LED Light problems

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lborne
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LED Light problems

Post by lborne » Mon Nov 16, 2009 3:57 pm

New here - first post.

I bought some Solar outdoor LED lights which are nice stainless steel, but can't recharge themselves so are pretty useless. I decided to hard wire them. I have 9 white LEDS, and a 6 volt, 1200 mA power supply. I wired each LED in parallel with a 100 ohm resistor for each. The first 5 on the string work great, but the last 4 flicker. I rewired those and still have the problem. When I remove one from the power, I can usually get one or two others to stop flickering. Currently, for some unknown reason, I have 7 working without flickering, but I had to disconnect numbers 7 and 8 from power. If I hook those two up, the last 4 flicker.

Thanks in advance.

sghioto
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Re: LED Light problems

Post by sghioto » Mon Nov 16, 2009 6:54 pm

Welcome to the Forum Iborne.

Honestly, from your description I would have to see this to believe it.
Unless those are some kind of special LEDs made for that effect.
Steve G.

SETEC_Astronomy
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Re: LED Light problems

Post by SETEC_Astronomy » Mon Nov 16, 2009 7:31 pm

Out of curiosity is your power supply outputting DC? Have you tried powering all of the LEDs individually to rule out faulty manufacturing? How far apart are the lights? Do you have only a single pair of wires running the whole length to power the LEDs?

dyarker
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Re: LED Light problems

Post by dyarker » Mon Nov 16, 2009 10:25 pm

And, what gauge wire and how long?

Sounds like a voltage drop problem over the feed lines.

Cheers,
Dale Y

lborne
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Re: LED Light problems

Post by lborne » Tue Nov 17, 2009 4:02 am

I have checked each LED individually, so I know each one is capable of not flickering. And when I mean flickering, I'm not talking 40 - 60 Hz, more like 5-10 Hz - very noticable.

I'm using 24 guage wire the entire run - about 90 feet total. Measuring the voltage at the wallwart gives about 8 volts (its unregulated) and at the end of the 90 feet it is 7.1 volts or so. The last LEDs are bright, but I guess that just means they are getting the amps required. I did hook up a 9 volt power supply and got the same results.

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MrAl
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Re: LED Light problems

Post by MrAl » Tue Nov 17, 2009 4:19 am

Hello there,


Flickering is a known behavior for white LED's when they have been overpowered.
That's not something that is unusual, however, they may already be damaged.
When they are *EXTREMELY* overpowered though they turn a deep blue color
and get very very dim too provided that they dont burn out completely.

When you connect LEDs to a power source like 6v dc you have to connect a resistor
in *series* not in parallel to the LED to limit the current getting to the LED.
Connecting a resistor in parallel does almost nothing at all for the LED, it has to
be in series with the LED. The LED wants to draw lots and lots of current until
it overheats and starts to flicker or go dim altogether, so a series resistor is
employed in order to limit the current to a safe level for the LED.
For white LEDs the resistor value is:
R=(Vs-Vf)/I
where
Vs is the source voltage in volts,
Vf is the nominal characteristic LED voltage in volts,
I is the desired forward current in amps which is the LED operating current,
R is the resistance in ohms.

Thus for a white LED that has nominal 3.5v forward voltage and a 6vdc source, the
required series resistance R would be:
R=(6-3.5)/0.020
which comes out to 125 ohms.
For longer life 15ma is used, so we have:
R=(6-3.5)/0.015
which comes out to 167 ohms.
To allow for some LED voltage variation we can go as high as 200 ohms and
get long life and safe operation.


That flickering can be very annoying, but if you think it's bad outside imagine
how bad it is when you are trying to see something with flashlight that has
even on flickering LED in it :smile:

You may have to replace the flickering LEDs if they appear dimmer than the rest,
but if not they may still work for a while. Just how long they will live now is hard
to say because part of their life has been taken away by the overpowering which
causes overheating which in turn causes accelerated aging.

When you have several LEDs the best way to run them is to provide one resistor
for each LED, connecting it in series with the LED, and then connecting all of
those sets in parallel. This way each resistor/LED set gets 6vdc.
It's also not a good idea to connect the LEDs in parallel and use a single resistor
in series with the parallel LEDs either. Although this has been done even on some
moderately priced flashlights of (somewhat) old now, some LEDs have a tendency
to draw more current than others and start to hog all the current and then
guess what...they start to flicker and then eventually burn out!
LEDs vs Bulbs, LEDs are winning.

