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LED's from 300-LED reel don't work - -

Ingeniero No1Ingeniero No1OGR Forum Member
Yesterday I opened the package with the 300-LED reel I bought back in October. Reference this LED Thread.

From the end of the reel that has the factory leads, I cut off four segments (12 LED’s) and connected the leads to a 12-VDC wall wart that has an open circuit voltage of 16-VDC. Only one LED lit up!

I cut off two segments (6 LED’s) from the reel, connected them to the wall wart, and none lit up.

I had scrapped the top of the end of the traces of the segment that did not have the factory leads to insure good connections. And I know that the connections were good because when I touched the VOM leads to the LED segment end opposite where I applied power, I got the 16-VDC reading, so power is getting through the cutoff segments from one end to the other.

Knowing what could happen, I touched the DC power leads of the wall wart to a single LED, and as would be expected, it lit up like a flash and went off – it burned up. I did the same to two other LED’s and they did the same. This would indicate that LED’s themselves are OK, but something else is bad.

Any ideas? Do I have a bad reel of LED’s?

Thanks!

Alex
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Ingeniero No1Ingeniero No1OGR Forum Member
Dale,

The wall wart is connected correctly; the (+) and (-) are clearly marked on each of the 3-LED segments. At this low load I couldn't even see any ripple on the wall wart output looking at it with a scope; but even if it were just unfiltered full-wave or even half-wave rectified, the LED's should work.

I went ahead and tried (just now) a 9-v battery and it barely lights up the one, single LED that lights up with the higher voltage. The reel package was marked 12 volts, BTW.

Any other ideas?

Thx!

Alex
gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
Where did you get the LED strips? I've bought some from Mouser, then a big strip from eBay, all have worked perfectly on 12 volts. Each three LED segment consists of series LED's and a resistor, the resistor is in the 100-130 ohm range, depending on which strip we're talking about.

When I first got mine, I connected the whole reel to 12 volts, nice and bright. I haven't found any that don't light, and they're still working in the half-dozen passenger cars they're already installed in.
S stan2004OGR Forum Member
As gunrunnerjohn states, each segment is simply 3 LED's in series with a resistor. Since it sounds like you have a meter (and a scope to boot), how is the 12-16VDC divided amongst the parts? The voltage across the resistor tells you the current (I=V/R) flowing through the string; what is it (probably not anything near 20mA I'd guess)? In normal operation each LED should see just over 3 Volts across it.

If your meter has a Diode test mode, this can test each LED at a "safe" current - usually 1 mA. If you test each LED using the Diode mode, it should light up dimly (but definitely visible) in one direction only. When it lights up, the meter will read the LED voltage which should be around 3V (probably less).

Each LED should have some package characteristic like a notch on one side so you can confirm the LED assembly orientation alternates up the string - anode of one LED to cathode of next LED.
Ingeniero No1Ingeniero No1OGR Forum Member
John:
“Where did you get the LED strips?
From here: LED source.

DPC:
The wall wart I have is not polarized as far as 120VAC hot/ground, but as all I have seen, it should have a step down transformer, rectifier, and some filter, and its output is clearly marked (+) & (-) which is really all that matters in this case.

Stan:
That is what I thought as well, and you can see in the pictures below, that is what it appears to be. But when I try to measure the resistance across the small SM device, I get an open circuit regardless of the setting of the ohmmeter. Perhaps it is a constant current driver similar to a CL2N3-G.

Here is my test setup.


Segment strips.


Single segment.


The ‘one’ lit-up LED. It is not bright at all, but it is the only one that has worked! (Third from the right)


Alex
Dale ManquenDale ManquenOGR Forum Member MEMORIALIZED MEMBER
I have used an identical reel of LEDs with excellent success in my passenger cars.

I also recently purchased a second reel of LEDs, but the ribbon is covered with a white surface. The entire reel lights up when I apply 12V - a little over 1 amp for a 5 meter reel.

Have you made the component-by-component voltage measurement requested above?
Ingeniero No1Ingeniero No1OGR Forum Member
Well, I tried the remaining part of the reel and only 21 LED's lit up. But to see them, you have to turn off the lights in the room.

I tried to measure the current, but with the meter set at 200 ma, I could not get any reading. I tried to measure the resistance across one 'resistor', and could not get a reading. I tried the entire string, and no reading. To verify the ohmmeter, I measured the the resistance across my finger with the probes about one inch apart: dry, between 10-11 megohms; 'moist', about 1 megohm.


Then I did one final test:
I powered several individual LED's directly with the 12-VDC and a 560-ohm resistor in series, and everyone I tested worked fine -nice and bright!

So the problem must be the traces or the connections of the devices to the traces.

I again wondered about my connections to the strips, but when I connect the 12v at any point, I can measure the voltage (about 16v) anywhere along the strip; so power is getting through.

I guess I just have a bad reel!

Oh well . . .

Thanks for your time and interest!

Alex
RailfanRonRailfanRonOGR Forum Member
I just got 2 reels from LED Wholesalers on the bay. They are ultra warm white. I put them in the kitchen under the cabinets to light the counters. I am very pleased with the output and the color. My guess is they are very close to incandescent lights in color. These are the ones that will also be going in my passenger cars soon. I will be dimming them as I think they will be to bright for the cars.
Ron
DH Dale HOGR Forum Member
quote:
Originally posted by Ingeniero No1:
Well, I tried the remaining part of the reel and only 21 LED's lit up. But to see them, you have to turn off the lights in the room.

