Epic 880TM Specifications and Requirements
100-88002 Rev B Page 15
AC Power Requirements 90-264 VAC at 47-63 Hz.
Thermal printers require high peak currents based on how many print elements are
being used and how often. High density printing requires much more current than low
density printing. High density printing in the horizontal axis will put extreme peak
loads on the power supply. These high peak currents can cause power supplies to
sag, roll back or even shut down. A power supply with an average rating sufficient to
meet the average printer requirements many not be sufficient to meet the peak
requirements. The power supply selection is critical to proper printer operation.
Typical power supplies are designed to provide a continuous well regulated voltage at
an average current that does not fluctuate too much and will typically have a wattage
rating based on that average current. A power supply suitable for the Epic 880TM
could have a wattage rating of 48 watts but unless it can provide peak currents of 8
amps (192 watts) and maintain 24VDC output, it will not function properly.
Some power supplies are designed to provide multiple voltages. These power
supplies typically provide a logic supply voltage that requires close regulation. The
other voltages are not as well regulated or have post regulation. In this case when
the 24 volt output is required to provide high peak currents, the circuitry within the
power supply must maintain the logic voltage and the 24 volt supply will sag. In some
cased the high peak load will actually shut down the complete supply.
Thermal printing has specific power requirements to develop the thermal paper. The
Epic 880TM printer monitors the incoming voltage and will increase its current
requirements if the voltage is low. The printer will adjust the print element burn time
and that will resulting in increased average current requirements. Input voltage
ranges from about 20 to 27 volts can be accommodated by the Epic 880TM. If the
input voltage is outside the acceptable range, the printer will issue a fault and will not
function.
A suitable power supply for a thermal printer will provide a constant voltage over a
wide range of loads with a low average current requirement.
Consider the following when selecting or designing a power supply for the Epic 880.
1) It must be able to provide quick response to step loads
2) Current will range widely with peaks at least 4 times the average
3) Load requirements for the power supply are as shown in the table below.
4) Consider a dedicated power supply for the printer.
5) If the printer is expected to print dense graphics, increase the average and
continuous current requirements by at least 25%.
6) Use power cables that are as short as possible and use adequate wire size based
on the cable length. Typically AWG 18 is the minimum wire size provided the
length is less than 3 ft (1 m).
7) Make sure the power supply uses a low ESR capacitor of at least 2200uF and
preferably larger in the output circuit.