If you get a lifepo4 48V15AH (720Wh) with ping:
http://www.pingbattery.com/servlet/Cart ... d=24782801
- Weight: 7.5kg
- 485$ battery + 119$ shipping (to uk)= 604$ total cost.
If you get 3s*2p (zippy 6S1P at 5AH) you have a pack of 44.4V15AH (666WH)
http://www.hobbyking.com/hobbyking/stor ... _20C_.html
- Weight: 6*0.844g= 5.06kg
- 296.88$ batteries + 85.15 shipping (to uk) = 382.03$ total cost the first 2 years.
- 382.03 * 2 = 764.06$ total cost the next 2 years. (And this total assume that the lipo price remains the same 2 years later)
Ok, at the end you would have lost around 150$. And you also have to pay for additional charger. But you have a weight advantage, you can swap your lipo when needed and after 2 years you have brand new batteries. Also, we should consider that the technology evolve and after 2 years we will probably have better performing batteries.
What do you think of this calculation? Do you expect to use your lifepo4 for more than 4 years? Don't forget that batteries loose its capacity over years naturally (shelf life), so most likely the battery is not going to have much capacity after several hundred of cycles + 4 years in the belt.
The LiFePO4 pack is 8% higher capacity than the LiPo that you are comparing, even though the ping was based on 48V nominal, and 3.2V * 16 or 51.2V is the apples to apples comparison, based on that, the ping has 768, and the LiPo would then have a 15% shortfall. On top of that, you would need to use the LiPo more conservatively WRT charge voltage and DOD so you'd want to use less than the available capacity, at least 10% and more likely 20%. The LiFePO4 already has an integrated BMS, that weighs a bit. Figure in 15% reduction in capacity to keep the lipo happy, a further 8% shorfall in the LiPo capacity, multiply that by the starting weight of 5.06kg and you now have a pack of 6.5kg compared to a 7.5kg ping which includes a BMS and can be charged from a simple charger, if calculated with 15% less capacity and 15% safety margin the LiPo equivalent is 6.8kg. Did I mention LiFePO4 is far less likely to burn your house down.
Now compare 1 of my offerings, apologies for the self promotion, just letting you and others know what is out there. A 12S 20Ah A123 pouch pack. Weight is 6.7kg all in, including BMS and some mechanical protection for the cells. Nominal voltage is stated as 39.6V, but lets call it 38V, it stays above that most of thime even with pretty high power, so lets say 760Whrs. Apply the same 15% reduction in capacity to the LiPO, to keep the cells happy and correct for the smaller capacity of the LiPo in your example and what do you have, the LiPo equivalent is 6.8kg, and that is without any BMS in the LiPo. Even if you use the full capacity of the LiPo, you have an equivalent weight of 5.8kg. A stack of 12 20Ah A123 cells is 5.95kg, if all I did was fit a power cables, a couple of balance plugs and shrink wrap, you'd have a pack of about 6.2kg as a guess.
The above pack will supply more current than most will ever need and a BMS upgrade for higher current is an option. Drop me a line if you are interested in prices, but they aren't bad at all. I really don't see how LiPo is head and shoulders above those figures, or any other cells for that matter when you figure in everything.