Dimmer switches

[Jack London]

We have three dimmer switches similar to this one.
http://tinyurl.com/8ulbg9m
Recently two have ceased to dim. Can they be repaired rather than
replaced. To a non electrician like myself the wiring on all three looks OK.
One room with a four light fitting seems a bit darker than it should be
as if the dimmer was not fully turned.
TIA
Jack

 

[Woody]

We have three dimmer switches similar to this one.
http://tinyurl.com/8ulbg9m
Recently two have ceased to dim. Can they be repaired rather
than replaced. To a non electrician like myself the wiring on
all three looks OK.
One room with a four light fitting seems a bit darker than it
should be as if the dimmer was not fully turned.
TIA
Jack

Replace - they are usually essentially sealed units and almost
impossible to repair.

Screwfix, Toolstation, or tlc-direct are your best sources.

 

[Andrew Gabriel]

We have three dimmer switches similar to this one.
http://tinyurl.com/8ulbg9m
Recently two have ceased to dim. Can they be repaired rather than
replaced. To a non electrician like myself the wiring on all three looks OK.
One room with a four light fitting seems a bit darker than it should be
as if the dimmer was not fully turned.

Normally caused by the Triac (semi-conductor which chops the mains)
being destroyed by the surge when a lamp blows at end of life.
For anyone into electronics and soldering, it's easy and cheap to
replace the Triac. Otherwise, you'll have to buy a new dimmer.

If the dimmer is an expensive matching wiring accessory, you might
be able to find a cheaper one from the same manufacturer which uses
the same dimmer module, and transplant it.

 

[Jack London]

Normally caused by the Triac (semi-conductor which chops the mains)
being destroyed by the surge when a lamp blows at end of life.
For anyone into electronics and soldering, it's easy and cheap to
replace the Triac. Otherwise, you'll have to buy a new dimmer.

If the dimmer is an expensive matching wiring accessory, you might
be able to find a cheaper one from the same manufacturer which uses
the same dimmer module, and transplant it.

Thank you, we had had several lamps blow when turning on one of the
switches.
Jack

 

[Jack London]

Normally caused by the Triac (semi-conductor which chops the mains)
being destroyed by the surge when a lamp blows at end of life.
For anyone into electronics and soldering, it's easy and cheap to
replace the Triac. Otherwise, you'll have to buy a new dimmer.

If the dimmer is an expensive matching wiring accessory, you might
be able to find a cheaper one from the same manufacturer which uses
the same dimmer module, and transplant it.

I contacted the makers of the two lamps we have been using recently.
Osram replied:

"The life expectancy of a conventional tungsten filament lamp is 1,000
hours (depending on supply voltage).

Mains voltage tungsten halogen lamps generally have a life expectancy of
around 2,000 hours or 2 years, but this is not a guaranteed life.

Conventional tungsten filament lamps can draw a large (short term)
current when the filament fails at end of life. I expect it is this
which may have caused the dimmer failure.

However, we manufacture an eco version tungsten halogen lamp that has a
built in fuse, which effectively cuts off the high surge current very
quickly at end of life, and should therefore be a lot more beneficial
for dimmer switches"
Jack

 

[Andrew Gabriel]

Once upon a time I had a dimmer switch with a built-in fuse. Now I know why.

Mind, I had a lamp go and take out the fuse on the board the other day.
And I then found I didn't have a spare...

IME, a triac blows much faster than a fuse.

On an expensive X10 DIN rail dimmer, I fitted a 3A type B MCB, in the
hope this would reduce the chance of wrecking it when a lamp blew.
It never did get damaged, but it's now driving 12V electronic
transformers anyway where this isn't an issue.

In another circuit where I'm switching the mains using power MOSFETs,
I used an FF fuse (very fast blowing), again with the hope it would
protect the MOSFETs, but this is a heater load with no switchon surge.