10.2 Ah LiPo Pack
- March 27th, 2011
- Posted in LiPo
- By punish3r
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This project came to me around 2006, when the presence of portable, high-capacity battery packs was limited in the U.S market. I thought it would be helpful to have the equivalent of a single-ended, low voltage lab supply in portable format. The design restrictions were price, weight and energy density. I wanted a relatively light, high capacity and inexpensive solution (don’t we all?…). Overall, this fit the bill, with just over 10 Amp-Hours of capacity, a weight of under 3 Lbs. and a price of $35 US.
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)
Single LiPo Cell (3.7V)
SparkFun LiPo Charger
PCM Board
3.7V to 12V Boost Converter
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.
Assembled Internals
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.
Great project. ~37 watt hours for less than a buck a watt hour in an enclosure is nothing to laugh at. Already having the enclosure you could add a few more batteries and bring the cost per watt hour down further. Key in this is the deal you got on batteries. 3.776. Watt hours for 99 cents is a fantastic deal.
what was the voltage output from the li-po bats before the 12 volt boost?
All twelve cells were placed in parallel, so the output voltage was the same as for a single cell: somewhere in the neighborhood of 3.7V, which was why I so desperately needed the boost converter.
not much need for <3.7V in most of my projects, however that may change soon with the proliferation of 3.3V chips and such in the hobby market.
Hi !
Where did you find those lipo’s for 99 cents ????
Yeah I know, heck of a deal, right?
Electronic Goldmine had a sale on them back in 2006, marked down from something ridiculous like $3.99 each to $0.99. Easily the best deal I have ever been in on; still have a dozen or so in their original baggies just waiting for the right project…
I think there is still a lot of value in your project. LiPo’s are not very inherently safe, and you need protection when using them. At the minimum… your fire retardant enclosure and voltage cut-off circuit would be necessary. And if you are doing all of that you might as well throw the charger in there as well!
True enough, however that fire retardant enclosure could easily hold five times as many batteries as it currently does; from an engineering perspective it’s a bit of a waste.
(Reminds me of the old joke about the glass half full vs. the glass half empty: The engineer says it doesn’t matter. The glass is inefficient because it’s twice as big as it needs to be…)
Second to that, I am sure there is some Hong Kong retailer who shall remain nameless selling a pack with the same capacity (or more) in a package the size of (or smaller than) a paperback book.