CELL RATING SPEC - Kokam 1250mAh (15C)
1. The primary guideline for use of Li Po cells and packs is the discharge
curve below, based on test of a statistically valid sample of production cells.
All tests are at room temperature with no cooling to the cells so that all ratings
are conservative. Please read the section "How
to Use Li Po Batteries Effectively" of the Li
Po Handbook to learn
the effects of failure to operate Li Po batteries below 140 Degrees F. The C-rate
promoted by some vendors is meaningless without knowing the temperature reached
by the inner cells at those C rates.
2. There are four curves in the set that define cell rating:
- C-Rate 1 Capacity rating: Cell capacity is
set by international standard at a discharge rate of 0.5 times the specification
capacity of the cell. For example, 0.5C for a 2000 mAh cell is 1 amp. Capacity
for any cell of any chemistry will be reduced more or less as discharge rate
is increased. The rate of reduction of cell voltage is called "Voltage
- C-Rate 2: Maximum continuous rate. The discharge
current that the cell can deliver continuously without failing immediately.
Recommended only for applications where it is absolutely demanded. Cycle life
is not more than 50 cycles at this rate; about the same as for Ni Cd or Ni
MH at extreme high rates. This is the "advertised" C-Rate that is
also called "burst rate". WARNING: operation for even one run at
> 170 Deg F can shorten life to just a few cycles.
- C-Rate 3: Maximum Life rate, continuous. Maximum
average discharge rate for cell temperature to stay below 140 deg F at an
ambient temperature of 68 Deg F. This rate will produce no degradation in
life cycle as measured at 0.5C in statistical tests.
- C-Rate 4: Maximum Life rate, cyclic. Maximum
continuous discharge rate that maintains cell temperature at or below 140
Deg F. This is the rate the cell will be operated at most times. As a rule
of thumb, this may be estimated at 70% of C-Rate 2. The maximum "burst
rate" may be much higher than C-Rate 2 for very brief periods (less than
a second) so long as there are periods of discharge rate less than average
that allow the average to be held.
HIGH CELL TEMPERATURE BRINGS SHORT CYCLE
USE TEMPERATURE SENSORS TO KNOW : TMP-86/140-R