Voltage range for CBus units?

I had the fortunate situation of sitting behind my PC monitorring my mains voltage when I suddenly saw it slowly drop from 230V to around 197V. At around the 200V mark my study light, switched via a relay, switched off and my PC's UPS kicked in.

I observed the voltage then slowly creep back up again and it peaked at 243V before it settled back around the 230V mark.

I just wondered 1. What the voltage tollerance for the Cbus units are. Checking the Bus I obviously didn't see a 'Switch Off' message so my Comfort Monitor software was under the impression that the light is still in the On state.

Is this a real-world problem that we have to live with or 2. Is there a way for the 'offending' - and I say this with respect, Cbus unit to send out a group update to update everyone of it's status after the power returned to a normal range.

Ingo

 

C-Bus output units are rated to operate over the range of 220V - 240V. In practice, they're tested to operate +/- 10% over this range, so that spans a range of 198V - 264V.

When an output unit sees the power go below this range, it triggers the unit to go into shutdown mode. At this time, the unit will switch to low-power mode and start storing the channel levels off to it's EEPROM, so that they can be recovered on power-up. The fact that you saw the channel turn off at ~200V is consistent with this.

Why the relay channel turned off at this point is still a bit of a mystery though. If the light was on a dimmer, I could understand, as the dimmer would go into shutdown. If the load type was anything other than an incandescent, I could understand it because what's going on inside a CFL/fluorescent ballast/LV downlight transformer/etc at that voltage could be anybody's guess. Being a relay, the outputs are latching, so they should just stay put when power fails. When power returns, the unit will apply the power-up setting to the relay channel (on/off/stored), so what you saw may have been the voltage dropping, and then on the way back up the power-up settings were activated in the relay as it returned to normal operation.

Check your power-up settings for the channels on that relay. If they're configured as "no change" then the relay channel should have remain unchanged by the voltage dip. If they're configured to power up in the Off state, then that would explain what you observed.

This happens automatically in C-Bus devices through the MMI mechanism. All input and output units are constantly checking their state and making corrections as necessary to keep everything in sync. This works great for regular C-Bus devices, but how 3rd party equipment behaves will depend on the thoroughness of the implementation of the C-Bus protocol in that device.

 

Thanks Newman, with low power conditions strange things happen. My study does have a fluorescent light so it might have been the light that switched off and not the relay channel.

I'll probably never be so lucky to be at my PC when something like this happens, but if by chance I witness this again then I will check all the variables.

Ingo

 

It was a strip fluoro and it didn't fire when the voltage went back up again. Well, I can't remember all the details now, I had about 5-10s to decide what to do and what to check, I might have gotten a few checks & tests wrong in the sequence before the voltage came back up again.

Ingo