AC/DC puzzle

[stevei]

I have a cooker hood with two lights. Each g4 12v light is fed from a 12v ac transformer. I wanted to buy two led lights to replace them with. Got two from a nice person in the far east for £6.50 for the pair. I can get easy access to the transformer to change it for an led driver but I thought I would try the ac transformer first to see what would happen. I disconnected both halogen lights and connected one led fitting. Switched on and the light from it was really low. To compare light output, I connected one of the halogen lights and one led, in parallel. The light output was much higher on the led; better than the halogen. Then I connected the other led, so two leds and one halogen, in parallel, and again, bright light on both leds and no flicker. Can anyone explain why this is happening? The only thing I can think of is that the halogen is pulling the correct current from the transformer with the leds benefitting from the increase.

[Someone-Else]

I would suspect what you are calling a transformer is actually a switched mode power supply.
A transformer is literally two coils of wire on a former (Something to "mount" the wires to)
A switched mode power supply is a "Bunch of electronics" that drop one voltage to another. (Usually)
Switched mode power supplies are often made for a specific task, with this in mind they often have a minimum rating. One LED lamp is not enough to meet the minimum rating, but one halogen lamp is, so with one halogen lamp connected the output is enough for the switched mode power supply to work.

You really need an LED "driver" to operate the LEDs on their own.

Just saying, if you take apart a mains LED you will find electronics in its base, that is why they work. (It's often a capacitive dropper) which can be made with very few (small) components.

[stevei]

Is it safe to run two 1.5w 12v leds with one 12v halogen bulb using the power supply I have?

[Someone-Else]

So long as the rating of the LED lamps does not exceed the rating of one halogen lamp I would say yes, but bear in mind you will be putting A.C. through a D.C. device, it won't explode, but it may shorten its life.
Also as the cooker hood was designed for 2 lamps, be careful where you put the halogen lamp (You don't want it to burn anything)

[stevei]

What led driver would you recommend for the two 12v 1.5w leds?

[ericmark]

I have noted some LED bulbs actually state 50 Hz, but I think it is likely it does not matter if DC, 50 Hz or in kHz range, they just need a power supply which will go down to zero, many of the new switch mode power supplies are rated zero to maximum output, often marked 0 - 60 VA, where older types often marked 20 - 100 VA, you can consider VA to equal watts, not quite correct, but close enough.

A driver was a current regulated device, but for some reason I don't understand now both current and voltage regulators are it seems called drivers if the output is DC, where drivers were back in the mid 80's AC devices.

So forget the name, look for 12 volts and current starting at zero.

[Someone-Else]

What led driver would you recommend for the two 12v 1.5w leds?

There are lots available, I have no preference as to which one, but you must make sure it is suitable to fit in the space you have.

[OnlyMe]

What led driver would you recommend for the two 12v 1.5w leds?

A 12V constant voltage driver of at least 5W (it's always best to leave to power space on drivers) that will operate down to zero or near zero amps.

[stevei]

New led lights and constant voltage driver fitted and working well. Access to the wiring and AC power supply was easily gained by removing the stainless steel chimney cover. I used the existing wiring. The led driver is about a quarter of the size of the original power supply. The light from the new lamps is much brighter and whiter than the halogen bulbs.

[Someone-Else]

The light from the new lamps is much brighter and whiter than the halogen bulbs.

That will be because of the colour temperature.

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[ericmark]

That will be because of the colour temperature.

Also caught me out when I first went from compact fluorescent to LED. I got the SES LED bulbs to try in reading lamps, but had some bulbs fail in the main room light, so put them in as a temporary stop gap. The, I think 1.8 watt bulbs, seemed so bright, that when Lidi did some 3 watt versions I changed all the 8 watt CFL for LED. This was OK until I tried to read a book, at which point realised too low of an output, changed to 5 watt all 10 of them so a room as built with two x 100 watt tungsten now lit by ten x 5 watt LED, so 200 watt to 50 watt, so 1/4 of the power required, plus the cost of 2 new chandlers, to take the 10 bulbs, and swap the thermostat to a programmable one, as missing the inferred heat from the bulbs in the evening, so thermostat had to raise air temperature 2 degrees C in evening to what it was.

Now moved, this house living room had one bulb, I would assume 150 watt would have been used, swapped to an eight bulb chandler, and 6 watt LED, so 48 watt, and not good enough, so have display cabinet lights 3 x 20 watt but dimmable, and up lighters 20 watt, to supplement the lighting when required.

I think the main problem is the LED directs the light different to tungsten, so there is no direct replacement. I love the new lighting, being able to walk into a room and say hey google turn on living room lights is great, does not matter if ceiling light, or plugged in, one command turns on/off all. But the claims as to how much light they produce, I take with a pinch of salt.

[dewaltdisney]

I thought that this thread was going to be about who wrote AC/DC's hit Back in Black controversy.

DWD