USE OF AN AMMETER WITH A SPECTROPHOTOMETER BATTERY
AND CHARGER*
DAVID H. MILLER, M.S.
From the Clinical
Laboratory,
Veterans Administration
Hospital,
Richmond,
Virginia
The spectrophotometer, found as standard equipment in many army and
Veterans Administration clinical laboratories, is issued complete with a 6volt storage battery and a tungar battery-charger. The spectrophotometer operates on current from the battery which is steady and constant when the battery
STORAGE
BATTERY
CHARGER
SPECTROPHOTOMETER
110 VOLT
LINE
F I G . 1. Diagram illustrating connection of ammeter in charging b a t t e r y
for spectrophotometer.
is well charged. When the spectrophotometer is not in use, the battery is charged,
according to instructions, approximately one and one-half hours for each hour
the spectrophotometer has been in operation.
In practice both the spectrophotometer and the charger are permanently
attached to the battery. In some models, like the Coleman Junior Model 6
(Coleman Electric Company, Maywood, Illinois), the charging is started by plugging the charger into a 110-volt outlet, and stopped by pulling the plug. Later
* Sponsored by the Veterans Administration and published with the approval of the
Chief Medical Director. The s t a t e m e n t s and conclusions published by t h e author are a
result of his own s t u d y and do not necessarily reflect the opinion or policy of the Veterans
Administration.
Received for publication, F e b r u a r y 10, 1950.
693
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694
MILLER
models permit the charger to remain plugged into the 110-volt line outlet, and
a switch on the spectrophotometer turns the charger on and off. In a busy
laboratory the spectrophotometer is in use most of the day, and the battery is
charged overnight. This is an acceptable procedure, since the battery cannot
be overcharged by this type of charger, and no harm can result as long as there
is sufficient liquid in the battery.
However, unless the charger replaces the current that is withdrawn, the
user may find the battery dead, perhaps when he needs the instrument most
urgently. Even a partially charged battery may cause the spectrophotometer
reading to fall while the instrument is in use and cause other inaccuracies. With
the equipment as described there is no way of knowing at what rate the battery is
being charged. In fact it is difficult to know it is charging at all. Failure to charge
may be due to a poor connection, blown fuse in the charger or a worn-out or
defective tungar bulb in the charger. In each of these cases when the charger is
turned on, the normal charging-hum is heard, and light is seen issuing from the
charger as though it were charging satisfactorily. In fact the charger hums and
emits the usual light even when not connected to the battery.
This uncertainty may be eliminated by placing an ammeter in the 6-volt
positive line. A 6-volt ammeter showing charge and discharge, 0 to 30 amp., is
used. This is the same type of ammeter found in the dashboard of an automobile.
The ammeters in many of the new automobiles are not graduated, but older
models are graduated to show a charge up to 30 amp. on the right, and a discharge up to 30 amp. on the left. A satisfactory ammeter can be purchased at
small cost from most stores selling automobile parts or accessories.
The ammeter is installed in the positive (red-wire) 6-volt line between both
the charger and the battery, and the spectrophotometer and the battery, as
shown in Figure 1. The negative (black wire) is left intact. If it is found that
the ammeter registers "discharge" when it should show charge and vice versa,
it indicates that the connections are on the wrong terminals of the ammeter and
should be reversed. Using this ammeter, the amount of current passing either
into or out of the battery is indicated. The spectrophotometer in use discharges
the battery at a rate of 8 amp., and it is recharged at 5 to 6 amp.
Recently it was noted that a charger was charging at the rate of only one
ampere. A new bulb was placed in the charger, and the ammeter indicated a
reading of 6 amp. Without the ammeter this would have gone unnoticed and
current would be removed at the rate of 8 amp. Charging would proceed at the
rate of one ampere until the battery would become discharged and useless. Any
other difficulty in charging is also indicated by the ammeter.
SUMMARY
The use of an ammeter while charging a battery for a spectrophotometer is
described and its advantages discussed.
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