Trace Engineering DR Series Owner’s Manual - Version 3.2 - 9/7/98 - Page 9
Battery Charger
Theory of Operation
Inverter to Charger Transition
The internal battery charger and automatic transfer relay allows the unit to operate as either a battery
charger or inverter (but not both at the same time). An external source of AC power (e.g., shore power
or generator) must be supplied to the inverter’s AC input in order to allow it to operate as a battery
charger. When the unit is operating as a charger, AC loads are powered by the external source (i.e.
generator or public power).
The inverter automatically becomes a battery charger whenever AC power is supplied to its AC inputs.
There is a 40 second time delay from the time the inverter senses that AC is present at its input and
when the transfer is made. This delay is built in to provide time for a generator to spin-up to a stable
voltage and avoid relay chattering. The inverter’s AC input is internally connected to the inverter’s AC
output while in the battery charger mode. The maximum power that can be handled by the inverter’s
internal wiring and transfer relay is 30 amps (20 amps for export models).
Transfer Switching Speed
While this inverter is not designed specifically to operate as an uninterruptable power supply (UPS)
system, its transfer time is normally fast enough to hold up computers. The transfer time is a maximum
of 32 milliseconds. Success as a UPS will vary with computer models, and cannot be guaranteed.
Charger Terminology
•
Bulk Voltage- This is the maximum voltage at which the batteries will be charged during a
normal charging cycle. The normal range is 2.367 to 2.4 volts per cell. For a 12 VDC battery
(6 cells) this is 14.2 to 14.4. Liquid electrolyte batteries are usually set to the higher voltage,
while gel cell batteries are set to the lower voltage. (See page 18, Battery Care and
Maintenance, ”Bulk Voltage”).
•
Absorption - During this part of the charge cycle, the batteries are held at the bulk voltage
and accept whatever current is required to maintain this voltage. This ensures full charging.
• Float Voltage - This is the voltage at which the batteries will be maintained after they have been
charged. A range of 13.2 -13.4 for 12 volt systems is appropriate for most sealed and non-sealed
batteries. 13.2 volts is appropriate for gel cell batteries, and 13.4 volts is common for liquid lead
acid types. Check with the specific battery manufacturer for actual float voltage figures.
•
Equalize - The batteries are held above 15.0 Volts DC for a period to “boil” or mix the cells thus
reducing stratification and lead sulfate build-ups. This is not necessary or safe with sealed
batteries.
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