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#21 |
A Fake Rubycon
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#22 |
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![]() Yes, we most certainly do
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Popcorn. |
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#23 |
master hoarder
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![]() LEDs will always have shitty life if they are overdriven with current or run too hot. Typically the former causes the latter, but now always! Sometimes an LED can fail simply from being over-driven with current.
I myself was disappointed with LED life way back a few years ago when a friend and I set up lighting for his workshop with a bunch of those flexible 12V white LED strips (the cheap rolls you can find everywhere on eBay and elsewhere online). Driven by a spare PS3 power supply, the strips were getting nice, regulated 12V power (about 12.3V IIRC when I measured it a few times) and so they ran absolutely cool to the touch - even the individual LEDs themselves. Nonetheless, most of the LED strips lost a substantial part of their brightness after just three months of being powered 8-12 hours per day. A lot of them even managed to blow a hole through a few of their LEDs. So then I took one brand new LED strip home and one of the "bad/weak" ones to compare them. The weak strip was pulling almost 2x the amount of current compared to the new strip. Thus, it looks like the LEDs in the bad strip were starting to get leaky or short out. But why? The new strip was drawing only 10-15 mA of current per LED at 12V. Didn't seem like much. As I couldn't find the maker of the LEDs, and thus not able to find a datasheet, I just took the new strip and tried running it on 9V. The strip seemed only a little less bright than at 12V, but it was drawing substantially less current - about 1/5 less. So I think the LEDs in a lot of these strips and light bulbs are just over-driven so that the manufacturer can get away with using less LEDs. Combine that with a hot-running bulb, and it's no surprise that LED bulbs don't last. So that's why your LED bulbs are bound to get poor life when left to run 24/7. The really expensive bulbs may have better, more efficient LEDs (Cree, for example) and with better heatsinks. But the cheap LED bulbs - forget it! I wouldn't trust the life rating on their box for squat. 10 years? Sure, if you never use the thing. ![]() ![]() As for what I use (in terms of lighting)? - I have a decent stash of incandescent and halogen-incandescent bulbs. Should easily last me the next 10 years, if not more. I don't use CFLs at all, as I find the UV-rich light too harsh on my eyes. The only CFLs we have in the house is one set with 2 T8 bulbs in the garage and a desk lamp (with a specialty CLF and linear ballast) that I use for my work area (which I almost never turn ON, as I work during the day most of the time, and I have a big window with plenty of natural light). |
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#24 | |
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![]() Quote:
![]() Also, those cheap LED strips are 100% the reason you had problems. I've sourced cheapo led bulbs that I could sell for 50 cents each and make a profit, and they lasted 6 months at best? They all ran not too hot, they just died easily thought because of heat and overcurrent. However, this circuit was running under 50v likely. There were 6 LEDs iirc. I'm guessing no more than 30v, so 6V per chip. Assuming these are multi-chip LEDs (I will microscope them to confirm this) They can be dissipating 3v or less per chip. I've yet to see non multi chip leds that can take over 3V. If these are 3 chips or more, the dissipation will be very low. That also helps with color temperature, which on these was very good. However, if that's true then they are going to run only slightly warm each, however combined with the shitty heatsink these had, it'll probably run a little hot. However, they're not being driven hard if that's the case and therefore should have a decent life. Also keep in mind, it wasn't the LEDs fault for the failure, it was a small SMD resistor that should've been bigger. |
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#25 |
A Fake Rubycon
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![]() Most cheapo LED strips have 3 single chip LEDs in series, if we do the math 3.2V x 3 = 9.6V! And they say these are made for 12v.
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#26 |
Great Sage 齊天大聖
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![]() they do have a resistor with those leds though.
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#27 |
A Fake Rubycon
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![]() The resistors on my LED strip are 39Ω each and there's only one resistor per set of three LEDs.
Last edited by RukyCon; 10-07-2017 at 04:36 AM.. |
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#28 |
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#29 | |||
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![]() But 20 years -WHERE is the main question here.
