The BOM was as follows:
- Flame Retardant, IP65 rated enclosure (8.75×5.75×2.25 inches) ($6.00 US)
- Twelve (12) LiPo batteries at 850mA capacity (Super steal at $0.99 each) ($11.88)
- SparkFun Lipo Charger Board ($3.95)
- LiPo PCM board from Battery Junction ($3)
- 12V Boost Converter (I don’t remember where this came from, but I do remember that – at the time – it was a pain to find and I had to order it as an engineering sample.)
- Barrier Strip ($1)
- Connectors ($1, Estimated)
- Lighted toggle ($2)
- Panel Jack ($1)
- Panel LED (Charge indicator) ($0.50)
- Wire ($1, Estimated)
Total Cost: $31.33 (without shipping)
Not shown in the system diagram is the charge indicator, which connected to the LiPo Charger board and can be seen in the completed image above towards the top right corner of the enclosure.
The modular nature of this system made for a very simple assembly, yielding a complete project in short order.
Note the small fan attached to the completed system, above the enclosure. As a test, I hooked up this fan and timed its run before the batteries gave out.
I can’t be sure of the exact time, as after 30 hours I got sick of paying attention to it and the buffer on my voltage monitoring program overloaded. Suffice it to say that 10 Amp-Hours is a significant quantity of charge when dealing with consumer level electronics.
This is all moot at this point however, as inexpensive, portable battery packs of varying voltage are readily available on the market for less than this particular project cost me.