Is this light switch ok

[Brian Gaff]

Are you sure the old one was not one of those with a timer on/off inside it for security purposes. I have one of these in my hall. Brian

[Scott]

[snip]

I was planning to use AC LEDs and not to buy the cheapest I can find. As an alternative, I did wonder if I could fit a rectifier after the transformer output but Mr Google suggest this might produce a fluctuating voltage.

[Roger Hayter]

Depending what sort of rectifier it will produce 100Hz or 50Hz flicker, which some people at least will find intolerable, and will reduce brightness. There are design criteria for DC power supplies, and you could no doubt build one, but by the time you dealt with electrical safety considerations it would be quite a project and cost more than getting a commercial LED power supply.

[Scott]

Thanks. Then I will stick with AC LEDs :-)

[Scott]

[snip]

I have now looked at the transformers. They are very heavy, round and

5 inches in diameter. I'm assuming there are no electronics involved but I could look inside if you could tell me what to look for.

[Roger Hayter]

Assuming the output is AC I should think it virtually certain that there are no active electronic parts. There could be some interference suppression components but they will come to no harm. Low load will do no harm to the transformers. As someone said, the low load voltage might be a little high, but probably not enough to worry about.

[ss]

I doubt it as it has benn left in every conceivable position and nothing has gone off or on or changed in any way. When I swap it over the next few days I will find out for sure.

[Scott]

Thank you. This is looking very promising. I hitherto assumed that upgrading to LED would be an impossibility. Could I ask you two more questions:

1. Is it worth checking the voltage with no load to see what it is?
2. Any recommendations about bulbs. Are some more tolerant to overvoltage than others? (The more expensive ones perhaps!).

[Roger Hayter]

Check it with a small load, say 5watts. If it is below, say, 13.5 volts I wouldn't worry. Especially if you haven't got an expensive true rms voltmeter.

No idea, sorry.

A cautionary tale about using a transformer other than the maker's one with a fan - probably doesn't apply at all to lighting. I have a Vent Axia Tempra fan and the mains input to their transformer includes live, and live switched, abbreviated to LS. This was for the usual fan purpose of supplying power when on timer or using a humidity detector, while the live switch turned the fan on manually. The terminals on the actual fan are marked 24v and LS (and 0v, obviously). You might possible assume that the LS connector required a 24v signal, although this is not that reasonable, since converting live switched mains to 24v would require a relay (or two transformers!) anyway. In fact the LS terminal on the fan is activated by shorting it to 0v, and is connected (directly) to a PIC input. So 24v was a remarkably bad idea.

[The Natural Philosopher]

The ones I have, have but one thing that has gone wrong (excepting the mouse that chewed through the mains cable ) and that is a thermal cutout, as they do overheat if buried in insulation. On one of these, instead of coming back on, it stayed dead permanently.

[The Natural Philosopher]

Not with LEDS, no. They are not nearly as sensitive to overvolatge as filaments.

I think you can buy in most supermarkets LED bulbs that will work fine on 12VAC that are designed to go in the MR16 fitting.

Or just google MR16 12V LED and see what strikes your fancy.

Some wont dim though.

[Scott]

[snip]

Thanks for all the advice on 12 Volt LEDs. I have now ordered four and will carry out some live testing on one of the lighting clusters.