19/09/18
Page 20 of 67
ASR650 Operational Manual
3.4
Power Supply Requirements
You might use power supplies between 12 and 24 Volts DC for the ASR650. It is very important
that these power supplies have low ripple and noise (50mV
PeakPeak
or less). Agrident highly
recommends using linear regulated power supplies (stabilized). Switch-Mode power supplies can
decrease the reading performance significantly if their switching frequency is too close to the
readers operating frequency. In addition, they change their behavior depending on input voltage
and load. You can also operate the reader from a 12 Volt car battery but please note that the
ASR650 will disable the transmitter if the input voltage sinks below 11.0 Volts.
The power supply should be able to deliver 3 Ampere per reader at 12 Volt DC since the maximum
input current can be 2 Ampere. For higher input voltages the required currents are smaller.
Regarding the minimum input voltage, it is also very important to consider the length and the
cross-section of the power supply cable.
Let
’s assume the output voltage of your power supply unit (PSU) is 12.0 Volts and you want to
use standard data cable with a cross-section of 0.5mm². The minimum input voltage for the reader
is 11.0 Volts and the maximum possible current about 2 Ampere. So, the maximum allowed
voltage drop is 1.0 Volt and thus the maximum allowed cable resistance is 0.5
Ω.
V
PSU
= 12.0V
V
In Minimum
= 11.0V
cable: 0.5² with 36m
Ω / meter I
Max
= 2.0A
𝑙
𝑀𝑎𝑥
=
(𝑉
𝑃𝑆𝑈
− 𝑉
𝐼𝑛
) ÷ 𝐼
𝑀𝑎𝑥
2 × 0,036
Ω
/meter
=
(12.0𝑉 − 11.0𝑉) ÷ 2.0𝐴
2 × 0,036
Ω
/meter
=
0.5
Ω
0,072
Ω
/meter
= 6,94𝑚
That means your power supply cable must be shorter than 6.94 meter in this case. If the cable
needs to be longer, you have to use cable with a higher cross-section or a PSU with a higher
output voltage.
For the most agricultural applications, standard non-shielded cable will work fine. However, there
might be applications where shielded cable is required, e.g. Abattoirs or other industrial
applications. In this case the shielding avoids the reception of unwanted signals via the power
supply cable
– at least partially.
You should connect the shield to Ground of the reader (ST2-Pin5) on one end and on the other
end to the enclosure of the power supply in case of using a metal enclosure.
The minimum cross-section of the power supply cable should be 0.5mm².
ASR650
– ST2
+V
-V
shield
shield
12...24V DC
Power Supply
GND