Chargers serve two important functions. The main function is to provide d-
c station power and to keep the battery charged. The second function is to
be able to replace the battery if the need arises. Two main types available
are silicon-controlled rectifier (SCR) and ferro-resonant. The two types
differ greatly. SCR chargers consist of a transformer with an SCR bridge
and filtering. All control and protection in these chargers is electronic.
These chargers are usually the cheapest type because the manufacturer can
buy SCRs and electronics "off the shelf." Ferro-resonant chargers uses a
transformer specifically designed for each application. When extreme
conditions occur, these transformers saturate and limit, by design, the
maximum current and voltage. Additional electronics are not needed. This
feature makes the chargers more durable and dependable in a power plant
environment. The ferro-resonant type charger is therefore recommended.
Chargers normally are bought and operated in pairs to share the load. Both
chargers operating, with all safety features activated on both, will less likely
have a double failure than if one is operating and one is in stand-by mode.
In an emergency, a charger on standby trying to power up and assume the
duties of a failed charger may exceed its current or voltage limits before
safety circuits are enabled. The result may be two failed chargers. The best
way to avoid this problem is to operate both chargers in parallel at all times,
each supplying half the load.
The size of the chargers is very important to the life and service of the
battery. The chargers must have enough capacity to easily gas the battery
under charging conditions. Chargers with too little capacity reduce battery
life. A smaller charger, though cheaper initially, can be the most expensive
on a long term basis.
A. Every Shift
A. Every Shift
Check the panel voltmeter to see if the correct float voltage is being used for
Check each charger by turning off one, then the other, and see if each
charger will carry the total load.
Check the accuracy of the charger panel voltmeter with the digital meter.
Post a battery data card form POM-157 in a conspicuous location near the
battery, and keep accumulated forms in a permanent file.
Loss of capacity over time is shown by a gradual change in specific gravity of