Powering 1000 LEDs in a grid

oz93666

Joined Sep 7, 2010
737
For example, say you use a constant current supply of 1Amp.
Then have 50 strings of LEDS to run at 20mA each. (assuming current sharing works)
Someone trips over your wires and disconnects 49 strings, Then the last remaining string has the full 1A driven through it. SMOKE!.
!!! Really ?? ...."If someone trips over your wires and disconnects 49 strings,...Smoke" ..... Are you serious ??

OP is planning to run the leds at 10mA .... There are slight variations in leds , but if selected randomly these will almost even out so perhaps one string of 20 will draw 9.93 mA ... another might take 10.08 .. all the rest somewhere in between , no noticeable difference in light , no overloading....

Our poor OP has been bombarded with conflicting advice ... I play a lot with leds , and can assure him it will work fine without resistors ...

Please try it first with no resistors and confirm it's OK.
 

dendad

Joined Feb 20, 2016
4,113
!!! Really ?? ...."If someone trips over your wires and disconnects 49 strings,...Smoke" ..... Are you serious ??
Yes!
Did you read the example?
Probably you are correct, no "smoke". Just a flash then open circuit.
And a lot does depend on the voltage headroom of the supply. But a constant current supply will SUPPLY CONSTANT CURRENT!!! Or at least try. So, if there is only one string of LEDs, it will have to carry the full current.

That is why it is a lot safer to have a constant voltage supply and a current setting resistor for each string.
If you have a single string, yes, a constant current is good. But many strings? If you want a separate constant current supply for each string, well go for it. Resistors are a lot cheaper.
 

wayneh

Joined Sep 9, 2010
17,167
That is why it is a lot safer to have a constant voltage supply and a current setting resistor for each string.
If you have a single string, yes, a constant current is good. But many strings? If you want a separate constant current supply for each string, well go for it. Resistors are a lot cheaper.
Exactly what was recommended in post #2 and still the best solution. The DC voltage to use is the only variable, as this dictates how many LEDs can be in series and the ohms value of the resistor needed for current limiting. Choosing 12V means more strings and more resistors but the lower cost of a 12V power supply makes it the better choice.
 

oz93666

Joined Sep 7, 2010
737
Yes!
Did you read the example?
Probably you are correct, no "smoke". Just a flash then open circuit.
And a lot does depend on the voltage headroom of the supply. But a constant current supply will SUPPLY CONSTANT CURRENT!!! Or at least try. So, if there is only one string of LEDs, it will have to carry the full current.
.
You've missed my point ... If you design ANY circuit , with safety measures in place ,solely as a precaution because "someone might trip over and disconnect some of the wires" then where will it end!! ...

This thread is bordering insanity , the constant current device pictured in this thread is sold in the thousands specifically for uses in projects just like this Nothing else needed!
 

wayneh

Joined Sep 9, 2010
17,167
... the constant current device pictured in this thread is sold in the thousands specifically for uses in projects just like this Nothing else needed!
Dead wrong. Constant current supplies are used for single series strings, not parallel. There's no point to constant current for parallel strings since the strings will not level out and the basic design is prone to failure as you've been told repeatedly. The fact that someone gets away with a bad design for a while is not valid support for that design, not for something being constructed by a noob (no offense to the TS) with 1000s of LEDs
 

MisterBill2

Joined Jan 23, 2018
11,605
Do I really need to say DON'T TOUCH WIRES CONNECTED TO THE MAINS ...

I did this sometime ago , connected 8 100w (32V ) leds in series to 240AC NO RESISTOR,,, there was an annoying flicker ...( these leds start to light at about 25V , max current at about 32V )

I just tried again with a 3W ...3.2V led in series with a 67K Ohm put straight into the mains ... no flicker ... why should that be???
YES, you need to remind folks to not touch wires connected to the mains BECAUSE if you don't warn them, some will touch and be shocked and try to sue. Like John Wayne said:"You Can't Fix Stupid." And it is certainly true.
With LEDs and any AC voltage, there is the fact of limited reverse voltage withstanding. LED devices will certainly suffer total failure with an excessive reverse voltage, so please believe the manufacturer's specification. It is REAL.
 
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MisterBill2

Joined Jan 23, 2018
11,605
I mean this would be great. And was my initial thought since thats how i saw led christmas lights i ordered from china set up. They are all in parallel. always two cables in and two cables out of each led except the last one.

And I like I could use 12V/20A power source. But yes, there seems to be some concerns about this that I still dont understand. What is the issue with the current not being under control in this solution? Do I need resistors or other parts in this circuit? (I am talking about the parallel-branched circuit suggested by Sensacell above.) Thank you.
The reasons for having a series resistor are two: IN a batch of LED devices, even similar ones, the forward voltage drop at a given normal current will not all be exactly the same. Close but not exactly. Second reason is that as an LED is switching on the forward current/voltage curves rather sharply, so that a very small increase in forward voltage will cause a larger increase in current. So it is easy to overdrive them from a fixed voltage supply. The series resistor solves the problem.
 

oz93666

Joined Sep 7, 2010
737
Dead wrong. Constant current supplies are used for single series strings, not parallel. There's no point to constant current for parallel strings since the strings will not level out and the basic design is prone to failure as you've been told repeatedly. The fact that someone gets away with a bad design for a while is not valid support for that design, not for something being constructed by a noob (no offense to the TS) with 1000s of LEDs
No leds run at 0.5A ,which the pictured device delivers (@70V) so it clearly was designed for parallel arrays like this one ...

this is a 20W , 35V 0.6A Max ..... it's two lines of leds in parallel NO resistors needed , you can see the two lines of leds in the chip itself .... two of these 20W chips in serries would suit that power supply perfectly ....

