Reason for Dimming of LED's Furthest from Supply

Your description is difficult to follow. If you show by diagram, it will help people to understand your problem to give solution.

... and specifications. (Power supply voltage and amperage, LED forward voltage and supply current, dropping resistors used.)

will do, give me a while

cnc

Curious. I'd like to see the schematic you used, to understand whether you were running them in series or parallel, and to know if perhaps you were over- or under-driving them.

Did the LEDs have a good heat sink? If not provided with a good heat sink, the internal structure of the LED will overheat which will cause premature failure, and the first sign of this is color (colour) shift.

In general White LEDs will last longer since the internal structure is simpler (it's just one LED die, not 3) and the color shift over time is smaller since the aging of the phosphor will produce less color shift than the differential aging of the RGB dies in a tri-color LED.

Transformer INTAW S-150-12 input 100-120VAC 3.2A /200 -240VAC 1.6A 50/60 Hz

(set to 230) OUTPUT:+12v--... 12.5A

LED controller Model CT308RF 1, DC input voltage 12/24V

2, Output power 5A(Max) per channel, 12V: 180W; 24V: 360W

LED's each module is 2 watts,

and waterproof, aside from that I have no info at the moment.

The letters are outside, so they have some cooling, but I would say the material theyare on is a dense foam, so more insulating than radiating, but they are on the front of a thick acrylic holder, so I don't know if it would make any difference. They only got slightly warm to the touch when operated, at least on the bench.

Yes the suggested layout should be better for you, depending on the number of LED's. If you have them all in series (like you do) you will draw less current but may not have enough voltage to power them all. If you put them in parallel (like suggested) you will draw a lot more current, but 5A should be plenty to drive your circuit, and the voltage shouldn't be an issue.

Do you have an sort of current limiting resistor to protect your LED's from being over currented?

Thanks for reply AP, there are 80 LED's in the string, and there is no resistor that I know of. How would I install one?

CNC

Did you buy the LED lit letters? Or did you make them yourself?

Purchased. In post 6 there is a pic of them.

To quote an anonymous poster back in april of last year, I suspect:

Who less spend more will spend!!!

CNC

My guess would be too much current running through them. So they will slowly "burn up" over time. But like stated above, very hard to follow you description of what is happening.

Here's the PDF for the controller:

http://www.euchips.com/1/euc/CT308RF%20EN%20V1.2.pdf

No need to worry about extra resistors, etc., it looks like you're doing everything correctly, the instructions even suggest that if you're having color shift then wire it the way you did in your second illustration, just make sure you solder all your connections carefully.

One more thing, you didn't say how you made your connections to each module, if they were mechanical using wire nuts or compression fittings then it might be best to solder them, or if they're soldered then look for a poor solder joint. You may find that one letter is still having problems, then check the connections in that one substring.

Thanks for that RAMConsult, yes it suggests the second option is the favourite, in that it has power in at both ends, but it also suggests the modules are all in a line, rather than branched off as in the second layout.

I did check the wiring in the first instance, most of the joints are soldered, but in and out of each letter is a connection block. I reconnected most of these, and it made no difference at all, so I am thinking something has burnt out.

The process of fading was gradual but constant, not like a wire coming loose, they all worked great, but just faded... working back to the transformer. I have to be confident about the joins, done carefully and heatshrinked afterwards.

That's a lot of ga's per post Fredski.

I can see that the layout I used on advice was not the best.

But what has happened? Have the led's failed because of low power supply? Has the transformer failed because of trying to push power to the end?I swapped the transformer and it made no difference,

Are you (CR4) saying changing the wiring will will light them all up again or are you speaking of the best layout for the new LED's?

If they are dim (or off) because of lack of power, why didn't this show up straight away, if they are burnt out due to overpowering how will supplying more help?

I can't seem to add it up.

Cnc

It's hard to give an exact reason without a record of voltage and current. The bottom line is DC only travels so far before the voltage drops (AC travels a lot further before dropping). I suspect you had a voltage drop from the first day. You probably had a bit too much current flowing through the LEDs, not enough to pop them. An LED needs the right voltage. Loose connections can also contribute. If I were you I'd just keep the wire runs short and check the voltage at the beginning and end of the string. If it's good, close it up and have a beer.

Feed them from both ends, or better still feed every 20, if you look at Christmas lights those with high numbers, you'll see several wires that leapfrog every 20 or so lights keeping them all bright,but are all fed from one source.

