Kitchen downlighter transformer problem

[Penners]

Our kitchen is lit with eight low-voltage downlighters - the kind that are recessed into the ceiling, with the transformers shoved into the ceiling cavity. Each 50W 12V halogen lamp is driven by an individual dimmable transformer, 20 - 60VA IP20 SELV (there is no dimmer in the circuit).

One of the lights has stopped working. The halogenlamp itself is fine (it shows a resistance-free circuit on an ohmeter). The leads from the transformer to the lamp are both fine (again, resistance-free). The mains feed to the primary side of the transformer is fine, but on the secondary side I'm getting only 1.5V. I'm therefore assuming that the transformer is kaput.

Rather than buying a new transformer, I'm considering fitting this particular ceiling hole with GU10 mains-voltage downlighter. I'm a bit anti-low-voltage, as I regard the transformer as just one more thing to go wrong.

That's the background - here's my question. Is there any technical reason why I should not put a mains-voltage lamp into this circuit, along with the seven transformers which drive low-voltage lamps? So far as I can see, the units will still constitute simply eight loads on the mains lighting circuit, and shouldn't make any difference. But am I missing anything?

All opinions and advice gratefully received.

 

[MdB]

I'm not sure exactly what you mean by resistance free...
"no", "low", "high", "infinite" are terms normally used when you can't be bothered to give an exact reading. If your bulb had a constant resistance with temp (it won't) then it would have a 2.9 ohm resistance (very low). The leads should be even less.

I can't see any reason not to mix your lights.

 

[Penners]

I'm not sure exactly what you mean by resistance free...
"no", "low", "high", "infinite" are terms normally used when you can't be bothered to give an exact reading. If your bulb had a constant resistance with temp (it won't) then it would have a 2.9 ohm resistance (very low). The leads should be even less.

I can't see any reason not to mix your lights.

Thanks for replying, MdB. I'm sorry that my terminology betrays my ignorance! What I meant was that, if I set my multimeter to x1K ohms, and touch the probes to each end of the circuit (whether it be a lead or a lamp element) the meter winds up to near the top end of the scale (ie: very low resistance), thereby showing that a circuit exists. This is my crude system for deciding whether a lamp/fuse/cable is functional or not. It's not so much a case of "can't be bothered" - more of "just hit my knowledge ceiling"!

I'm reassured by your views on the lights, thanks.

 

[Flyfisher]

Have you tried simply swapping bulbs between the failed fitting and a working fitting? If the failure moves with the bulb then the bulb if faulty, if it stays with the fitting then the fitting is faulty.

I share your feeling about transformers being an unnecessary complication and also agree with MdB that there should be no problem mixing different types of fittings on the same circuit.

 

[Penners]

Have you tried simply swapping bulbs between the failed fitting and a working fitting?

Thanks for that sensible suggestion, FF. I haven't exactly done as you suggested but I have tried two different, brand-new LV lamps in the fitting, without success. I've used my ohmeter to check the circuit on the lamps, and all are good. I've also checked the leads from the secondary side of the transformer by touching one probe on the transformer terminal and poking the other one into the lampholder pin hole - both leads give me a circuit. I'm satisfied that the fault lies in the transformer itself.

Thanks for your confirmation that my plan shouldn't present any technical problems. I'm going out this afternoon to buy a GU10 fitting.

 

[FamilyWiggs]

Have you tried simply swapping bulbs between the failed fitting and a working fitting?

Thanks for that sensible suggestion, FF. I haven't exactly done as you suggested but I have tried two different, brand-new LV lamps in the fitting, without success. I've used my ohmeter to check the circuit on the lamps, and all are good. I've also checked the leads from the secondary side of the transformer by touching one probe on the transformer terminal and poking the other one into the lampholder pin hole - both leads give me a circuit. I'm satisfied that the fault lies in the transformer itself.

Yeah but, isn't Flyfisher's way, you now, like, much easier and quicker? :wink:

BTW Blast you Penners... now I'm niggled by the fact that 1 array of our 2 arrays of GU10s in the kitchen hasn't worked for about 18 months. Now I'm going have to go and work it out and fix it... :evil: 8)

 

[Feltwell]

Is there not a danger that you will end up with one fitting that looks different to the rest?

