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Replacement Transformer/driver for ceiling light

Postby bramley4600 » Wed May 19, 2021 4:11 pm

Elderly lady has asked if I could help in finding a replacement transformer/driver for her ceiling light. Currently has this Sunrise one that lights 12 G4 halogen bulbs.
Been to 3 electrical suppliers and none could help. Either not bothered or just didn't know. I probably won't find an exact replacement but that doesn't matter as long as it fits.
Would it be possible to use one of these (Varilight ones) with 12 led lamps at 2w a go? (Crompton G4)
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Postby Mr White » Wed May 19, 2021 4:52 pm

It will not work. If you look at the "Power supply" you have it clearly says 50 -150 watts.

12 x 2w LED's is only 24 watts, your power supply says it has a minimum of 50 watts. Having a minimum load is quite common on electronic power supplies.

If it were me, I would buy a dedicated 12v DC power supply (Some LED lamps flicker unless they are supplied by DC) I guess that is why wholesalers were reluctant.
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Postby bramley4600 » Wed May 19, 2021 5:05 pm

[quote="Mr White"]It will not work. If you look at the "Power supply" you have it clearly says 50 -150 watts.

12 x 2w LED's is only 24 watts, your power supply says it has a minimum of 50 watts. Having a minimum load is quite common on electronic power supplies.

If it were me, I would buy a dedicated 12v DC power supply (Some LED lamps flicker unless they are supplied by DC) I guess that is why wholesalers were reluctant.[/quote]

Mr White

Many many thanks for the reply.
The 'power supply 50 - 150 watts' is the one that's not working. One supplier told me he may be able to get a straight replacement but it would be about 50 quid.
I was wanting to replace it with the Varilight one. This was the one that was sold to me by the electrical supplier. He didn't seem 100% sure so I just wanted a second opinion.
If you could point me in the direction of a 12 V DC unit I would be very grateful - I could use this as a backup as the lady has another identical light.

Cheers

P
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Postby Mr White » Wed May 19, 2021 7:19 pm

I found These for you. Other suppliers are available.
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Postby ericmark » Thu May 20, 2021 7:11 am

You really do need to follow manufacturers instructions, if it says 50 Hz then it needs a toroidal transformer, and if the power supply says halogen only then only use quartz halogen lamps, and if it says not dimmable don't try to dim. And if it says maximum cable length 1 meter, then keep to 1 meter.

The problem is a diode can result in making a radio transmitter, and many switch mode and pulse width modulated power supplies work in the kHz range, and when using a capacitor as a current limiter the frequency is critical.

Unless you dissemble a bulb you have no idea if it uses a simple resistor or complex pulse width modulated chip to control the current draw.

Even the quartz bulb coil of wire could cause problems, but in the main they simply worked, but with LED packages, and remember the bulb has more than just the LED, some are designed for AC and some for DC, and some must have 12 volt others can work 10 - 30 volt.

Other than outside and in bathrooms there is no real point in using extra low voltage lamps. When the quartz lamp first came out, having a thicker filament increased their life, also having a very precise power, both under voltage and over voltage will shorten the life of a quartz bulb, and so they should never be dimmed, and having a switch mode power supply at 12 volt so any mains voltage variation was removed and filament was thicker was a really good idea.

So we got a whole host of 12 volt lamps, originally using a toroidal transformer then latter the electronic transformer which was both cheaper and regulated the voltage. There were versions which could be dimmed, but these caused the bulb to go black and fail early.

As we moved to compact fluorescent or cold cathode and then LED the whole idea of 12 volt became pointless in most cases, a few bathrooms where light too low still need 12 volt and some outside lights, but in the main we no longer need extra low voltage, and the standard low voltage (230 volt) lamp is far better.

LED's are still a problem with 230 volt, as specially if using an electronic switch they can fail to turn off, flash when switched off, and shimmer when switched on. With a good lamp there is a small resistor to leak any small current caused by induction or capacitive linking with cables or the small amount of current used with an electronic switch without a neutral, and a smoothing capacitor to stop the shimmer, but there seems to be nothing on the bulb to tell you if this is included or not, so it is a suck it and see.

However you are more likely to find the resistors and capacitors in large bulbs, so where you can avoid G9 bulbs, and also had problems with some GU10. The SES (E14), ES (E27) and Bayonet (BA22d) bulbs seem to have all the resistors and capacitors required.

The lighting trade name things after what they replace, so often the name now does not really tell you what it is, so an electronic transformer is a lot more than a transformer, and it is so easy to without realising build a radio transmitter by using them with LED bulbs.
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