Project circuit current consumption calculation

Question

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?

Answer 1

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