Dimmer Ratings

[tim20vt]

Hi, I recently installed a touch dimmer rated at 40Wmin 400Wmax to control a light fitting with 6x40W G9 bulbs. Everthing worked fine for approx 3 wks until I came home today and the light is on full (it was off when I went out) and I can't switch it off. Also the switch was pretty hot. I've put the old rocker switch for now. Any idea what has happened and whether this dimmer is suitable for the load
Thanks in anticipation.

 

[breezer]

evidentaly not.

most dimmers have to be de rated by 50% for halogens

 

[Adam_151]

sounds like thr triac has died to me, would be caused by it being overloaded (see breezer's post above), the dimmer is fit for the bin now

 

[plugwash]

50% is a conserative rule of thumb and i'm quite surprised at a 400W dimmer failing on 240W of mains halogen. Especially failing whilst OFF!

i'd guess the dimmer had a manufacturing fault of some sort and just took a while to actually fail

 

[tim20vt]

Thanks for the replies. I didn't realise the 50% rule, but as mentioned running 240W with a 400W dimmer isn't completely over the top. Plus it failed with no load on!? Any explanation as to why, when the light was off it would switch itself on and then not function to either dim or switch off the light?

 

[mapj1]

The triacs are easily damaged by an overvoltage spike - possible if there has been a thunderstorm or even if you share your supply with poorly suppressed motor loads.
It is possible to add filtering components, but the easiest short term expedient is to just change either the whole dimmer for a bigger one, or just the triac in it, if your soldering skills are up to it. (If you do go for just change the TRIAC, if it uses a 600V part, which some of the cheaper ones do, I'd suggest an up-sizing to an 800V part - the extra 50p reduces the risk of a repeat failure significantly. )