How to get longest battery life
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@dbemowsk you won't get nearly as the half of that with those cheap cells. I've seen some on Aliexpress boasting 9600mAh and in the end user comments pointed to capacity around 1000mAh...
I can buy some cheap ones in local electronic market here in Vietnam, the cheapest are 1.5$ and only 1200mAh. If you want genuine 3400mAh it's around 8$...
I would buy from Aliexpress with good seller and lot of comments so you can have some feedback on the real capacity of the batteries. -
Let's put this in perspective: according to Wikipedia ( https://en.wikipedia.org/wiki/D_battery), an Energizer Alkaline D-cell battery has 20,000mah at a 25ma draw, which is obviously far higher than the average current draw of the modified PIR. Also in the D-cell's favor is that it has comparatively low self discharge as well as little risk of spontaneously bursting into flames....
So, you'd definitely get at least 2 years, and probably 3+ years from a pair of D-cells. Maybe a lot more years than that even. Good enough? Those are just some lower bound numbers, but even so, that sounds like a winner to me. :smile: By all means, though, use a sharper pencil and see what you figure it at. Of course, it will be a larger physical package than if you were running from a coin cell, but for the low cost, simplicity of construction, and long battery life, it seems like a worthwhile trade-off to me. :grinning:
Wow. I really didn't expect anything worthwhile to come from this thread, but now I'm glad I stuck with it. :smiley:
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Let's put this in perspective: according to Wikipedia ( https://en.wikipedia.org/wiki/D_battery), an Energizer Alkaline D-cell battery has 20,000mah at a 25ma draw, which is obviously far higher than the average current draw of the modified PIR. Also in the D-cell's favor is that it has comparatively low self discharge as well as little risk of spontaneously bursting into flames....
So, you'd definitely get at least 2 years, and probably 3+ years from a pair of D-cells. Maybe a lot more years than that even. Good enough? Those are just some lower bound numbers, but even so, that sounds like a winner to me. :smile: By all means, though, use a sharper pencil and see what you figure it at. Of course, it will be a larger physical package than if you were running from a coin cell, but for the low cost, simplicity of construction, and long battery life, it seems like a worthwhile trade-off to me. :grinning:
Wow. I really didn't expect anything worthwhile to come from this thread, but now I'm glad I stuck with it. :smiley:
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Looking at the costco price for D-cell batteries (http://www.costco.com/Duracell-D-Alkaline-Batteries-14-Unit%2C-2%2B-Pack-Pricing.product.100322549.html), two D-cells would cost just over $1 plus tax.
So, rough BOM:
$1 for batteries
$1 for PIR
$1(?) for battery holder
$4 for atmega328p+RFM69HW mote (maybe $2 for an nrf24L01 mote)Total: around $6 to $8
At that price you could afford lots of them, which would also offer a way to correct for possible false positives.
