LED lighting should be simple, right?

Miscellaneous and Personal Stuff I Must Share
1

This is driving me up the wall! I have a lot of bookcases and was dithering around for a long time about how to light them. I finally decided to make LED light bars and mount them under the top lip of the bookcases. Sounds simple, right?

Not if you’re me!!!

Let me enumerate the obstacles…

  1. The little clamp-on connectors have a positive and negative side. The LED strips have a positive and negative side. The connectors are all oriented the same way, so I either have to attach one upside-down on one end of the LED strip, or attach it rightside-up and hand label one of the black wires as being positive. I am still figuring out if the connectors work at all when attached upside-down.

  2. Wire stripping! That turned out to be a success story after I bought an automatic wire stripper. One thing went right!

  3. Today I tried attaching two bars together. The first one lights and the second doesn’t. I’m afraid of the electricity even though they are low voltage DC. So I wasted an hour on Amazon trying to figure out what kind of voltage detector to get. I finally ordered one. Will find out next weekend if it works.

  4. But then I still have to figure out what I did wrong. Did I attach the connector the right way? Did I damage the LED strip when I attached the connector? I still don’t know about the upside-down thing. Did some of the glue from the LED strip get on the metal part of the connector and prevent it from working?

I did all of this to save money and get some nice lighting for my bookcases. It is driving me crazy and making me feel like an idiot!!!

2

You can buy LED strip lighting from China very inexpensively. It comes coiled up and every third diode it says “cut here” and you can cut it to length at that point. You remove a plastic backing to expose adhesive and it sticks where you put it. You connect a wire from the control box and it just works. It’s $6-7 for a 5 meter length on Amazon. For a little more you can get RGB LEDs and a remote control to change colors and brightness if that’s your thing. Feel free to drive back down the wall :smiley:

3

That’s basically what I have. Deceptively simple…

4

You’re going to fail this class over unsolicited extra credit, my friend.

5

what are you using to power the LED strips? if it’s just a DC power supply, do the LED strips have built-in ballast resistors? If not you risk burning them out in short order.

6

LEDs are simple – you just have to make sure you’re applying the voltage in the correct direction, make sure it’s the proper voltage, and make sure that you have a current-limiting resistor in place (or are using a regulated current source.

Here are the basic directions:

If you put a lot of LEDs in parallel, then you need a separate current-limiting resistor for each. It’s better to put them in series, because then if one LED + resistor is a lower resistance than the others it won’t end up taking extra current. When I ran a batch of diode lasers at the same time*, I ran them in series for exactly this reason, even though it would have been easier to hook them up in parallel. I knew that they were all running the same current.
*Laser Diodes can be viewed as a very special case of LEDs. Electrically, they’re pretty much the same.

7

Basic DC Fundimentals. Series and Parallel circuits.

Before you open your wallet really wide to buy your lighting, I’d suggest you get buy a digital multimeter (you’ll find other uses for it), a little breadboard, some 1.5v batteries and a holder with leads, some resistors (for current limiting), some LEDs, some hookup wire, some small dykes, and a wire stripper and do some experimenting.

8

Hi guys, thanks for the ideas. I got everything at an LED online specialty store and followed their online recommendations for the power supply, etc. Basically it’s one power supply with 4 branches going to various groups of bookcases. Each individual bookcase would have a 22-inch length of LED strip, and the strip would connect to the strip in the next bookcase with some connection wire. Each of the 4 groups of bookcases would contain between 2 and 5 individual bookcases. I will review the links you gave, and after I get the tester, I will continue to try and figure out what is wrong where.

9

You are going in the right direction. I have installed these kinds of lights both in my kitchen and as backlighting for a cross I built for our church.
I used a higher grade LED than you probably are referring to, the 120 LED/meter stuff from here. But the process should be the same.

You were correct in following the site’s instructions–they have specific power supply recommendations based on feet of run and number of branches. The power needs drop if you have multiple branches rather than running everything in series.

The LEDs are installed in parallel in the strip, presumably with the necessary resister built in. This means that it doesn’t matter how long the strip is, the voltage needed is the same; you only need to worry about the total power consumption, and that should have been handled when you chose the power supply.

If I understand correctly, you have 4 branches, with each branch consisting of multiple lengths chained in series.

The challenge is all in the connections. Make sure one edge is “+” from end to end of your full run, and the other edge is “-” from end to end of your full run (don’t overthink it and try connecting positive of one strip to negative of the other–they aren’t batteries).

If you get one accidentally swapped, there is no danger: the LEDs won’t light, but nothing will burn out. This means you can start with one section, then add the second section and see if that lights. If it doesn’t, reverse the leads connecting section 1 to section 2. If it still doesn’t light, then your connection is bad (are you making contact?).

If the connection is bad (i.e. not connected) make sure you clipped the tape in the correct spot. With mine I had to clip exactly on the line in the middle of the copper pads, so that the copper pads were at the very end of the segment.

Work your way slowly through each leg, getting them all lit. Then you can hook the legs up in parallel. Again, if the leads are swapped the lights will not light, but nothing will burn out since they are diodes and won’t allow current to flow the wrong way.

10

Thank you so much, minor7flat5. It’s very reassuring to know I can’t blow out the lights, and you have understood my setup. So my plan is good, I just have to keep on fiddling around with the connections! When I get the tester I will try again.

11

This whole thread has me flabbergasted, with the talk of current and voltage direction and resistors… what? I bought some LED strips a couple years ago that I installed under my computer desk. There were 3 steps to installing them:

  1. peel off the adhesive backing and stick them in place.
  2. Connect the strips to a central hub thing, which just involved plugging it in like a USB (it’s not USB, but I don’t know what the proper term for this type of connector would be).
  3. Plug the hub thing in to an outlet.

And that was all I had to do, and it just works. There was nothing complex about it; certainly nothing that would require measuring voltage or stripping wires or having a degree in electrical engineering. Just stick, plug, plug, done.

I can’t even really envision all the steps you are going through but it sounds really, really complicated - like you are hand-wiring and soldering all this stuff from scratch. Unless you are an enthusiast or student trying to learn about circuits and electricity, I don’t understand why you’d want something that complicated when there are much simpler products out there. Did it even come with instructions? I would link to the strips I bought but I believe I got them from a site other than Amazon and I can’t find it again right now.

12

the shortest version I can come up with:

LEDs are rated for a certain voltage and current. typically for a bright red LED, this will be around 2.2 volts at 15 mA. You can’t simply connect one to, say, a 2.2 volt battery or DC power supply, though. LEDs are “negative temperature coefficient” devices which means their resistance drops as they heat up. They’ll just draw more and more current until they burn out.

so you can do one of two thing:

  1. use a DC supply voltage above the LED’s rated voltage, then wire an inline ballast resistor to drop the voltage and current down to within the LED’s rating, or

  2. use an “LED driver” circuit which has built in current limiting. Most of those “peel and stick” strips like you describe have these built in, either into the strip or into the power supply they give you.

13

To Rigamarole’s point, simple stuff like strips to put under your computer desk have straightforward connectors and no ambiguity. The higher-end custom installation stuff has all kinds of places where questions can arise. They have little joiner clips that will join two custom-length strips and end clips that have wires.

The problem is that any custom installation will require cutting the stuff to length, and will also require using regular low-voltage wire and wire nuts here and there. It’s not rocket science, and anyone who has done home wiring should have no trouble with it, but I am not surprised if someone is running into issues.

Regardless, there should be no need for a test meter, nor should there be any thought of resistors or other things. Just follow the manufacturer’s recommendations for calculating the correct power supply and Bob’s your uncle.