power supply requirements

I seem to recall reading that it is possible to have too many power supplies on a network, as they can somehow interfere with the C-bus data transmissions. Is this correct, and is there any guidance on the maximum number of power supplies that a c-bus network should have?

When calculating the number of din rail units requiring power supplies, the power calculator software assumes that all output units have power supplies. A cost saving can be made if some units do not have there own power supplies, so using the software calculator I usually add output units until the power supply requirements of the network are met (ie the red line disappears from the calculator screen), and I then assume that the remaining output units can be supplied without power supplies.

It obviously would be safer, although slightly more expensive, to arrange for all output units to be shipped with integral power supplies. However, I am concerned that if these power supplies can interfere with the C-bus logic signals, then as well as being more expensive, the system will be problematic.

Your comments will be most thankfully received on this matter.

 

C-Bus power supplies

The issue is not with over voltage affecting communications. The Cat 5 cable is only rated to carry 1A per pair. Therefore, with C-Bus utilising two pairs, the limit is 2A or 10 integrated power supplies per network.

This also equates to the typical power allowance of 20mA give or take per unit, and you get a total current current load of 2A for a 100 unit network.

 

As Darren points out, the limit to the number of allowed power supplies is primarily the current limit of the Cat#5 data cable, although there are a few other "nerdy" considerations as well. That means that you can have up to 10 DIN Dimmers or Relays with built-in power supplies on a network, since each one provides 200mA of power, giving a total of 2A.

I suggest you try creating a database for the network you're considering and then click on the 'Network' node in the Toolkit tree view (the bit on the left). It will then give you a summary of the power available on your network.