Folks talk about C-rate, but what you really care about is specific
power. That is the maximum number of watts that a cell will put out,
divided by it's weight. Power to weight is what it is all about. (A
capacitor has phenomenal C rate, but only a _tiny_ capacity. What good
does that do you at the end of the 1/4 mile?) A good quality car battery
will put out 300 w/kg, just to give you a sense of scale for the number.
The high power and high capacity version of the A123 Systems cordless
tool cells, 26650 M1 -B, can easily put out 50C. (Not to be confused
with the factory seconds or "B" cells.) When warmed to the optimal
temperature, they will put out over 70C. This is ~180+ amps from a 2.5
a-hr cell. About 4500 w/kg.
If you need a lot of energy, then cordless tool cells are a bit small,
so their hybrid pouch cells are more like it. Their hybrid pouch cells
will put out 32 C (450 A from a 14 a-hr cell) continuously. This is what
is in our land speed vehicle. About 2700 w/kg.
Their 20 a-hr "energy" pouch cell, which has smaller tabs and internal
interconnects, will only put out about ~15C continuously. Larger under
short duration loads. Basically, the tabs overheat and limit the
current. These were originally built for the Volt.
The A123 Systems F1 cells are absolutely the king as far as specific
power. No one makes anything even close. Their F1 18700 1.5 a-hr cell
will put out an unbelievable 500 amps (continuous!) Over 20,000 w/kg.
Over 300C. There newest cells for Formula 1 put out much higher numbers,
but they won't even tell me the exact numbers.
The high capacity high power cordless tool cells cost about $8 each, and
you have to weld a _lot_ of tabs together to build a drag racing pack.
The upside is, these cells will last forever if properly cared for. Well
over 15,000 cycles. The pouch cells will last awhile as well. I think
their spec sheet says greater than 5000 cycles.
The pouch cells cost about $700 per kw-hr, (in quantity) and they are
already built into a pack.
The F1 cells cost so much that if you have to ask, you simply can't
afford them. They are insanely expensive.
Bill D.
On 1/15/2016 9:42 PM, Cor van de Water via EV wrote:
People who build racing packs, such as Lightning Motorcycle,
use brands not really available to "hobbyists/converters"
such as Enerdel.
Enerdel expects that their cells (in pairs, each on one side) are
sitting against a metal sheet that is heatsink for the cells, this is
brought out to the side and can be pressed against a surface that
conducts the heat away.
I asked Derek Barger from High Tech Systems and he did not want to
reveal
which pouch cells he is using and I did not want to press him, I was
happy enough that he would entertain me on my visit to his place and
discuss EVs and battery packs in general and his racing designs
specifically. He noted that he could reach extreme high power and energy
density because he did not need to contain the pouches, they never
swelled and never got hot, he only needed to stabilize them against the
vibration and G forces of racing.
He did include a BMS with his packs though.
Then there is the famous A123 20Ah pouch cell that sustains 20C, in
other words that small cell can dish out 400A and almost melt its own
tabs off.
I do believe that it needed containment (pressure from the side) to
avoid swelling up.
Just some more datapoints.
Cor van de Water
Chief Scientist
Proxim Wireless
office +1 408 383 7626 Skype: cor_van_de_water
XoIP +31 87 784 1130 private: cvandewater.info
http://www.proxim.com
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-----Original Message-----
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of via EV
Sent: Friday, January 15, 2016 8:21 PM
To: Paul Dove
Cc: Electric Vehicle Discussion List
Subject: Re: [EVDL] Leaf donor car? Re: Books on converting a car to ev?
Thanks Paul. I had seen those C references on this list in the past but
had no clue what the significance was.
On Jan 15, 2016, at 10:08 PM, Paul Dove <dov...@bellsouth.net> wrote:
I can try to explain the significance.
I believe he uses Kokam LiPo cells. The have a very high energy
density. They can operate continuously at 10 C but will cause heating
and capacity loss... C being the capacity of the cell so a 2Ah cell can
put out 20 amps continuous and up to 8 C without significant heating
(around 50 degrees Celsius).
The KOK 340 HSC can be operated at 20 C. The effect is that the user
can tailor a pack to do what is needed without excessive size, weight,
capacity and cost.
John has a very small powerful pack but without having a high capacity
since he's drag racing.
Sent from my iPad
On Jan 15, 2016, at 8:19 PM, jackinausti...@gmail.com wrote:
Paul replied:
John metric uses lithium polymer batteries like the ones used in
quad copters.
Can you enlighten the ignorant on the significance of that? It
doesn't mean anything hing to me.
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