I have a bit of an electrical problem and of course I decided the best place to ask for help is a cycling forum.

I have fitted 2 banks (one bank of 4 light and a second bank of 7) of halogen down light in my kitchen ceiling they are switched two ways from each end of the room. They work perfectly when I use a normal 2-way switch but when I wre in a dimmer switch they flicker and the switch humms.

Now I would just have them on/off but the wife is dead set on the dimmers…. Help…. Any ideas folks???

you need a different sort of dimmer (electronic not just a rheostat???) I think

Are they 12 v halogens with transformers?

What rating its the switch? Could be underrated, they’re usually 250w or 400w. Generally those lamps are 50w each. Its normal for some dimmer switches to hum though

They are mains not 12v

Thank god a reply and so quickly…. wife reconed I was mad asking on a cycling forum…. I love it

No idea what rating there is on the switch…. how would I find out?

T-J…..The ones I have are rheostat I think…. any idea why they wouldn’t work?

It shouldn’t be a problem – we have banks of 6, 6 and 4 all running off one three gang (isolated) dimmer (240v). Not had a problem in nearly 3 years (not even a blown bulb). Are they wired correctly? Ie, series or parallel? I believe that is important (IIRC)

Thinking about this more – I think you will be in trouble if they are in series – they should be parallel and the in/out feed to a junction box.

That could be ballcocks though – just what I dimly (see what I did there) remember of things my late dad used to try to teach me about electronics when I was a kid.

MF – If they were is series they would only be very dim as would only be getting 20 v not 240 each. 🙄

Eypic – if they are 240 v halogens then what I said does not apply I think,

Teh switch rating might be the issue – check onthe back of it or on the instructions on the box

Probably right – just trying to cast my mind back to what happened when I had mine fitted and I am sure it had something to do with the wiring in order to run with a dimmer on one side of the two-way switch in order for the lights to operate correctly (as in all coming on together rather than one after the other).

But I didn’t pay THAT much attention as it was only a small part of the extension project I was doing.

http://www.thelightbulbshop.co.uk/GuidetoDimming.htm

When using Mains Voltage Halogen lamps such as GU9, GU10, GZ10 and Linear halogen lamps, dimmers should be de-rated by 25%.

This helps compensate for the additional load due to arcing at the end of the lamp life cycle. This extra load can damage the dimmer. Where possible it is better to use branded lamps such as those produced by GE, Osram, Philips and Sylvania. Generally these have an in-built thermal link and, should the lamp filament short out, the thermal fuse stops the inrush of current which can damage a dimmer. (LIF Technical Statement No.25). Many cheaper imported lamps do not have this thermal link.

In some cases the number of dimmers on a plate must be de-rated because of the heat generated during normal operation.

(assuming mains halos – low tension ones are different, ideally the transformer should be dimmable natively)

Not a lighting expert but:

(i) It won’t be a rheostat controlled as such – this term means that a variable resistor is adjusted so that the amount of power it “takes” from the circuit is variable. So:
(a) at high resistance not much current is flowing in the circuit and the bulbs are dim. Bulbs and rheostat are dissapating little power and are cold.
(b) at medium resistance a decent amount of current is flowing and the bulbs are on, but huge amounts of power are being dissapted in the rheostat and it will be very hot. Hence they are inefficient and went out (in most cases) with the ark.
(c) at low resistance a lot of current will flow, the bulbs will look fully on and the rheostat will be cool.

(2) The confusion in terms come from the fact that in most dimmers a variable resistor (rheostat) is used to control some form of electronic switch (normally a triac) so people assume it is the same as the early versions (pre – 60s?). It ain’t.

(3) The newer version generally employ a form of phase control (ie not all of the cycle (sine wave)) is available to the load. Many modern lights that need a voltage to strike don’t get on with this. Likewise with some transformer (low voltage) based systems.

(4) Can’t think of a domestic situation where you would connect any lights in series – one out, all out.

(5) Suspect you have a wiring fault or something based on (3) at the root of your problems, but there my generic knowledge runs out.

…and I bet someone has given the correct answer in the time it has taken to write this!

Can’t think of a domestic situation where you would connect any lights in series

Christmas trees. (-:

Christams trees ….really.

I have had one bulb fail without the whole lot going …. even used a set 6 months ago with missing bulbs.

The vast majority of Christmas tree lights sold in the UK will be wired in parallel not series.

Step aside everyone, I know this one, you can only have one dimmer switch on a two way.

…. might well be the issue … , but the OP does say “a dimmer”.

Over-loading still an option as well.

Christams trees ….really.

I have had one bulb fail without the whole lot going …. even used a set 6 months ago with missing bulbs.

In the olden days Xmas lights were wired in series, there are still a few around, but with LED Xmas lights they are parallel.

Make sure your dimmer is resistive, not inductive. Check that your two way dimmer is 400W per dimmer,

you can only have one dimmer switch on a two way

Which means that the other switch down the other end of the room should be a normal two way switch.

And as said before, some dimmers do buzz a bit.

Re-read. You ambitious son of a gun, total load will be somewhere between 220 and 550 depending on the lamps.

220 (20w lamps)
385 (35w lamps)
550 (50w lamps)

You can lower the load by getting dimmable cfls or leds if you have the money.

Ahh OK thanks for the help folks.

How do I move forwards with this??

Can I have a dimmer on just one end of the two way switch?

Do I just need to get high load switches?

Do really apreciate those that have offered advice here.

Can I have a dimmer on just one end of the two way switch?

You can only have one dimmer on the load, as mentioned above. If you have two dimmers then its never going to work. Im presuming that you currently have two? If thats the case remove one and that will be the first step to solving it. The general standard rating of the switches are 400 watts, while your load is probably 550 watts, again mentioned by others above. if your switch is rated at 400 watts it will eventually fail.

If that is the case then your choices are either:

To get a switch with a bigger load capacity
or
replace some or al of the 50W (assumed) lamps with 30W
or
replace lamps with dimmable LED lamps

hth

turin – Member

Can I have a dimmer on just one end of the two way switch?

You can only have one dimmer on the load, as mentioned above. If you have two dimmers then its never going to work. Im presuming that you currently have two? If thats the case remove one and that will be the first step to solving it. The general standard rating of the switches are 400 watts, while your load is probably 550 watts, again mentioned by others above. if your switch is rated at 400 watts it will eventually fail.

If that is the case then your choices are either:

To get a switch with a bigger load capacity
or
replace some or al of the 50W (assumed) lamps with 30W
or
replace lamps with dimmable LED lamps

hth

I agree with everthing Turin has said but would just like to add that two way dimmers are available.

http://www.tlc-direct.co.uk/Manufacturers/Varilight_Saturn/Wiring_Accessories~Dimmers_5_Satin_Chrome/index.html

In reality you have one “dimmer” which can be controlled remotely by another “switch” (slave).

But your problem is too much load (too many 50w lamps) for the switch to control.

HTH

I’ve never seen a wall plate dimmer rated at over 400W, 350W running off the one in our living room and they don’t last that long even at that.

once you start getting into the 400W plus range your talking more heat than a wall plate can accommodate. You’d need to install a dimmer device in the roof space and a control plate on the wall.

Solution would be to fit lower power lamps.

I’m not really think i’ve seen a room in a normal house that actually requires 550W of halogen lighting, that’s a lot of bright!