Adding a fuse to my circuitry with LED lighting, a good idea? - Page 1
Forum section: electronics / beginners

author: Decoman
author_rank: Regular Contributor
timestamp: December 08, 2017, 04:15:58 pm
content: So I will be working on a rather large scale model kit, 70 cm long, and I will be installing LED lighting, and having the LEDs powered by some 9V or 12V wall wart as you guys call it, with an on/off button to turn the lights on and off.Given how fragile LED's seem to be, I was thinking that maybe it could be a good idea to try protect the circuitry, or rather, try protecting all the LEDs from possible voltage spikes by adding a quick or delicate fuse.So, could it make sense to add a small fuse to my circuit in one or more places to try protect 2-3V LEDs in the circuit?It isn't clear to me if it is high voltage or high current that would either kill off, or even reduce the longevity of 2-3V LEDs. I think someone commented on that particular issue elsewhere on this forum recently, but I am afraid I forgot the details.But maybe it could be a 3V fuse with some max current value that matches the maximum expected amp draw from my entire circuit?Somehow, I suspect that simply adding a fuse won't truly protect the circuit if the fuse doesn't blow fast enough, but maybe that is just a question of choosing a quality fuse I am now thinking.

author: Benta
author_rank: Super Contributor
timestamp: December 08, 2017, 04:32:50 pm
content: Driven correctly, LEDs are extremely rugged.You wall-wart already has a fuse for fire protection, leave it at that and make your circuit so the LEDs are given correct current in all circumstances.

author: Decoman
author_rank: Regular Contributor
timestamp: December 08, 2017, 04:38:41 pm
content: A point of mine would be, to not only to try prevent having the LEDs burn up outright, but also prevent stress that maybe (what do I know) could lessen the longevity.Longevity of my LEDs ought to be made as long as possible, because these LEDs will be inside a closed model, that I rather not want to re-open again, certainly not several times.This is my interesting in exploring the idea of having a delicate fuse (which, if making sense having, must be accessible, and not packed inside the model).

author: Nusa
author_rank: Super Contributor
timestamp: December 08, 2017, 04:56:11 pm
content: Fuses don't do anything to stop incorrect voltage. If that's your concern, you'll have to come up with a different solution.Fuses blow from high current flow, and even then they're slow to react unless the current is massively over the rating. They're primarily there to keep a bad situation from turning into a fire. Saving the circuit is usually a secondary function over the safety function.

author: Benta
author_rank: Super Contributor
timestamp: December 08, 2017, 05:13:15 pm
content: Decoman, your questions reveal that you haven't found a drive strategy.LEDs arenotvoltage controlled, they are current controlled.If you supply them them with the correct current, they will last forever (provided you buy brand LEDs, not crap China stuff).You can increase longevity by derating the current, although this can give colour shifts in white LEDs.If we are talking power LEDs here, thermal management (=keeping them cool) is a prime consideration.

author: Decoman
author_rank: Regular Contributor
timestamp: December 08, 2017, 05:46:27 pm
content: Ok, so I see two issues here:1) Buying/using quality stuffbut also..2) Trying to prevent the LEDs being ruined or burdened, by ANY form of unexpected power surge, or whatever can happen, when having my project powered by a 9V/12V wall wart, plugged into the 10A fused sockets in my apartment. After all, I just want to try avoid having my installed LEDs being damaged in any way, at all costs so to speak, by being extra careful if there is a way to be extra careful in how the circuitry is designed.I really want to try add some stuff to the circuitry if that can help against obvious or not so obvious power surges, but ofc, I am not that knowledgeable to even know if or even how power surges could possibly affect my LED project if I were to have that stuff plugged and maybe running all day.I could be wrong, but I do not expect heat to be an issue with my led setup, as these are well, tiny LED's. I guess I can add to that comment, saying that the LEDs will be inside a closed model with no ventilation, with the model placed in room temperature, and afaik the LEDs would work with maybe 10mA or such. I am only at the start of collecting the LEDs and I haven't even started testing/playing around with the LEDs yet. My newly acquired variable power supply has shipped though, so it should show up in a week or two and so I can start playing with this stuff before committing to designing or installing the LEDs for the project I am working on.Regarding branded LEDs, feel free to add some link where I might get to buy those from some website. I have so far been using eBay to get the cheap stuff, but I am willing to try get the possibly more reliable stuff elsewhere.Off topic: Speaking of LEDs, today I had to return a pack of 5x 7W LED spots used for my ceiling lamp to the store (I still had the receipt), as all five had either died or stopped working properly. The pack of 5 LED spots cost $35. I have NO idea why they failed, and neither does the seller. The spots previously installed in a new ceiling lamp for 4x spot lighting (the fifth one was used as a replacement as some point when the installed spots started to fail). My three LED spots in the kitchen (different design) seems to be working still.

author: floobydust
author_rank: Super Contributor
timestamp: December 08, 2017, 06:14:48 pm
content: I think you are trying to do two things, and asking a big question that usually causes a heated debate here.You have not said what kind of voltage and current we are looking at for all the lighting, how many LED's.First, protection against the model or LED's or ac adapter burning up if a fault occurs.Shorting out your AC adapter would not cause a problem, the AC adapter is required by safety codes to have a fuse and protect itself from fire. Buy a good quality one with proper agency approvals.The next danger is the wiring in your model, if it is very thin magnet wire it could get hot during a short circuit. The wire must be good for the AC adapter's output, or have a fuse or current-limiting device upstream to protect the wire.In a series-string of LED's, some could short-circuit and cook. This depends on the power of this whole thing, if resistors are present etc. if this could be a potential fire hazard.Second, protecting the LED's.A fuse cannot protect LED's. A fuse is too slow, and usually requires >167% of rated current to melt. This is all too much for LED's.If you have say a 12V 0.1A LED string, put in a 0.1A fuse, you would have to power it off something like 17V to get to 0.167A; your AC adapter would not overvoltage this much. And it is taking 235% power to melt this fuse, so the LED's lose as they can't take that much over power.Do put in a reverse-diode to protect LED's against reverse-polarity and -ve ESD surges.Best to wire it up in a star approach (compared to daisy-chain), so you can actually find a short-circuit without going crazy. If your wiring is very tiny.If you can tell us more about the lighting, then better advice is possible.

author: Benta
author_rank: Super Contributor
timestamp: December 08, 2017, 06:33:46 pm
content: I'm still missing the current-control approach here.A variable power supply will not help on that point, if you want this to work properly you need to design current sources for your LEDs. That's the only way to reliability. And a well-designed current source will keep ANY power surge away from your LEDs (well OK, perhaps not a lightning strike. But then you'll have other more urgent problems...).