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#11
09-27-2010, 04:26 AM
 Crash Senior Member Join Date: Oct 2009 Location: Los Angeles, CA Posts: 122
Re: I need help to figure range before I buy LiFePO4

2 Parallel strings means that you'll double the amp-hour capacity of the batteries you're using while getting half the voltage of the sum of all the batteries:

46 / 2 = 23..

So your pack would be represented as 23s2p (23 batteries per series, 2 parallel strings)

The math is as follows:
Voltage: 72v (3.13V per cell)
Amp Hours: (2 parallel strings of 200AH batteries) = 400AH
Total Pack Watt Hours: 400 * 72 = 28800Wh.

Although, nominal voltage with the same pack would be:
Voltage: 85v (~3.7V per cell)
Amp Hours: (2 parallel strings of 200AH batteries) = 400AH
Total Pack Watt Hours: 400 * 85 = 34000Wh.

Driving distance would be figured out by your average w/mi.
Assuming that you're averaging 300w/mi with a max 80% DOD:
72V pack: 28800/300 = 96 | 96 * 0.80 = 76.8 miles
85V pack: 34000/300 = 113 | 113 * 0.80 = 90.4 miles

Some people have noticed that the Thunder Sky batteries have more capacity than Thunder Sky claims. 40AH batteries sometimes discharge 46AH for example. With 200AH Thunder Sky batteries, you'll probably get a bit more than 200AH and you'll likely exceed 100 miles before 80% DOD.
#12
09-27-2010, 06:54 AM
 JRP3 Senior Member Join Date: Mar 2008 Location: Central New York Posts: 7,591
Re: I need help to figure range before I buy LiFePO4

Quote:
 Originally Posted by Crash Although, nominal voltage with the same pack would be: Voltage: 85v (~3.7V per cell) Amp Hours: (2 parallel strings of 200AH batteries) = 400AH Total Pack Watt Hours: 400 * 85 = 34000Wh.
Not sure where you get nominal voltage of 3.7, nominal voltage is 3.2 for LiFePO4. As soon as you put a load on a fully charged cell it will drop to 3.3 or lower. Just as 12V is nominal for a lead acid battery which fully charged will sit at 12.75V until loaded.
#13
09-27-2010, 05:25 PM
 Crash Senior Member Join Date: Oct 2009 Location: Los Angeles, CA Posts: 122
Re: I need help to figure range before I buy LiFePO4

Thunder Sky cells say their nominal voltage is 3.7V. 4.25V max charge. Meaning, if you're charging that pack to 3.7V/cell (85V) you'll get more out of the pack. Am I incorrect?
#14
09-27-2010, 07:01 PM
 JRP3 Senior Member Join Date: Mar 2008 Location: Central New York Posts: 7,591
Re: I need help to figure range before I buy LiFePO4

TS has changed their max charge to 4.0. If you look at the discharge graph you'll see they operate under 3.3V for most of the discharge rates
http://www.thunder-sky.com/pdf/2010723131240.pdf
#15
09-27-2010, 08:06 PM
 Crash Senior Member Join Date: Oct 2009 Location: Los Angeles, CA Posts: 122
Re: I need help to figure range before I buy LiFePO4

Ah. Gotcha...

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 Tags amp hours, buy, calculation, lithium, range estimates

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