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dacflyer
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Re: LED Light problems

Post by dacflyer » Tue Nov 17, 2009 4:34 am

i work in traffic signals - i constantly see many green ball leds get sections that will flicker..the led units have a switcher in them, and the led array has no resistors for each string, the power supply does drive the leds very brightly (actually overpowering them somewhat ) and after some time you will get a string of leds start to fail flicker blink at various rates, and then some sections will actually go totally out. i do not know why the MFG will not put a series resistor on each string. the leds would last much longer. at night they are very harsh on the eyes as well, especially in a area where there is no street lighting..

you might want to try using a different value ( higher resistance ) and see if that solves the problem.
good luck.

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MrAl
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Re: LED Light problems

Post by MrAl » Tue Nov 17, 2009 5:02 am

Hi dac,

You'll notice that his post says that he is using the resistors in parallel, so he needs to ALSO
change the placement of the resistors so that they are in series with the LEDs. Simply
increasing the value will not help at all.
LEDs vs Bulbs, LEDs are winning.

lborne
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Re: LED Light problems

Post by lborne » Tue Nov 17, 2009 6:49 am

I am really sorry for any confusion... I do have a 100 ohm resistor in series with each LED. The LEDs have not been overpowered. Also, if I switch a flickering LED with one that does not flicker, then the one that was fine starts to flicker, and vice versa. It only affects the ones on the end of the line - the last 4, and only when I have all 9 hooked up.

What I will try when I get home is hooking them all up right to the power supply without the long run of wire. It could be that I have a short, or small nick in the wire somewhere along the way.

If that does not work, I will also try a higher ohm resistor. I have a bag of 200 ohm resistors.

Here is a bit more info that might be of use... Each LED has a solar panel built in that was used to recharge the single 1.5 (1.2) volt battery. If I shine a flashlight on the solar panel, it will power the LED by itself (just got an idea for an over unity device :) ). If I shine it while the LED is flickering, it stops the flicker. I thought maybe that was indicating I did not have enough voltage. However, per my multimeter it does, and also going up to a 9 volt power supply did not solve the problem. I've disconnected the solar panel on some of the LEDs that were flickering and it has no affect.

SETEC_Astronomy
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Re: LED Light problems

Post by SETEC_Astronomy » Tue Nov 17, 2009 7:15 am

If you're hard wiring the LEDs you should probably remove all other circuitry that isn't the LED or resistor. Sometimes nightlights flicker when the light they put out is reflected back into the sensor (LDR) that makes them only come on at night. Pull everything out and your problem may go away, plus your left with some solar panels to play with.

lborne
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Re: LED Light problems

Post by lborne » Tue Nov 17, 2009 7:42 am

Unfortunately, the solar panels are part of the cover, so they must stay. I did remove the photo electric switches from the circuit on all LEDs, and clipped the leads from the solar panels on some of them that were flickering, but that did not help.

Anyway, I really appreciate all the help. If I find a solution, I'll be sure to post it here.

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CeaSaR
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Re: LED Light problems

Post by CeaSaR » Tue Nov 17, 2009 9:24 am

Sounds like the wire gauge to me. You could try just powering just the end light (last one) and see if it still
flickers. If it stays on, work your way back toward the beginning by adding just one at a time until one starts
to blink. The previous amount is the max you can have on that particular line.

Try connecting the power to the middle of the line to cut the length of the run in half. That might help with voltage
and current drop in the run without changing the wire size. You might find that your problem could be a combo of
voltage drop and current loss.

Lastly, try a larger size wire - 18 or 16 gauge and try your run again. 24 gauge sounds a bit small for 90'.

Good luck,

CeaSaR
Hey, what do I know?

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dacflyer
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Re: LED Light problems

Post by dacflyer » Tue Nov 17, 2009 8:23 pm

HMMM if i understand right, you have all the lights on a single power supply
whats the rating of the supply ? volts / amps. and is each light parallel on the string ?
try this...try putting a large value cap midway or at end of the line and see if that helps any.
thinking you might be loosing current twards the end ??
and i recomend disconnecting all electronics / solar panels etc from the leds .
keep us up to date,, currious here..

lborne
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Re: LED Light problems

Post by lborne » Wed Nov 18, 2009 6:40 am

Power supply is 6 volts and 1200 mA. This morning I was able to hook all lights in parallel directly to the power supply and not going through any significant length of wire. They all work perfectly. I'm leaving it on all day and when I get home tonight will check it out. If they behave, I'll next try a larger size wire - maybe even go so far as to purchase landscaping wire and not use whatever spools I have laying around.

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dacflyer
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Re: LED Light problems

Post by dacflyer » Wed Nov 18, 2009 10:39 am

how much current is each light using ? and how many lights ( units )

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