|03-01-2012, 04:26 PM||#11|
Joined: Sep 2011
Location: Tulsa, Oklahoma
learning how to properly charge and learning cold start procedure for LiFePO4 greatly increases odds of success, using li-ion batteries in our motorcycles.
let's visit a commonly used term in batteries... "C" ... example, A123 has a recommended max charge rate of 4C. a discharge rate of 30C, etc.
so what exactly does "C" mean. actual amp hour rating = 1C ... one A123 26650 cell = 2.3 AH @ 3.6v fully charged. 4x A123 wired in series = 2.3 AH @ 14.4v fully charged. (AH=amp hour) (26650 = 26mm x 650mm)
4x A123 2.3 AH LiFePO4 battery pack is spec'd at 4C .. so max charge rate is 10amps.... but not so fast... folks in the RC world has been charging A123 packs at 10C 1,000+ cycles with no ill effects.
Shorai LFX21 AH (pb eq) or 7 AH actual is rated at 3C conservatively. Shorai's prismatic cells can easily take 5C with no sweat.
not telling you to purposely overcharge LiFePO4 cells... but these cells are very rugged and are able to withstand a huge amount of abuse. including operating in unbalanced condition.
where all this matters is due to relatively low AH ratings of LiFePO4 vs lead acid batteries. Peukerts law says as internal resistance goes down, losses from high amp discharges goes down accordingly. this heavily favors LiFePO4 vs lead acid batteries during starting discharge when experiencing 70-185amps.
at lower amps Peukerts losses are very close. in other words current draw by accessories like lights, heated gear, GPS, etc. discharge efficiency are close for both types of batteries.
alternator will be constantly recharging for both types of batteries. but LiFePO4 will be drawing larger amps loads for shorter durations. using test mule R80G/S .. current delivered to battery is 22.5amp with higher output regulator @ 3,000 rpm. at that rate battery will be charged back to 85% level within minutes. then battery will take on less amps to fully charged condition.
whew... sorry about drilling in ... but really helps to understand basic terms
SYCL 2.3AH on top of Shorai LFX21 AH(pb eq) for size comparison
Bringing BMW R90S back to life, R80G/S, LiFePO4 testing
Which is more reliable ... Points or Electronic Ignition for Airheads? for airhead charging issues scroll down to #898
_cy_ screwed with this post 03-24-2012 at 05:29 PM
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