Just to confirm my diagnosis [Ikea uplighter]

[David W.E. Roberts]

Hi,

we have one of those floor standing lamps from Ikea which have an uplighter (150W screw in bulb) and a reading lamp.

All worked via a foot switch with a slider (rheostat?) for the uplighter and an on/off switch for the reading lamp.

The uplighter isn't working - hasn't been for some time as I thought it was the bulb and they don't sell them apart from in Ikea.

I now have a new Ikea bulb, but have also checked the old one in another Ikea uplighter and it works.

I have cleaned up the contacts with (dry) wet&dry so they are shiny.

I have checked with my little analogue multi-meter and I am getting about

240 volts to the contacts in the bulb holder.

As far as I can tell, the bulb is touching both contacts (bent them out, the bulb pushed them back).

So all I can think of is that the rheostat is knackered - putting out 240V but at such low power that it won't light the bulb.

As the switch is a sealed unit I can't get at the innards.

Any suggestions about what to do next (apart from just use the reading light)?

TIA

Dave R

[brugnospamsia]

... or the mains is wired backwards and the dimmer (electronic) is on the neutral. We mended one at work and had to replace a fast blow fuse.

I've never put a meter on the output of a dimmer, but I guess it might read

240 volts on the average multimeter if for some reason the slider had become disengaged from the slider potentiometer - might just not be enough mark to space to light the lamp visibly.

... I never found an electrical appliance that couldn't be opened BTW - if you discount the coffee percolator which saw me in casualty when the 3mm drill snapped and went through my finger :-(

Jeremy

[brugnospamsia]

sorry - this would only expain a lit neon screwdriver which you didn't use... (previous poster)

=================

[bigcat]

uplighter and

reading

150w bulbs are standard kit in both GLS and halogen, just not very popular domestically.

If you get 240v oc but 0v when bulb is in, you'd be right to say youve got a high impedance source. I'd wire over the dimmer, so its on a switch but doesnt dim, thats your most likely culprit at least.

NT

[Dave Plowman (News)]

Unlikely to be a rheostat - a 150 watt one would get extremely hot. It will likely be a 'conventional' triac dimmer with a slider pot rather than the more usual rotary one.

And trying to measure the output of one of these with a meter is pretty meaningless.

[No Spam]

No reason why. Even if the meter is not true RMS you can usually get a reasonable indication of a phase switched dimmer output with any meter.

[Christopher Key]

Only if there is a load though surely. The current drawn by a DMM will be many orders of magnitude smaller than that required.

Chris Key

[No Spam]

Agreed, but that detail was obvious to me ;-)

[Christopher Key]

I didn't doubt it ;-) ! I did get the impression that it wasn't to the OP though, hence the post.

Chris Key

[Dave Plowman (News)]

My thoughts. He mentioned getting 240 volts at the bulbholder, so I assumed that was without the bulb in place.

[David W.E. Roberts]

The point about getting a reading with a multimeter was that there was

*some* current getting through.

If there was none, then the lack of light is obvious.

If 240V is present then there isn't a break in the circuit somewhere else.

In the same way, I would check a normal 240V light fitting to confirm that power was getting through.

My meter isn't fancy enough to measure the load - just that the current is there.

If there is current, the (confirmed O.K.) bulb won't light and there is a dimmer in the circuit then the first logical conclusion is that the dimmer is being a little too effective.

I was just wondering if there was anything I had overlooked.

So far, apparently not :-(

Thanks to all for the comments, anyway.

Cheers

Dave R

[brugnospamsia]

The most likely thing to have failed is the horrible slider pot - can you prise off the foot operated bit to see it's properly engaged ?

If it IS engaged the pot probably needs replacing - should only cost a quid - though you might try WD40 first

Jeremy

[Christopher Key]

Agreed, if you're measuring 240V then there certainly is a very minimal current getting through. If this voltage collapses when you put some load on it however, then it suggests that there is a high impedance somewhere in the circuit. This is most likely a broken dimmer, but could also be a poor connection elsewhere.

Chris Key

[David W.E. Roberts]

Has anyone managed to take one of these apart?

At the moment I have a working reading lamp.

My training course notes on "Sods Law - domestic applications" suggest that if I try to disassemble the switch I will have a fully functional lamp standard with a broken switch box.

I suppose I could always replace the existing box with a simple double light switch in a surface mount box but this might be a little unsightly.

Thinking about it, a double push/rotate dimmer switch would replace the slider box, although you would lose the ability to regulate it with your foot (unless barefoot and very prehensile).

But can you get it in black, dahling??

Cheers Dave R