Again, a good idea bazzer, but if poor supply is the problem, why did it take 6 months to start to show itself as lights dimming, and why did this continue until all were virtually out?

Cnc

Jim,

LED's will color-shift when they are over-driven (current is what matters to LED's). If they are run in this state for any length of time, they will heat up, and they will be permanently damaged. It seems some of your modules have suffered damage. I need to read the whole thread here to get a better handle on your setup.

EDIT: I see others have already mentioned the color-shift from over-driving. Sorry for the repetition! :)

I've taken a look at the datasheet for the controller, but I don't see where they tell you how to set the string current. They give the maximum output current (5A/channel), but don't tell how to set the current. Was there anything in the literature you got with the module that told how to set the output current?

Tom D.

Nice one. There was no data at all with the LED's, but there is a V ADJ on the transformer, and I don't know what that is set at. The system was sold as 'plug and play'.

Cnc

No- Thanks for the input. I get that they may have been overdriven, but how have the furthest ones suffered first....oh wait,, they are all overdriven, they all degrade due to this, at the same rate, and the ones at the far end show this up first because they are getting least power.

Sweet.

Cnc

Do you have any kind of data for the LED modules themselves, other than the stated fact that they are 2W? You really need to know how the individual LED's are connected on the modules, and you need to know the "safe" operating current for the modules. Last, but not least, you need to have a way to control the current output from the LED driver module.

Tom D.

Mmmm. I have none of that information. I guess, since the customer has gone off rgb, and fancies white, it is information I should have had to make a proper job. Information I didn't get. There was some printing on the bags they came in, I'll see if I can find one.

CNC

Here's one possible way the modules could be setup. I based this off the fact that there are three LED's and three resistors on the module shown in the picture.

If this is the way they are built, then the resistor (marked with ?) limits the current. Can you tell if the LED's are wired up this way on the little modules?

Tom D.

I'll have a close look at one in the morning, I suspect that is the layout.

Thanks for all the attention you guys.

CNC

Well, something isn't adding up. The way you had them hooked up, the LED modules at "the end of the line" would have less voltage going to them because of the wire and connection losses. If they have less voltage, then by Ohm's law, the current would be less.

You really need more information on the LED driver, and the LED's themselves to figure out exactly what's happening here (and to prevent further/future failure).

LED driver modules are controlled-current devices (usually). They will put out whatever voltage is needed to output a preset or settable current level. In order to select or set one up, you need to know what current you should be driving the LED's at. Without that information, it's all guesswork.

With a little electronics knowledge and a digital multi-meter, you could experiment and get some of the missing information, but do you have either of those?

Tom D.

something isn't adding up? I thought i had it figured out, they are all being overdriven, and the fault shows up first where the power is lowest.

'With a little electronics knowledge and a digital multi-meter, you could experiment and get some of the missing information, but do you have either of those?' Well I can get them both, given time.

It looks like the modules are designed to run from a fixed DC input voltage and pass that DC voltage through to the next module for each short string. The second diagram would be the correct way to wire the sign and just make sure the total number of 2W units do not exceed ~60% of the supply power rating. The color shift starting at the end of the string was due to excessive current through the string. The excessive current caused degradation of the string (increased resistance) leading to greater power dissipation and so on. Blue drops out first as it has the highest forward voltage requirement. Hence the redshift in color.

My guess is that all the modules are still OK but you may need to feed the elements that were closer to the source in the original wiring scheme from both ends or possibly each module in parallel with in the character.

"total number of 2W units do not exceed ~60% of the supply power rating."

Well that didn't happen Regsoft.

Transformer(set to 230) OUTPUT:+12v--... 12.5A= 150w

LED controller 180W;

LED's each module is 2 watts, x 80 = 160w.

I need a supply of 240w+. But isn't this going to overdrive them more, or is that overvoltage.

If the modules expect 12VDC and draw 2W that means each module draws 0.167A. Power or W = Volts * I(current).

You say that you are pulling 160W out of a 150W supply? I am prized the supply is holding up. The dimming at the end of the string when they were all in series was almost certainly due to voltage sag. If you are drawing 160W I recommend a 300W 12VDC supply.

I just did a quick look at my power supply book mark section and this used to be my favorite supplier for things like this but the new site is not particularly friendly. I recommend you call them and tell them what you are driving and where the supply will live. They may tell you that a 200W supply is OK. Be sure to tell them the max ambient temp the unit will operate under. IE if it is where the temp may be >30C this is VERY important!

http://www.astrodyne.com/Product_EnclosedPowerSupplies.asp

You may also check here

http://www.onlinepowersupply.com/

As I said before, something isn't adding up.