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Like I said, a lot of my cheap 12V strips nearly doubled their current use after a few months of 8-12 hours per day operation. I wouldn't be surprised if an LED or two in those chip LEDs shorted out and drew a massive current through the resistor. Though the only way to know for sure is to buy one of these bulbs and measure the current going through the resistor. With: W = R * I^2, you can easily find out how much power the resistor is dissipating and whether its power rating was chosen properly or not. Quote:
That's why I am able to run mine on a 9V power supply (SMPS, regulated - not some linear transformer outputting 16V unloaded ![]() Quote:
![]() 39 Ohms is insane, actually. At 12V operation, there will be approximately 3V for that resistor to drop. So at 39 Ohms, you are looking at 1/13 of an Amp, or 77 mA passing through each LED! ![]() Last edited by momaka; 10-10-2017 at 04:04 PM.. |
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#30 | ||||
A Fake Rubycon
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#31 | |||
master hoarder
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![]() Hmmm... I don't know about that. Even Japanese caps will have a hard time "waking up" after 20 years sitting unused.
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That said, the more current you try to pass through an LED, the higher its voltage drop will become. It's a non-linear relationship, though, so doubling the current won't really double the voltage drop. Quote:
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Regarding those cheap SMD LED strips: I also read a technical article somewhere sometime ago that these LEDs use have a soft lens/case to cover the die. Because of that, cheap LEDs tend to have poor seals and it said this was one of the main reasons why they failed so quickly. On the other hand, the article said that cheap standard through-hole 3 mm, 5 mm, and 10 mm LEDs with clear epoxy lenses/cases didn't have that problem, as they were generally sealed better. And personally, I think there is some truth to that, because I haven't seen those fail as often as cheap SMD LEDs. So if buying cheap LED bulbs, you might be better off with ones that have those through hole LEDs. Of course, they won't last long either if their LEDs are over-driven with current and they run hot. But if not, and if they are powered by a good PSU inside, then they should last a more reasonable amount of time. |
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#32 | |
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![]() Quote:
Anyways, I tested the LEDs on the board of the lamp, they're 6V LEDs! So two chips per I assume? I put 7v across one and it went to full brightness immediately (by this, I mean the chip was absolutely blindingly bright.) So x6 chips equals about 32V that this would've been running at. None of the LEDs drew excessive current going through my meter, so I'm going to rule that out. Also, as you said before, the LEDs could've been shorting causing the resistor to go bad, the only problem I have here is the resistor is the size of a quarter watt SMD resistor, and it's on the + side of the rectifier, going straight to the capacitor, and then to the output. I think that's probably wayyyy too small for a job like that. I keep forgetting to upload pics, therefor right after I post this I am going to upload some. Edit: added pics Last edited by jazzie366; 10-13-2017 at 10:21 AM.. |
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#33 |
Great Sage 齊天大聖
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![]() R1 is burned, interesting the board can take a parallel pair.
i wonder how many franctions of a cent they saved by only fitting one!!! |
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#34 |
Badcaps Veteran
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#35 | ||
master hoarder
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![]() Quote:
If you don't have a variable current source, use a resistor with a voltage source. It takes all of 20 seconds to run through a simple Ohm's law calculation to determine what resistor you need. Otherwise, you risk burning your LEDs or severely shortening their life. Depending on the current capability of your source, sometimes even a split second is enough to nuke the anode's wire bond on the die. Quote:
Last edited by momaka; 10-14-2017 at 02:30 PM.. |
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#36 | |
Badcaps Veteran
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If I was working on sensitive electronics I would've used a proper PSU with current limiting. |
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#37 | |
master hoarder
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![]() Quote:
But even when I don't care just like you, I still take a random spare resistor from my scrap box and use it. Typically 1 to 10 KOhm will do the trick fine just to test the LED. Thus I always keep my resistor box handy. Besides, I sometimes find the need to discharge large caps for safety reasons. ![]() Last edited by momaka; 10-14-2017 at 06:11 PM.. |
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#38 | |
Badcaps Veteran
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#39 |
Great Sage 齊天大聖
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![]() lol
big clive checks for a charge with his fingers! |
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#40 | ||
master hoarder
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![]() Quote:
![]() Though I usually use a 4.7 KOhm, 5W resistor. Takes 2-3 seconds tops, usually. Quote:
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