HUNTER’s power control system is designed to optimise battery life by adopting power consumption to the computer's level of activity. This means that power consumption varies according to the level and nature of use, making calculations of battery life slightly more complex than usual. However, if it is known how long HUNTER will be used in its different modes, it is possible to calculate with reasonable accuracy the expected life of a set of batteries.
Battery capacity is measured in mAH (milliamp hours) and by knowing the battery type in use, life may be calculated.
Battery capacity is affected by a number of factors including age, charging method, ambient temperature, However typically available from the two types of battery used by HUNTER is as follows:
Because capacity can vary significantly, the application planning should always assume reduced available capacity. There are no firm guidelines for this, but 50% of capacity is considered conservative.
A factor affecting apparent battery life is the 'end point , or voltage at which the battery is considered to be exhausted. Hunter sets this end point at 4.6 - 4.8 volts for battery warning.
This value yields virtually 100% of Nickel Cadmium batteries capacity and gives good results for Alkaline cells, but means that manufacturer’s specifications for capacity may some times be misleading.
HUNTER'S power consumption has three principal modes:
POWER SAVE 15mA
(awaiting keyboard or serial port entry)
OPERATING 90mA (208K)
(running a program for calculation, data storage, screen updating or any operation involving continuous execution of user program).
COMMUNICATING 125mA (208K) 115mA (80K)
(connected to a fully equipped RS232 port and operating)
As can be seen, the POWER SAVE state current is very low. Although the screen is on and the keyboard responsive to any key depression, this is the condition in which HUNTER is expected to be most of the time.
A typical application example might be a salesman using HUNTER for order entry purposes at a number of customer's premises and returning to base for communication.
The day is 7.5 hours long, during which he makes five calls. At each call he uses HUNTER for 40 minutes for stock checking and order entry purposes. The communication time takes 15 minutes, with a further 5 minutes left powered up.
Of the 40 minutes use at each call, only 5 minutes is considered 'operation' since most of the time HUNTER is waiting for keyboard entry.
Operating Power 80 x 5 / 60 = 6.67 mAH
Power Save Power 15 x 35 / 60 = 8.75 mAH
Total Visit Power = 15.4 mAH
Total Day's Power:
5 visits at 15.4mHA = 77 mAH
Communicating 115 x 15 / 60 = 28.75 mAH
Waiting after comms 40 x 5 / 60 = 3.33 mAH
Day Total = 109 mAH
Total Time in use through the day: 3 hours 40 minutes.
It would be expected that the HUNTER would last approximately 4 days (or 14 hours 40 minutes total) on a set of rechargeable cells. Alternatively, HUNTER would last 10 days (or 36 hours 40 minutes) on a set of manganse alkaline cells.
A chart of the current used by a HUNTER may be shown as follows: