Cutler Hammer, Div of Eaton Corp PSS Application Note
IT.
24V DC Power Supplies
Application Note
Electromechanical
Contactors and Starters
Why is 24V DC control power becoming more prevalent in industry? There
are several main drivers — safety concerns, reduction in product size and
cost, functionality and reliability
improvement, and the growing availability of 24V DC products such as
sensors, instrumentation systems,
PLC I/O, and other signal, conditioning
and power control devices.
This application note is intended to
help in the selection of the proper
24V DC power supply, by taking into
account the continuous (sealed) and
inrush (peak) current or wattage
demands of multiple devices,
when connected to a single 24V DC
power supply.
The characteristics of interest for the available Cutler-Hammer
supplies are shown in the following table.
Table 1. 24V DC Power Supplies
Catalog
Number
PSS10E
PSS25E
PSS10F
PSS25F
PSS55A
PSS55B
PSS55C
PSS160E
PSS160C
PSS300E
PSS300C
PSS600C
Before sizing the power supply, the
continuous and inrush watts or
amperes of each load must be identified. This is not much different than
adding up the volt-ampere requirements when sizing a control power
transformer. In addition, the sequence
of operation of the devices needs to be
determined to ensure that the worst
case conditions are used in sizing the
power supply.
For example, a system being designed
requires:
tors,
one
indicating lamps, and
relay. The power requirements for each
device are given in the following table.
Table 2. Power Requirements
Device Watts Per Device
A-Frame IEC
Contactor
C-Frame IEC Starter 3.6 90.0
Indicating Lamp 1.2 1.2
Auxiliary Relay 1.2 7.2
Continuous (Sealed) Inrush (Peak) Input
Wattage Amperes Wattage Amperes
10
25
10
25
55
55
55
—
—
—
—
—
0.4
1.0
0.4
1.0
2.3
2.3
2.3
—
—
—
—
—
20
165
20
165
250
250
250
—
—
—
—
—
0.8
6.5
0.8
6.5
10.4
10.4
10.4
—
—
—
—
—
In the first example,
will be operated at the same time
available line voltage is 230V AC. Two
calculations are required — the first, to
determine the continuous wattage
requirement and the second, for the
peak wattage.
■
Continuous watts = sum of continuous (sealed) watts of each device.
Continuous watts = (2 x 1.3) +
(1 x 3.6) + (3 x 1.2) + (1 x 1.2).
two
IT.
A-Frame IEC contac-
C-Frame IEC starter,
one
auxiliary
three
Continuous watts = 11.
■
Peak watts = sum of inrush (peak)
watts of each device.
Peak watts = (2 x 20) + (1 x 90) +
(3 x 1.2) + (1 x 7.2).
Peak watts = 140.8.
In this case, a PSS25E power supply
Continuous
(Sealed)
1.3 20.0
Inrush
(Peak)
would be chosen, since it has a continuous rating of 25 watts and a peak
rating of 165 watts which are appropriate for the calculated 24V DC
power requirements.
IT.
24V DC power
Voltage VAC
90 – 260
90 – 260
360 – 500
360 – 500
90 – 140
180 – 260
360 – 500
90 – 260
360 – 500
90 – 260
360 – 500
360 – 500
all of the devices
. The
Application Note
Page 2
As a second example, the same
devices will be used but the operation
will be different. In this case the
designer wants to be able to
device while all of the others are operating
. The worst case peak power
requirements will occur when all of the
other devices are operating and the
C-Frame starter is picked up. Again,
two calculations are required, one for
the continuous (sealed) and one for the
inrush (peak) power requirements.
Continuous watts = sum of continu-
■
ous (sealed) watts of each device.
Continuous watts = (2 x 1.3) +
■
(1 x 3.6) + (3 x 1.2) + (1 x 1.2).
Continuous watts = 11.
■
■
Peak watts = sum of continuous
(sealed) watts of each operating
device plus the inrush (peak) watts of
the worst case device being picked up.
■
Peak watts = (2 x 1.3) + (3 x 1.2) +
(1 x 1.2) + (1 x 90).
■
Peak watts = 97.4.
In this case the PSS25E power supply
would be chosen to meet the calculated requirements.
It must also be noted that the power
requirements above are based on the
devices being operated in a 20ºC (68°F)
environment. If the temperature differs
from 20ºC (68°F), the wattage requirements will change for many devices.
The device instruction literature will
supply information as to which if any
factors are to be used for other operating temperatures. As an example, for
the
IT.
IEC contactor and starter products, the following table is published in
the User Manual, pub49400, which
provides an equation for determining
power requirements at temperatures
different than 20ºC (68°F).
Effective: February 2002
close any
IT.
24V DC Power Supplies
Table 3. 24V DC Power Supply Requirements at 20°C (68°F)
Contactor/Starter Size Sealed In Inrush
Catalog
1
Number
E_11A_ _X3N A 27 1.3 0.054 20 0.83 30
E_11B_ _X3N B 45 3.7 0.15 80 3.3 50
E_01B_ _ _3A B 45 3.2 0.13 80 3.3 50
E_11C_ _X3N C 54 4.2 0.18 90 3.8 50
E_01C_ _ _3A C 54 3.6 0.15 90 3.8 50
E_ _1D_ _ _3_ D 76 5.0 0.21 130 5.4 65
E_ _1E_ _ _3_ E 105 5.6 0.23 140 5.8 85
E_ _1F_ _ _3_ F 140
1
Indicates missing digit of the catalog number may have multiple values.
2
Consult factory.
Note: At other temperatures expressed in °C, for either inrush or sealed, use the 20°C value
from the table in the following:
Watts = W
For example, inrush requirements for a D-Frame starter at -25°C would be:
Watts = 130 [1.1-0.005(-25)] = 160
Amps = 5.4 [1.1-0.005(-25)] = 6.6
Frame mm Wattage Amperes Wattage Amperes Duration
22222
[1.1-0.005(T)] and Amps = A
20
[1.1-0.005(T)]
20
(msecs)
In addition, operation at ambient temperatures greater than the 24V DC power
supply temperature rating will require that the power supply be derated. See
the applicable power supply installation manual.
© 2002 Eaton Corporation
All Rights Reserved
Printed in USA
Publication No. AP03903001E
February 2002
Loading...