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2.3.2 Using Other Battery
Chargers
2.4 Model 948 Lead-Acid
Battery
• Do not overcharge the battery.
• Unplug the charger from the AC supply before discon-
necting the battery. This will prevent any sparking that
could ignite the gases produced by charging.
Charge retention is substantially better for lead-acid batteries
than for nickel-cadmium types. While a nickel-cadmium battery
can self-discharge completely in a matter of months, a lead-acid
battery will still have 50% of capacity for nine months to a year
when stored at room temperature (70° F or 23° C). At 100° F (38°
C), the time drops to four months. At 40° F (5° C), the time is over
a year.
However, if a lead-acid battery does self-discharge completely, it
will often be ruined, due to sulfation of the plates. This is very
different from the nickel-cadmium battery, which is not harmed
by remaining in the discharged state, even for considerable
periods of time.
The voltage available from a lead-acid battery drops in a straight
line as the battery discharges. This is due to depletion of sulfate
ion from the electrolyte, raising the internal resistance. Available
voltage drops gradually from approximately 12.5 at full charge to
10.5 at total discharge (under load). Note that it is important to
measure the battery under load. A discharged lead-acid battery
may still show 12.5 VDC, when measured with no load.
Nickel-cadmium batteries show essentially constant voltage
across most of the discharge range.
Note that an earlier version of the five-station charger is for use
with nickel-cadmium batteries only. It is possible to use
chargers for Isco nickel-cadmium batteries to charge
lead-acid batteries, but it is NOT recommended!
Yo u m u s t b e c a r e f u l t o a v o i d o v e r c h a r g i n g , s i n c e a
nickel-cadmium charger delivers too much current in the latter
stages of charging. Since its open-circuit voltage is high (30
VDC), the current will remain constantly high, no matter what
the charge state of the battery is. If not turned off at the proper
time, the charger will boil the electrolyte. There is a table printed
on the lead-acid battery that tells you how long to charge with a
nickel-cadmium charger.
B e c a u s e o f t h e r i s k o f d a m a g e t o t h e b a t t e r y f r o m a
nickel-cadmium charger, consider using an accurate digital volt-
meter to monitor the charge voltage. Discontinue charging when
the battery voltage reaches 15.0 VDC. Charging until the
battery "feels warm" is not a reliable indicator for these batteries,
as you may already have overcharged them. Discontinue
charging if you hear a bubbling sound coming from the batteries.
In addition to the Model 946 and 947 Lead-Acid Batteries,
Teledyne Isco offers a much larger battery, the Model 948. This
battery, which resembles an automotive battery, has a capacity of
45 ampere-hours, eight and a half times the capacity of Models
946 and 947.
Power Products Guide
Section 2 Batteries
2-11
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