The Engineering Case for Fusing Your LED Strips

Modern LED strips are magical things. The WS2812 has allowed the quick and easy creation of addressable RGB installations, revolutionizing the science of cool glowy things. However, this accessibility means that it’s easy to get in over your head and make some simple mistakes that could end catastrophically. [Thomas] is here to help, outlining a common mistake made when building with LED strips that is really rather dangerous.

The problem is the combination of hardware typically used to run these LED strings. They’re quite bright and draw significant amounts of power, each pixel drawing up to 60 mA at full-white. In a string of just 10 pixels, the strip is already drawing 600 mA. For this reason, it’s common for people to choose quite hefty power supplies that can readily deliver several amps to run these installations.

It’s here that the problem starts. Typically, wires used to hook up the LED strips are quite thin and the flex strips themselves have a significant resistance, too. This means it’s possible to short circuit an LED strip without actually tripping the overcurrent protection on something like an ATX power supply, which may be fused at well over 10 amps. With the resistance of the wires and strip acting as a current limiter, the strip can overheat to the point of catching fire while the power supply happily continues to pump in the juice. In a home workshop under careful supervision, this may be a manageable risk. In an unattended installation, things could be far worse.

Thankfully, the solution is simple. By installing an appropriately rated fuse for the number of LEDs in the circuit, the installation becomes safer, as the fuse will burn out under a short circuit condition even if the power supply is happy to supply the current. With the example of 10 LEDs drawing 600 mA, a 1 amp fuse would do just fine to protect the circuit in the event of an accidental short.

It’s a great explanation of a common yet dangerous problem, and [Thomas] backs it up by using a thermal camera to illustrate just how hot things can get in mere seconds. Armed with this knowledge, you can now safely play with LEDs instead of fire. But now that you’re feeling confident, why not check out these eyeball-searing 3 watt addressable LEDs?

 

 

44 thoughts on “The Engineering Case for Fusing Your LED Strips

    1. Or heavier gauge wires?

      It seems like a design flaw in the strip itself, because the power leads are resistive enough to limit current, which means they’re resistive enough to produce I^2R losses even in normal operation.

      Suppose for example the shorted out strip resists enough to keep the short circuit current below the 20 Amp margin for ATX power suppies. It must have a resistance of around 0.6 Ohms, and that’s very bad if you’re stringing them together end to end.

        1. Right, because people that buy a LED string that draws many amps and then don’t take the right setup to power them it’s the fault of the LED string supplier? OK, sure.
          Thanks for making america great with your comment.

        2. Can’t help but feel it’s a little fucked up / racist for us to drive up the demand for ultra-cheap manufacturing, outsource it ourselves, refuse to produce anything domestically, hire indentured servants on starvation wages, and then insult them and the country which manufactures everything we own. Seems pretty damn ungrateful.

        3. Just because someone isn’t personally responsible for societal problems doesn’t mean they can’t contribute to them, due to the nature of participating in society. You can’t make comments like that without considering the circumstances that led to these situations.

          That is all I have to say.

        4. Yes I can make comments like this because he said, “it’s racist for us”. So he is either calling the commenter racist, or all of America racist. If he is calling all of America racist then he is stereotyping (exactly what he wanted to avoid when directed at China). If he is calling the original commenter racist, then my original current stands.

    2. It can better but my guess it adds too much cost to the product. And where do you add this fuse? After 10, 100, 1000 leds? How do you maintain the abbility to cut the strip at any given length? Adding a fuse in the lead to the strip (and precisely calculated) is the best option.

      My guess is to use a smaller fuse then the 1amp in the example. A 1amp fuse trips at 1.6 amps in about a second. See this page about fuse characteristics: https://etrical.blogspot.nl/2016/07/hrc-fuse-construction-working-and-characteristics.html?m=1

      1. That’s why the user needs to add the fuse. It’s not suggested it come with the strip – it’s suggested that it should be designed into the final project by the end user.

