Connecting Power

Video Transcript

It is possible to daisy chain the power connectors so that all modules share the same power supply. But in many applications, it is wise to power the modules separately. If possible, use the power from the monitored/controlled device to avoid unwanted galvanic connections.

The SE400 can handle 9 to 35 Volts DC, but the add-on modules require 24 Volts DC.

We will use 24 Volts DC in the example. We will only use one power supply here, but please check your needs before connection to your equipment.

Kvaser does not recommend daisy chaining power.

One SE400 can handle four add-on modules. The RIO consumes most power according to the user manual. Each RIO consumes typically 2.5 Watts. One SE400 consumes max 3.2 Watts. That indicates that a power supply which can deliver 15 Watts, or 550 milliamps at 24 Volts DC, should be enough. Here we’ll use a standard 24 Volt DC/750 milliamp power supply from XP Power when testing the units.

Please note, in a real implementation, it is wiser to power each module separately to achieve real galvanic isolation between modules and not introduce unwanted interference.

If we select a cable with 0.5 square millimeter, then we’ll have a maximum transfer of 0.75/5 which equals 1.5 amps per square millimeter. That’s equivalent to AWG 20, and according to many AWG wire gauge tables it is possible to use up to 3 amps here. So, in our example, 0.5 square millimeter will do the job.

Disclaimer: Always follow local rules and recommendations regarding dimensions of cabling and type of cable.

A note on protective earth, terminals marked ground on modules are connected to functional ground, not protective earth.

All modules are galvanically isolated from each other. But there are some internal exceptions that might be important to remember, particularly when there is a connection to a common power ground. If the modules are supplied with separated power, the maximum DC level between them should never exceed 100 Volts DC.

On the SE400 in particular, all four CAN channels are galvanically isolated. There’s no need for external insulation. There are a total of six marked ground pins on this module. Two on the four-pin power connector on the top, and four on the CAN connector block on the front. The two power ground pins are connected to each other. This connector can be used for daisy chaining power to other modules. The four CAN ground pins are not connected to any other ground pins. Each CAN block is galvanically isolated from the rest.

Let’s look at ground isolation on the Kvaser DIN Rail S010-X10, or DIO as we’ve been referring to it.

The DIO, it has 16 digital inputs and 16 digital outputs. The module is divided into two parts, one digital input block and one digital output block. Each block is has a ground connection. The ground is isolated between the two blocks.

The digital output block has a power and ground connection. This power/ground supplies the digital output with power, and also the control logic is powered by this connection. Power must be supplied to the digital output block, even if digital output is not used. The digital input block is powered via a DC/DC converter and is totally insulated from the digital output block.

Important: If the digital output is galvanically isolated from the rest of the modules, a separate insulated power supply must be used, a Class 2 or SELV power supply.

The Kvaser DIN Rail S020-X10, the analog I/O module does not separate any ground from each other. All ground pins, input and output, and power ground are internally connected.

On the Kvaser DIN Rail S030-X11, the relay module, the power ground connection on X3 is DC/DC isolated from the rest of the module and all eight relay outputs are galvanically insulated.

The ground for the eight digital inputs are isolated from power ground.

Lesson tags: #automotive, #canbus, #controllerareanetwork, #ethernet, #testcell
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