4230 Flow Meter
Section 1 Introduction
1-9
1.7 How to Make Battery
Calculations
To calculate battery life expectancy for an installation, you must
know two things:
• The capacity of the battery you are using
• The average current draw of the flow meter or (other
device) powered
Battery capacity is expressed in ampere-hours. The battery man-
ufacturer provides this information for each battery. This value is
the product of a load current times an arbitrary time period, ten
hours for nickel-cadmium batteries, and twenty hours for
lead-acid types. The terminal voltage of the battery at the end of
this time period is the discharged cell voltage, 10 volts for
nickel-cadmium and 10.5 volts for lead-acid types. Batteries are
considered fully discharged well before the terminal voltage
drops to zero volts.
Isco batteries are rated at 4 ampere-hours for the
nickel-cadmium and 6.5 ampere-hours for lead-acid types.
Convert the battery current capacity into milliamperes and then
divide this figure by the average current drawn by the unit. This
will give you a number in hours. Divide that figure by 24, and
you will have the number of days.
Note that the published ampere-hour figures do not mean that
you can expect to draw 4 amperes from the nickel-cadmium
battery (or 6.5 amperes from the lead-acid battery) for one hour.
At the one-hour rate, discharges are typically less than half the
ten- or twenty-hour rate.
To convert ampere-hours to milliamperes, multiply by 1,000.
Examples:
4 ampere-hours × 1,000 = 4,000 mAh
6.5 ampere-hours × 1,000 = 6,500 mAh
Notes
1. These figures are approximations based on calculations; actual
times for your flow meter may deviate due to factors of battery
age, charge condition, operating temperatures, and component
variations. “Minimum” settings are those providing the lowest
average current draw. “Maximum” settings are those requiring
the highest current draw. Your program should draw somewhere
between the two.
2. The default settings are the program entered at the factory. You
can reset the flow meter to the default program at any time by
pressing the 1 and CLEAR ENTRY keys at the same time.
3. This battery has a capacity of 4.0 ampere-hours at room tempera-
ture (20° C).
4. This battery has a capacity of 6.5 ampere-hours at room tempera-
ture (20° C). (Both batteries are assumed to be fully-charged with
at least 95% of rated capacity and in good condition. These calcu-
lations also assume a 5% safety factor at the end of discharge.
Lead-acid batteries should never be completely discharged.)
5. All fractional times are rounded down, rather than up.
Table 1-5 Battery Life Expectancy (Continued)
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