| Electronics > Beginners |
| How to measure average power use over time for small fluctuating circuit? |
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| mtdoc:
--- Quote from: ogden on September 21, 2018, 10:42:28 am ---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. --- End quote --- Yes, excellent point. If the OP has a limited budget, that is really likely the only way he will be able to do what he wants. |
| ziplock9000:
--- Quote from: mzzj on September 21, 2018, 10:34:23 am ---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. --- End quote --- What size capacitor would you recommend? 90% of the time the device is using ~26-40mA, with spikes up to maybe 400mA. The power cycle repeats itself after 1 minute, but I'd like to get a few repetitions of this if possible to average out over several cycles. Thanks. |
| ogden:
--- Quote from: ziplock9000 on September 23, 2018, 03:39:14 pm ---What size capacitor would you recommend? 90% of the time the device is using ~26-40mA, with spikes up to maybe 400mA. --- End quote --- You shall specify "spike". Ambient temperature spike can last few days ;) |
| ziplock9000:
DSO screenshot in the OP. I'd need to take further measurements at a higher time base to get accurate figures, but it's in the order of ~1ms ;) |
| ogden:
--- Quote from: ziplock9000 on September 23, 2018, 04:34:34 pm ---DSO screenshot in the OP. I'd need to take further measurements at a higher time base to get accurate figures, but it's in the order of ~1ms ;) --- End quote --- It's easy then: Source: https://en.wikipedia.org/wiki/Capacitance |
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