I have had the little plastic bubble that covers the LED chip come loose. I doubt it was heat related, just faulty.
LED lighting on a budget!
- Thread starter kcress
- Start date
I have had the little plastic bubble that covers the LED chip come loose. I doubt it was heat related, just faulty.
You are absolutely right. I recheck the other LEDs and it seems that the lens are all the same. It is not permanently fixed. There's somewhat gel in between the inner and the bubble lens. The lens must've fall off and the melted gel I found is the thing that hold the lens. Thanks reefmusic.
I'm about to add another string of white. Excellent thread, kcress! Thank you so much!
:beer::celeb3:
How densely are your LEDs packed? How far apart are they placed?
Hello,
Thanks kcress.
I like the low cost of this and I actually once did this as well, but i have a warning for those who will try this. (I do have some EE background)
So repeating the numbers in this example:
24/3.5 means you can use 6 leds.
6*3.5V=21V, meaning you have to burn 3V.
Leds Max constant current is 700mA, resulting in 4.3Ohm
My warning:
Not all leds will over their life time have the exact same forward voltage drop of 3.5V
at 700mA as stated in the datasheet. This might vary depending on temperature, manufacuring tollarances and how you drive them.
Lets say two out of the 6 will start having a forward voltage of 3.2V only 0.3 volt less.
Then the voltage drop over the string will be:
(4* 3.5V) + (2*3.2V) = 14V+6.4V=20.4V
Now the voltage over the same 4.3ohm resistor will be 3.6V (was 3V)
Current now is 3.6V/4.3Ohm=837mA
This is more than 130mA than the maximum allowed constant current of 700mA!
This will result in a runoff, meaning that the other leds will also start getting effected
and that the current will rise over time.
Please note you are still under the 1A of your fuse, and you are running 8 Hours a day.
So your LEDs will deteriorate, and you will notice that some leds will shine less bright.
At some point one might totally fail, and your whole string might go off, because
the broken led is "OPEN" or the broken led is "CLOSED" meaning your fuse will burn as well. But effect is the string is out.
Not only that, the other leds in the string will already have deteriorated as well now.
Now in this example I just changed the Forward voltage suddenly from 3.5V to 3.2V
But the change can be much smaller. lets say it starts with 3.45V but slowly because of the higher current (slightly higher) it will get worst (slowly, little by little) and then some day you are at 3.2V.
I did some cheap setup similair to this with a PC Power supply and over a time period of about 6 months I lost some Leds.
So I also love the cheap idea but based on my experience, it might be expensive on the long run as slowly your Led's die and never reach the prommised 50000 hours.
One more test you can do:
You need a variable powersupply and a way to measure current.
Connect a led and a resistor in series to your power, and then slowly increase the voltage, from 0V up to the moment your current reaches the Maximum constant operating current (in this case 700mA).
Now take a voltage meter and measure the voltage drop over the LED, it will most of the time be less than the expected Vf of 3.5V. Meaning that if you increase your power supplys voltage to when the voltage drop over the LED is 3.5V you will have a higher current. Not good. LEDs are current rated, don't over drive the current, it lessens their life time.
Long story but hope this helps those who are going into the LED DIY.
For short term projects ok, but running a setup like this long term, I would not recommend it.
Thanks kcress.
I like the low cost of this and I actually once did this as well, but i have a warning for those who will try this. (I do have some EE background)
So repeating the numbers in this example:
24/3.5 means you can use 6 leds.
6*3.5V=21V, meaning you have to burn 3V.
Leds Max constant current is 700mA, resulting in 4.3Ohm
My warning:
Not all leds will over their life time have the exact same forward voltage drop of 3.5V
at 700mA as stated in the datasheet. This might vary depending on temperature, manufacuring tollarances and how you drive them.
Lets say two out of the 6 will start having a forward voltage of 3.2V only 0.3 volt less.
Then the voltage drop over the string will be:
(4* 3.5V) + (2*3.2V) = 14V+6.4V=20.4V
Now the voltage over the same 4.3ohm resistor will be 3.6V (was 3V)
Current now is 3.6V/4.3Ohm=837mA
This is more than 130mA than the maximum allowed constant current of 700mA!
This will result in a runoff, meaning that the other leds will also start getting effected
and that the current will rise over time.
Please note you are still under the 1A of your fuse, and you are running 8 Hours a day.
So your LEDs will deteriorate, and you will notice that some leds will shine less bright.
At some point one might totally fail, and your whole string might go off, because
the broken led is "OPEN" or the broken led is "CLOSED" meaning your fuse will burn as well. But effect is the string is out.
Not only that, the other leds in the string will already have deteriorated as well now.
Now in this example I just changed the Forward voltage suddenly from 3.5V to 3.2V
But the change can be much smaller. lets say it starts with 3.45V but slowly because of the higher current (slightly higher) it will get worst (slowly, little by little) and then some day you are at 3.2V.
I did some cheap setup similair to this with a PC Power supply and over a time period of about 6 months I lost some Leds.
So I also love the cheap idea but based on my experience, it might be expensive on the long run as slowly your Led's die and never reach the prommised 50000 hours.
One more test you can do:
You need a variable powersupply and a way to measure current.
Connect a led and a resistor in series to your power, and then slowly increase the voltage, from 0V up to the moment your current reaches the Maximum constant operating current (in this case 700mA).
Now take a voltage meter and measure the voltage drop over the LED, it will most of the time be less than the expected Vf of 3.5V. Meaning that if you increase your power supplys voltage to when the voltage drop over the LED is 3.5V you will have a higher current. Not good. LEDs are current rated, don't over drive the current, it lessens their life time.
Long story but hope this helps those who are going into the LED DIY.
For short term projects ok, but running a setup like this long term, I would not recommend it.
kcress
New member
???
Key word here is "slowly".
You have resistors in every string. You can measure the current anytime you feel like it with the strings running, just by measuring the voltage dropped across the resistor and its resistance setting.
I've suggested a person check their string currents every month or so until you get a feel for the drift.
Key word here is "slowly".
You have resistors in every string. You can measure the current anytime you feel like it with the strings running, just by measuring the voltage dropped across the resistor and its resistance setting.
I've suggested a person check their string currents every month or so until you get a feel for the drift.
TheFishMan65
New member
Do you have access to a PAR meter? That would tell you the efficiency.
ronald7410
New member
Is it necessary to go from 16AWG wire to 20AWG? I cant seem to find 20AWG at HD...
And those are threaded right? Not solid?
And those are threaded right? Not solid?
ronald7410
New member
So the number value doesnt vary orderly in size? Ok when looking for 22AWG, this needs to be stranded correct? while the 16AWG remains the same from the PS in and out. Solid for the 16AWG?
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