Chattering outputs

My customer, a school, has a library with many metal halide down lights. These are wired in banks for switching eg. 30%, 20%, 50%. This is to enable switching of 30%, 50% (30+20) and 100% (30+20+50). The relay outputs are wired to contactors with normally closed contacts, relay on > lights off (this posed a problem for me with leds on push buttons).

During a recent storm lights were set to 50%. Customer rang me and advised there was a loud banging coming from the switch boards, contactors chattering. The first 50% (30+20) which were on, stayed on. It seems as though it was the other 50% chattering. I advised them to turn off the CBus control power then reset it, this fixed the chattering. All controll operations returned to normal. The builders electrician after investigation advises all control gear on the last 50% are now blown. Large invoice to follow?

The consultant engineer on the job specified ?dynalite? and I talked the school into CBus. It?s not looking good for the next building stage!

Any ideas? How do I defend CBus ??

 

Hi
Was wondering if the cbus switch was programmed to toggle ??? If so maybe the switch got a glitch and was sending repeated toggle commands....If this was the case then would be better to program the switch , short press on say and long press off.....

Frank

 

Interesting problem.

The fact that the channels which were "off", which I assume were allowing the 50% light setting to be enabled resulted in no damage, but the channel that was "on" and preventing the other contactors from closing resulted in damaged contactors might be a clue. I really think that the chattering could not be caused by C-Bus, but is more likely to be caused by some electrical feedback in the contactor circuit.

Let me explain:

1)C-Bus key units have been extensively tested under transient conditions and are proof against most transients. This doesn't say that they could never be upset, but it makes it very unlikely that a sustained chattering could happen which required a key unit to behave as if a key was pressed repeatedly due to noise.

2)In event of a lot of transient noise (sufficient to upset key units), it is unlikely that messages would be successfully transmitted over the bus to the relay unit. Communication is more likely to be upset by noise than the key unit's interface to the key, because the communication wires are a lot longer than the pcb tracks from the keys to the microcontroller.

3)C-Bus output units (din) have a power-up cycle that requires 5 seconds continuous mains over a threshhold in order to energise the loads. If any limit cycle oscillation could be set up involving the output unit and a marginal mains voltage, the cycle time would be on the order of 10 seconds. Hardly "chattering".

I'm not sure what caused the chattering, but it would seem to require either a faulty unit, or some limit-cycle oscillation related to marginal mains voltage and perhaps the starting current of the halogen lamps.


As another issue, I assume that the inverted drive for the lights is to ensure that in event of failure of C-Bus power, the lights are at least left in the on state. If you use a latching relay unit (the 12 channel model), the relay contacts will remain in the last state despite power loss, and would allow positive logic and easy LED programming.

 

Slow down you move too fast

Also were the High Bays Hot or Cold restrike? If cold restrike the re aplication of power when the light is off but still hot (as may occur due to a momentry power cut) may cause the lamp fitting and control gear to cycle on/off (you may need to check with fitting manufacturer to find out how their equipment deals with this situation and what if any damage it may cause). To eleaviate this problem the C-bus DIN series relays have a feature to allow a delay time to be specified so that a relay channel will stay off for a specific period to allow High Bays to cool down (typically 2 minute or so). Any on commands are stored and ignored until the time is up and the on command is actioned (you find this feture under 'ReStrike Delay' on CoolKit and 'Delays' on V2 Software GUI's).

 

Thanks Don that was great, engineer should be happy with that. Further information reveals that they may have had a brown out, as a submersable pump burnt out during the same storm (low voltage to the external contactors caused chattering?).
Thanks for the info UncleDick that will be put to good use