30
higher capacity cells (of the same capacity/C rating) will typically have lower IR than lower capacity
cells.
A 3S 11.1V 2250mAh 45C battery will have lower IR than a lighter weight 3S 11.1V 2250mAh 25C
battery. General speaking, if properly rated, the 25C cells will have higher IR, hence the reason they
are only able to handle 25C versus 45C continuous discharge rates.
Some additional notes, hints and tips:
Regardless of the C rating, in most cases if the IR of one 2250mAh cell/battery is lower than that of
another 2250mAh cell/battery it will be capable of higher charge and discharge rates. However, in
some circumstances, due to the typical IR measurement method of most industry equipment, it is not
possible to account for all actual variables. For example, if a 2250mAh cell has slightly higher IR than
another 2250mAh cell when checked on the TP820CD, it is possible that under a higher load than the
TP820CD places on the cell, and with the associated heating in the actual application, the IR of the
cell actually changes to become lower than the other cell when used in the same application. This
can come as a result of differences in chemistry, materials, actual internal cell construction and/or
battery construction. As a result, while measuring the IR with a unit such as the TP820CD can
provide a good baseline reference you should still take the time to test the batteries side by side in the
same application in case the other variables affect the actual performance accordingly.
And unfortunately it is not really possible to create a chart that shows what a good IR value versus a
bad IR value may be for a given capacity, C rating, make/model of cell/battery. Because even if a
cell/battery has twice the IR of another cell/battery of the same make/model, as long as it continues to
perform adequately in your actual application it is still very usable. That said, in many cases if the IR
of a given cell/battery increases by 50+% from when new it will typically offer noticeably less
performance. However, especially in lower discharge rate applications (such as slow flyer, trainer and
‘cruiser’ airplanes), an increase in IR can have little to no noticeable impact in performance for quite
some time. This in mind, you should continue using batteries regardless of the IR if they continue to
perform well enough in your given application.
Also, the various equipment in the industry that offers IR measurement will measure and deliver
values based on their own methods/standards. As a result it is not practical to compare the IR
measurements for even the same make/model of battery on different makes/model of equipment.
And due to variations the calibration of actual units, ambient conditions, etc. is it not typically practical
to compare the measurements for the same make/model of battery even on the same make/model of
equipment or even between the two ports of a dual port charger. Instead it is best to make all
measurements and to compare the relative results from a single port/the same unit whenever
possible.
To Measure Battery Internal Resistance
While on the Battery.IR screen/menu in the Data View Mode, simply connect the battery to the main
power/charge lead. Then, press the ENTER button once and after a relatively quick check the
charger will display the approximate IR of the battery. Again, this value is not absolute and will vary
per the variables previously noted, however, it is still a valuable reference. Also, if you continue to
press the ENTER button over and over do not be alarmed if the value changes. This in mind you
should allow the battery to sit/stabilize for at least a 10-20 seconds before making more than a single
check of the IR. And in the event that the charger ever seems to ‘stick’ during the IR measurement
process without giving the IR measurement after ~60 seconds, please disconnect the battery (and
any other battery connected to the other port) and power the charger down immediately.
To Next Page
Loading...