T fly004's Page on Packs
Yes, I've built a "few" Liion packs :)
In this, I've learned 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. Never buy any cell with less than 3000mAh capacity as you won't get the power density under load required to get an advantage over Lipo packs. Here are some of the better cells-
- Sanyo/Panasonic NCR18650GA (10A)
- Samsung 35E 18650 (8A)
- Samsung 36G 18650 3600mAh (10A)
- LG MJ1 18650 3500mah (10A)
For vendors Iuse these-
- IMRBatteries.com
- Liionwholesale.com
- mtnelectronics.com
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".
For testing, these guys in Germany do an excellent job of cell reviews-
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
