BEHLMAN BL10000 Series, User'S Manual And Technical Reference Manual

Page: 20 / 59

14
3.9 OPERATIONAL CONSIDERATIONS
GENERAL
All BL series incorporate an input rectifier system followed by a capacitive filter. To limit the in rush current to
the unit, a soft start circuit is employed. This circuits prevents nuisance tripping of protective circuits in the line
circuits as well as reducing stress on internal components . When the unit is switched off for any reason a period
of about 30 to 60 seconds is required to allow the soft start circuit to “reset” . Failure to do so may cause the front
panel breaker of the power supply to trip repeatedly as power is reapplied. This may lead to eventual failure of
the breaker. In automated systems, a time delay relay should be considered to handle power interruptions.
OPERATION INTO LINEAR LOADS
The BL series will provide the best overall performance into a linear load. A linear load is characterized by that
fact that its current wave shape is sinusoidal. The phase relationship between the voltage and current may be
anything between 0 and 90 degrees (leading or lagging). Some examples of linear loads are as follows:
Most AC Motors Power Transformers Heating Elements
Resistors Capacitors Most Inductors
Incandescent Lighting ( without dimmers ) Most Solenoids
Operation into these types of loads usually cause little interaction with the output stage of the model BL6000.
The main concern with a linear load is the “in-rush” current associated with it. Most heating elements and
resistors have no in-rush concerns and usually do not present any problem for the power source. Inductive and
capacitive loads may present a special problem based on their construction and the way in which they are
energized. Motors and tungsten filament lamps also present some special “start-up” concerns. The following
is intended to give the end user some insight into applying the AC source to these types of loads.
DRIVING REACTIVE LOADS
Capacitors and inductors are reactive in nature. If the load is applied during the peak of the AC cycle there may
be a considerable in-rush of current several magnitudes larger than the steady state current. This current is only
limited by any series resistance that may be present in the load circuit. Under the right conditions, this could trip
the overload protection circuits in the power source. Certain transformers and solenoids (inductance) present
the same problem.
Several methods can be used to prevent tripping the protection circuits in the power source . One common
method is to insert a limiting impedance in series with the load. This could be in the form of a fixed resistor or
NTC (Negative Temperature Coefficient) thermistor. Also, zero crossing switching can be employed. The most
obvious way to prevent a high in-rush current is to apply the load with the voltage set to zero (or some
low value) and energize the load slowly by turning up the voltage.
DRIVING LAMPS
Tungsten filaments lamps, when cold, present a very low resistance. Once they are energized, their resistance
quickly climbs to it’s steady state value. This characteristic must be accounted for when driving tungsten filament
lamps. The same methods for driving reactive loads can be applied to tungsten
.