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Old 04-18-2014, 05:00 PM   #46
_cy_
Beastly Adventurer
 
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 5,439
Quote:
Originally Posted by Warin View Post
Batteries = Chemistry + physics

A cell will have a given voltage no matter what the weight... simple chemistry provides the voltage.

A cells weight will be proportional to the energy it can carry .. usually measured in Ah (Ampre hours). So weight ~ Ah.

Look at an AAA sized battery .. now a D sized battery same voltage (given the same chemistry eg Ni-MH) but different Ah.
+1 .. now let's apply above to Li-ion chemistries .. lithium cobalt and it's derivatives typically have a nominal voltage of 3.7v .. 4.2v fully charged. LiCo advantage is it's high energy density .. disadvantage is chemical stability or more accurately lack of and lower number of charge cycles. typically about 500 cycles.

LiFePO4 which also is correctly called li-ion, but completely different in terms of stability and life. LiFePO4 is inherently stable and survives wild overcharge abuse without going into thermal runaway. yes it's possible but I'm not aware of a single example of a motorcycle LiFePO4 going into thermal runaway. vs all sorts of examples abounds for LiCo exploding... E-cigs to Boeing 787 to cell phones to laptop batteries exploding.

let's talk energy density .. for smaller cells like 18650 .. LiCo has huge advantages vs LiFePO4. for example LiCo 18650 have been at 2.5AH @ 3.7v for 8+ years. VS latest A123 26650 are 2.5AH @ 3V

now let's switch to larger cells ... now LiFePO4 catches up in energy density with LiCo .. the energy density gap narrows close to parity. this is why mass battery storage folks are looking at LiFePO4 .. costs is higher but charge cycles goes up 2,000 to 4,000+ cycles for LiFePO4.

reason LiFePO4 is the future ...LiFePO4 voltages matches perfect with existing 12v and 24v charging systems designed for lead acid.
lithium cobalt cannot work with 12v charging systems on our motorcycles or cars or any other PB systems without complicated voltage management systems in place.
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