# [EVDL] How many LifePo4 for 72 Volt system?



## EVDL List (Jul 27, 2007)

we have been using these cells for some time now, I like them !
we use 4 cells to make up a 12 volt battery, 24 for a 72 volt pack.I
have not seen any 200 ah ones yet, we just double up the 100ah ones .
Brian Hall
thunderstruck motors


Looking at China HiPower 200ah blocks - LifePo4 HP?P200Ah

They are rated at 3.2 Volts and when I divide 72 volts I get 22.5.
Should I get 23 or should I get 24 and consider them 3 Volts instead?

Also the max discharge of these is 600ah or c3 for longer life?

http://www.chinahipower.com.cn/ http://www.chinahipower.com.cn/

http://www.nabble.com/file/p19583384/1-1.jpg

http://www.nabble.com/file/p19583384/1-2.jpg

http://www.nabble.com/file/p19583384/1-3.jpg


-- 
Brian D. HAll
Thunderstruck-ev.com
3200 Dutton Ave #319
Santa Rosa, Ca 95407
707-575-0353 voice
707-544-5304 fax

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## EVDL List (Jul 27, 2007)

Thank you Brian Im interested in the 200ah for safer higher discharges
as Im going Direct Drive and it would be nice to have that ability.
I didnt think paralleling 100ah ones would give 600ah safely no?




> Brian D. Hall wrote:
> >
> > we have been using these cells for some time now, I like them !
> > we use 4 cells to make up a 12 volt battery, 24 for a 72 volt pack.I
> ...


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## EVDL List (Jul 27, 2007)

A couple of points:
Going direct drive doesn't increase the battery side amps, unless you are
also increasing total mechanical power in going to direct drive.
Even with a contactor controller, the current drawn shouldn't be
particularly high, if it is properly designed.

Parralleling 2x 100AH will give 200AH, and roughly twice the output current.
In the case of these cheap cells, the limitation on current output is
internal resistance, rather than a finite max current output.
As long as you are parralleling at the cell level, electrically the two
cells will look like a single cell.

There are other ramifications to such a setup.
The approach to safety usually used with these cheap large format cells is
to suspend the cell in a phase change material, that has very limited oxygen
solubility, and encased in a high temperaure rated plastic.
There is usually enough phase change material in a cell to prevent a shorted
cell from breaching the cell and destroying nearby cells (or at least
stopping them from catching fire etc.)
If you parrallel two cells, there wont be enough phase change material in
one cell to absorb all the energy from both cells in the case of a short.

Instantaneous current draw is measured in A, not AH (perhaps here I am being
a bit pedantic here, it could have been a typo ). 
So you would mean 600A (3C) current draw.

Matt 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of AMPrentice
Sent: Sunday, 21 September 2008 6:34 PM
To: [email protected]
Subject: Re: [EVDL] How many LifePo4 for 72 Volt system?


Thank you Brian Im interested in the 200ah for safer higher discharges as Im
going Direct Drive and it would be nice to have that ability.
I didnt think paralleling 100ah ones would give 600ah safely no?




> Brian D. Hall wrote:
> >
> > we have been using these cells for some time now, I like them !
> > we use 4 cells to make up a 12 volt battery, 24 for a 72 volt pack.I
> ...


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