Power at light dropping to 0V

Hi there
I am having trouble with one channel on my Cbus system. I have some strip led lighting on on relay channel that when switched on turns on the led for a second then they turn off. It is wired to a plug base which has the 12v transformer plugged in which powers the leds. The relay channel remains on. I switch it on and off and same thing.

I thought it was the power supply ie the 12v transformer so swapped it for another and same thing.

I put a multi meter across the power supplies out put and the voltage drops from 12v down to zero slowly. I know the power supply works as I have tested it at another gpo. It looks like he channels power 240v is dropping away to 0V. I checked and the led light circuit isn’t shorted. This has worked well for 5 years and now it’s doing this.

Is the cbus channel faulty?

 

Will let the experts chime in on this one, but I can't say that I have ever seen a relay that has contacts that connect then break. Normally faulty relay contacts = stuck on or stuck off. Fault finding suggestion for you - can you move the circuit to another channel and see if the same thing occurs? Would confirm if its the channel or the field circuit pretty quickly.

 

@Marcus
Call an electrician to track it down.
Poorly made wiring connections sometimes do show up after a period of time and he can also check the relay contact resistance.

 

Actually this is possible

Cbus relay units use latching relays that require power to change but are held in place with fixed magnets (so they require no continuous power to hold). Because the holding magnets are not as powerful as the switching magnets the force on the contacts is not as great once the power is removed after a fraction of a second. If the contacts are damaged you can get this situation where they work while switching but then go high resistance when the switching power is removed. You don't say what size power supply you are using, but linear dc supplies with a transformer and rectifier draw huge starting currents. Firstly the transformer is a purely inductive load, and secondly the filter capacitors on the dc side are an effective short circuit until they charge. So after time the relay contact can be damaged sufficiently to give the observed behavior (I've witnessed this first hand). When driving large linear power supplies I always use a separate high current (e.g. 40A) contactor driven by the cbus relay.

 

Cheers for the correction Ashley.
Always good to learn more about the inner workings of these beasts.

 

Of course I'd still be checking out all the connections before replacing expensive output units

 

@Ashley
Thanks for the useful information.
It will be valuable for fault finding.

 

Thanks everybody for your replies. I will have a look at it all and let you know what I find.

 

Hi guys can anyone recommend someone that can come and look at this for me that are Melbourne west baccus marsh way?

 

I have one relay channel in a L5512RVF with exactly this fault. Working for 10years fine then 2months ago this one channel turns on, but the output relay pulses on but does not stay on.