"The dimming at the end of the string when they were all in series was almost certainly due to voltage sag."

The LED modules at the end of the line are going to see reduced voltage, thus, reduced current and power, ohms law says so. Now, I might be convinced that those at the end of line started to dim and shift as the voltage sag got worse over time (power supply output reducing, series connections getting more resistive, etc.), in which case, those modules would be fine one they are driven at the proper voltage again. If you have a voltmeter, you can check voltage at the power supply, at the beginning of the series string, and then at the end, and get an idea of how much your wiring and interconnect are costing you. If you want to measure the strings' current, you would do so in the common anode leg of the circuit, since that would be the sum of the three colors' current (if they are wired up per the circuit I sketched, anyway).

Jim, can you read the numbers on the resistors that are on the LED modules? They are probably different values, as they probably have to run each color at a different current, to get the apparent brightness about the same.

Does the LED driver module run hot? I would agree that you are pulling too much from your current supply. Rather than buying a new supply, you could reduce the number of LED modules.

You can get to the bottom of what's going on here, but it's going to take some sleuthing.

Tom D.

"can you read the numbers on the resistors that are on the LED modules? They are probably different values"

R1=151 R2=361 R3=151

After thinking about this a bit more, I realize that my schematic is not correct, the resistors would have to be one per color, not one per LED. I'm trying to update it to what I hope would be the correct connections. I may not have the time to spare to continue on this thread, but I'll try.

Tom D.

OK, here's another try at a schematic.

From the resistor values you found, I assumed that the 360 ohm is probably on the red, since red LED's are some of the most efficient, it's going to need less current to appear as bright as the green and blue. From your picture, I can see what looks like 6 leads on the LED's, so it looks like they have all three colors isolated within the package, but they almost have to be wired up on the board so that all the anodes are common.

So...........now would be a good time to ask; are you still looking for some direction/guidance on this project, or am I spending time answering a question that has not been asked?

I still don't think that the end-of-line LED's would suffer damage if the voltage was dropping out. So if they are damaged, I think the cause is still up in the air.

Tom D.

Tom D. You have supplied me with loads of questions that I need to answer to find out what went wrong.

Don't bust a gut trying to guess all the possible answers, if I can't be bothered to find out the answers for myself. I will investigate as far as I can. The thing is up in the air, literally, and takes two men and long ladders to get to it, but I will try voltage at the various points, and compare new and old units, and if I come up with something I will get back.

Meanwhile, I would like to thank you and all the other responders for the useful info.

For my application, it would seem that either some part of the setup is faulty, underspecced, or not as plug and play as it was portrayed, which is significant.

I attach a better photo of the unit, just for your interest.

Thanks again guys

CNC Jim

Jim,

Thanks for the feedback, and the great picture of the module. Since you've got one of those in front of you, and you don't need a ladder to get to it, I'd start by using an ohmmeter to verify the module is connected the way I have it drawn. There is the little issue of the 6 pins vs 4 on mine, but the electrical connectivity is probably the same, the difference is that my schematic shows the common anode connection inside the LED, not at the board level, which is how I suspect the modules you have are wired up. If you want to create a "netlist" as it's called in the business, I'll try update the drawing to match exactly what you have there. I see the "B R G V" label, and I would have to guess the "V" is the common anode, does that sound right? The others are self explanatory, if my assumptions are correct.

I'll try to come up with a 6-pin LED symbol to use for an updated drawing, but I'd need you to verify the correct pin-out. That black dot indicates Pin one of the LED's.

I can't help but wonder, in your signage example above, it has "CR4", is that a true representation of the sign, or just an example you chose?

I'll try to keep up with this thread, waiting for your input, and I'm sure others may have their own ideas as well. I'm having fun trying to help out, as long as that's true, I'll keep trying :)

Tom D.

Hi Tom:

"B R G V" label, and I would have to guess the "V" is the common anode," That's correct, but I don't need a netlist I don't think.

Yes mine have six pins, it appears they go into the LED and out again at the other side.

It's a hairdressing salon, so it doesn't say CR4, I just thought I would make it personal.

Thanks again, and I will update.

CNC Jim

I did have a 6-pin tri-color LED in my CAD library after all.

When I mentioned the net-list, I meant "I" would need that in order to verify the schematic is correct. I'm hoping the the general circuit is correct, but I would need your input to verify the proper pin connections on the LED's, if order to have a correct schematic.

Tom D.