How do I dimension the power
supply of my SmartWire-DT
topology?
43
02/11 MN05006002Z-EN
The SmartWire-DT gateway is supplying the SmartWire-DT
topology sufficiently.
Calculation of the voltage drop in the contactor
supply
DC operated contactors with the control voltage U
AUX
+24 V DC switch dependably in the range +24 V DC
(-20 %/+10 %), i.e. from +19.2 to +26.4 V DC.
For safety reasons assume that the supply voltage U
AUX
=
23.5 V DC on the supply unit for calculation of the voltage
drop.
The following is valid: U
AUXmin
= 19.2 V DC
The maximum voltage drop U
Lmax
is calculated as follows:
Calculation of the voltage drop in the contactor supply is the
same as that for the device supply, with the exception that
no current flow due to a network termination has to be taken
into consideration. A higher electricity consumption has to
be assumed, so the simultaneity factor also has to be taken
into account more intensely in the calculation.
The following is valid in accordance with figure 5, page 39:
i
Warning!
If the voltage drops below the minimum voltage, depend-
able operation of a contactor is no longer guaranteed.
U
Lmax
= U
AUX
- U
AUXmin
= 23.5 V - 19.2 V = 4.3 V DC
h
Rule of thumb value
: if you are only using ribbon cables
and the maximum current of 3.0 A is consumed, the
maximum voltage drop in the contactor supply is achieved
at a line length of approx. 8.4 m.
U
V
= U
AUX
= 23.5 V DC
U
1
= U
V
- R
L1
x k x (I
1
+ I
2
+ I
3
+ … + I
n
)
U
2
= U
1
- R
L2
x (I
2
+ I
3
+ … + I
n
)
U
n
= U
n-1
- R
Ln
x I
n
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