DIN Rail Dimmer - LED and Loading

Hi,

There seem to be a lot of discussions about the use of LED with and without success.

I am looking at using the Philips Master LED range - probably the GU10 replacement. They are a 240V 7W bulb, I rather naively thought that this would mean I could put a decent number on a single 1A output of the DIN Rail Dimmer pack.

7w / 240V = 0.029A

therefore max number of bulbs: 1A / 0.029 = 34?

so perhaps install max of 15 in case there is any start-up load.

Seems from reading around that this may not be the case and I can only get 4 7W bulbs on one dimmer circuit?

Why does a 7W bulb not draw that current - surely the point is that they are efficient.

Starting to panic that all the wiring that has been done is now designed on flawed logic.

Thanks,

 

When designing around incandescent bulbs everything was easy. Provided the load size in watts was below the rating of the dimmer, everything would be fine.

Since the advent of electronic loads (low voltage transformers, LEDs, etc) there are other factors to consider. Firstly, some electronic loads simply aren't designed to be dimmed using phase control dimmers. Secondly, leading-edge dimmers typically have a maximum amount of capacitive loading that they can handle before flickering and overheating starts to occur.

For the C-Bus DIN Leading-Edge dimmers the capacitive limit is 300nF per channel. If your Philips Master LED bulbs are designed to be dimmed, and they have, say, 33nF of capacitance (a guess, a not unreasonable assumption) then you will be able to put 300 / 33 = 9 lamps on the dimmer channel.

If you've already wired assuming that you can put 34 lamps on a channel, you're either going to have to re-wire or change the dimmer for an L5504D2U universal (leading/trailing edge) unit.

 

Thanks

Hi,

That makes sense, shame that Philips don't seem to list the capacitance.

I've written to them, let's hope they come back. If it is 8-9 then I can manage without a rewire.

Thanks,

Ben

 

Just remember that these 7W Philips Master LED GU10's have a much lower light output than a 50W halogen. At 230 - 290 lumens (depending upon which datahseet you read) that puts them at only 1/4 to 1/3 the light output of a typical 50W halogen, so make sure you space them accordingly. I think someone in the marketing department got a bit over-ambitious with their "equivalent to 50W halogen" statements. They do claim the ability to be dimmed on a wide variety of leading edge dimmers though.