Sorry - labouring the point a bit here ...

Still on light bulbs. I have lots of the MR16 style halogen downlighters in my house, as well as a few of them in one of my wife's cafes. They all use

20 watt versions of the MR16 lamp. Why has everywhere stopped stocking these ? You still seem to be able to get 50 watt bulbs almost anywhere, but not 20s. You used to be able to buy them on cards of six in pound shops, but not any more. I have had to order some from an online supplier, but I even had to go through a few of those to find 20s. The thing is that there is not even any suitable replacement for them. The place that I have ordered these from of course keep the LED replacements, but they state quite clearly that they should only be considered as an 'accent light' and are not suitable as a primary light source. Well what use is that ? A few years ago, these lamps were sold in multipacks by all the sheds, and were used a lot to provide 'primary' lighting. Certainly they do in the 'well' over my stairs, and all along the upstairs corridor that goes from one end of the house to the other.

It worries me a bit that with 20 watt lamps not being readily available, Joe Public will start subbing 50 watt bulbs on the basis that the wattage is not particularly critical with mains bulbs, and the fact that the fitting is the same on both 20 watt and 50 watt bulbs. Where these lamp sets are powered by a conventional iron-cored transformer, as the sets of three invariably were, this will give rise to a severe overload that the transformer will try to cope with, generating a lot of heat as it does. Given that these transformers are usually just lying loose in the loft against a joist, and covered by roof insulation, surely this is potentially a recipe for disaster ? Or am I missing something here ? Thermal fuse in the tranny, perhaps ?

Arfa

Reply to
Arfa Daily
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In article , Arfa Daily writes

I think you are right to be concerned but yes, there is always a thermal fuse in the transformer, it's part of the BS/EU spec for them.

No idea on the availability issue, they're not something I've ever used (or fancied).

Reply to
fred

Didn't know this: thanfully they rarely fail and I still have quite a few spares.

We did get 'failures' in the early days but it turned out that this was indeed where someone had put a 30W one among the 20s: this made the lights turn off after a few minutes, so, yes, they do have cut outs, but whether these are thermal or electrical, I don't know.

S
Reply to
Spamlet

They're definitely electrical. And if they cut out after a few minutes, they're definitely thermal

NT

Reply to
Tabby

Not necessarily so. The three lamp sets were invariably supplied with a conventional iron cored transformer to supply them. It was usually an enclosed oblong job about the size of a flourescent light ballast choke. With three lamps at 20 watts, this equated to around 5 amps at 12 volts, which a reasonably sized transformer such as this could cope with. However, the five lamp sets usually had a switch mode power supply to drive them. Similar physical size, but much lighter, and easily able to cope with the 8 or so amps needed to run five of them. Not so much of an issue with these when a lamp fails, as they are reasonably load regulated, so the voltage does not rise, as it does with the iron cored transformer supply on the three lamp sets. Also, not an issue if an over-rated bulb is fitted, as the switchmode power supply has over-current sensing, and will shut down if it detects an excess load that it cannot cope with. If a bulb that is only a little outside of the nominal rating is fitted, as that poster suggested with a 30 watt bulb in place of a 20, then the power supply may well take it for a while, before deciding that it is going to shut down. I have never come across an auto resetting type of thermal fuse in these lighting sets. Most thermal fuses incorporated in transformers, are buried in the primary winding, and are once only types.

I recently replaced two light fittings in my lounge, which each used five MR16 20 watt bulbs. The central unit which was fixed to the ceiling, was a circular silver plastic enclosure about 6" across. Contained within this housing, was an absolutely bog-standard 12v torroidal transformer. It is actually rare to have thermal fuses incorporated into this type of transformer. I have kept them both, as the trannies will come in handy one day for some project or other. I will try to remember to have a look at them tomorrow, to see if there is any evidence of them containing any sort of overload protection. Imagine loading one of these fittings up with an ever increasing number of 50 watt bulbs over the correct 20 watters, as they fail over the years.

Interestingly, I have also found the 20 watt MR16s to be very long-lived. I installed the downlighters in my stair well and upstairs corridor probably

10 years ago, and the first bulb has just failed a couple of weeks ago ... They run continuously in our cafe the whole time we are open, and I would say that we probably end up swapping out all of them around once a year - and these are the cheapies that we used to be able to buy from pound shops.

Arfa

Reply to
Arfa Daily

I find the colour temperature of the 20 watt MR16 halogens to be lower than the 35 and 50 watt ones. Perhaps they last longer because the filament runs slightly cooler?

Reply to
Caecilius

some numpty online supplier once sent me 10w rather than 20w i ordered

- they were like yellow fairy lights, ghastly! who uses em and for what?

Jim K

Reply to
Jim K

Very possibly. I find the colour of the 20s very pleasant. I have one 50 in the house, and that is in an over-shower extractor fitting. Its light is definitely rather whiter than that of the 20s, but still not unpleasant.

Arfa

Reply to
Arfa Daily

They *are* like fairy lights. We have twenty of them in the ceiling and three in a dividing arch where a dividing wall was removed. They are on dimmers and are used like the lights in a cinema: however, dimmers being what they are, in some positions the lights flicker - even more star like, but irritating.

Incidentally the same 'bulbs' are used in our in cupboard kitchen lights, and they blow the most frequently, whilst the sets on the dimmers haven't blown at all.

S
Reply to
Spamlet

The one 50W we have is also over the shower: it was so bright it kept you warm while the water was running to temp. Now it's a warmer pink as the waterproof cover is full of dead harlequin ladybirds.

Incidentally the failures I have had have generally been the pins melting rather than the filament: Obviously this is more likely, the more watts you have.

S
Reply to
Spamlet

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