This 1C test is the standard test that allows inter-comparison of cells
from brand to brand. You need some sort of a test under standard
conditions, for different size cells, for different voltage cells, etc.
You need some test that is uniform for all manufacturers. This is the
test everyone settled on.
It is kind of like the 20hr rate for lead-acid capacity and the Cold
Cranking Amps test. Everyone decided and those are the format they
picked for the tests.
Folks often do these standard tests for lower and higher C rates, if
that is any consolation. They also test at higher and lower
temperatures, sometimes.
Bill D.
On 4/17/2020 11:32 AM, Michael Ross via EV wrote:
As shown by the research at Dalhousie, 16000 cycles is meaningless if the
conditions are watered down.
That kind of cycle count is falsely impressive, and a huge waste of time
and resources.
Are there any useful testing standards becoming a tradition? As in
standards that actually stress the cells in some way other than cycle count?
Part of Tesla's success with cell life comes from actually breaking cells
and trying to make them better.
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On Thu, Apr 16, 2020 at 6:19 PM Bill Dube via EV <[email protected]> wrote:
The A123 systems 26650 cylindrical cells have a _huge_ cycle life.
Way over 5000 cycles at a 1C rate. 100% SOC discharge. (They have cycled
a 26650 cell more than 16,000 times and still have greater than 50%
capacity.)
The main trouble with higher rates is the elevated cell temperature
while testing. Higher rates => higher temperature => shorter life span.
The issue becomes entangled with calendar life. Calendar life is a steep
function of temperature. Exponential, actually.
Bill D.
On 4/17/2020 9:09 AM, Michael Ross via EV wrote:
Then you run up against an insignificant sample size. Can you get specs
and
trust them? When I was trying to sort this out in the 2014 time frame,
testing was ALL crap. You couldn't believe much of anything. Partly
because no one really know how to test well, and many did not want to
know.
The tradition was to run a lot of cycles at levels that caused no damage
at
all.
I sort of forget the original query, isn't this about A123? Prismatics?
Those are pouch cells. I have developed a cognitive bias against that
form.
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On Thu, Apr 16, 2020 at 4:59 PM paul dove <[email protected]> wrote:
Good point but you don't know how much faster it will degrade at 50
amps.
75% in 800, 500, 200 cycles, etc.
I would buy one and test it first.
On Thursday, April 16, 2020, 1:54:04 PM CDT, Michael Ross via EV <
[email protected]> wrote:
It is important to figure out what the #cycles means to you personally.
1000 cycles is a lot even daily - for some people.
On Thu, Apr 16, 2020 at 2:39 PM paul dove via EV <[email protected]>
wrote:
Cycle Life (retaining 70% capacity) at 20A Discharge, 100% DOD: >1,000
cycles
This tells me you don’t want to discharge at 50A if at 20A you are down
30% capacity in 1000 cycles.
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