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I'd like to calculate how much my project circuit is drawing for estimating the duration of my battery. My circuit consists of a near-real time sensor which is measuring and sensing some data over WiFi. My project is alternating 1 minute of deep sleep with 3 seconds of active time during working hours (~8 hours a day), and for the rest of the day could be deep sleeping, or just off.

Let's take the case where it is operating ~8h a day, then it is off:

  • 1 minute deep sleep - current consumption: 1,18 mA
  • 3 seconds active - current consumption: 55,0 mA
  • 1100 mAh battery

So I've estimated the duration of my battery like this

  • passive consumption in 1h = (60 minutes / 1 minute) * ((1 minute*60 seconds)/3600 seconds) * 1,18 mA
  • active consumption in 1h = 60 * (3 seconds/3600 seconds) * 55,0 mA
  • battery duration (h) = 1100 mAh / (passive + active consumption)
  1. Is my calculation right?

  2. If I would also consider the case of a continuous operating case, so adding those 14h of pure deep sleep, how could I do that? Would I just need to add to the passive consumption already calculated the passive consumption in 14 hours?

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  • \$\begingroup\$ Your equations are not clear. What is the factor (60 minutes/1 minute) in the first equation, and what does the value 60 represent in the second equation? You should make sure that your units cancel properly What is the minimum voltage required by your system, and is your battery capacity given at that voltage? Adding a link to battery datasheet would help. \$\endgroup\$ Mar 8, 2021 at 17:59
  • \$\begingroup\$ The factor (60 minutes / 1 minutes) represents the amount of active events in an hour. I actually used the same factor in the second equation, which i think it might be wrong. About the battery, here it is the datasheet tme.eu/Document/89b65ec6de44062e426f7190968d7279/cel0066.pdf Thank you very much for your answer. \$\endgroup\$
    – Nic Hub
    Mar 8, 2021 at 22:23

1 Answer 1

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I think you are making your calculations more difficult than they need to be.

The average power consumption contributions are:

  • deepsleep, for 57 out of every 60 seconds: 1.18 mA * 57 / 60 = 1.121 mA
  • active, for 3 out of every 60 seconds: 55 mA * 3 / 60 = 2.75 mA

average = 3.871 mA

So for over the deeplseep + active period, your battery would last 1100mAH / 3.871 mA = 284 hours.

If you want to calculate the 8 hour operational, 14 hour deepsleep into the calculation you could caculate the contributions as:

  • 8 hour out of 24 hour operation at 3.871 mA = 3.871 * 8 / 24 = 1.29 mA
  • 14 hour deepsleep of 24 hour : 1.121 * 14 / 24 = 0.6539 mA

average = 1.944 mA, battery lasts 1100 mAH / 1.944 mA = 565 hours

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  • \$\begingroup\$ Thank you very much for aswering and for taking your time to do these calculation. Yes you are right, I might have overcomplicated everything. About the deepsleep contribution, should I actually make it sleep for 57 seconds instead of 1 whole minute? I'm not quite understanding why I can calculate the whole functioning in a whole minute (active + passive) if I'm actually making it active for a minute and making it sleep for 3 seconds. Maybe my question is dumb, but I'm pretty tired right now. Sorry and thank you very much again. \$\endgroup\$
    – Nic Hub
    Mar 15, 2021 at 11:06

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