Hi guys,

I know some dont like Instructables but that's where I found this tutorial:

Im trying to work through it so I can understand it enough to apply it to my own project. I have some doubts as to the power charging and battery pack and consumption numbers.

STORAGE

In the tutorial he uses 2 pairs of 1300mah - 2.4V cells. 1300mah because 2 cells are wired in series and 2.4V because each cell is 1.2V. And he has 2 of these series so he ends up with a total storage of 2600mah and 2.4V battery pack.

He goes thru a calculation where he must charge at a current no greater than 1/10th his capacity. If each pair has 1300mah, he needs a current of 130ma. Not sure why he mistakenly talks about a "current" of 130ma"h" since that would be a capacity, not a current.

In this sense, I only have 3.7V, 380mah LiPo battery pack (1.4W) from a hubsan drone.

POWER GENERATION

The tutorial talks about a power source with 1.5x the voltage of the battery pack. Since it uses a 2.4V battery pack they choose a 3.6V panel. For me that would be 3.7V x 1.5 which is 5.55V or 6V.

Then it talks about needing to cover the current needs for the UNO as well as for charging the pack. They estimate 100mah for UNO and 100mah for charging the pack. This means their project requires 200ma of current from the panel. This because the pack cannot take more than 130ma of current.

POWER CONSUMPTION

Finally they talk about consumption. Using the LowPower library we can reduce total consumption by 32%.

According to this formula they calculate power consumption:

Iavg = (Ton*Ion + Tsleep*Isleep ) / (Ton +Tsleep)

where Ton is 250 ms & Ion is 16 mA

where Tsleep is 300 s & Isleep is 200 uA

Iavg comes to 0.205 mA which at 5V operating voltage comes to 1.025mW. They have a 3000mah pack which gives them 3.7V x 3000mah = 11,100 mWh. That comes to 11,100 mWh/1.025 mW = 10,818 hrs.

For me, assuming the same Iavg would be 3.7V x 380mah = 1,406 mWh / 1.025 mW = 1,371 hrs.

Does this look right?