weird led problem... need help

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purplegrower02

Well-Known Member
I've never encountered this problem before, everything always works the first time but...

I have 10 cree xpe running at 700ma. The entire vf for the string is between 20 - 24vf my driver is good between 20-40v. When I plug it in only some leds come on and they are justtt barely lit.

All the connections are secure and soldered. At first I thought it may have been the driver so I switched it out for a 600ma driver and the same thing?

I have a "solid" circuit as a tested it with a meter at the start/end of the led string and everything is connected... so what's going on? Faulty leds?
 
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purplegrower02

Well-Known Member
I just hooked the driver up to a 3070 and it works fine so it's something with the string.

i just don't get why only some leds come on in the string.

i have them all + to - to + to - so I'm thinking something is up with the leds.
 
Mechmike

Mechmike

Well-Known Member
purplegrower02 said:
I've never encountered this problem before, everything always works the first time but...

I have 10 cree xpe running at 700ma. The entire vf for the string is between 20 - 24vf my driver is good between 20-40v. When I plug it in only some leds come on and they are justtt barely lit.

All the connections are secure and soldered. At first I thought it may have been the driver so I switched it out for a 600ma driver and the same thing?

I have a "solid" circuit as a tested it with a meter at the start/end of the led string and everything is connected... so what's going on? Faulty leds?
Click to expand...

Just make a small jumper wire to short around each diode starting with the closest one to the + input. Power it up and check them out. If you have a bad one the string will light up when you bypass it. This is assuming they are now wired in series. I've made the mistake of getting one in backwards more than a few times. Seem like even though I looked at it I didn't see it.
 
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purplegrower02

Well-Known Member
I did that. I would take the live wire and start at the end of the string eliminating one at a time this did nothing as well
 
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purplegrower02

Well-Known Member
That's what I thought supra but I stripped such a small piece and when soldered it's still on the star.

first two pics shows the stars the last shows the whole piece. I know it's blurry but you can see c what's going on I put an X where the + and - driver wires were connected.20140716_140454.jpg20140716_140520.jpg 2014-07-16 14.15.14.png 20140716_140454.jpg 20140716_140520.jpg 2014-07-16 14.15.14.png 20140716_140454.jpg 20140716_140520.jpg 2014-07-16 14.15.14.png
 
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purplegrower02

Well-Known Member
If an led was fully blown wouldn't it break the circuit not along electricity to go threw it like a normal like bulbor are leds different Iin that manner?
 
Positivity

Positivity

Well-Known Member
Holy smokes..need to work on the soldering. If the wire isn't confined to the solder pad it'll probably short out on the sides of the star or anything else it manages to touch.

It's definitely shorting..

Looks like your rushing or something. Figure out the layout first. Use the small stars to secure the long wire runs strategically since your incorporating them. Get a small pair of flush cut pliers...use them to snip the excess wire down to a tiny 1/8 and solder that down...not big pieces of wire. Don't put the leds so closely together...distributing the heat evenly is just as important as color blending.

And get some ISO alcohol to clean all those stars and cobs up. All the TIM and solder residue isn't helping
 
Positivity

Positivity

Well-Known Member
I swear all these solder jobs I'm seeing are from people using small solder irons on stars on big heatsinks.

Use a big solder iron with a pen tip and a seperate power supply. It really does make a huge difference in how well the soldering comes out.

That wire going to the cob is way too long. 1/8" or even better use a holder.

Just trying to help you get on track..

image.jpg
 
Da Mann

Da Mann

Well-Known Member
I have never seen a LED go bad and still work. I am talking about a single LED. If wired in series if one goes out they all will. Opens circuit. I very seldom use a series circuit. It is easier to series but one failure and you loose whole thing. In parallel you only loose the one LED. And be careful with that solder gun. You can overheat the drivers or what ever you are soldering and damage them.
 
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purplegrower02

Well-Known Member
Well I figured it out o took a 4 aa battery holder and went to each light and some light up some didn't I took out the ones that didn't and it works fine.

I bought these off eBay because they were top bin cree's but came from china $2 each think it's worth trying to get my cash back
 
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purplegrower02

Well-Known Member
So your saying if the bare wire is touching the white part on the star it can short? I thought it had like a electrical "paint" on it to stop that.

and when I take my 4 a as and put it to the bag leds it doesn't light up.... guessing these were blown but somehow still completing the circuit
 
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purplegrower02

Well-Known Member
How can a light not work but still complete the circuit? And this would cause the lights to be extremely dim maybe from not enough vf?
 
SupraSPL

SupraSPL

Well-Known Member
This is a place for a possible short.
Possible short.jpg

Glad you got it figured out. It is possible for a "blown" LED to continue to pass current through the circuit, sometimes they partially blow. It could be due to a faulty reflow job (the solder pads between the chip and the star).
 
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purplegrower02

Well-Known Member
How can that short... it's barely touching the white part.

I removed the leds that wouldn't light up with my aa's replaced with blue and everything works perfect.
 
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