Downlight requirements

[JohnW2]

One of my daughters lives in a rented flat. It's living room+kitchen (something like 4m x 5.5m, and over 3m high) has no less than 11 downlights in the ceiling, with 12V 50W GU5.3 'MR16' halogens in all of them (most of which are currently dead!). 550W for a room of that size is surely ridiculous?

Debates about the desirability of downlights are futile, because she is stuck with them. I have so far been unable to find whatever transformers/PSUs are driving them, so can't be at all sure that LEDs would be an option (and nor would be changing the transformers/PSUs, even if I could find them).

We might suck it and see with some 12V LEDs, but may well end up having to stay with halogens. If we do, 50W ones seem way OTT (given the number), with 20W and 35W ones seemingly being fairly findable. Without any arguments about the desirability of such lighting, does anyone have an idea as to whether 11 x 20W would be adequate (220W sounds like a fair bit to me!)?

Kind Regards, John

 

[ban-all-sheds]

does anyone have an idea as to whether 11 x 20W would be adequate (220W sounds like a fair bit to me!)?

SIAS with those too.

They all have a fairly short life anyway, so buying a bunch and then finding they are inadequate won't be significant in the long run.

 

[winston1]

I have so far been unable to find whatever transformers/PSUs are driving them, so can't be at all sure that LEDs would be an option (and nor would be changing the transformers/PSUs, even if I could find them).

Do you have, or access to, a 'scope? If so the easiest thing is to look at the output waveform at one of the lights.

 

[JohnW2]

Do you have, or access to, a 'scope? If so the easiest thing is to look at the output waveform at one of the lights.

I have several 'scopes, and that would certainly be an option. Even simpler would be a capacitor and resistor of suitable values, plus a multimeter. I don't get there that often since it's a significant and tedious journey (in hours, not miles, since most of London is in the way!), but will certainly go appropriately equipped next time.

In the meantime, as BAS has said, the obvious thing is, at least for the time being, to advise her to suck it and see with 11 x 20W halogens. When I got there on Saturday only four of the 11 were still working, but that seemed to be producing a fair amount of illumination, and by the time I had installed the three spare 50W ones she had, it seemed extremely bright. We had to stop there, since there seemed to be nowhere remotely local where one could get 12V GU5.3 'MR16' halogens of any wattage.

For what it's worth, my multimeter on its AC range showed about 12.4V. Your logic might say that that indicated that it was 50Hz, but I really don't believe that. There spec of cheapo multimeters often says little/nothing about frequency, but the more up-market ones do. Fluke multimeters only specify the voltage measurement accuracy remaining unchanged (at about 1%) up to 1kHz, and say nothing about accuracy beyond that frequency. However, this bit about frequency measurement on various AC voltage ranges seems to indicate that they can make at least a stab at measuring voltage (with whatever accuracy) up to 50-100 kHz ...

Kind Regards, John

 

[ban-all-sheds]

I have so far been unable to find whatever transformers/PSUs are driving them, so can't be at all sure that LEDs would be an option.

Buy them from a shop where you can examine the packaging.

If they document no restrictions, then given that 99.9999% (approx) of existing halogen MR16 G5.3 lamps will be powered by some sort of SMPS, you'd have good grounds for returning them if they didn't work.

 

[JohnW2]

In terms of LEDs, the greatest potential problem is probably the minimum load of the SMPSU, which is commonly stated as 20W for a 'halogen electronic transformer'. I haven't got a clue as to how many SMPSUs there are, but if it's 'one per downlighter', then that could be a definite problem, quite apart from winston's concern about frequency.

Kind Regards, John

 

[ban-all-sheds]

True.

Buy 1 - you could still take it back.

 

[JohnW2]

I would probably have to buy several - since if it is not 'one SMPSU per lamp', it could be that several LEDs would work, whereas one might not.

 

[ban-all-sheds]

Could you have a look in the ceiling void with a small torch & inspection mirror?

 

[333rocky333]

Sometimes if you look at the lamp through a camera phone, you see a visible flicker with an electronic transformer, something your daughter can do herself, wont tell you how many on each transformer though.

In my experience Its rare to have more than 1 of 50w lamp on a single transformer
2 of 20w lamps on a 50va is rare and 2 of 50w lamps on a 105va even rarer, a big tran doing 11 off 50w lights is massive.
Most people used to design to take a 50w per fitting to be safe.
35w seem more common now and you will likely get better prices on them.
If they have put 2 of 50w on a 105va tran, then using 20watt lamps can become a problem when 1 lamp blows as 20w sometimes wont exceed the minimum load rating

 

[333rocky333]

Your first post implies you looked and could not find the transformers, what sort of wire is at the fitting, would that give an indication of whats going on, mine are wired in 2mm twin so its pretty clear to see they go back to a box transformer somewhere, my corner downlights are larger to allow for the bigger 200va tran to pass through.
I could drop some 35w lamps off on way home sometime for a cup of tea

 

[JohnW2]

In my experience Its rare to have more than 1 of 50w lamp on a single transformer...

Yes, that's what I imagined - but I just don't know for sure. If that is the case then given that most halogen PSUs seem to have a minimum 20W load, there might well be a problem with LEDs.

Kind Regards, John

 

[JohnW2]

Your first post implies you looked and could not find the transformers, what sort of wire is at the fitting, would that give an indication of whats going on, mine are wired in 2mm twin so its pretty clear to see they go back to a box transformer somewhere, my corner downlights are larger to allow for the bigger 200va tran to pass through.

It's not easy. As I said, the room is well over 3m high ( blame the Georgians!), and even my tallest step ladder (platform at about 1450mm) is only just about tall enough to enable me to do things to the light. The bulbs/lamps are plugged into nasty little ceramic sockets (some of which are not going to last much longer) from which a couple of singles covered in some sort of heat-resistant braiding disappear into the dark depths. The holes in the ceiling are not big enough for me to get my hand through (even if I could reach properly!). I tried pulling fairly gently on the wires to see if anything would 'appear', but nothing seemed to want to budge, and I didn't want to pull too hard, and I didn't have a small enough mirror with which to try to get a look!

Kind Regards, John

 

[333rocky333]

As you well know most limit there length to about 500mm so it does appear you may have them tucked away elsewhere, i have a small A frame ladder if you ever want to meet there let me know

 

[JohnW2]

As you well know most limit there length to about 500mm so it does appear you may have them tucked away elsewhere ...

Indeed, but they are quite probably very close to the 'holes', if I dared to tug a bit harder on the wires.

... i have a small A frame ladder if you ever want to meet there let me know

That's kind of you, and I'll certainly bear it in mind. However, the step ladder I've got is just about tall enough. I would also imagine that it's a bit out of your way (SE London - Camberwell) ... and if you had as much trouble finding somewhere to park as I did on Saturday, you would probably retract the offer

Kind Regards, John