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Old 01-20-2012, 08:56 PM   #4
_cy_ OP
Beastly Adventurer
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 6,437
Originally Posted by nulluser View Post
I am looking forward to what you come up with, specifically in regards to Peukert and temperature effects.

AGM batteries were chosen for my electric bike because of price considerations. I picked up the batteries for around $20 each and decided to design a bike around them:

The plan is to experiment with the Thunder Sky lithium iron yttrium phosphate batteries in a Geo Tracker next summer.
hmmmm ... was not planning on getting Peukert law, but was going to experiment with effects of temperature on lithium iron phosphate battery once I get them in. it's well known li-ion cells can drop dramatically under cold temps. the same with AGM which could loose about 45% of rated capacity at 4f degrees.

what Peukert law basically states is high amp draws will use up more capacity than slower amp draws. efficiency loss could be 15% to %40+ vs lower current drain rates will achieve close to full rated capacity.

which leads us up the some of the mumbo jumbo used by some folks trying to sell these new li-ion batteries. we get to hear about effective amp hour rates. vs actual AH rates. marketing strikes.... 6 AH becomes 18AH for an effective increase of 3x.

let's cover one important aspect of li-ion cells... which is it's ability to discharge at an extremely high rate. this is why CCA (cold crank amps) rating for li-ion batteries means very little. Li-ion cells will deliver full power, then fall flat. little to no warning battery is running low.

different li-ion chemistry deliver different voltages and capacities. some are more stable then others. lithium iron phosphate is the most stable of all the li-ion chemistry so far. li-ion cells is a dynamic field with improvements being discovered constantly.

for instance...Aleees claims new double-layer nano-carbon coating technology enhances battery cycle life 2.7 times ... if this claim pans out... implications could be HUGE for electric auto mfg.

_cy_ screwed with this post 02-02-2012 at 01:34 PM
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