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4 LED's in series rated 3v to 3.2v work on 12v with no resistor?
4 LED's in series rated 3v to 3.2v work on 12v with no resistor?
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Old 10th November 2017, 11:31 AM   #1
realflow100 is offline realflow100  United States
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Default 4 LED's in series rated 3v to 3.2v work on 12v with no resistor?

and they dont burn up. ive had them running for 2 days and the current is only about 25mA and the LED's are rated for 30mA

I tried it just to see what would happen and it works pretty good
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Old 10th November 2017, 07:34 PM   #2
kodabmx is offline kodabmx  Canada
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It's common to run LED's from 12V in series parallel connection, or at least it was before the drivers because constant current.
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Old 11th November 2017, 06:29 AM   #3
realflow100 is offline realflow100  United States
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i'm just surprised it works without any resistors and the current is staying pretty average around 25mA and they are super bright and barely any warmer than ambient room temperatures

I thought they would just instantly go BANG as soon as they get attached because they have no resistor
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Old 11th November 2017, 06:36 AM   #4
basreflex is offline basreflex  Spain
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depends on the color and internal resistance (sometimes quality related)
white leds need the largest voltage, up to 3.6V for very high currents, only in pulse mode allowed usually. just check the spec sheet ..
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Old 11th November 2017, 07:14 AM   #5
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by realflow100 View Post
and they dont burn up.
Your question is unanswerable unless you post Brand/Model/Datasheet so we can see the V/I curves.
So please do.

* Brand
* Model
* link to datasheet

otherwise your question is incomplete .
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Old 11th November 2017, 08:00 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by realflow100 View Post
and they dont burn up. ive had them running for 2 days and the current is only about 25mA and the LED's are rated for 30mA

I tried it just to see what would happen and it works pretty good
3.2Vf across each of the three LEDs accounts for 9.6V
Subtract that from the 12Vdc supply and you have an excess of 2.4V.
If only 25mA flows, then you have an effective resistance of ~96ohms (2.4V/0.025A)

Where is your 96ohms hiding?

It's there !!!
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Old 11th November 2017, 09:40 AM   #7
DF96 is online now DF96  England
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He said 4 LEDs. It just happens to be fortunate that the supply voltage is within the window between almost no current (so no light) and too much current (so a brief and happy life).
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Old 11th November 2017, 09:49 AM   #8
AndrewT is offline AndrewT  Scotland
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Old 11th November 2017, 10:56 AM   #9
infinia is offline infinia  United States
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Quote:
Originally Posted by realflow100 View Post
and they dont burn up. ive had them running for 2 days and the current is only about 25mA and the LED's are rated for 30mA

I tried it just to see what would happen and it works pretty good
Look Mom no hands
Which only proves you have a stable 12V source and the LED temperature is at equilibrium. Besides that, parts don't let out the majick smoke once they hit some "rating" number.
Take a heat gun on those LEDs and watch the current. I'll bet you can see 'thermal runaway in action.
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Last edited by infinia; 11th November 2017 at 11:04 AM.
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Old 11th November 2017, 01:59 PM   #10
realflow100 is offline realflow100  United States
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why would I want to take a heat gun to them? that would just be stupid and a waste of good LED's

they are chanzon warm white straw hat LED's from amazon
Chanzon 100 pcs 5mm Warm White LED Diode Lights (Clear Straw Hat Transparent 3000K DC 3V 20mA) Super Bright Lighting Bulb Lamps Electronics Components Light Emitting Diodes - - Amazon.com
3 to 3.2v

very good quality I have an array of 36 and I can give the array 2 amps for about 10 seconds and the LED's are only a bit warm and not hot so they work good as a photo light to take photos of miniature scenery with the warm white color the array of 36 can handle 1 amp continously they stay cool for hours (barely a degree above ambient temperature.)

I have a power supply with constant current function to power the LED's I was just testing something with them.

Last edited by realflow100; 11th November 2017 at 02:07 PM.
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