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Author Topic: Questions about testing LED setups  (Read 127 times)

Offline Decoman

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Questions about testing LED setups
« on: November 27, 2017, 03:00:49 am »
I feel wholly inadequate in evaluating the quality any LED I buy off eBay, so I thought I should try test the LED's and have them run 24/7, until they break. This way, if they do break, for no good reason, then it would be a very bad idea to use them inside any model.

I am not yet familiar with rigging led's but, would this work?

1) Using a 9V power supplier (non battery) rated 500 mA (0.5 amps)
2) Connecting the power, the resistors, the wires and the LED diodes onto a small bread board.
3) Simply add more LED's as you feel like it, in parallel (not serial)

Working with Ohm's law seems easy enough.

V = I x R
voltage = current x resistance

So I am thinking, with a 9V parallel setup, every wire going to a LED this way, will have 9V, and I can use the same type of resistor, as long as the LED are the very same, and the very same color.

As I understand it, a red led uses less voltage, while a purple led, uses more voltage (maybe I am wrong).

So, if I got this right then I can just keep adding lights in parallel, and I need only worry about reaching the limit of 0.5 (power supply rating)?

Am I right in thinking this?

Also..

4) Don't electrocute myself. Not sure what the dangers are from a 9V source.


Testing LED's this way, as I understand it, would allow me to test the same type of LED, but with difference power levels, making the LED brighter but perhaps not lasting as long as the one you power is more weakly lit.
« Last Edit: November 27, 2017, 03:09:23 am by Decoman »

Offline RossW

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Re: Questions about testing LED setups
« Reply #1 on: November 27, 2017, 09:40:59 am »
I feel wholly inadequate in evaluating the quality any LED I buy off eBay, so I thought I should try test the LED's and have them run 24/7, until they break. This way, if they do break, for no good reason, then it would be a very bad idea to use them inside any model.

I am not yet familiar with rigging led's but, would this work?

1) Using a 9V power supplier (non battery) rated 500 mA (0.5 amps)
2) Connecting the power, the resistors, the wires and the LED diodes onto a small bread board.
3) Simply add more LED's as you feel like it, in parallel (not serial)

Working with Ohm's law seems easy enough.

V = I x R
voltage = current x resistance

So I am thinking, with a 9V parallel setup, every wire going to a LED this way, will have 9V, and I can use the same type of resistor, as long as the LED are the very same, and the very same color.

As I understand it, a red led uses less voltage, while a purple led, uses more voltage (maybe I am wrong).

So, if I got this right then I can just keep adding lights in parallel, and I need only worry about reaching the limit of 0.5 (power supply rating)?

Am I right in thinking this?

Also..

4) Don't electrocute myself. Not sure what the dangers are from a 9V source.


Testing LED's this way, as I understand it, would allow me to test the same type of LED, but with difference power levels, making the LED brighter but perhaps not lasting as long as the one you power is more weakly lit.

Yes, that is essentially it. And I highly recommend doing a burning in to ensure you got LEDs that will last.

Some notes:

  • It is unlikely you would electrocute yourself with 9V @ 500 mA, but it would not be pleasant (try touching a 9V battery to your tongue. Or, do not) so always be careful.
  • Reds and greens typically take around 2 - 2.5V, so with a 9V power supply you'd want a resistor of around 390 ohms @ 20mA (I use this online LED resistor calculator: http://led.linear1.org/1led.wiz). Blues & whites have a higher forward voltage so their series resistor would be less.
  • Do not think you have to run your LEDs at 20mA; that is just the general rating but it is usually too bright for a lot of LEDs. You can run them at lower amperages and they will last longer.

Offline Decoman

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Re: Questions about testing LED setups
« Reply #2 on: November 27, 2017, 11:18:08 am »
I will go buy a multimeter soon. :) I've had fun today trying to figure out which one would be adequate and nice.

