Help with huge LED circuits

[chiragjn]

i am arranging 30-40 leds for a project
so parallel connections between them is the obvious choice
i am using 1.8V 20mA LEDs
and power supply is through AC to 1.5V-12V DC adapter

the circuit looks like railway tracks
|--------|----------|-----------|-----------|-----..(more LEDs in between)...|----positive terminal of battery
|--------|----------|-----------|-----------|-----..(more LEDs in between)...|----negative terminal of battery

where
| are LEDs
|
and -------- is single stranded copper wire


so if i supply 1.5V with all LEDs in parallel, will i need to connect resistors?Also what about resistance of single stranded wire?
i need to make quick connections as i have to make many such linear one dimesional arrays, so i am looking forward to not to connect any resistors.

please help me with selecting proper voltage value and proper circuit connections

 

[BobK]

You are much better off using a higher voltage and series / parallel connections. If you connect all of them in parallel, then the current required is 40 x 20mA = 800mA .
Whereas, if you use say 12V and put 5 LEDs in each series string it is only 8 x 20mA = 160mA. Each series string would require a resistor that drops the difference in the sum of the forward voltages and the supply voltage at the design current.

See this tutorial for lots of info:

https://www.electronicspoint.com/got-question-driving-leds-t256849.html


Bob

 

[Harald Kapp]

In addition to Bob's recommendation: Not all LEDs are exactly equal. Small differences in the characteristics will lead to an uneven distribution of the current and uneven lighting will result.
Besides: LEDs are not operated on a defined voltage, they are operated on a defined current (as explained in the tutorial Bob linked). Therefore any combination (be it series, parallel or mixed) connected to a voltage source without some current limiting (resistor) runs a risk of frying the LEds by too much current. You need some form of current limitation, the easiest being a series resistor.

 

[Arouse1973]

Connecting too many in series might not be acceptable if one LED goes OC then the whole string goes out. And too many in parallel as Bob mentioned will draw a lot of current. There is another option and that is drive series parallel chains with a constant current and cross connect the LEDs so if one LED goes OC then there is still a path for current through the other LEDs.
Adam

 

[chiragjn]

Thanks to all of you for suggestions
but i had very less time and many leds to assemble and very less space to connect resistors properly,
so i implemented my railway tracks circuit design and supplied 3V through AC to DC adaptor without any resistance and bam! it went well
here are some photos:







P.S
i used 3V 25mA white LEDs
the uneven glow among different leds is because some leds got bent and were not placed properly

 

[Arouse1973]

Looks great. love it !