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LEDs - Series or Parallel?

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panic mode

Well-Known Member
It depends........

I would rather try to keep them in series. It's the
current that dictates the brightness so if you want
same brightness this is definitelly way to go.

All diodes are different and have different curve.
If you put two in parallel, one is always going to draw
more current than another meanining different brightness.

It is possible to select diodes with very similar
characteristic specially if they come out of same batch.
However this requires patience and maybe quite few LEDs
to match one perfect pair.

It is possible but rather unpractical to do this for three or four
LEDS and very difficult for ten or more and even more so if
they are different color.

Sure you can parallel them and if you are lucky all of them
will also illuminate (even the different color ones) but
this will stress some of them more than other.

You can however put resistor in series with each LED
instead of one resistor for ten LEDs in parallel.

This way current for each LED can be regulated individually.

Connecting LEDs in series means less resistors and simpler
wiring. Only problem is if the supply voltage doesn't allow
LED string of size you want. In that case, brake it into two
or more strings (each with one resistor) and put those
in parallel.

Resistors should be selected to keep current in reasonable
limits (14-16mA for classic LED or ca 2mA for Organic LED).
 

sjaguar13

New Member
I'm not really good with electronics. It took me 7 months to figure out how to make the 10 LEDs blink. I have a 9 volt battery with one resistor total infront of 10 red LEDs. Are you saying to use more resistors or use do it in series? Should I put them in series, but go from resistor to LED to resistor to LED for all 10?
 

dingo

New Member
sjaguar13 said:
I'm not really good with electronics. It took me 7 months to figure out how to make the 10 LEDs blink. I have a 9 volt battery with one resistor total infront of 10 red LEDs. Are you saying to use more resistors or use do it in series? Should I put them in series, but go from resistor to LED to resistor to LED for all 10?
You should be able to put 5 LEDs in series without any resistor at 9v
or you can put them in parallel with one resistor in series, or in parallel each with their own resistor. In the long run if you are using identical LEDs it does not matter.
 

Sebi

Active Member
For best efficiency apply this circuit for 9V. The normal red LED forward voltage about 2V, the super-brite about 1,7V.
 

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sjaguar13

New Member
The LEDs have to go in a straight line, and space is limited. It would be easier to do them parallel with one resistor total, but I heard that wasn't the best because of battery life. In a couple hours, the battery would be dead. Is that true?
 

ChrisP

Member
In a given series circuit of simple resistances, the current remains constant throughout the series string, while the voltage divides, or is dropped by each successive resistance.

In a given parallel circuit of simple resitances, the voltage to each parallel branch is the same, with the current s of each branch adding to yield the total circuit current.

Simply put, 5 15mA LED's in series will, if properly limited, be seen by the souce as a single 15mA load, whereas 5 15mA LED's in parallel, assuming each is properly limited to that current, will be seen by the source as a 75mA load. Hence, the parallel circuit will likely deplete the source (battery) more rapidly...
 

sjaguar13

New Member
Series it is. How do I get them to be equal in brightness, or doesn't that matter because they are all red? Do I use one resistor at the beginning, or one resistor infront of each LED?
 

ChrisP

Member
Assuming that all of the LED's are the same type and of the same specifications, a single limiting resistor before the series string will do the trick. The current, and therefore the perceived brightness, will be the same through each of the LED's in the series string, and will be limited through that string by the single resistor.
 

sjaguar13

New Member
So 10 LEDs of the exact same kind with one 330 resistor in series would make all of them the same brightness and use less of the battery?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
sjaguar13 said:
So 10 LEDs of the exact same kind with one 330 resistor in series would make all of them the same brightness and use less of the battery?
Yes, bearing in mind that your power supply needs to be high enough to power 10 LED's in series - at about 1.7V each you need 17V for the LED's, plus 3.3V across the 330 ohm (for 10mA through the LED's) - giving a total of 20.3V. At that you would only be wasting 33mW in the resistor, as you are going to flash them it will be less than that - 33mW when on, nothing when off (50/50 would give 16mW wasted). Identical LED's in series should all be the same brightness as they all get the same current.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
sjaguar13 said:
So 1 9 volt battery won't be enough. I'd really need two 9 volt batteries?
Two would just about do it, but it would be close, and the LED's might well stop working as the batteries fade. Best solution is probably that posted above by Sebi - where you have three rows of LED's, you would simply have to choose the series resistor for the row of four to give the same current as the two rows of three.
 
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