Weird Relay Behaviour

Hi all,
New member here, hoping some of you gurus could kindly impart some of your wisdom to help with a weird problem I'm having.
So a couple of nights ago, my Cbus system went into learn mode, despite no-one pressing any buttons anywhere in the system. It somehow cancelled itself and all was well. Fast forward to tonight, and again it went into learn mode, but I left it and it didn't go back.
So I completely powered down the whole system from the consumer unit for a good hour, switched it back on and it's still behaving weirdly. Three dimmers all seem to be OK (albeit when switched on every channel powers on) but the 12-channel relay is going nuts. When I switch it on all the channels power on, but when I use the manual override buttons on the actual relay, other channels will switch on and off almost randomly, individually and in groups. Also, I noticed a couple of DLT's were flickering rapidly, so I have disconnected these from the network. The Saturns seem to be OK in that the LEDs aren't flickering, but none of the switches work.
Has the relay gone kaput ?
And another thing that I've never noticed before, is that a couple of the override buttons on the relay are rigid i.e. I can't press them in. I've never noticed this before, why could this be ?
Thanks in advance for any pointers you can give, I would like to narrow the problem down before I call out the expert as he's a good few hundred miles away and might not be able to get here all that quick !
Info: System is around 10 years old, never had any problems. Most LV (pink) cable is star wired back to a patch panel, but a couple of switches daisy chain from another switch. Relay is L5512RVF.
Thanks,Greg

 

The most common fault on a system of that age is a failing power supply, so the first thing to do is check the bus voltage. This is easiest done from the back of a switch as the terminals are exposed. If you get anything under around 20 VDC you have a problem. Powers supplies are usually part of an output unit (the unit will say "200mA power supply" on it's top. There are also separate din rail 320mA power supplies. If you have a very old system it might have a white power supply and these often cause random problems when they get old.

Apart from power, water on units or connections can cause random problems, as can rodents.

It is also possible that a unit has failed, although it is rare but not impossible for them to take out the whole system.

If it is star wired, you can start splitting the system to isolate the problem. You just need to make sure you have enough power on the segment you are testing.

 

Thanks for that, I'll check the voltage in the morning. Of the 3 dimmers, 2 of them also say they have a 200ma power supply, is it currently using all of these or is it only using the power supply in the relay ? In other words could I potentially re-configure it to remove the faulty power supply (if that's what it is) ? Will try to attach a photo if I can, though not sure it will help much.

 

All power supplies will contribute current to the system. Whether it will run with one less depends on the excess power installed. Ideally there should be 200mA more available than required so that one failure won't take out the entire system, but that depends on the installer as it increases the cost. You can get a rough idea of power needed by assuming each input device (i.e a switch or sensor) requires about 25mA (it actually varies a bit depending on the device). Output devices connected to 240V require no power from the bus. Unpowered output devices like shutter relays, fan controllers etc generally require 18mA each.

 

Ive had a lot of cases ( because of storms etc)
Of power supplies going “noisy” , they appear to give out the correct voltage/ current , but produce a lot of noise on the cbus communication network , so that messages are missed, random nesssges are generated etc.

If you can take one power supply / unit with cbus power out at a time and see if the network stabilizes. ( you will have to have enough units with power , that taking one out doesn’t leave you with too little power, to power the system)

Note: there maybe more than one that’s an issue, but even removing one , will help .

 

Thanks both for your help, much appreciated. Seemed to have stabilised it and all outputs and switches are working again now.
I measured the voltage with the dodgy relay switched off and it was down at around 14v, but with the relay powered on it was up at 29/30v.
I managed to get in to the Toolkit and switched Learn mode off from all the relays and dimmers which has allowed everything to return to normal.
I’m convinced it’s related to the “stuck” buttons on the main relay, I have a feeling one or two of these are constantly pressed in and hence triggering the learn mode. Weird thing it, no-ones touched these manually in years.
So now everything is working again except my Wiser app on my iPhone, pressing the buttons on there isn’t triggering anything currently. I can look at that later, at least I have lights back now !
Is 30v too low or should it be up around 36v ? I will work out how many inputs there are later, rough count at the moment is about 18, soon to be one more when I fit a new DLT in the garage (which is itself at the end of a 25m run of cat5 cable), and the relay in the garage doesn’t have a power supply.
If I need more juice can I install a stand-alone power supply on a spare rail in the garage enclosure which currently just has one 8 channel relay (plus the DLT).

 

30V is fine. The voltage will drop as you add more devices. This is normal as the power supplies have a designed output impedance to allow the bus to work correctly. (This is why you must use Cbus power supplies!) Anything over 20V is fine. The specs say 15V but in my experience that is very marginal. The fact that the voltage dropped to 14V when you switched off the relay tells you that you have less than 200mA spare at the moment. Since you have toolkit it will tell you the current power usage, however you need to make sure the output units have been entered correctly as Toolkit can't tell the difference between powered and unpowered output units (Unpowered Units have a P suffix. Powered units have it written on top). Since you only have a few output units you can easily check this manually. A DLT requires 22mA and Toolkit will tell you how much spare current you currently have.

 

Thanks Ashley. Any ideas on if anything can be done about the non-depressable buttons on the relay ? I’m guessing the blue casing isn’t designed to come off easily to see if there’s a problem behind it. My worry is that the button(s) is/are still being pressed in permanently and sending signals on the network (or do override buttons not send any data signals ?)

 

Can't say I've ever seen that problem. The blue covers are glued on along the edges but it is possible to remove them if you are careful by sliding a thin knife in from the side. If it's out of warranty you have nothing to loose