My choice for my very first multimeter ever, ended up being the 'UNI-T UT61E'



* This model has ceramic circuit breakers (Edit: To be safe, I would never ever use this for measuring any mains voltage)
* Generally good reviews, thought EEVblog find several flaws with this cheaper DMM.
* This is a modern digital multimeter with some kind of auto evaluation function (I forgot the proper term for this), and one don't have to manually set the specific range in order to measure voltage, resistance, or other value.
* The display is not backlit, but that won't be an issue for me. Why would I want to work in the dark anyway for my refit model? :D
* This is the E variant, which is different, and in ways said to be an improvement over the D version (which has back lit display, but lacking other things)

This guy running the 'EEVblog' on youtube knows a thing or two about electronics, and he has a 50+ min long quick guide. :D Well worth the watch. Apparently the more cheaper multimeters are/can be hazardous to use.
https://www.youtube.com/watch?v=gh1n_ELmpFI

An interesting review of this digital multimeter:
https://www.youtube.com/watch?v=PzoVao2BOUk

And then there is this:
https://www.youtube.com/watch?v=i2Tkm21dI1g (EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)) :)
The 'UNI-T UT61E' model is mentioned 25 min into that video.

I eventually saw that somebody had posted a photo of a Euro version, labeled with more plausible capabilities if I understood that correct:
Notice the extra logo, and the different ratings at the lower right bottom side.


A forum user comments: "As you can see, the ratings are very different from the International version (feel free to compare with your own unit)! Also inside, the PCB and electronics are very different: more components and higher quality more expensive components, fuses, etc. Some trace sections of the PCB are similar but about 40% is different, easily seen from the traces and populated components. Yeah sure, mostly for better input protection and for really matching the ratings printed on the front. Those lowered ratings were then certified by the top highest German Authorities both GS and T

Edit: I am tempted to look at this one too. I am already committed to an offer on eBay so I can't just go buy the one below, but I'll keep it in mind.
https://www.eevblog.com/product/bm235-multimeter/


I'll add this scathing review of an el cheapo variable digital power supply:
https://www.youtube.com/watch?v=tL12onTZMzA (Cheap bench power supply tear-down (it's bad!)
« Last Edit: November 27, 2017, 04:29:11 pm by Decoman »

Offline RossW

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Re: Questions about testing LED setups
« Reply #3 on: November 27, 2017, 03:01:41 pm »
I will go buy a multimeter soon. :) I've had fun today trying to figure out which one would be adequate and nice.

My choice for my very first multimeter ever, ended up being the 'UNI-T UT61E'



* This model has ceramic circuit breakers (Edit: To be safe, I would never ever use this for measuring any mains voltage)
* Generally good reviews, thought EEVblog find several flaws with this cheaper DMM.
* This is a modern digital multimeter with some kind of auto evaluation function (I forgot the proper term for this), and one don't have to manually set the specific range in order to measure voltage, resistance, or other value.
* The display is not backlit, but that won't be an issue for me. Why would I want to work in the dark anyway for my refit model? :D
* This is the E variant, which is different, and in ways said to be an improvement over the D version (which has back lit display, but lacking other things)

This guy running the 'EEVblog' on youtube knows a thing or two about electronics, and he has a 50+ min long quick guide. :D Well worth the watch. Apparently the more cheaper multimeters are/can be hazardous to use.
https://www.youtube.com/watch?v=gh1n_ELmpFI

An interesting review of this digital multimeter:
https://www.youtube.com/watch?v=PzoVao2BOUk

And then there is this:
https://www.youtube.com/watch?v=i2Tkm21dI1g (EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)) :)
The 'UNI-T UT61E' model is mentioned 25 min into that video.

I eventually saw that somebody had posted a photo of a Euro version, labeled with more plausible capabilities if I understood that correct:
Notice the extra logo, and the different ratings at the lower right bottom side.


A forum user comments: "As you can see, the ratings are very different from the International version (feel free to compare with your own unit)! Also inside, the PCB and electronics are very different: more components and higher quality more expensive components, fuses, etc. Some trace sections of the PCB are similar but about 40% is different, easily seen from the traces and populated components. Yeah sure, mostly for better input protection and for really matching the ratings printed on the front. Those lowered ratings were then certified by the top highest German Authorities both GS and T

Edit: I am tempted to look at this one too. I am already committed to an offer on eBay so I can't just go buy the one below, but I'll keep it in mind.
https://www.eevblog.com/product/bm235-multimeter/
A multimeter is invaluable for model electronics, but you only really scratch the surface of what it can do. I use mine to measure Voltage & resistance, sometimes amperage (to get an idea of the average draw of a whole circuit setup so that I know the wall wart can handle the load) and the continuity feature (unit beeps when there is a direct connection between the 2 leads of the unit and your circuit).

