| Electronics > Beginners |
| How to measure average power use over time for small fluctuating circuit? |
| << < (3/8) > >> |
| maukka:
If you're not in a hurry you could take a battery with a known capacity in Wh and see how long it lasts and calculate from that. If operating voltage is a concern, take into account the efficiency of the regulator. |
| ziplock9000:
Yeah that would work, but I was hoping for something a bit more elegant. It's looking more and more like a new Arduino based project maybe based on TM7705 based Data Acquisition Module. But I'd have to read up more on it. 500sps might be good enough: https://www.instructables.com/id/Arduino-16-bit-500SPS-Dual-Channel-DAQ/ |
| mzzj:
One trick you can use for very low average currents is to use capacitor as a charge integrator. Measure voltage at the start and after 1 minute, calculate current from voltage drop and capacitance. (For best results measure the capacitance) If the capacitor size gets non-practical for higher currents or longer durations you can use Li-ion battery as a charge integrator. Li-ion coulombic efficiency(amh-hours in vs amp-hours out) is very high, for a good quality cell something in the range of 99% to 99,9% (you discharge 1Ah and charge 1.001Ah) Measure the current during charge and charge to exactly same voltage where battery was when you started the discharge and you can get better than 1% accuracy. |
| ogden:
--- Quote from: ziplock9000 on September 21, 2018, 09:02:50 am ---Yeah that would work, but I was hoping for something a bit more elegant. It's looking more and more like a new Arduino based project maybe based on TM7705 based Data Acquisition Module. But I'd have to read up more on it. 500sps might be good enough: https://www.instructables.com/id/Arduino-16-bit-500SPS-Dual-Channel-DAQ/ --- End quote --- You don't need ultrahigh sped sampling in case only thing you want to measure - average power. The trick is - additional bulk capacitor between current shunt and device under test, to smooth current spikes and be able to run lower sampling rate. |
| mikerj:
Another possibility I have used in the past is to power the circuit from a pre-charged capacitor and measure the total voltage drop over a fixed period. More suited to very low power circuits, so the wifi might discount this. |
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