      1. Came here to say the same. Fuses belong as close to the power source as possible, not at the load! Looking at it in the direction coming from the power supply a fuse only protects against shorts in whatever comes after the fuse. If there is ever a short in the wire somewhere between the fuse and the power supply the fuse does nothing to protect you and your house may burn down.

      2. Well, actually its always a question of: what to protect.Best is to add fuses “everywhere”. Like in a house. In the house i live in are multiple fuses: 3 big ones where the energy comes in (3x 80A my case – 3phased system ) .. then there is a fuse in front of my counter with 3x32A and from there is a cable comming into my flat with multiple fuses @16A for the actual rooms/users. ( light, sockets, cooking, etc )

        same would apply here: here 60A fuse directly behind the psu would only protect the cables behind it, but it would not blow in the error i show in the video. ( approximatly 15A ).

    3. Resettable (PTC) fuses add a significant resistance (and therefore voltage drop) to the circuit. Since most LED strips are just using a repetitive layout pattern, there would be a number of fuses in series in a long strip. This would lead to reduced brightness (or total failure) of the LEDs on the far side of the strip. Traditional, non-resettable fuses (or even PCB trace fuses) might work better due to the lower resistance (and still prevent a fire in the unlikely case of a short circuit).

      A fuse integrated in the strip itself would also not help against faults in the wiring leading to the LED strip (e.g. at the solder points to the strip). So adding a fuse next to the power supply is probably the better option.

  1. See people doing dumb crap all the time with high current power supplies, no protection and their own circuits. At least when its on a USB port there is usually some protection from significant over current – except on terribly cheap 12 port chargers which lack anything.

  2. For 5V strips, voltage drop across the fuse can be an issue – TI do some really nice USB port protectors which are basically electronic fuses with resistor-programmamble current trip. For 12 and 24V, IR do some nice automotive high-side protected switches, e.g. AUIR3315

  3. Fuses fuses and more fuses.
    I have a 12V lighting system threw out my house
    On almost every line out I have them fused at 5 Amp
    Some that I know will be drawing more then 5 Amps I would of used thinker wire and larger fuses.
    At the end were The Light is I am looking for around 11.3 V For my led lighting on a 12 volt power supply.
    I really like the lower voltage, The leds last so much longer. i have gone threw so many leds to get to this point.
    There has been around 4 versions of my fuse layout. This one Im using now is the best.
    This is my basic lay out.
    Batteries 100A each
    Going into Relays 30A to 40A
    Coming into my main splitter I have a double 40A fuses
    then from there it goes to 15 fuses of 5 amps and 5 fuses at 7 amps.
    Most of the wiring is #18 to #16 wire. There is a lot of slitting in the panel.
    And we cant forget about communication wiring.
    I have tested my fusing system here and there and am very happy there It all seams to work nicely.

    I have discovered a new IC, at least for me, The 5A Hall Current Sensor Module ACS712
    I will be using it on my devices to help keep everything balanced.
    My system is a ongoing and growing system. And I wonder if I will ever get it fully going.

    But you have to keep it safe and fusing and wire size is so so very important.
    Please for give me in grammar and so forth.

    1. Wow I don’t understand how spell checker is supposed to work in here.
      I type one thing and see the right thing on the screen and when it gets printed on the poset there are always words that are changed. I read and reread and read again. It happens way to much. Sorry.
      This time – thinker is to be thicker.
      and slitting – splitting.

    2. I have a 12V lighting system, originally with halogen lamps. The transformer also delivers lower voltage than rated – 11V to 11,5V. I hate this. It is argued, that the lamps have longer lifetime, but what is not said, that especially incandescent lamps like Halogen loose very much brightness and efficiency. It makes the light ugly yellowish. In reality the only reason seems to be that the manufacturer can overrate the transformer. It is rated “12V/240W” But it has lower voltage, more so at the end of the rails, so lamps with a combined power of 240W draw much less than 20A, the transformer delivers less power – for even much less light.
      I don’t see, why LED lamps should last longer, they normally have a constant current driver anyway. Fortunately their color temperature does not change when they are underdriven.

