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Published 20 hours ago • verified publisher icon stuartpittaway

False current readings

Open red0909 opened this issue 2 years ago • 8 comments

Hi, now i have detailed information about this issue.

so first i have a 200A 60mV shunt in discharge mode current readings are correct to 20mV shunt voltage below this voltage the current readings start to decrease and rise again randomly.

in charge mode this problem occures at -30mV over this voltage the current readings drop and rise again randomly.

additional the mV readings start to be inacurate for more than -30mV in charge and less than 20mV in discharge mode if i stay within this limits all works fine.

you can use a small shunt like 50A 60mv to test this

thanks for your work.

red0909 avatar Jul 23 '22 19:07 red0909

The INA228 chip has a scale of ±40.96 mV

If you are using a 200amp shunt (60mA), and driving 200A through it, it will be inaccurate, as the ADC will be saturated.

stuartpittaway avatar Jul 24 '22 07:07 stuartpittaway

does it mean -40 to 40mV or -20 to 20mV scale? i thought the first.

red0909 avatar Jul 24 '22 08:07 red0909

Yes the first.

stuartpittaway avatar Jul 24 '22 15:07 stuartpittaway

but the -40 to 40 does not work, maybe a hardware problem on my shunt pcb? have you tested this range?

red0909 avatar Jul 24 '22 21:07 red0909

How are you reading the mV value? Is this the value shown in the web page?

What cells and current/voltage is the battery?

stuartpittaway avatar Jul 25 '22 06:07 stuartpittaway

i am reading it with a precise voltage meter. the readings correspond with the web page readings, if i stay in the range of 20 to -30 mV i have 16s lifepo. at the moment limited to 100A charge and 65A discharge, i am waiting for a new shunt to be able to get 300A readings in future. so if you can, please test this range in your shunt you can use a smaller one if you dont have the load for test.

red0909 avatar Jul 25 '22 06:07 red0909

Hi @red0909, did you resolve this issue in the end?

Its probably worth updating the code on the current shunt as the SoC calculations have changed, along with the amp-hour counters.

I don't have a 60mV shunt to test what you are seeing in the previous tests.

stuartpittaway avatar Jan 25 '23 09:01 stuartpittaway

i have solved this issue with a bigger shunt 500a 50mv so that i stay in this -30/20mv range. but i can test this new code with the 200a shunt again, i will let you know.

red0909 avatar Jan 25 '23 11:01 red0909