It is known that a Li-pol battery performance depends strongly on the temperature. However, the hard data are scarce – so here is my contribution.
The following data were obtained using the following equipment:
- motor Phasor 15-4, propeller Ae 10×6 (40 mm yoke), ESC MGM Expert 33A
- accu 2S 2200 Hyperion LVX 23C, charged to 4.1V/cell at 10 °C
- temperature measured by a „inaccurate“ aquarium thermometer, voltage, current and power by a wattmeter, time by a transmitter timer
- the temperatures are approximate: about 10 °C were in a basement of our house; about 0 °C were in snow outside (measured in March 2010) – battery left in the snow for about an hour and then wrapped in insulation cloth for measuring at about 10 °C, the battery remained in the wrapping during the measurement; 30 °C obtained similarly – a radiator used instead of snow
- values recorded using a camera
All values as shown on the wattmeter device.
On the following diagrams:
– blue line corresponds to 0 °C
– red line corresponds to 10 °C
– green line corresponds to 30 °C
– on the horizontal co-ordinate is a time in seconds
Voltage in volts
Current in amperes
Power in watts
It is obvious that the battery temperature is of absolute importance. Please note the power increase after the cold battery has been warmed and internal resistance reduced.
The battery can be characterised by its internal resistance. This resistance should depend on the temperature as predicted by a Bolzmann law in the form of R=C1*exp(C2/T). The internal resistances at individual temperatures are calculated from the voltage drops at about 6-7 seconds into the run. Suprisingly, the expected curve fits perfectly. For this particular case the internal resistance can be approximated by the function of
resistance = 1.1e-6*exp(3131/(273+temperature)) [ohm;centigrade]
(values below 0 °C and over 30 °C are extrapolated)
Please note, that the internal resistance roughly doubles with every 20 °C temperature drop.
Keep you batteries warm!
24.7.2010 (in Czech published on 6.3.2010)