Kantech KT-400 - Manual (Page 28)

DN1726-0811 24
SPI Expansion Port
The SPI (Serial Peripheral Interface) expansion port on the KT-400 is used to connect expansion modules, in order to
add more inputs and outputs such as relays. The maximum current draw for the SPI expansion port is 500 mA when the
12V AUX terminals are not used. The 6-pin SPI cable must be connected to the SPI IN of the first module. See Figure 9
and Figure 11 for examples of interconnection between the KT-400 and expansion modules.
Figure 9: KT-400 Interconnection Examples with Expansion Modules
The number of expansion modules that can be connected to the KT-400 SPI expansion port, without an additional
external power supply, can vary depending how much current is drawn from all the modules in the SPI chain.
Check the following table to calculate the SPI chain current draw:
Example of current draw calculation:
1. 15 modules (KT-MOD-OUT16) x 750 mA = 11250 mA
2. 11250 mA - 500 mA (or 0 mA if the 12 VDC AUX of the KT-400 is used) = 10750 mA
3. 10750 mA divided by 1850 mA = 5.8 which means in fact 6 external power supplies 12 VDC, 2 Amps are required.
4. Connect an external power supply at every expansion module where the current draw has reached 1.85 Amps.
5. Make sure the power jumper on the modules is in the correct position when using external power supply(ies).
Expansion Module Qty of modules x Maximum current draw Total
Current
KT-MOD-REL8 _______ x 330 mA ______ mA
KT-MOD-INP16 _______ x 40 mA ______ mA
KT-MOD-OUT16 _______ x 750 mA ______ mA
Maximum current draw from KT-400 SPI expansion port when the 12 VDC AUX terminals are not used. - 500 mA
If the total current is between 0 mA and 1850 mA (1.85 Amps), 1 external power supply is required.
If the total current is between 1851 mA and 3700 mA (3.70 Amps), 2 external power supply are required.