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Somebody initially wired up six 12 vac 10 w halogen bulbs under my kitchen cabinet, wiring them in parallel. The 12 vac power supply was putting off a lot of heat, and within a day or two appeared to burn out. Prior to that I questioned that the power supply was enough to power the 6 bulbs and, trying to recall some basic calculations from physics class 25+ years ago, I think the math showed that we were pushing the transformer beyond the load that it was created for.

So with with the wiring in place, I'm thinking about replacing them with some form of LEDs instead. I think that the power requirements for LED's will be significantly lower and I do have a large box full of assorted transformers that might work as a power supply.

Rather than purchase a kit from a store, I'm thinking of using the existing wiring that's running through the cabinets, purchasing high output LED's and whatever components I might need (resistors?), warming up my ancient soldering gun to wrap this job up.

How would I go about this? What types of LED's should I use, and how would I go about figuring out the power requirements for this set of 6 lights? Should they run in parallel or in series?

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3 Answers 3

You can buy LED fixtures off the shelf, which are basically ready to go. I've seen these as puck-shaped lights that are basically designed for under-cabinet or shelf lights.

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There are other pretty simple off-the-shelf solutions as well, such as using rope light.


If you are talking about using raw LEDs and literally doing everything yourself, it's pretty simple. You need to get some high output LEDs (pay attention to color temperature, beam angle, etc to make sure it is suitable). You can get LEDs in different packaging: clear/diffused, large/small, forward/side-emitting. Likely your best bet will be a large frosted one. How many you need will just depend on how much area you're covering, and how bright you want it.

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You'll need a DC power supply. The exact values are all dependent on what you use, so it's very hard to give an answer here. There are online LED array calculators available, which can give you something like this:

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One of the major disadvantages of serial wiring (shown here) is that if one LED is disconnected or burns out, they all go out. Finding which one is broken can be difficult, and if you've ever done this with x-mas lights you'll understand what I mean.


Another possible disadvantage of the DIY solution is that you are either going to have to come up with a nice way to package this all underneath, or you'll have a bunch of wires and bare LEDs hanging under your cabinets (maybe hidden by some moulding, but still). This may turn off future potential buyers. Off the top of my head, using some split-loom tubing may be a way to hide the wires and make it look at least half-decent.

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I got a bit LED obsessed and started using them everywhere I could. One thing I came to realise is that they save allot of electricity but do not depend on them as a primary light source(in some places). They lack the luminance of a halogen or florescent tube.. they are getting better though. That said..

Do not bother making your own arrays: waste of time and very prone to failure. You can buy led strips that when one fails only a segment will fail and not the entire array. (well the array within the entire strip- earlier version the entire things fell over what an annoyance)

On ebay (pretty cheap)

You can also look at dx.com or seeedstudio.com-sehnzen4u; they used to be cheap here but it seems they quadrupled in price and ebay fell.. they just do not know how much to charge for them so be careful not to get robbed in day light.. look around..

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So in reply to your question:

Keep the cables you have but the transformer are most likely not going to be any good(you said you had halogen) most main stream halogens run off 12 volts.. but AC so this will cause flickering in the LED.. and reduce live they claim.

So you get rid of those and buy some 12 volt DC power supplies BUT you need to pay attention to how many amperes they can provide. Ebay once again you could find 4 Amps 12 volt and they should be more than enough to supply up to 6~8 metres strips no problem.

How to know how much amperes?

You need to calculate the collective Wattage that will run on the one adapter. So lets say you get a 5metre led strip = 25 watts (typically 5W per metre (30LED per metre))

  • 25Watts = 2A
  • 25w / 12volt = amp

or in other words

  • 4A = 48Watts
  • 12volt * 4amp = watts

If you put to many LEDs for 1 power supply to handle they will dim.. LED's are curious little things and do not overload the power supply because they can adapt to lower power, without side effects to the power supply. A light bulb demands that there be enough power if not.. then it causes issues.

Some advice

I put over 20 metres in my house in various places. In my kitchen i removed the old dingy under cabinet florescent tubes and run the entire length of the cabinet.It is actually pretty good light as it about 40CM from the table top.

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And under my aquarium for sump lighting(used an offcuts I had lying around about 30CM)and also other side off my kitchens under cabinet LED lighting...

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Led lights of any type that you want to replace in the ceiling is the issue.. you would need to triple up on the sockets to get some good enough light.. otherwise it makes it seem like the room is misty.. even thought the light is on..

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If you only want to use 1 power supply then pop into your computer store and ask for 550Watt power supply (the smallest ones now a days and they are cheap)

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What you are interested in there is the SATA and Molex cables. Each one is connected to a separate rail within the power supply. there are 3 rails usually and 1 rail for CPU (ATX connector with all the wires) Each rail is rated on the power supply 12v@5A 5v@20A for example.. so there you have 12 volts with 60 watts capability. Computer supplies are nice because they offer stable, clean power so the LED life are increased thanks to that. It has overload protection (but LED's do not cause overload like I mentioned earlier.. but a short circuit will) so it has short circuit protection too in case something off happens (like LED outside, water or cat taking a bite into the strip .. who know.. cats are dumb) Obviously computer shop will stock "GAMING" power supplies at the price of an arm and leg.. go for the cheapest ones or ask for a used one even.. usually loads lying around in the workshop.

FAILURE

Yikes.. things break! yes they do. I have seen LED's introduced into many places around the world.. the funniest must have been a local council in South Africa that replaced all the traffic lights with LED arrays.. back in 2006. They were amazing- nice and bright and promised a 60%~90% decrease in traffic light power consumption over old 60 watt bulbs BUT.. after 6 months they started failing.. 1 bad LED killed the entire bulb.. oooops. they started melting.. ooops. sometimes only 1 led lit up? huh.. hahah.

That is why I recommend to buy pre made strips.. Look it also happened to me.. why? I do not know.. But its not an issue because...

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I can cut that segment out and replace it.. but I just cannot be bothered.. :-)

GOOD LUCK

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I think an LED bar would be better for your case.

If you want to replace 6 lights with LED, MR11 or MR16 is OK too. Both MR11 and MR16 are 12V. To replace a 10W halogen light, 6 units, 1W MR11 is OK.

Some clients use T5 LED tube light. Or an LED strip is OK too.

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