I tried to measure the current, but with the meter set at 200 ma, I could not get any reading. I tried to measure the resistance across one 'resistor', and could not get a reading. I tried the entire string, and no reading. To verify the ohmmeter, I measured the the resistance across my finger with the probes about one inch apart: dry, between 10-11 megohms; 'moist', about 1 megohm.


Then I did one final test:
I powered several individual LED's directly with the 12-VDC and a 560-ohm resistor in series, and everyone I tested worked fine -nice and bright!

So the problem must be the traces or the connections of the devices to the traces.

I again wondered about my connections to the strips, but when I connect the 12v at any point, I can measure the voltage (about 16v) anywhere along the strip; so power is getting through.

I guess I just have a bad reel!

Oh well . . .

Thanks for your time and interest!

Alex


Check one of the resistors in the reel with an Ohm meter. Every 3 LEDs should have one. It is possible that at the factory the wrong resistor value was put in the reel. Since the input is 12 volt and 3 LEDs are in series the resistor should be around 300 ohms. If it is a lot more than that,that is the problem.

Dale H
Ingeniero No1Ingeniero No1OGR Forum Member
quote:
Check one of the resistors in the reel with an Ohm meter. Every 3 LEDs should have one. It is possible that at the factory the wrong resistor value was put in the reel. Since the input is 12 volt and 3 LEDs are in series the resistor should be around 300 ohms. If it is a lot more than that,that is the problem.

Dale H

Dale,
I have done that - from my previous posts, above:

Jan, 06:30 PM
. . . But when I try to measure the resistance across the small SM device, I get an open circuit regardless of the setting of the ohmmeter. Perhaps it is a constant current driver similar to a CL2N3-G.

Jan 15, 08:44 PM
I tried to measure the current, but with the meter set at 200 ma, I could not get any reading. I tried to measure the resistance across one 'resistor', and could not get a reading. I tried the entire string, and no reading. To verify the ohmmeter, I measured the resistance across my finger with the probes about one inch apart: dry, between 10-11 megohms; 'moist', about 1 megohm.

I know that the multimeter is OK, but just for fun, I just tried another one of the six I have (four shown below) and the result was the same - open circuit at any setting.


BTW, the second multimeter from the right is the last one I bought, and I did so because it measures Alternating Current to 10 AMPS! None of the other five I have measure alternating current. They do measure AC voltage, of course.

Remember the last test I did last night:
Then I did one final test:
I powered several individual LED's directly with the 12-VDC and a 560-ohm resistor in series, and everyone I tested worked fine -nice and bright!


I am going to order another strip and see what happens. The same strips are now $12 instead of the $8 I paid back in October.

Thanks!

Alex
gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
quote:
Originally posted by stan2004:
On Alex's sections, there appears to be a trace that runs down the center and appears to surface as a via right under the resistor as circled. It even appears to connect to the bottom pad of the resistor?

I'm not familiar with this feature. What is the purpose? Do all you guys with 12V strips have this?



Mine has the same little nub next to the resistor, looks like the same design. They have a white mask over everything, so it's difficult to see the line you're talking about on mine.

Ingeniero No1Ingeniero No1OGR Forum Member
Today I received the second reel of 300 LED's. I did the same as I did before, but this time they work! Big Grin

One difference is that the new LED's have a plug at the free end, and the black and red leads at the inner end. The other reel just had plain leads at the free end. Other than that they look alike.

This reel, with all LEDs lit using the same Wallwart rated nominal 12VDC @ 1200 ma.
Actual readings:
Current draw = 1100 ma
Measured voltage across reel leads = 11.8 volts

Like this:



And now to make the best use of them!
- - - Hope they don't go bad when I start cutting 3-LED segments!

Alex
Ingeniero No1Ingeniero No1OGR Forum Member

By the way, mine are working fine. So far, out of the reel, I have used two segments, each approximately six feet long. I am using these to illuminate a new "subway shopping center" I just added over the weekend. I'll post pictures soon.

 

The only thing I have to say about these LED's is that with the recommended 12VDC supply, they are REALLY bright. I one case I will have to either lower the voltage or add a resistor in series with the strip.

 

The adhesive backing also makes it very easy to mount them.

 

Alex

S StoshuOGR Forum Member

The 5 meter 2700 are the ones I just ordered last Sunday. From neon mart....

Amazon said it has shipped....

 

Your estimated delivery date is:

Thursday, October 18, 2012 -
 Monday, November 5, 2012

1 package via Hongkong post

Why tracking information may not be available?

 

In stock yea... but where ? Oh yea, Amazon Hongkong

Hopefully I'll get them by weeks end.. I'm not holding my breath...

 

Bruce...

Last edited by Stoshu
S StoshuOGR Forum Member

Well the LED's showed up on the 6th. 2 weeks ahead of time.

I just could not wait to try them out. Thanks to fellow formites I'm very

pleased with the results and it was also a fun project.

 

I did a couple silhouette passenger cars. I run them at a Christmas in a dark

room so the extra light is going to work out well.

 

In the picture the top is at 5v. LED's are lit. The bulbs are barely visible.

the middle is 10v and the bottom is 15v. Running conventional this is going

to make a big difference. I used the 100 ohm resistor on the regulator.

 

Now the vista domes are going to be a little more of a challenge. I'll worry

about that later....

 

 

led

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