12volt led lighting

[caveman]

Hello All,
I bought 20 of these on ebay, cheap. They are 12volt MR16 led lamps and are designed to replace those 20 watt and 50watt halogen guzzlers people use as down lighters. They plug into the fitting either way around which is a clue that they are designed to run of an AC supply and so they must have some simple electronics inside to convert the AC to the DC current that LEDs use.
I could see that the leds were mounted on a printed circuit board (pcb) which was then glued into a old style MR16 halogen reflector. I tried to dig the pcb out with a knife but I did not get very far. A more brutal scheme was devised. I put the lamp into a strong envelope and, resting the rim of the reflector on concrete, I taped the opposite edge with a hammer until I heard it crack. I rotated the now crunchy lamp through 90deg and hit it again.

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[caveman]

Very carefully I removed the broken glass from the pcb and cut the wires. It seems to me that the edges of the reflective coating are even sharper than the glass. Every time I crack one of these lamps I manage to cut myself.

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[caveman]

With the edges cleared of any small pieces of glass I could handle the board and get a good look at the components. The 12 VOLT AC comes in on the two white wires and goes to a rectifier. This is the device which converts the AC to DC. The output of the rectifier is connected to a capacitor which smooths the current and ensures there will be no flicker.
You can see from the picture the DC terminals are conveniently marked on the board. If they weren’t I would have relied on the capacitor to indicate where the red (+) and black (-) wires were to go. Capacitors of this type always have their negative terminal clearly marked.

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[caveman]

I desoldered the rectifier which cleared the view of the tracks on the board and soldered the + and – wires to the most secure spot on the board. It is not necessary to remove the rectifier. No current will flow through it so long as the + and – are connected correctly. However if you leave it there and the DC connections are reversed, even for a second, there will be a small bang and a bad smell! With it removed the leds will look after themselves in such an event.

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[caveman]

This is one running at 220mA on 12 volts DC. It is very bright, too bright to look directly into. Because of the way the electronics worked these leds will work up to just over 15volts. Here are the sums for those who might be interested:- 12 volts RMS, minus 1.2 volts lost across the rectifier, multiplied by 1.414 gives 15.27volts DC on the capacitor. This means you could run these lamps off a battery while it is being charged without worrying about blowing it.

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[caveman]

Here are 2 fittings I have converted. They are both in our 1970s campervan. The white one was a MR16 fitting. I just ignored the socket and fished the red and black wires down through the shell and out the back to a switch. The brown one originally used a car bulb. I took the holder out and glued the led board in place with silicone. This light uses 8 times less current than it did.

I hope this is of use to someone. Any questions- just ask.

Conor

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[johnboy]

Check out the 4 watt MR16 Cree bulbs. They draw a bit more than this sort but are miles brighter. The down side is that they retail at over £20 each at the moment. Price should drop as technology marches on though.

[caveman]

These were very cheap, If I remember they were about £2.50 each. I bought them a year or 18 months ago. LED technology is developing very fast and 'Cree' produce some great technology but it is expensive. Luxeon are another company at the same thing. The lamps I used are not the most efficient because they use simple resistors to limit the current through the leds. Posh lamps use active electronics. Also these lamps produce a cold bluish colour of light which is not that nice in the evening and less so in the winter. Another problem with them (and many more expensive led lights) is the output angle. Each led produces a beam of light which is 15 degs wide. With errors in construction the beam from 38 leds is only a little wider. This is fine in the sort of fittings shown above, they make a good reading light or spot light but for general lighting they require an imaginative design of reflector such as those found in led lanterns. They did offer the advantage of being adaptable. The board is flat and so lent itself to bodges such as those above. I have a few more fittings to adapt. The job is usually simple, glue and solder does the trick. When better leds become cheaper they will be easy to replace. I will post pics as I bodge.

[anern]

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[jcinta]

As Led light bulbs are expensive they were not in frequent use until recently or were used as a single bulb application in lighting pens, remotes, electronic items etc. But as technology is getting improved day by day, the cost of led light bulbs is also getting lower and resulting in their use in applications where clusters of bulbs are used like battery items, flashlights and headlamps etc.

[Reilly]

I use about 12 LEDs in out house but they're not our main lighting source although they do help to make a room feel bigger and create a nice ambiance. You can use shades to soften the colour and I use red nail varnish - one thin coat to give a nice rosy glow and it wears well. [URL="http://*****cye *** another SPAM link removed. if you are interested in this spammer you can google soluna green .we will not allow commercial spam linking posting here

[tomhill]

If you look at previous posts you will see that spam is not welcome on this forum. I am sure admin. will be along soon to clip your link.
BTW.
It is usually the case that LED lighting is cost effective but HOW the LEDs are produced and HOW they are used determines how 'eco-friendly' it is. How eco friendly is the factory and its suppliers? How eco friendly are the lives of the employees? What about your company and your fellow employees?

The flashing red nose on a superstore festive reindeer may well be cost effectively rendered with LEDs but don't tell me that it is an eco-friendly thing to do.

If you are actually interested in this sort of stuff, engage thoughtfully and don't spam.
Tom