OPERATION MANUAL CompoBus/S

Supplying Power to the Slaves Section 2-3
Master
Power supply
(24 V DC)
3. Allowable Current for CJ-series Communications Connector
The allowable current for the communications connector of the CJ-series
Master Unit is 4 A. The total current consumption of Slaves must be no
more than 4 A when the CJ-series Master Unit communications connector
is connected to the communications power supply. (The same applies
when there is no distinction between main and branch lines.)
I 1 +I 2 + ... +I N ≤ 4 A
(I 1 , I 2 , w..., I N represents the current consumption of each Slave being supplied
with communications power supply.)
Master
Power supply
(24 V DC)
Slave
Current: I 1
Slave
Current: I 2
4. Cable Length Limit Due to Voltage Drop
The voltage drop can be calculated from the cable’s length, the cable’s resistance,
and the Slave’s current consumption. (The cable’s length is multiplied
by 2 because there are two wires carrying current, + and –.)
Voltage drop (V) = Current (A) × (Cable’s length × 2 × Cable’s resistance)
(Ω)
The allowable voltage range for the Slaves is 14 to 26.4 V DC, so the maximum
voltage drop is 10 V DC when using a 24-V DC power supply.
The equation yielding the voltage drop for the following system is shown
below. This is an approximate equation allowing some margin for error.
L 1 L 2 L N
Slave
Current: I 1
Slave
Current: I 2
10 ≥ (I1 + I2 + ... + IN) × L × 2 × R
10: Max. voltage drop (V)
R: Resistance of the Special Flat Cable (Ω/m)
4-conductor VCTF cable: 0.025
Special Flat Cable: 0.027
L1 + L2 + ... + LN : Length of cable between the Slaves
The maximum cable length (L) can be calculated from this equation as follows:
L ≤ 10 / { (I1 + I2 + ... + IN) × 2 × R}
↓
L ≤ 200 / (I 1 + I 2 + ... + I N ) ... 4-conductor VCTF cable
185 / (I 1 + I 2 + ... + I N ) ... Special Flat Cable
Slave
Current: I N
Current consumption of Slaves being supplied
with communications power supply.
Slave
Current: I N
Terminator
Terminator
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