 

[Penners]

isn't Flyfisher's way, you now, like, much easier and quicker?

It's easier and quicker as a way of finding out whether the lamp itself is to blame. But having established that it wasn't, I went on to demonstrate my advanced knowledge of electronics, by seeing whether the meter needle moved or not (even that was somewhat above my paygrade).

BTW Blast you Penners... now I'm niggled by the fact that 1 array of our 2 arrays of GU10s in the kitchen hasn't worked for about 18 months. Now I'm going have to go and work it out and fix it.

Yes, well I won't tell you the details of the private arrangement between Mrs FW and me. But I can now reveal that she and I hatched up this fictitious story of a fault with my kitchen lighting simply in order to get you off your @*se.

 

[Zebra]

There wouldn't be any problem in terms of load on the circuit, in mixing the types of lights. You will just have to buy a mains voltage GU10 lampholder, and swop it from the low voltage one. However, the GU10 mains voltage light will look different from the rest. They give out a different kind of light, more yellowy and more diffuse, less bright and white than the low voltage ones.
I agree, that the transformer is just one more thing to go wrong, and cannot fathom why many new build houses are built with dozens of low voltage downlighters throughout, meaning that after a while the inhabitants are having to call out an electrician every few months.

 

[Flyfisher]

isn't Flyfisher's way, you now, like, much easier and quicker?

It's easier and quicker as a way of finding out whether the lamp itself is to blame. But having established that it wasn't, I went on to demonstrate my advanced knowledge of electronics, by seeing whether the meter needle moved or not (even that was somewhat above my paygrade).

Thing is, a no-load secondary voltage reading on the transformer may not tell the whole story. If the transformer is of the switching type rather than a linear type (which I'd guess it's quite likely to be because low-voltage lighting requires quite high currents and switching transformers are much smaller and more efficient that linear ones in such applications) then, depending on its design, it may require a minimum load to operate correctly. A blown or removed bulb means the transformer will be operating without any load and its circuitry may, depending on the design, 'shut down' leading to a fairly low and meaningless output voltage. Perhaps as low as 1.5v.

Since there are multiple lighting units available, I would want to compare the no load secondary voltage output of an identical known working unit before drawing an absolute conclusion that 1.5v means a faulty transformer - which it could do but might not.

But I wouldn't want to complicate matters . . . :wink:

 

[Penners]

I wouldn't want to complicate matters

Well, if anybody has complicated matters, FF, it's me - by not understanding such minutiae! I knew that transformers could be overloaded, but not that they were able to take a spontaneous decision to shut off their secondary circuit in the event of no-load.

However, for the sake of a tenner I have solved the problem with a new, fire-protected GU10 unit. As Zebra pointed out, the light is slightly different, but it's not enough to worry me - or, more importantly, for Mrs P to have noticed (ssssh)!

Many thanks to everyone for your thoughts and advice on this matter. Much appreciated.

 

[Flyfisher]

I wouldn't want to complicate matters

Well, if anybody has complicated matters, FF, it's me - by not understanding such minutiae! I knew that transformers could be overloaded, but not that they were able to take a spontaneous decision to shut off their secondary circuit in the event of no-load.

'Transformers' is a bit of a wide term though. The typical 'period', lump-of-metal, transformer with primary windings that connect directly to the mains and a secondary winding that gives the lower voltage are, as you rightly say, not able to 'decide' to shut down under no-load conditions.

However, these days, most 'transformers' are rather more complicated and use high-frequency switching circuitry to allow a much smaller 'lump-of-metal' transformer to be used. The result is a smaller unit and a far more efficient conversion of mains AC voltage to low-voltage DC. Their internal circuitry gives them the 'intelligence' to adapt to any mains voltage or frequency, which obviously makes the manufacturer's lot an easier one because they only have to provide a single power supply regardless of which country they are selling into.


Anyway, the job seems to have now been done, so all is well again!

 

[Juju]

I don't understand any of the technical stuff but we have the same problem with our kitchen downlighters. I feel tempted to get rid of them and try something else. The problem in our kitchen though is that the ceiling is so low I'm not sure what the alternative would be.... I seem to remember a thread about this so I'll do a search. We have a beam across the room so maybe we could have something fixed to that but not sure whether we could get the light where we want it. Still I don't like the light from the downlighters anyway...
Juju

 

[Penners]

The problem with a low ceiling, Juju, is that it's difficult to know what else you can use, other than downlighters.