  4. 12V push-to-reset breakers are cheap/easy to find have been used in vehicle applications for decades, and can be gotten with a “pull off” feature so you can manually open the circuit. This winds up being SOP for in-air electrical malfunctions in aviation (and has produced more than one tall tale*).

    5V winds up being a bit harder since there aren’t easy vehicle parts to use. – there are things like the LTC1153 programmable, polyfuses and the like but once an installation is in and running properly (read “you’ve done all the accidental smoke letting”) inline tube fuses are good enough. It might be an interesting project to build a temporary fuse “black box” to allow safe project fiddling while still on the bench – most people don’t bother with overcurrent protection at all, and the hazard is leaving something running while unattended.
    ______
    *It was rumored that the F-14 could be put into “oversweep” configuration while in flight putting the wings swept fully back — this was normally used for storing the airplane on a carrier flight deck since the wings didn’t fold upward — by pulling the breaker on the gear squat switches. If true, I don’t think I’d care to be the first to try it in actual flight.
    http://navyaviation.tpub.com/14315/Figure-2-8-Wing-Oversweep-Position-Manual-Control-F-14-55.html

  5. Nice article. I would hope that most folks know to add fuses to their circuits and the correct place to put them, but I am sure a lot of folks do not and I hope they read your piece.

  6. Been there, done that. (in the bad sense) A project at my employer a few years ago involved 3 watt RGB LEDs, 4″ apart, on a beam structure that would end up being 23 feet tall for a video/media facade for a 3 story clothing store on New York’s 5th avenue. The company that developed the design (for the architectural firm hired by the store) made breakout boards to supply power to 5 beams for the required 24 hour burn-in. Each beam pulled 5.5 amps. So, the 24v 40A power supply feeding the breakout board could easily supply the required 27.5 amps of current, so no problem, right?

    Except that the terminal block connectors the designer specified were only rated to 18 amps.

    The first morning after the first 10 beams ran burn-in brought the smell of burnt plastic, luckily, no fire. The PCB traces near the connector heated up enough to break and stop the flow of current, but the incoming 24vdc connector was heavily melted and charred. I was the one that analyzed the design for root cause and found the terminal block current limitation. The setup change to feed power to 3 separate points on the breakout board to limit the current on the board and through the connectors (the breakout board had 10 blocks). After that, the boards didn’t even get more than 10 degrees above room temperature. Crazy how quick current draw can bite you. I still have the pictures and use them for training purposes occasionally.

    To aid in the resistance issue across the end to end boards inside the beam, secondary cables ran along the inside of the beam to provide a direct connection to the 24vdc source directly to sections half way down the beam.

  7. I bought a lighter from a Chinese vendor and when I held it at my curtains for a while my curtains caught on fire.
    I mean really China, why didn’t you prevent me from doing that? Geez.

    And it’s not the first time, another time I bought a frying pan and filled it with oil then when the oil was piping hot I threw a nice chilled glass of water on it and at that time too it showed how irresponsible those Chinese products are. We should ban China and build our own government controlled 5G network based on Donald’s personal design is what we should do, that’ll show them commies am I right?

  8. It beggars belief that it takes a whole Hackaday article with associated comments to advise the use of a fuse where excess current could cause overheating. Every horny handed electrician knows that. Nay every fule noes that..

  9. With a few LEDs, dropping resistos make sense. With folks stacking 64 bit processors, why can we not see the responce might be, a dc-dc convertor to drop V to led use? Why use 12V when 2 or 3 is the need and waste 3/4s of the energy to install energy efficient lamps? Someone will, and state the efficiency gain overall, and many will flock.

  10. Ok… It’s a strip of leds. A cheap fuse could be at the end w the cabling. It would be like several ribbons of aluminum foil in a perhaps 1×1″ matrix. Instructions say, scratch 1 ribbon away for each foot of led strip that you cut away. Similarly, place such fuse-ribbon at 1 ft intervals. Idiot resistant. A fuse holer with 2 fuses supplied would cost more but be more flexible.. maybe 500 ma and 1a… Xmas tree lights have these in the plug.

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