.com/shorts/1RuZ9lI0fHI?feature=share

That's the constant current battery discharge mode not DCR, you can see it in the bottom left. 

[Tjuurko]

T1 is always equal to 1s.
Internal resistance is calculated using the classic formula: R=-(U2-U1)/(I2-I1).
The higher "I2-I1", the more accurate the measurements. It is important not to exceed the maximum current of the measured device.
Time T2 can be selected greater than 800 ms (measurement with any averaging is guaranteed).

[TheDefpom]

Well well, I looked at my unit today and indeed DCR is to calculate an approximate DC resistance..

It is buggy though, as selecting 5 seconds for both results in a 6 second test time... as mentioned T1 is always 1 second.

I did a test on a 18V Lithium pack I am repairing at the moment and it gave me 312mOhm... my proper I.R. tester gave 88mOhm (this is including the cable connecting to the battery pack).

[mbarszcz]

Looks like it's just a load of rubbish then I guess.

[TheDefpom]

I don’t use external sensing so that might improve the accuracy, also as mentioned, having a larger difference in test currents would also improve accuracy, I might dig into this in more detail later if I get time.

I think in reality though if you want to test internal resistance, just buying a dedicated meter for it would be a good idea, even the cheap ones such as the one by FNIRSI work pretty well for that task, I own a few  including a HP and they all are in the ballpark with each other.