LED Control

[amberelectrics]

Im installing some LED lighting into an oak framed seating area at a pub. The LEDs are run from a couple of transformers very similar to laptop PSU's.

Now I happen to have a shed load of CBus wireless gear lying around so I planned on using a couple of two channel relay units outside in the main control box and a single 8 button relay in the building. Basically the 8 button to give me some control options and the two relays units externally to do the physical switching.

Problem is, it doesnt work.

The LED's remain powered on at all times, or the relay units simply cease to respond (loss of power I guess).

So the question is, how do I go about getting these relay switches to work correctly without adding an incandescent load for leakage?

Thanks

Simon

[Newman]

It sounds like the LED transformers are not meeting the minimum load requirement of the relay unit. Remember that the C-Bus Wireless Relay units are 2-wire devices and so they derive their power from the load that it connected to them. They require 25W of load to be connected.

If the transformer is a switch mode type then it's possible that it's interacting with the power supply in the unit and upsetting it, hence the unit stops responding.

Something to try:
The Relay units derive all their power from the load connected to the first channel. The second channel is purely for switching (although there is 100pF across the contacts so it won't read 0V on a meter).

Try connecting an incandescent bulb to channel 1 and the transformer to channel 2. Get the unit operating the way you want it to with this configuration first. If you then put the power supply for the LEDs back on channel 1, and it still misbehaves, then the problem is insufficient or incompatible loading on channel 1.

[amberelectrics]

That actually gives me an idea. As I have quite a few 2 channel relay units lying about, I could in theory, connect a lamp across channel 1 of each and put my LED load on channel 2. If I then program the switches so channel 1 never switches on then no more problem.

A little wasteful on kit but a possible solution I guess.

Alternatively, would it be possible to put a 25W or 50W resistor in the load line to give a current sink or am I having a giraffe?

[Newman]

Whilst possible, the power dissipation in a power resistor is going to be pretty significant. Remember also that it needs to handle the case where the channel may get turned on and not cause problems, even if you've programmed it not to (you can't predict who may re-program the site in future). The power rating and resistance would need to be carefully chosen to ensure enough current was flowing and the rating of the resistor was not exceeded.

A light bulb is a nice predicable load that will almost certainly work just fine. The advantage of using a light bulb is that it will act like a fuse if there's a fault, but you've got the light and heat to deal with. However, it will eventually fail if it gets turned on regularly.

A better bet would be to use a mains-rated capacitor of about 2uF as the load on channel 1. You may even find that putting a capacitor like this in parallel with your LED transformer may give the relay unit sufficient loading that you can use both channels.

Hold that giraffe for now :)

[amberelectrics]

Thanks Newman I shall give that a go.


The giraffe is standing by, I can see its knees from my office window LOL

[amberelectrics]

Ok, well that seems to work.

A 2uF 440V capacitor in parallel with the load works a treat. It does seem to need one per load channel though. Without this, on start up, the switch does its thing and then tries to turn on the non loaded channel. When it does this the switch dies and will not do anything unless powered cycled.

I will leave this running overnight to ensure it lasts without burning the place down or anything LOL.

Thanks

Simon

[ashleigh]

From memory I think you need to check you have an X rated capacitor. These are mains rated types designed for this kind of application.

If its not X-rated, change it for one that is. See here for more info: http://www.okaya.com/FAQ1.html

[Darpa]

I could be wrong here, as I have a massive headache at the moment, but from memory you need an "X2" class cap. Like I said, I could be wrong though...

[amberelectrics]

I used a couple of LCR capacitors. These are motor start types which I think are X types, not sure which level though so will check it out.

Thanks