Thorigol

Again, you make good points but I can take issue with most of them:- I've used these kinds of strips for several years and have yet to see an LED go bad. No doubt someday it will happen, but if the strips are long with many LEDs, the impedance change from one LED going out will be negligible, on the order of milliamps. The OP is running strips that are 40' long - it will take a lot of bad LEDs on strips that long to throw off balance enough to make any difference.- The idea here is to NOT need any specially adapted power supply, but rather configure the load to run at line level. If you're concerned about too much current, you could use additional strips to further divide the voltage.- I agree, every strip must be exactly the same length and the project would have to be carefully pla...see more »Again, you make good points but I can take issue with most of them:- I've used these kinds of strips for several years and have yet to see an LED go bad. No doubt someday it will happen, but if the strips are long with many LEDs, the impedance change from one LED going out will be negligible, on the order of milliamps. The OP is running strips that are 40' long - it will take a lot of bad LEDs on strips that long to throw off balance enough to make any difference.- The idea here is to NOT need any specially adapted power supply, but rather configure the load to run at line level. If you're concerned about too much current, you could use additional strips to further divide the voltage.- I agree, every strip must be exactly the same length and the project would have to be carefully planned to make that work out.- There is little chance anything would damage a strip to short out the rails, but if that did happen, or if over time enough LEDs went out, there could be a situation where too much current could flow. Therefore, such an installation would clearly need a fuse, and that would protect against any such hazard. That's what fuses are for.- As for dangerous voltages, you'd really only see them at the line connection, which as I said, should be appropriately insulated. The potential across any given strip is exactly what it would be in a 12V power supply installation.- Old computer power supplies as the OP employed are not without risks. They themselves have numerous failure modes which can include flame-outs. In several of my other LED installations, I used Zurik LED driver power supplies which are nothing more that well built boxes with a transformer, bridge rectifier, and a fuse; they work great but waste energy as dissipated heat and cost a fortune.- I will grant that Electrical code and insurance issues may be valid reasons to not try this.

Thank you for your thoughtful reply brico63,I completely agree with your analysis. My drawing was in error, I was careless and have fixed it below.I have seen various LED strips that have other arrangements of LEDs and resistors than you have drawn, for instance one resistor per LED, but always across the power rails along the edge as you indicate. Thus the impedance across the rails of any given strip is a function of the number of LEDs.I thought it went without saying, but as your numbers clearly show, my solution would only work if each strip in series has exactly the same number of LEDs. With that precaution, would you agree that it would work?

I'm talking about putting the STRIPs in series. You are obviously correct that the LEDs within each strip are in parallel and that ain't going to change. That doesn't mean you can't put the strips themselves in series - I've done a little drawing with just 2 strips to show what I mean.

No additional resistor needed - These strips all have built-in surface mounted limiting resistors, that's how they make an LED that lights up with a 1.2v drop work at 12v. Your point about the higher peak potential is true, but those are very short periods of time where there will be higher current - if the LEDs are drawing too much RMS current, you could use 11 or 12 strips in series to further divide the line voltage.

You could do this, but then you'd need twice as many strips as the voltage would need to be divided by 10 for each phase.As for any illusion, human persistence of vision would prevent anyone from seeing the difference between 120Hz and 60Hz, although some can perceive the flicker of European 50Hz.

This warning is just plain paranoia. Even with 220v mains, you wouldn't have enough potential to bridge across any of the traces on these strips (which is what I'd assume you mean by "tracking internally"). Plus, the line voltage is distributed across all the strips so the potential across any single strip is still just 12v or 17v p-p. Plus, the waterproofing is silicon which isn't flammable.That said, certainly one should use appropriate caution to fully insulate or enclose any exposed connections.

Yeah, as I said, LEDs are diodes, thus no conduction when the AC cycle goes to the wrong polarity, thus the LEDs would be lit only half the time. Or, as I said, use a 4 rectifier bridge in front of the LEDs to make DC (or at least 120Hz pulses all in the same direction).

Here's a whacky idea - how about NO power supply. All you engineers out there can let me know what you think of this:Take 10 of these strips and wire them in series instead of the standard parallel configuration. That's 12v drop across each for a total of 120v. And LED's are diodes after all, so in theory you can just hook them up, they'll light up for half the cycle and not for the other half. Or you could just put a fullwave bridge rectifier in front of the strips.Of course this means some dangerous voltages so you'd want to use the waterproof strips which encapsulate all the exposed copper except at the ends where you'd want to take appropriate precautions to make sure there is no exposed wiring. But with the safety issue address appropriately, shouldn't this work fine? I'd thi...see more »Here's a whacky idea - how about NO power supply. All you engineers out there can let me know what you think of this:Take 10 of these strips and wire them in series instead of the standard parallel configuration. That's 12v drop across each for a total of 120v. And LED's are diodes after all, so in theory you can just hook them up, they'll light up for half the cycle and not for the other half. Or you could just put a fullwave bridge rectifier in front of the strips.Of course this means some dangerous voltages so you'd want to use the waterproof strips which encapsulate all the exposed copper except at the ends where you'd want to take appropriate precautions to make sure there is no exposed wiring. But with the safety issue address appropriately, shouldn't this work fine? I'd think you could even use a standard lighting dimmer with it. Comments?

Last time I tried to shoot in a local mall, the security guard came around on his Segway and told me photography wasn't allowed. I tried to argue that everyone with a cell phone was breaking that rule constantly, but he just pointed to my big SLR and said it was different and escorted me to an exit :(

Nice wood block. I went for a wall mount as I didn't want to have yet more stuff on my limited counter space.

Wow, I had to google everything in your comment just to figure out what you are saying. Lotta stuff to learn but could be part of the solution I want - thanks!

Thanks for the reference szabonandi! What I'm really looking for however is a local solution to do what you've achieved. This seems easier than others I've seen using Google Gadget and Xively, but I'd like to make the whole solution within my intranet.

I got started by picking up a copy of "Programming Arduino- Getting Started with Sketches" by Simon Monk. From there, the Arduino site itself is a terrific resource and google any question you have: the Internet is full of answers!

Thanks for the reference szabonandi! What I'm really looking for however is a local solution to do what you've achieved. This seems easier than others I've seen using Google Gadget and Xively, but I'd like to make the whole solution with my intranet.