I have been running some measurements on my DUT while being powered by the Otii Arc Main power.
Now I run my DUT over the external battery and I’ve added a 0.4 ohm shunt on the positive side, and connected my DUT GND to the AGND, exactly as described here: Documentation - Qoitech
I notice that my measurements were very inaccurate, a curve that just kept going up and was in the negative. I noticed that when I connect AGND a short happens. Even when I disconnect AGND, I can’t measure the voltage, but should be able to measure the current; I am also unable to measure any current (I’m pressing buttons on the DUT that should bump it to around 60mA):
Now when I switch the ADC- and ADC+ pins to the SENSE- and SENSE+ pins ánd have the AGND connected I seem to get correct readings, but lose the ability of current measurement (due to the shunt value in the software):
What could be causing this? What am I doing wrong? I’m not using a Kelvin connection in my setup right now, knowing it won’t be the most accurate, but I’m not getting actual readings right now at all.
Thanks for any help!
Hi and welcome to the forum,
Not sure about your connection, but connect like this:
Shunt resistor in series with battery positive pole and DUT positive battery connector.
ADC+ on high side of the shunt resistor
ADC- on low side of the shunt resistor
AGND to DUT GND
Enable channels ADC current, ADC voltage and ADC power
Turn on the recording
Does this solves your problem?
Thanks for the reply!
Yes that is my exact setup. Here is an image of my setup (battery disconnected in image):
The brown wire is connected to the + DUT (DUT is not shown in image).
The gray/purple wire is the GND, gray wire goes to DUT.
This is the setup that does not work and creates a short when ADC+ and ADC- are connected AND I connect AGND (no short when AGND is disconnected). However when I move my ADC+ and ADC- wires to SENSE+ and SENSE- I can read voltages as expected, but that’s not what I want, since I want to measure current over the shunt. Am I missing something?
Also, for my own understanding, am I using a Kelvin Connection in this setup? I’m not sure. However the ADC+ and ADC- wires are the black ones connected close to the shunts resistor body (514mOhm), and are short wires going into the Otii Arc.
I have done some additional testing and I can’t figure it out. I have tried measurements on the low-side and this does not seem to create a short, however the ADC measurements are negative. I’m not talking about a small microampere current, but ~60-70 milliamps (for testing purposes I swapped ADC+ and ADC-, without results, this does not seem to measure anything).
I do not want to measure on the low-side so this information is just extra information for readers to hopefully help me figure out what’s wrong.
My low-side setup is:
Vbat- to low side shunt, ADC- and AGND.
High side shunt to ADC+ and GND DUT.
Vbat+ to DUT+.
Test if there is some issues with your Arc by doing like this:
- Connect your Arc and add it to your project
- Enable channels Main current, main voltage, main power, ADC voltage
- Set to 3V
- Set OC protection to 100mA, Cut-off
- Connect red banana connector to ADC+, nothing else connected.
- Turn on the recording
- Turn on power for a second and then turn off
- Now connect red banana connector to ADC- and repeat 6 and 7.
What is the current flowing into ADC+ and ADC-
If possible, also test this:
9. Connect your 0.4ohm shunt between ADC+ and ADC-
10. Connect red banana connector to ADC+ (high side of shunt)
11. Connect a known resistance between ADC- and black banana connector (1k for ~3mA, 100 for ~30mA depending on what resistors you have available, but recommended between 1k and 10)
12. Also enable ADC current and ADC power channel
13. Set ADC resistor to 0.4ohm
14. Repeat 6 and 7 again.
Is the ADC current and ADC voltage showing the right values?
Thanks for your reply once again!
Connect red banana connector to ADC+, nothing else connected.
Now connect red banana connector to ADC- and repeat 6 and 7.
I’ll try step 9-14 later today and report back. Do you see anything odd already on these screens? I think step 5 should show 3V on the ADC+ as well?
Ok I tried step 9-14 as well, and it does not look good. It seems to confirm my own testing where a short is created. I used a ~570ohm resistor.
Yes, your ADC input is broken.
I propose that you create a case in our case system for repairing the Arc.