Offline Decoman

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Re: Questions about testing LED setups
« Reply #4 on: November 27, 2017, 04:32:12 pm »
The continuity feature seems to be favorable for this model (UT61E), which sounds nice. With the unit beeping quickly, according to a couple of reviewers/testers.

Offline Decoman

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Re: Questions about testing LED setups
« Reply #5 on: November 27, 2017, 04:34:33 pm »
Btw, I could use a recommendation for a digital variable power supply if anyone has a suggestion. :)

Admittedly, I am not sure exactly why I would need such a power supply. I guess it would be useful for slowly ramping up power (voltage) to light and test LED's.

I am not familiar with such products so I am currently bewildered about what might be available, without it being rubbish (or dangerous/hazardous to use).

This one sounds nice to me: Korad KA3005D (30V / 5A) (This model must be from around 2012 and earlier by the looks from the youtube videos.)
https://www.youtube.com/watch?v=ONT9xW010K4

https://www.youtube.com/watch?v=Fya-4mjV4N4 (early production flaw?, also the P version apparently, not the D one)

Edit: Hm, seems like the P version comes with an USB port, while the D model doesn't. I wonder if the 5 amp power supply works with max 3 amps for 220V countries.


Ah, I no longer find this psu appealing, as the build quality seems iffy. If I understand this correctly, the unit pushes a maximum of 150 W with 5A and 30V, which maybe the unit can't handle. I don't know how if at all, this model has been improved upon, but it sort of seems like the unit might end up failing badly, in a bad way, pumping out voltage when you think the unit is not.
« Last Edit: November 28, 2017, 06:26:59 am by Decoman »

Offline Markeno

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Re: Questions about testing LED setups
« Reply #6 on: December 02, 2017, 12:42:35 am »
You could burn-in test LEDs like that.  I might suggest using a 5volt power adapter instead.  The resistors have to take the "overvoltage", so if the LED is using 1.9volts of 9volts the resistor is "burning" off 7.1volts at .20mA (or whatever current the LED is getting).  If you are doing 1.9volts for the led at 5volts input the resistor only has to take 3.1volts, although you have to adjust the ohms rating of the resistor lower to get .20mA flowing in the LED.

I don't see a lot of point in running some at 20mA and some as 10mA.  Running an LED at 10mA it will last longer.  If you can successfully run 10 or more at 20mA for a week or four weeks and none of them fail then none of those 10 would have failed if run at 10mA for the same length of time.

BTW, I would not recommend using a variable power supply for such a burn in test.   I would stick with a regulated set voltage DC Adapter, they are made for constant use for long periods of time at their rated levels.  I would not keep a variable power supply running solid of days or overnight myself, you never know what may happen if it is unattended.

You will probably find using a multimeter to measure the current going through an led to be difficult if you try to do it.  That is because the voltages are low and so are the currents, making the meter's resistance to throw off the readings.  You may even notice the LED gets dimmer if you hook a meter up for current measurement with it.   I find the meter built into a variable power supply better to give me current measurements of an individual LED.  That is something I trust better, although maybe the output is lower than it says it is, it is always there so it doesn't change the behavior of the circuit. 

I got a Unit ut139c meter myself, I like it.  It is good for anything I do.  I don't know if Dave over at EEV Blog would be happy, but I ordered in a set of his Gold EEV Blog Leads for it.  They are very nice although I would rather that they had alligator clips than the screw on bannana plug tips with them..  They really make the continuity check instant, where the standard Unit leads had a little bit of "stutter" on the continuity tester buzzer.

Offline LynnInDenver

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Re: Questions about testing LED setups
« Reply #7 on: December 02, 2017, 09:30:01 am »
BTW, I would not recommend using a variable power supply for such a burn in test.   I would stick with a regulated set voltage DC Adapter, they are made for constant use for long periods of time at their rated levels.  I would not keep a variable power supply running solid of days or overnight myself, you never know what may happen if it is unattended.

