Flickering downlight - advice?

[timbo]

Hi everyone, some advice sought.

We have halogen downlights fitted in our bathroom ceiling, with a transformer in the loft. One of the lights (and one only) flickers constantly, and randomly. The last bulb didn't last very long.

A new bulb hasn't fixed the problem. I've pulled the light fitting down from below and had a good look and can't see anything amiss, and also had a brief look in the loft (though access is difficult) and couldn't see anything wrong with the wiring, though this was only a cursory glance.

What is the most likely cause? A fault with the connection between bulb and lamp, or a fault with the wiring in the loft? I've very little electrical knowledge and no tools to test circuits etc but am happy to have a go at basic stuff with a screwdriver etc.

We don't know a handy electrician to come round and have a look for us.

Any advice appreciated.

PS we have heard that these downlight circuits are dangerous if a lamp is missing or faulty, is there anything to worry about if using it in this state?

Cheers Tim

[Clive Mitchell]

In message , timbo writes

Take a look at the pins on the lamp and see if one is slightly burned and pitted. If it is then the lampholder and lamp will need tossed and replaced. Don't fit a new lampholder and then re-use the same lamp since the pitting on it's pins will result in contact burn again.

If the holder has been arcing then the lamp may fail early due to the heat generated damaging the seal on the lamp.

It's not dangerous to leave a lamp out, but where several lamps are connected to large transformer the voltage will float slightly higher to the other lamps when one goes out. This can reduce their lifespan a bit. Probably not an issue with just a single lamp out.

Cheapest way to get a new lamp holder may be to buy a complete cheap fitting.

[timbo]

Thanks for the advice, Clive.

The lamp itself is a brand new one and I've already chucked the old one, so can't check it for pitting. But I'm fairly sure now there isn't a proper connection between lamp and lampholder.

Looks like the best thing is to replace the lampholder. If I disconnect the two wires in the loft which feed to the lampholder and temporarily put insulation tape on them , will the rest of the lights still work and is this safe?

[meow2222]

You've got a bad connection, but where? Could be any of the bulbholder itself, the cable to holder connection, damaged LV cable, cable to transformer, inside the transformer, or on the mains side. Either way its not safe to use it like that, as the bad connection is probably generating a lot of heat, and probably isnt able to handle it.

Best thing is to clean and tighten the various cable connections, scrape the bulbholder contacts clean if you can get to them, and try it again.

NT

[Clive Mitchell]

In message , [e-mail] writes

The short life of the lamps suggests it is the lampholder since the localised heat causes seal failure. There's no harm checking out the other connections associated with that lamp though. (Or even check ALL connections.)

Scraping lampholder contacts is not a fix. It just leaves the contact surface pitted.

[Clive Mitchell]

In message , timbo writes

You can just remove the lamp to solve the problem in the meantime. You can get a complete new fitting for about 3 quid and just use the lampholder and terminal that comes with it.

[渠云]

In message , [e-mail] writes

The short life of the lamps suggests it is the lampholder since the localised heat causes seal failure. There's no harm checking out the other connections associated with that lamp though. (Or even check ALL connections.)

Scraping lampholder contacts is not a fix. It just leaves the contact surface pitted.

-- Clive Mitchell

[timbo]

Thanks for the advice, Clive.

[meow2222]

Depends what caused the problem. If the contacts have not lost their springyness, then it is. It also is diagnostic, and the easiest way to diagnose the fault.

Which is not a big problem. It may last 8 years instead of 15 before it needs cleaning again.

NT

[Clive Mitchell]

In message , [e-mail] writes

It's a bodge that will quickly lead to arcing again since the current is high, the contact area small and the metals less than ideal, particularly in cheap holders. The heat of arcing destroys the springiness of the contacts and scraping will never remove deep pitting, but will remove any contact coating that had been applied to the metal.

The only true fix to a burned holder is a new holder and new lamp. Also check other spare lamps in case they've been in that holder and have pitting on their pins.

I'm not dissing you meow2222, just being the voice of reason against false economy.

[Stuart Noble]

Downlights are about as reliable as Xmas tree lights, which is reflected in the price I suppose.

[The Natural Philosopher]

In my experience they are a lot better than that.

I have had precisely zero problems with connections to the lamps..I have a couple of disty 'theree on a rail' units that have other issues mind you..transformer to track connections and mechanical disintegration being two..

I spent an hour yesterday reclaiming a pair of double wall lights I got S/H at Camden market in 1975, from the garage, and stripping out the excellent brass bulb holders to replace those in the modern ones I bought two years ago.. what a joy to have the things made out of brass and ceramic, rather than infinitely degradable thermoplastic.

[Clive Mitchell]

In message , Stuart Noble writes

And they were LESS reliable when they were first introduced to the UK market and aimed at the retail industry. I was sparking with a shopfitting company at the time and recall that the lamps cost 10 quid each at first (back in mid eighties when 10 quid was worth even more than it is now), and the lampholders were always burning out and the transformers were cobbled together to make a quick buck and typically pushed the lamps to their limit. I ended up using a bit more cable length on some arrays to try and drop the voltage a bit. (With suitable cable protection maintained of course.)

[meow2222]

Well, its the quickest way I can think of to find out whether the bad conect is in the lampholder itself or elsewhere. And if it turns out to be the lampholder, in some cases it'll work, but only when springiness isnt lost. So its still what I'd try if in the OPs position, only takes a moment with a rats tail file.

NT

[Ian_m]

Had a similar problem in my bathroom in my new house, one downlighter flickering, nothing to do with connectors etc due to failed transformer in loft. Got new one off builders, wired it in, flickering stopped. I assume faulty from new. You could hear it clicking as it flickered which I assume is the thermal cut out operating.

[Clive Mitchell]

In message , Ian_m writes

Electronic transformer?

Believe it or not you can get flickering problems if the mains input leads cross the low voltage output leads. The rather spiky "low voltage" output couples onto the mains in and causes circuitry instability.

The input and output leads should be kept well apart.

[Ian_m]

Not electronic it was this type,

is toroidal but has a thermal cut out which was faulty from new.