Reverse currents

Technical Discussion
1

Hi,
I am setting up to characterize the charge/discharge performance of some LTO batteries for a client. To do this I need to insert the JS between the charger and load, and the battery. Charge current should be in the range of 200-500mA and a similar range for the load to discharge the battery during that test. I think I only need JS to accurately log either charge or discharge, however, my concern is if the magnitude of the reverse current is OK for JS.

What I plan on doing is setting up some automation to cycle the batteries between charge and discharge. I have no problem reconfiguring the JS connection when I need to change between charge and discharge characterization.

Does that sound OK?

This exercise also means I need to have JS sample the current at a low rate. I seem to remember reading about doing that, but cannot recall where. Any pointers would be much appreciated.

2

Should have read the manual first :frowning: It appears JS will be fine with the level of reverse current that may flow during testing.

Looks like I need to study pyjoulescope to understand the kind of logging I need to do. If you had a sample to help bootstrap the process that would be outstanding :slight_smile:

1 Like
3

Hi @SidPrice

Yes! As you noted, your Joulescope can measure in the reverse direction down to -1.5 A. While your Joulescope will autorange in the negative current direction, the super-fast hardware autoranging is only in the + direction. Autoranging on negative current overflow takes around 10 µs, which is typically more than fast enough for battery charging.

Check out the pyjoulescope_examples. If you are looking to record a JLS file, see capture_jls.py. If you only want the 2 Hz statistics data, then see statistics.py and trigger.py.

4

Hi @mliberty

Thanks for the links the examples look like a great starting point :slight_smile:

5

Hopefully they help! If you run into any issues or have questions, please feel free to post here or under a new topic.

6

@mliberty Is it possible to have the UI running at the same time as a logging script is running? The downsample_logging example seems to do what I want :slight_smile:

7

Well, yes and no. Yes, both can run at the same time, but Joulescope access is exclusive. If you only have one Joulescope, then only one program can use that Joulescope at any one time.

If you want the UI, you can record to the statistics to a CSV file, which is similar to downsample_logging but without the ability to recover / resume a capture.