There is a good point here. Probably best to do the final "burn in" test with the power supply you actually intend to use with the build.

Offline Markeno

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Re: Questions about testing LED setups
« Reply #8 on: December 03, 2017, 08:09:38 pm »
I'm curious about this though a bit.  Here is what I typically think about with LEDs, if an led works after it is installed properly and is powered at proper current levels it should last for years.  That is not to say there are not reasons it wouldn't, and quality of the component may be a factor in that.  I just think most of the factors of premature failure have to do with installation, environment and the circuit or wiring.

Variations in the LEDs, such as Brightness, color, the viewing radius (how wide the light spread) etc are the kinds of things that would be different from one to the other.   Even if it is 25,000 hour lifespan for a cheap led, over 5 years of constant use is still a long time until failure (half that is a rather long time too considering that a model is not likely powered on 24/7/365).

I would expect that most premature failures in LEDs for lighting models etc, are due to bad connections, broken or crossed wires, over driving with too much current, connecting too many LEDs to a board or circuit that can not supply sufficient power (be it an Arduino output with to many LEDs on it (usually more than 2 directly connected sometimes only 1), or a purpose built or generic controller board with to many LEDs on it), incorrect wiring of some type (parallel installation of 2 or more LEDs that have different voltage requirements without proper resistors or some other design mistake), physical or heat damage during soldering and installation.  Heat softens the plastic of the LED and the pins can turn or pull breaking them internally.  Heat also can directly melt the LED internally.

I do a quick test of an LED before installing it and then test it again after soldering it.  If it lights for a minute, it should light for years.  For actual burn in type testing, I do that more at points along the way check assembiles, and then full on final circuits for a few hours or something like that before closing things up for good.  Doing a testing of partial or full lighting setups etc tests more than just the LEDs to make sure everything is holding up well.  Putting a bad part in a good circuit is a waste, but putting a good part in a bad circuit is no better.

Has anyone found that to not likely be the case? I mean premature failure of just LEDs for the sake of their quality cheap Ebay ones or from proper suppliers when the circuits powering them are proper?

---
My thoughts on the variable power supply method for such a burn in test, being it an unattended long running test, there is just too much risk in running a cheap variable power supply like that in that manner.  Then you can throw in other factors that make it even worse, such as kids, or pets, or having it setup in an area you are actively working and bump up the voltage knob yourself..  For me though the biggest one is not trusting to run the power supply like that long term.  I would generally trust them when present and monitoring them, but not while away from home, certainly a sleep, or even out of the room for extended periods.  A simple wall plug in fixed ac adapter for 5 or 9 or 12volts for such testing would be much safer.  Again the factor of kids or pets knocking the breadboard and causing a short exists an the simple ac adapter may or may not have very good short circuit protection. 

All of my power supplies and soldering and other AC powered equipment is unplugged when I am not using the workbench.  Most of that is just incase of a lightning strike causing damage to it or something along those lines, but also so I don't forget and leave something on unattended by accident.  I don't want a chance my soldering iron is running for days on end.. etc because I forgot to turn it off.  Also my soldering iron has a portion of it that is always on even if the power switch is turned off, although all of my other equipment is really off when "off".
« Last Edit: December 03, 2017, 08:15:02 pm by Markeno »

Offline LynnInDenver

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Re: Questions about testing LED setups
« Reply #9 on: December 03, 2017, 09:31:40 pm »
I would expect that most premature failures in LEDs for lighting models etc, are due to bad connections, broken or crossed wires, over driving with too much current, connecting too many LEDs to a board or circuit that can not supply sufficient power (be it an Arduino output with to many LEDs on it (usually more than 2 directly connected sometimes only 1), or a purpose built or generic controller board with to many LEDs on it), incorrect wiring of some type (parallel installation of 2 or more LEDs that have different voltage requirements without proper resistors or some other design mistake), physical or heat damage during soldering and installation.  Heat softens the plastic of the LED and the pins can turn or pull breaking them internally.  Heat also can directly melt the LED internally.

"Burn in" tests are to make sure that circuits work correctly... and for the off chance that you've got a part that's not even going to get 1% of the rated lifespan because of manufacturing defects. The odds are that such marginal components are going to fail within the 24-hour powered test of the circuit.

 




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