2
795-20
3.
Power Supply Requirements
. In elaborate installations you may combine many Xantech keypads,
IR receivers, controllers and emitters in a system. Having sufficient power supply voltage and current
available can be critical to achieve proper operation. To be sure you have adequate power supply
capability, take the following factors into consideration:
a) The maximum current available from a 781RG Power Supply for proper operation is 200 mA
(milliamps).
b) The maximum current from a 782-00 Power Supply is 1000 mA.
c) Most IR receivers draw 2 mA without signal and 10 mA with signal (check specs. on actual model).
d) Each 730 SmartPad draws 7 mA without signal and 65 mA with signal.
e) Each SmartPad
2 or 3
draws 85 mA with or without signal and with Status.
f) Each emitter connected to the Zone and Common Ports of the 795-20 draws 3 mA with signal and
0 mA without.
g) Add 10 mA for each 794 or 797 Interface module used, if they are powered from the 795-20.
h) When using combinations of these devices, add up the currents as shown in the following example.
Then choose a power supply that has a maximum available current that is higher than the total
current required.
For example, the power supply needed for the system shown in
Fig. 2
is arrived at as follows:
1) Three IR receivers at 2 mA x 3 + one at 20 mA = 26 mA.
2) Assuming a SmartPad
3
keypad, the current for one is = 85 mA.
Note: Since only one IR source can operate at a time, the lower current IR receivers (and 730
keypads if used) do not need to have their "with signal" currents included.
3) The current for one 794-60 Interface module = 10 mA.
4) The current for six emitters at the Common ports is 6 x 3 = 18 mA. (The 286-00 dual emitters
count as only one, since they are in series).
5) The current for the emitters at the Zone ports is 1 x 3 = 3 mA. (Since it is not likely that the zone
emitters will be operating the zone equipment at the same instant in time, only one need be included).
6) Now add up all the currents from steps 1 through 5.
26 mA + 85 mA + 10 mA + 18 mA + 3 mA = 142 mA total. Since this is considerably less
than 200 mA, a 781RG power supply is used.
When a system requires more current than a 78RG can handle, simply step up to the 782-00.
NOTE:
To avoid current "hogging",
never
connect regulated supplies, such as the 781RG and
782-00, in parallel!
CAUTION:
Do not use unregulated 12V power supply adapters from other manufacturers. These may
deliver excessive voltage to the IR receivers and cause them to “latch-up”. When this occurs, the “talk-
back” LEDs in the IR receivers and on the 795-20 Zone Controller may stay on continuously!
4.
Considerations For Shielded Wire and Long Lead Lengths
. When using long lengths (> 50 feet)
of inter-room shielded cable (> 75' unshielded), it may be necessary to connect a 470 Ohm 1/8 Watt
resistor between
IR IN
(signal) and
GND
at the 3-screw terminals of the 795-20. Refer to
Fig. 3
.
Fig. 3
Using a 470 Ohm
Capacitance Discharge
Resistor.
470
Ohm
resistor
Shielded Cable(s)
to remote room(s)
795-20 Input
Terminals
Ground Shield as shown
ZONE 1
+12 I
N
G
The resistor discharges the cable capacitance more quickly, allowing IR codes of high bit rates to pass
without data loss for consistent command executions.
