LED Driver sizing query/confirmation

[Cordless Crazy]

Looking to run some LED lights as a feature in the house, but want to hard-wire a transformer instead of having to use two wall warts.

I have two kits of ten, but only plan to use 14 of the small LED's.

Going back to basic maths, please correct me if I am wrong...

The kits do not state the LED wattage, so will work it out from the info on the plug-in transformer, which states an output of 12v at 200mA. Seeing that a max of 10 LED's can only physically be connected to one tranny, each LED equates to (0.2*12)/10 = 0.24W

I plan to connect 14 of these LED's thro a hard-wired tranny, which needs to be rated as 14*0.24 = 3.4W, which equates to 3.4/12 = 0.283A or

283mA

So as long as I buy an LED driver rated at 3.4W or above, all is good?

And before the Part P brigade jump all over me... oppps.... snore.... sorry I fell asleep.. all I want is clarification on the above, hence asking people in the know!

[Dave Plowman (News)]

What matters with an LED is the current flowing through it. On a basic setup, this is limited by using a series resistor. Pukka LED drivers use electronics to achieve the same thing. Some pulse them to allow a higher perceived brightness.

If they are small LEDs where efficiency isn't an issue, series resistors are the easy way to go. Either one per LED wired in parallel, or one shared with several wired in series.

[fred]

In article , Cordless Crazy writes

Kit implies that the LEDs are already connected in some kind of series/parallel arrangement and without knowing the details of that it is not possible to advise the best way to connect them up.

Are these lengths of LEDs on flexible tape, or something else? More info or a link to the kit and you'll get more reliable information.

A white LED will normally drop about 3V so the norm is to run 3 in series off a 12V dc supply and then use a series resistor to get the current right.

On a separate note, are you ever going to get decent access to this newsgroup instead of using that third rate ripoff of usenet that is diybanter? They rip our content without permission and make money off the sponsored and affiliate links. IMO the worst possible kind of leeches.

[NT]

There isn't the necessary info here. Your best bet is to power a set up and measure the v across and i through one of the LEDs.

NT

[Adam Aglionby]

As long as they are wired back individually to the trafo which would suggest 12V per LED.

That sounds about right for a single LED with a resistor soldered on its leg.

CCTV PSU`s are available in handy packaging, at sub 10W any 12V wall wart will just about do.

Just keep the 240V bit dry and out of reach.

Cheers Adam

[Andy Champ]

Oh so THAT's why cheapskate car manufacturers make the tail lights flicker.

You know, those cheap brands like Mercedes & Audi...

Andy

[Andrew Gabriel]

It's the same reason HID headlamps are blue-white. To quote one of the manufacturers, if they made them the same colour as regular headlamps, no one would know you'd spent £1000 on them, so no one would spend £1000 on them, and they wouldn't sell them.

[dennis]

Nothing to do with the emission spectra of the gas then.

[Dave Plowman (News)]

Lots aren't these days. Mine if anything are a touch green.

[Andrew Gabriel]

You can make that (almost) whatever you like, depending how you dope it.

[Andy Champ]

I'm not sure they are. It's just we're so used to yellow lights... Anyone like to compare some with daylight?

And _some_ manufacturers can make non-flickering LED tail lights. You can recognise them by the fast on-off time. My high-level brake light is LED and is noticably faster than the others.

I always thought the real reason they flicker is that they use that to reduce brake-light brightness down to tail-light levels, and only fit one set of LEDs.

Cheapskates.

Andy