Battery Ratings (Ampere-Hours) - Teledyne 913 Installation And Operation Manual

Power Products Guide
Section 2 Batteries
2.1.2 Battery Ratings
(Ampere-Hours)
2-2
The product you have purchased contains a rechargeable battery.
This battery is recyclable. Disposal of this battery at the end of its
useful life in the municipal waste stream may be illegal, depending
on the laws of your state or locality. Check with solid waste officials
in your area for information on recycling options or proper disposal.
Battery manufacturers rate the capacity of batteries in
ampere-hours, (availability of current over time). Typically,
manufacturers rate battery capacity at a certain current over a
specific period of time. The product of this value is the
ampere-hour rating of the battery.
Typical ratings for the discharge of nickel-cadmium batteries are
over 10 hours and for lead-acid batteries are over 20 hours. As
a result, a rating of 4 or 6.5 ampere-hours for a battery does not
mean you can draw 4 or 6.5 amperes from the battery for one
hour. The actual amount at the one-hour rate is typically
one-half the "rated" capacity of the battery, or less. To determine
the actual battery rating, you must take the nominal capacity
(4 or 6.5 ampere-hours) and divide it by 10 or 20, depending on
the battery type.
In the case of the Model 934 Nickel-Cadmium Battery, you use a
figure of 0.4, and for the Model 946 Lead-Acid Battery you will
use 0.325. Customarily, currents below 1.0 ampere are expressed
in milliamperes (mA). This means you can expect to discharge
the nickel-cadmium battery at 400 mA for 10 hours. You would
expect to discharge the lead-acid battery at 325 mA for 20 hours.
Battery manufacturers provide curves in their literature
showing the discharge rates in percentages of "C," which stands
for rated capacity in ampere-hours (Ah). If you discharge the
battery at rates greater than the 20-hour rate, you can draw
more current, but for a considerably shorter time; that is, the
value of time multiplied by current will amount to much less
than "C." For more than 20 hours, you can draw less current for a
longer time.
For times beyond 20 hours, the product of current and time will
amount to more than "C," at least, up to a point. The value of
"C," or more likely a percentage of it, is also used to describe the
proper charging current for a battery.
"C" is useful for determining how long you can power an Isco
instrument from a particular battery. Teledyne Isco provides
average current consumption figures for most equipment. You
can use these figures as a rough estimate to calculate the
expected life of a battery connected to that equipment.