Universal Dimmer Problem

I got a call from a customer complaining that 2 lighting circuits come on spuriously at roughly 3 - 4 hour intervals. The circuits are on a 4 chn universal dimmer (5504D2UP). Problem arose after customer came back from holiday about 1 month ago. He states that everything was fine beforehand and the install was done 2 years ago. No other circuits appear to be affected. I swapped the dimmer channels over and reprogrammed the GA's. After I left, the customer phoned and said all 4 chns (max 6 x 50W halogens per circuit) were now coming on together. The individual chns were functioning OK (On/OFF/DIM) from DLT's or B&W touch screen. I decided to swap out the dimmer, but problem returned some 4 hours later. I once saw the problem when I had toolkit open and was monitoring the lighting app. The GA's involved were not set on, however all 4 override LEDS on the dimmer were on. I have checked clocks/burdens/C-Bus power/cabling where possible, but all appears normal (when I'm checking). Customers says that no work has been done to the house (electrical, plumbing, etc) for awhile. Any suggestions?
Harro

 

When the channels come on, do they just come on a bit or do they come on at full brightness?
When they come on, how long do they stay on for?
The door on the cabinet is not touching the buttons on the front of the unit is it?
When the channels come on, can they be turned off by sending C-Bus messages?
Do the local toggle buttons on the front of the unit operate normally, i.e. they're not jammed?

If the Channel indicators are on when this occurs, and there are no C-Bus messages being sent, the most likely cause is an intermittent short on the remote override lines. Can you check if the Unit LED on the unit is flashing at about 90% duty cycle? If the Unit led is blinking then it means the state of the channels is being overriden, either by local button presses or by remote overrides.

 

Thanks Newman - responses below........
When the channels come on, do they just come on a bit or do they come on at full brightness? YES
When they come on, how long do they stay on for? FOREVER AS FAR AS I KNOW
The door on the cabinet is not touching the buttons on the front of the unit is it? NO
When the channels come on, can they be turned off by sending C-Bus messages? FROM MEMORY YES, BUT I'LL CHECK AGAIN
Do the local toggle buttons on the front of the unit operate normally, i.e. they're not jammed? NORMAL OPERATION
Can you check if the Unit LED on the unit is flashing at about 90% duty cycle? WILL DO

I thought about the remote over-ride lines, but I would expect adjacent output units daisy-chained to dimmer would experience similiar problems.

I also fired up the diagnostic traffic analyser and saw some errors. I phoned the Clipsal support guys to find out what is an acceptable error rate i.e. 1%, 3%, etc, but was told that more blue than red was required??? I like tools like the traffic analyser, but I like to know what I'm looking at. What do you believe is acceptable?

Harro

 

Er, that was an either/or question, not a yes/no question. I assume that they come on at full brightness?

In general that's true, but wiring faults are not always predictable. It could be that one of the conductors is actually broken at the connector, for example. If you're on-site already it's hopefully a quick and easy thing to just replace the patch leads connecting this dimmer to the adjacent dimmers to rule this out.

I would consider an error rate of more than 1% as not acceptable. C-Bus is pretty robust so anything more than this would indicate something is fairly seriously wrong.
The only thing to watch out for here is when things like Touchscreens or PACs try to communicate with a device that is not physically present it will result in communication errors, as the commands are not acknowledged. Whilst this will increase your error count, it's not because of an electrical problem, and it tells you that something is programmed incorrectly.

I'd also check the programming of the unit again. It's possible that there is a logic group in use in the unit and some device is turning the logic group on, not the normal channel groups on. This may explain why you didn't see a message turning those channels on.

Set up Diagnostic utility, turn on the Log Commands feature and note the exact time the lights turn on. Look through the log for commands around that time that may be related.

 

Hi Newman, I've been crook with the flu, but have managed to get back to this problem. Using the diagnostic tool, the traffic analyser consistently showed 4% - 5 % error rate for the whole network. Voltages for units varied between 25V - 29V. I split the network up into upstairs/downstairs and found upstairs to be OK, but downstairs to be still 4% - 5%. I started disconnecting parts of downstairs network and found error rate dropped, but could not isolate fault. Finally I temporarily installed an extra 200MA PSU (on an old 12chn relay) and retested network. The network voltages increased a bit i.e. 26V was the lowest. The result after 2 days is that the error rate of 4% - 5% is still there, but the dimmer fault of spuriously turning on has not re-occurred. This leads me to think I may have a PSU problem on the downstairs network. I have seen the older C-Bus 1 supplies cause network problems, but not the newer ones. When I go back in a few days I will isolate the downstairs PSU's one at a time to see what impact this has on network errors.
Harro

 

4% to 5% is definitely too high. There's definitely a communication problem on that network that you need to resolve.

On the graph, set the update rate to 3 seconds. The errors will show up as red area on the graph. If the error rate is relatively constant then there is an electrical issue with the network. If the errors come as regular spikes then it is probably a C-Touch/PAC/Wiser programming issue.