Manufacturers don't experience the problems you invision ,they just put lines of leds in parallel in one chip ...a 100W chip has 10 lines in parallel NO RESISTORS NEEDED

100W ... 10 lines in parellel, each with 10 leds 33V ...3.3A
 

dendad

Joined Feb 20, 2016
4,113
There is considerable difference with LEDs from the same die lot and random LEDS.
That is the same reason why for precision amplifier applications, so called identical transistors are tested and selected to match. They are not all the same. As has been stated, you may get away with parallel LEDs without balancing resistors, but it is pretty bad design practice.
I design industrial control equipment, and have for the last 30 odd years. (some odder than others).
Always a good idea is to not take short cuts, but design for long life. We have equipment that has been in continual service in pretty harsh industrial installations for over 20 years. That is a good thing to aim for.
Run your LEDs as you like, but try to give best practice advice, and after that, short cuts if it suits. But to decry those that are giving good advice is pretty poor.
 

Sensacell

Joined Jun 19, 2012
2,985
No leds run at 0.5A ,which the pictured device delivers (@70V) so it clearly was designed for parallel arrays like this one ...

this is a 20W , 35V 0.6A Max ..... it's two lines of leds in parallel NO resistors needed , you can see the two lines of leds in the chip itself .... two of these 20W chips in serries would suit that power supply perfectly ....

Manufacturers don't experience the problems you invision ,they just put lines of leds in parallel in one chip ...a 100W chip has 10 lines in parallel NO RESISTORS NEEDED

100W ... 10 lines in parellel, each with 10 leds 33V ...3.3A
The LED's you show here are ISO-THERMAL, they are all mounted on a single heat-sink.
This type of high-power LED also uses carefully matched LED dies to achieve relative Vf matching.
This is not a valid comparison to the situation at hand, individual diodes that have no thermal connection between them.

Were you to connect up a similar array of LED's that were not mounted on the same heat sink, they would quickly become imbalanced and fail.
 

WBahn

Joined Mar 31, 2012
26,398
No leds run at 0.5A ,which the pictured device delivers (@70V) so it clearly was designed for parallel arrays like this one ...

this is a 20W , 35V 0.6A Max ..... it's two lines of leds in parallel NO resistors needed , you can see the two lines of leds in the chip itself .... two of these 20W chips in serries would suit that power supply perfectly ....

Manufacturers don't experience the problems you invision ,they just put lines of leds in parallel in one chip ...a 100W chip has 10 lines in parallel NO RESISTORS NEEDED

100W ... 10 lines in parellel, each with 10 leds 33V ...3.3A
Very much apples and oranges. The LEDs in an array like that have two critical things that an array of discrete LEDs lack -- intrinsic matching and isothermal operation. The design of discrete circuits and integrated circuits are very different critters -- in each case you can do, and in fact routinely rely, on things that you would, or at least should, never contemplate in the other.
 

oz93666

Joined Sep 7, 2010
737
Absolutely no problems with running as I have suggested ....

TS is planning to run at HALF max current , so the very minor differences in leds will be NO PROBLEM ...
 

-live wire-

Joined Dec 22, 2017
929
Maybe try a constant current HV supply? 3.5kV max 15mA, soft start, turns off if large overcurrent (like person). Hypothetically it would be the ideal setup.

Or what about a COB LED, like others have suggested?
100W LED:
https://www.amazon.com/dp/B01DBZHSC8/ref=twister_B01DBZHR1A?_encoding=UTF8&psc=1
Heatsink:
https://www.amazon.com/dp/B01D1LD68...olid=1Y6UE1RJ7JXQ5&psc=0&ref_=lv_ov_lig_dp_it
12 PS for fan and LED:
https://www.ebay.com/itm/Regulated-...488455&hash=item2f1ff4cb78:g:qJUAAOSwVc5bVuGC
Overkill constant current boost converter to drive LED:
https://www.amazon.com/Aideepen-Con...-10&keywords=constant+current+boost+converter
Total cost: ~$60
Max output: ~10k lumens.
 
Hello, I am making a light installation of 1000 leds in a grid 20x50 leds. I want to connect 20 leds in a series and then connect each series in parallel (50 lines in total). Each led is about 3.1V 20mA. Can anyone help me with what adapter I would use to power this? (I have a regular EU plug 230V 16A). And do I need to put resistors? And where? Final question, because of the design restrictions I can fit max of 24awg cables in the series part of the installation, but I can put any size of a cable between the lines - for the parallel connection. What size of a cable would I use? I hope someone finds this possible and challenging enough to help me out. View attachment 159595
It seems that many times posts of this nature don't give us quite enough information. Is there a particular reason the array needs to be 20x50? Does it need to be switchable, such as halving the brightness by switching all even or all odd #'d strings of lights off, or some other combination? I used to own a camera store - this looks like the LED light arrays which are popular for all sorts of video and studio lighting these days. My son also made a skin treatment array which was not quite this large, and had similar general requirements, but the purpose for each of the two types were wildly different. A little better sense of any added requirements which may 'pop up' would help.

The caution (thank you for that) about not powering directly from the mains should be heeded. It is shocking how deadly running a project without transformer isolation can be.....

There are many standardized power supplies out there, from 12V - ??? at all sorts of current ratings, which can be had literally off the shelf. I have several of the Mean Well (MW) supplies and they are so cheap and well-made it does not pay to try to design and build your own. MW supplies also have short-circuit and overload protection designed into the unit itself, the voltage is somewhat 'tweakable' as well so you can set it for the nominal voltage you require, if it isn't quite where it should be from the factory (ex: came at 5.12 V, adjusted it with my meter to 5.00 V, the nominal spec rated voltage.

I am not pimping for MW, just that I have bought their units and they were well done, and I have one set up right now for an LED over-bench lighting unit I built, works great!
 
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