Battery calculations

A project log for Open SolarMote

A perpetually running wireless sensor mote.

dhqdhq 05/16/2017 at 00:293 Comments

The idea behind Open Solar mote is to use it as a greenhouse monitoring node. A LIPO battery was used. Now LIPO's require constant current for fast charging. This means that the battery can only get recharged when the solar panel is exposed to sun.

Some calculations follow:

•Imax = 100.38 mA (Approximate current draw by the system, worst case) •System wakes 60 times an hour •127.5 mAh battery capacity (accounting for leakage)

Daily Consumption=

24((〖Active Cycle〗_( per hour)×100.38 mA)+(〖Sleep Cycle〗_( per hour)×455 nA))=0.8131 mA/Day

Life expectancy=(127.5 mAh)/(Daily Consumption)=157 days

This is without recharging.


dhq wrote 05/16/2017 at 23:58 point

Those aren't units. I have updated the  calculations. I used a LIPO battery calculator online and I get the same results.

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K.C. Lee wrote 05/17/2017 at 01:03 point

Should be current consumption in [mA]
Life expectancy has unit of [mAH] / [mA] = time unit because mA cancelled out.

Edit: in your case it should have been mAH / day
so life expectance have the rest of the units cancelled out except for [1/ per day] which gets to [days].

What you have numerically okay, but is nonsense for anyone that understand Dimensional analysis.

Your calculation has units of: mAH / mA/Day = Day * Hr which is gibbish

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K.C. Lee wrote 05/16/2017 at 02:41 point

You units looks funny.

[(Active Cycle〗_( per hour)  i.e. t * 1/t This should be unit less because cycles is a unit of time.  
Daily consumption should therefore be average current as the unit is in mA.

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