JVL MIS17 Series User Manual page 126

5.8 Absolute Multi-turn Encoder
5.8.6 Position retention time
A special high temperature "Poly-carbon mono fluoride" lithium cell is used as backup for
the absolute multi-turn encoder. Compared to standard cells this one has extremely
good performance at high temperatures up to 125 degrees Celsius.
Normal lithium cells self-discharge very rapidly just being exposed to a temperature of
60 degree celsius.
The retention time of the position when the motor is not supplied is better than 10
years. This depends of how long time the motor is in use and the temperature.
The self-discharge at 85 degrees celsius (185 degrees Fahrenheit) is 6% per year, and
2% per year at 40 degrees celsius (104 degrees Fahrenheit).
Concerning the retention time, there is no big difference if the motor is in use at a high
temperature or it is powered down (low temperature).
The absolute multi-turn encoder's current consumption from the battery when the mo-
tor is not externally powered, is max. 1.5μA.
The curves below shows what is considered as a worst case scenario for the retention
time. The curves are based on 40 and 85 degree celsius (108/185F) without any exter-
nal power applied to the motor meaning that the internal battery have to supply cur-
rent to the encoder circuitry all the time. The current consumption of the encoder
circuitry is not dominant compared to the internal leakage current in the battery.
Hints to optimise the battery lifetime:
1. Avoid to place the motor in an environment with high temperatures.
2. Set the running and especially the standby motor current as low as possible in order
not to heat up the motor unnecessarily.
3. Keep the external power applied as much as possible.
4. Connect an external battery to the terminal "EXTBACKUP" at CN4 (17 pin connector
pin 16) - see also: Connecting an external power source for the H3/H4 encoder, page
127
126 JVL Industri Elektronik A/S - User Manual - Integrated Stepper Motors MIS17x, 23x, 34x, 43x
Battery life time as function of temperature
Batt. level (%)
120
100
80
60
40
20
0
0 1 2 3 4 5
Battery level when temp. = 40deg.(108F)
Battery level when temp. = 85deg.(185F)
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Only MISxxx---H3/H4--
Batt. Le
Batt. Le
Years