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Noobie needs help on how to construct LED light project

Hi,

I need help on what and how to achieve the following:

I want to use led's to create an indoor ceiling lamp in the configuration as shown on the attached image. This consists of either self constructed strips (or bought strips //sources in the uk would be appreciated) of Leds, which even with my pitiful knowledge of electronics and components, I know, requires 12 VDC. As it is an indoor light in will run from a uk mains of 230Volts. So how can I safely rig this light, with the voltage difference?

What I need to know is 'What' components I need to set this configuration. I found this web page,
but not being electronics savy, I dont really get the jist, apart from a capacitor and resistor is required. see (http://www.marcspages.co.uk/tech/6103.htm).

I need to know what I need of what, and at what resistances etc? and
'How' to wire it all together, in laymen fashion please!!

Also, I have shown a total of 21 LED's in my image, but this is not set and could very to 4/9 a strip. I just want to cover a distance of 20cm. again sources on pre-built strips/kits would be cool.

many thanks
Dan

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opticron8 years ago
Hey Dan, There are a couple of different ways to do it. You could go raw bare to the metal and step the mains down using a transformer and with some rectifiers get approximately the voltage you want (this is the Hard Way and you need to be versed in electrics and power conversion). A better option is to harvest a 12V switching power supply from somewhere and integrate it into the base or hide it in the middle of the triangle behind a panel. If you have trouble finding the strips, I can probably help you design a set. By the way, LEDs generally don't require 12VDC. The value varies between models of LEDs, depends on color and manufacturer, and generally ranges between 2V and 4V for each individual LED. I just happened to make my modules (consisting of 3 or 5 LEDs) run on 12VDC, because I had high amperage 12V switching power supplies on hand and could get more if needed. You may want to browse through sites like digikey.com to get a feel for what values of LEDs are available, even though it may be overwhelming. Good luck, Kinsey
danskimanuk (author)  opticron8 years ago
would use these (x3) if i could but they are $24 a piece.

http://www.superbrightleds.com/specs/LB3.htm

so, at a basic level I either need a 12V switching power supply (which I think is out as the design has no place to hide it) or go the hard 'raw bare to the metal and step the mains down using a transformer ...'

I think this is the way I will have to try to go.
Can anyone help on how I may wire this up to work in terms of a schematic.

This is a design for part of my MA project in product design. If you are able to help me deliver this, of course total credit will be given on your consultancy with regards to electronics.

I still recommend against going with the build your own power supply approach. You can probably find a sufficiently small 12V switching power supply from your local electronics store (or your junk hardware bin). I don't know what kind of bulb sockets you have in the UK, but if you can find a supply of the right size, you could strip the case off of it and try to hide it in the connector/housing. An other alternative (if you want to skip the power supply all together) is to design the LED circuit with a diode and run it directly from the mains, but this is a little trickier and you might not be able to use prebuilt kits/modules. I'll look up some specs and see what can be done, assuming some basic values.
danskimanuk (author)  opticron8 years ago
Thanks Opticron. This is the kinda size we are looking at for the light housings in th UK (dont have the dims at present). I think I would like to attempt to create my own strips and chain them myself, so I could possibly do the direct route from mains to negate the need for the switching supply altogether, although if it can be placed inside the ceiling housing that would be ok. I appreciate your efforts. Its for an MA product design lighting concept that I have that I would like to prototype. I will of course give full credit to anyone who helps make this possible, so would be great if you could help make this happen
photo.jpg
If that's the size, you probably won't have an issue getting a small power supply in there. (if I interpret the size correctly from the picture)
danskimanuk (author)  opticron8 years ago
Are we talking about the housing that is closest to the ceiling? If so its roughly 2cm deep by 7.5cm wide... can you help them further by listing the necessary components and how they should be wired? I will then need to source them. I am looking to make 3 strips each containing 5 white LEDs.
Given the size you specified, you should be able to find a power supply to fit in that area. It would be nice to keep the housing on the supply, but you may have to remove the plastic to get it to fit. If you get the prebuilt strips, all you need to do is connect them to the supply in parallel to get them working. If you are going to create your own, I recommend you use this site to set it up: http://led.linear1.org/led.wiz
I would buy the power supply and LEDs that you want, and then use that link to figure out what resistor you need. Please take care to remember that you need to consider the voltage of the power supply when choosing the LEDs. With a 12V supply, your LEDs need to be 2.4V or less to get 5 in a single strip and white LEDs are typically 3V to 4V.
danskimanuk (author)  opticron8 years ago
Ok, just tried the link. I input 12V for charge and 12V (wasnt sure about this) for forward diode value. Selected 15 LEDs (3 x 5 strips) An got the attached image: even to me the results dont look right!!!;(
led config.tiff
danskimanuk (author)  danskimanuk8 years ago
how about this as a Mains DC to 12V transformer_LED Driver found at this link (its the one that needs to be run in series):

http://www.reuk.co.uk/Transformers-for-12V-LED-Lighting.htm
That actually looks like a really good option to hide in the base! Good job finding it! The result you got from the wizard is because forward diode value is supposed to be the voltage from each individual LED, not several. Also, the current is probably going to be around 20mA, but it will vary by make and model.
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