Halogen track lights - problem.

[Velvet]

Put up two sets of these a couple of years ago. One set is now behaving oddly. They're both operated from the same switch, but I'm not exactly sure how they're wired together, I didn't do that bit.

They're 12v systems with a transformer integral to the mounting point on the ceiling for the track - so not recessed at all. 4x35w halogen lights on the track, one transformer per track.

A couple of weeks ago, one set didn't come on. From past experience I know if a single halogen blows, the others remain lit, but started replacing them one by one anyway. First one I swapped, it all lit up when I tried it again, so I swapped the 'old' bulb back in, still worked, so I figured maybe it had worked loose from the heat or something.

Then a few days back I noticed in the periphery of my vision that the lights (again, just this one set) seemed to be intermittently going brighter. I've seen this sometimes when the supply's been a bit ropey, but nothing else was affected. It cleared up, and I thought no more of it.

Tonight, having had the lights on a couple of times today, I discover the entire set is out again. Having changed the bulbs one by one it's still not working, and I'm none the wiser.

Having left it off and tried again, it's still dead. I'm not taking the cover off till I can see what I'm doing tomorrow when the sun makes an appearance again, but would appreciate some ideas on what I can look for and try.

I have a multimeter and have a vague idea on how to use it, though most of my experience has been on much lower voltage stuff, not mains, which is another reason why I'm leaving it till tomorrow, so I can see exactly what I'm about to electrocute myself with :-)

Anyone else had this, I'm assuming it must be something to do with the transformer, but a bit puzzled why changing the bulb last time seemed to kick it back into life. I've checked all the track is secure and tight etc.

TIA,

Velvet

[Harry Bloomfield]

Velvet wrote on Monday (09/02/2004) :

Many of these LV units suffer the same problem, high current causing burnt and poor connections.

As the voltage goes down, the quantity of current has to rise to make up for it to achieve the same wattage. If all lights are out on a track, then look at the connections between the "transformer" and the track. If it unplugs from the track check for signs of burning and blackening.

Less likely, but still worth checking are the mains connections to the "transformer".

Failing either of the above, there could be a problem inside the "transformer".

[Velvet]

Thanks, I was going to give it a quick visual for that sort of thing. There's no evidence between transformer and track - it's the sort where the track is a pair of rigid metal poles, with a screw clamping them into place against each of a drop-pole. Hard to describe - they slot in between two fingers, which have a fairly wide screw-thread on the inside surfaces, and the big screw thus screws up from the bottom to apply pressure both between itself and the track, and between track and upper surface of mount.

Would something along the lines of what you describe cause the intermittent brightening of them though? like an irregular pulse of brightness then dropping back to normal again (or alternatively a pulse back to proper brightness then dropping back to slightly dim). It's very hard to see, not very noticeable at all, but my vision is very sensitive to changes in light levels around the periphery (part of the reason why I now have these instead of the ghastly flourescent that used to be up there).

Velvet

[r3duf]

they melted. Currently trying to replace same at a cost of about £80.00 for

2. Regards JD

[Velvet]

Hmm. Mine run hot, but I expect that of halogens - certainly they've never got hot enough to melt anything! I did find a cheap set of mini-spots (non-halogen) ran hot enough that they literally fell apart, having cause the crappy welding to fail where the housing meets the adjustable arm bit. Mine have all but the narrow bit on the bulb exposed (they're sealed bulb things c/w reflector and front uv-glass) so the heat radiates away better than if they were enclosed and just had the fronts showing (more like traditional incandescent spots tend to be).

There was absolutely no sign of heat damage when I was up there changing the bulbs either - I'd expect the little 'max 35w' labels to have crisped if they were getting seriously hot, but they all look fine.

Velvet

[Harry Bloomfield]

Velvet wrote on Monday (09/02/2004) :

The brightening could be a symptom of the switch mode power supply ("tranformer") becoming confused due to a poor connection to the track, but it could equally be a symptom of a fault in the switch mode power supply.

Could you perhaps take it back to your supplier for replacement?

[Grunff]

They do what now?

In an Ohmic resistor, the current is *proportional* to the voltage. There is no magical way with which you can "raise the quantity of current" to make up for a drop in the applied voltage.

[John]

Mine had springy contacts in each lampholder to make contact with the conducting bars. Dust and cheap manufacturing had caused poor contacts in each holder. A strip and clean sorted it.

[Velvet]

Ah, that's a point. I can get the entire track down, not sure how far the individual units will strip, but I'll have a look at that tomorrow.

Harry, I'd get nowhere taking them back to the supplier - no longer proof of purchase, and I doubt they make the same units any more (twas one of the sheds).

My family are heavily biased in the electronics/electric skills, so there's a possibility of fixing if it's the transformer that has a fault

- I'm just interested in working out what it is as well as I can before I start asking for a visit from them :-) If it's something simple that I can fix then it's less hassle all around, really!

Velvet

[Parish]

If they won't strip down far enough you could try blasting them with an electronic cleaning solvent aerosol - removes dirt, grease, and oxide film, great stuff. Not sure where you would get it locally though, I used to buy it from work who got it from RS, Farnell, CPC, or similar.

[Velvet]

That's another good idea (well done uk.diy!) - the chances are that one of my family have such a thing ;)

Velvet

[The Natural Philosopher]

Yes, interminably. In my case it is the contacts between the transformer unit and the rails. They are simply NOT good enough for the current in a steamy kitchen.

Usually woggling the transformer fixes it: Occasionally I take it all apart and file back the areced contact areas.

[The Natural Philosopher]

Yes. Bad cionnection on teh LV side. If they are all 'in harmony' its transformer-to-track. If one goes dim as the other goes bright, its track-to-light.

[The Natural Philosopher]

Switched mode power supplies are anything but ohmic.

[Grunff]

I'm well aware of that - but if a switcher needs to push more current through a filament bulb, the only way it can do so is by increasing the applied voltage. This is not what the first two lines (quoted) of this post say.

[Madeline C. Rolfe]

For parents and carers for kids, rather than the vandals. They begin a systematic to trashing which changes in detail, to outwit killfiles. For instance the name may remain the same and the worst possible course of the name etc.

Insults!

[Kelvin Cullen]

They have ways of keeping the killfile facilities, and some cannot handle them when pointed out. The old hands find it so simple. Even very technically savvy, usenet hands are often unwilling to subscribe to the Target newsgroup.

It's a hard grind.

[The Most Rev. Peter Parsnip]

The Lord alerted my mind to the presence of this EVIL article by Harry Bloomfield, and I thusly replied:

Why is "transformer" in quote marks?

[The Most Rev. Peter Parsnip]

The Lord alerted my mind to the presence of this EVIL article by Harry Bloomfield, and I thusly replied:

Shame we can't do that with you.

[Andy Wade]

Can I be allowed to disagree? I think you're tilting at a windmill. He (Harry) didn't say that "as the voltage goes down the current rises ..." but rather that the "current has to rise ...". IOW 12V lamps will take ~20 times as much current as mains voltage ones of the same power. That's all.