T fly004's Page on Packs
Yes, I've built a "few" Liion packs :)
So, there has been a lot of bad info on Liion pushed out by lesser vendors so be careful what you purchase.
Here are a few points you sould know (sorry if this is not new)
Lipo battery pack advantages
They can be found cheap
They will survive huge C ratings
Higher quality packs have large charge cycle numbers
Lipo disadvantages
They are often made cheaply
Their C ratings are generally determined by marketing, not real testing
Higher quality packs can get very expensive
Their USABLE power density is about 25% lower than Liion
Liion pack advantages
Higher power densities are available
You can customise the pack shape and fit them almost anywhere
Higher quality cells have large charge cycle numbers
Liion disadvantages
You mostly have to build your own
They have large voltage drop under load compared to Lipo
They can't be charged as fast as Lipo
So, to get any advantage over a good quality Lipo pack you need to beet the power density numbers Lipo's can deliver. This is looked at in terms of Watt Hours per Kilogram or how much power they will deliver by weight. A good quality lipo can deliver up to 175Wh/kg. To get this number, mutiply the pack size in Amp Hours x the pack nominal voltage so for a 5200/4S Multistar this would be 5.2Ah X 14.8v = 76.96Wh. Now divide this by the pack weight which in this case is 430g or .43Kg = 178.9Wh/kg.
OK, now lets look at Liion. One of the best and most popular cells out there is the Sanyo/Panasonic NCR18650GA cell. If we look at a 4S1P pack of these cells the power density comes out to 3.45Ah x 14.2v / .212kg = 234Wh/kg - MUCH better.
-but wait, there are caveats-
Liion has the same end voltage as Lipo, around 3.1v becaise the voltage depression under laod is higher.
The GA cell has a maximum continuous current of 10A and really it is closer to 5A when you package the pack inside a foam fuselage. This means you need at least a 2P pack to fly a Mini Talon. There are higher current cells out there but they do not have the Power density of the GA (and similar) cells so they do not provide an advantage over Lipo.
Cells
ALWAYS buy cells which are "unprotected" made by Sanyo, Panasonic, LG and Samsung. There are other high quality brands but they can be inconsistant are are more often cloned by cheap manufacturers.
If you do decide to try an off brand cell, make sure you get the manufacturers data sheet and find some testing that shows whether the cell is any good. Don't just "take a chance".
Never pull cells out of laptop or power drill packs, these are very low power density cells that will not last in our applications.
Assembly
I weld all my packs with a spot welder I built (see below). You can also solder, just make sure you use a 40w soldering iron (not a gun). Make the joint super clean and use NoKorode solder paste and move quickly so you don't overheat the cell. The links below are a couple builds I posted of both soldered and welded packs.
OK, I'll shut up now...
Links
