I’m sure the simplest way to figure this out would be to invest in some kind of circuit tester or something.  But since I don’t have that, I was hoping someone could shed some light one what they think could have gone wrong.

First, some background info on my LEDs and the resistors being used:
http://nuigroup.com/forums/viewthread/2417/

Basically, groups of 8 with a 1 ohm resistor for each group.  As suggested by the LED wiring wizard and Tinkerman.

So I finished wiring up 6 groups and they all seemed to be working without problems the night before last.  Last night I got my new camera, removed the filter, and was ready to start checking for blobs.  (I wanted to see how it worked with just half the LEDs in.) For some reason, only a single set of my LEDs is now working.  As far as I can tell, the wiring is still fine.  All LEDs are soldered together along with the resistor on the last LED in the series.  Each end of the series is connected to the power source via some regular stranded wire not yet soldered.

It would seem to me that the problem has to be in an LED going out or a resistor going bad.  I would have thought that in either situation some damage would have been visible on the component though.  Correct?  I tried replacing one of the resistors, but that didn’t have any affect.  So, what would be the best way to test for a bad LED?

I took a spare LED and started touching the leads to the ends of LEDs in the non-working grouping.  One grouping didn’t do anything, but another grouping lit up when I touched the leads for one of the LEDs.  So it seems that the LED I basically bypassed has to be bad.  I tried again on other groups and could not replicate this.  When I tried again on the group that I had success with previously, nothing happened!?  (The LED I was using was still good since I could get it to light up on a working group.)

So now I’m confused.  Did I just have a second LED go out in one of the groups?  Do I have multiple LEDs out in the other groups since I could get them to light up by bypassing them?

Is it common for LEDs or resistors to go bad?  Could I have caused an issue by a crappy job of soldering?  Any help or suggestions would be appreciated.

Thanks

A 1 ohm resistor seems awfully low.  What are you powering them off of?  Also, were you able to verify that all of the LEDs worked?  It could be that some are bad, which in most cases breaks the circuit, thus not lighting anything up.

They all lit up properly the first time I powered it up.  I never check them individually, but each time I complete a set of 8 I test them.

I’m using a 12v wall adapter.  1 ohm is what the calculator told me to use when wiring 8 of them up.

Specs of LEDs are:

Emitted Color Infrared
Lens Color Water Clear
Bulb Size (mm) 5
Peak Wave Length(nm) 850
Forward Voltage(V) 1.5~1.6
View Angle(°) 15~30
Luminous Intensity (scd) N/A
Continuous Current (mA) 60mA
Peak Current (mA) 120mA
Static Sense No

I was looking at the wizard again and plugged in 1.6 instead of 1.5 for the Forward voltage and noticed that it really changed things.  Says I should use a larger resistor and fewer in each series.  Although it seems to me that worst case scenario, my LEDs get a bit underpowered.  That shouldn’t cause them to stop working, should it?

No, if it wants a higher resistor that means they got over powered, which could mean bad things.  Try hooking up a few individually, that would be the test.  Resistors block current, so the more ohms(say ohmage if you want to annoy electrical engineers, it drives them crazy) the less current.  This can be calculated with E = I*R.  Voltage = Current*Resistance.  Therefore, A lower resistor blocks less current, allowing more to get to the LEDs, which is some cases would cause it to go boom.  Were you plugging the peak or continuous current into the wizard?

Good luck and hope you didn’t fry your LEDs,

Alex

I was using the continuous current in the wizard.  The reason I asked if I could have been underpowering was because of the difference in results when I use the 1.5 vs the 1.6 in the wizard.  With 1.6, the wizard never gives me 8 LEDs in series, only 7 with a 15 ohm resistor.  With 7 LEDs using 1.5 it says I need a 27 ohm resistor.

Since I wired it up in a series of 8, if I used the wrong forward Voltage I would have ended up just underpowering the LEDs.  Does that make sense?

I’ll try testing each LED that I’m using with a 180 ohm resistor to see if I can identify any bad ones.  (The wizard suggests that for a single LED, although it says I will dissipate alot of power through the LED.  Hopefully that won’t be a problem for just a few seconds of testing.)

Thanks.

I was reading another post that mentioned making sure that you had a voltage regulating power supply.  Could my cheap RadioShack 12V 1.5A wall power supply be the cause of the problem?  I didn’t see any indication on it that it included a voltage regulator.

http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productId=2190632&accessories=accessories&kw=12v+power+adapter+1500ma&techSpecs=techSpecs&currentTab=features&custRatings=custRatings&sr=1&features=features&origkw=12v+power+adapter+1500mA&support=support&tab=summary

If it says it outputs 12 volts it probably does.  Check it with a volt meter, that would rule it out.  Definately test each LED with a 180 Ohm.  It does not matter how much energy is dissipated at the resistor(until a certain(high) point), it will just get pretty hot.

Good Luck,

Alex

Yes, ohmage drives me nuts

In terms of voltage regulated, I wouldnt worry about it. A regulator will be fed with around 15v and step it down to 12v so you always get that whereas an unregulated supply will give you wall voltage (120 or 220) divided by either 10 or 20… therefore if the wall gives 125 you get 12.5 volts. The extra half a volt wont do any harm.

In terms of the LEDs not working, I would have to guess that you more then likely toasted them. Imagine a resistor is like a damn, the more its open the more the water flows. Current is like water, the less resistance it has the more it flows. Having a resistor in front of the LED limits the amount of current that can pass through it. Your leds can only take 60mA cont current and with a 1 ohm resistor you would have got pretty close to whatever current your power supply can generate it.

If I had to guess, Id say you fried the LEDs.

So perhaps I should use the a larger resistor or just add another LED to each series an just go for underpowering them, just incase?

I thought that the continuous current value wasn’t really affected by the resistor, just the Voltage?  The LEDs just pull the current that is needed...?  I noticed that with the LED calculator it didn’t seem to mater what continuous current I put in the boxes.  It just changed the information provided as to how much current was needed, but never had an effect on the diagram itself.?

(But not an EE, so correct me if I have misunderstood something....  bottom line, if underpowering will keep me from frying them, I’m all over it.)

I have the exact same configuration and its working alright, just as a safety i recommendation you add 1~2ohm resistor at the power supply

You mean add a single resistor right at the power supply from the wall so that it affects all of the series LEDs?  I have a 2.2 ohm resistor that I could use, so that would work out pretty well.  Thanks, I’ll give that a try next week when I get some free time right before testing and replacing the blown LEDs.

well i’ve got my arrays setup as the wizard shows you, also i attached an extra 1.5ohm resistor just as a safety measure....