Number of power supplies and burdens?

[ETsang]

I used C-Bus calculator and C-Bus Toolkit to calculate the number of power supplies and burdens for a network, why does my C-Bus network still have problems?

[Anonymous user]

I wonder what kind of problem do you have ? normally you can give one network burden and 3 C-Bus clocks into your single C-Bus network

[sesa96364 · Accepted solution]

you are correct, This is a good rule of thumb for general C-Bus network design.

The calculator gives you a result based only on some straight forward maths. It calculates the current consumption of all units, the current available by all power supplies in the database, then tells you whether the power supplied is enough and indicates whether you need a burden.

The difference between the calculated result and the real world result varies due to location of power supplies, number of burdens, voltage at the unit and problems such as network loops and interference. Problems typically only occur on large networks.

A few rules for a C-Bus network are as follows:

• no more than 100 units
• no more than 2A of power supplies in total
• no more than 1km of cable
• 3 clocks enabled per network
• minimum 20V at each unit
• use burdens on small networks, not on large networks

Network Layout:

When designing the layout its common to locate all the power supplies in distribution boards and run cable out to all other units on the network. A cable will usually daisy chain many units together along a single run. The units that are located further away from the power supplies will have a lower voltage. As the voltage get lower and unit counts increase the signal quality drops and this can result in communications problems between units on a network.

The ideal scenario involves distributing the power supplies evenly across the C-Bus network. C-Bus is very robust when it comes to communications using long runs of cable and varying numbers of units & power supplies. The problems only occur when you break any of the rules. As you creep past the limits the system will most likely still work however problem will occur intermittently and become more obvious as you creep further.

Two examples of a problems that I have seen on a large networks:

Problem:

Occasionally a key unit would blink its LED's indicating that the C-Bus network had lost its clock. Otherwise everything was reported to be operating correctly.

Investigation:

It was found that the unit that was in control of the clock was changing continuously. The cause was an excessive amount of burden on the network which caused a communications failure. One of the units with clock enabled would think there was no clock and enable its clock, at a later time another unit would take it back. This occurred as a result of the network being commissioned in sections, a small network was first created and programmed that required 2 burdens. As more units were added the burden became unnecessary and as more units were added the excessive burden caused communications failures.

Solution:

The solution was to remove burdens since the network was large enough to not need it.

Problem:

3 key units in a warehouse were not always turning the lights on and off however there were no other problems on the network

Investigation:

By looking at the voltage reported by each unit on the network we could see that all units were reporting steady voltages of about 30V except for the 3 key units which reported about 20V. Since the key units were located in a warehouse the length of cable between them and the rest of the C-Bus network was quite long resulting in a voltage drop. The voltage at the units became borderline and they were not always able to communicate with the rest of the network.

Solution:

Add a power supply near the key units to boost the voltage. This means there was a slightly better distribution of power supplies across the network.

Regards,

Matt

[ETsang]

Thanks Matthew~ I see Toolkit is reporting the voltage is a bit low on some units. I'll try relocating a power supply to another distribution board