My daughter thought it would be a good idea to have high-level spotlights (well, as high as her ceiling would allow) in each corner of the kitchen, shining sideways across the room. This was awful! Whichever way you looked across the room, there was always at least one light shining right in your eyes.

You don't say exactly what you dislike about downlighters. Is it perhaps the "pooling" of the light? If so, you might want to try buying some bulbs with a wider spread of light - you can choose the angle of spread as well as the wattage of your bulb.

 

[AMc]

I don't understand any of the technical stuff but we have the same problem with our kitchen downlighters. I feel tempted to get rid of them and try something else. The problem in our kitchen though is that the ceiling is so low I'm not sure what the alternative would be.... I seem to remember a thread about this so I'll do a search. We have a beam across the room so maybe we could have something fixed to that but not sure whether we could get the light where we want it. Still I don't like the light from the downlighters anyway...
Juju

Sounds like your problem may be with the colour characteristics of the bulbs? Bulbs can go from warm white at around 2700K to cool daylight at 6500K which is much more blue.
The crucial thing is to get a colour temperature you like
http://www.lightbulbs-direct.com/article/colour-temperature/

I bought some cheap GU10 LED bulbs from Beenandqueued which gave a delightful morgue blue - thankfully I was able to replace them with a pendant when we changed the room from a kitchen into a dining room. In some cases the longevity of modern bulbs can be a drawback

 

[Juju]

The main problem for us is that 2 of the fittings don't work very well. We've had an electrician look at it once but we'll get another electrician in soon to look again - one fitting won't work at all and another is intermittent - must be a loose connection somewhere... I will look at different bulbs as suggested - we just tend to buy them in Sainsburys and hadn't thought about colours and spread of light etc.
Juju

 

[AMc]

Very few lightbulbs give you information about the colour temperature, spotlight angle and lumens (amount of light they output).
My kid brought home a "free" Megaman 9W CFL bulb from school with a request for a donation so they can buy recycling bins. The packaging mentions this 9W CFL is a equivalent to a 60W bulb but doesn't give you its actual output so you can't really be sure.
I gave up trying to find "good" GU10 LED bulbs as mistakes are quite expensive and we now use the room with them in much less so I'm less concerned about the amount of energy being used in there.

 

[MdB]

9W CFL is a equivalent to a 60W bulb

A factor of 6.6 improvement :shock:. They either have come up with something new that I haven't heard of or they found the worlds worst 60W bulb to do the comparison.

A good rule of thumb ratio to use for CFLs is a factor of three. i.e. Your 9W CFL will produce something like the same amount as a typical 27W filament bulb. The fact that most manufacturers put a ratio of 4 or 5 (and now 6.6) on their packets is one of the reasons that people dislike CFLs because they are dim. It is something the EU was looking into with the idea of making the lumins rating a requirement for the packaging. I've no idea what has come of this.

 

[Penners]

The main problem for us is that 2 of the fittings don't work very well. We've had an electrician look at it once but we'll get another electrician in soon to look again - one fitting won't work at all and another is intermittent - must be a loose connection somewhere

If they're low voltage lights, Juju (the kind that just have two thin pins on the bulb) then you may well have some poor connections. In my experience the cables that connect the lampholder to the transformer can be very susceptible to heat corrosion at the lampholder end.

Don't bother trying to repair them - replacements are much safer and very cheap: http://www.amazon.co.uk/gp/product/B004OK8B1C/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=103612307&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=B003T04248&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_r=146V6F9S0PEM44V60P00

Check to make sure that this is the correct fitting for your lamps!

 

[Zebra]

another is intermittent - must be a loose connection somewhere... I will look at different bulbs as suggested - we just tend to buy them in Sainsburys

if they're the low voltage type, then intermittent-ness can be a sign that the transformer is on its way out. You can change the transformer yourself if you feel confident. Also, with these type of bulb you tend to get what you pay for, I find, so if they don't last long it might be worth buying a better brand. Also remember, as with any halogen bulb, not to touch them with your fingers when you put them in - the oil from your fingers supposedly gets on them and makes them not last so long.