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# Question regarding series and parallel circuits? Answered

Hi Guys,
I'm a bit confused in parallel and series circuits and was hoping that someone in the instructables community could help me out.
If I wire 3 Blue LED's (3v 20mah each) in parallel their amperage will add up but the voltage will remain same, which means I would be able to run those 3 LED's off 2 AA batteries and it would last for umm.. 2200/60 = 36 Hours. And if I wire those LED's in series the voltage would add up and I would be able to run them off a 9 volt battery for um.. 300/20 = 15 Hours. I wanted to know that if my calculations were right and that in both the ways will they be equally bright.

UPDATE

I was a bit confused how to wire it up in parallel so I made a diagram can you guys tell me if it is correct?

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Yes, presuming 1 AA battery can deliver 2200mah and a 9v battery is good for 300mah. You understand series and parallel properly.

BTW don't forget the very necessary three identical resistors in series with each blue LED because you will probably need 3 AA Batteries in series for 4.5vdc.

Each resistor will need to be (4.5-3.0)/.020 = 1.5/.02= 75 ohms.

Similarly only one series resistor is needed when the LEDs are linked in series BUT you have a problem the 9v battery is equal to the sum of the three LEDs there is no voltage to spare. I would recommend at least a ten ohm resistor in series.

Your next interests with LEDs, how series are not affected by order and how a light dependent resistor LDR and 2N2222 or 2N3904 transistor can turn LED cubes off during the day saving the battery.

BTW start now and buy 10 or 100 resistor values that you need.

Do I have to add a resistor cause I dont have any atm. And can you check my diagram please

I have made some video tutorials going over the all you would need to know about electronics basics here:

The first video does have a practical lesson in it actually using LEDs, and I cover the calculation for a series resistor. When it comes to LEDs, it is usually safe to assume that when the correct amount of current is flowing, close to the rated amount or less, the LED will have a constant voltage drop, that is, in this case, about 3-3.5V for blue LEDs. The more you have in series, the bigger that drop. Make sure your power supply can deliver at least that much voltage, and use a current limiting resistor to drop away the excess voltage, and control the current though the LEDs.

Here is the 4.5v 36h circuit

I'm one of those guys who just got started with electronics and i dont have any resistors atm so i was wondering what will it be too bad if i dont add resistors in parallel as they are only 3 leds

if you use only 2 AA BATT probably they light up.

If you use 3 AA BATT explosive light show in less then a second before your face !!!

To be honest both ways are incomplete and the second is never good unless the LED's have identical (measured) specs.

In parallel each LED needs a current limiting resistor.

I series you still need a current limiting resistor but have the additional problem that the internal resistance of the LED's might be different.

As long as each LED receives the correct voltage and current it won't really make a diffence in brightness, no matter if in series or prallel.

But as said if one LED is different you will see a difference in series more than parallel.

Also if one of them fails in series none will light up.

This is what happens to identical LED brightness when all of those LEDs are wired in parallel without individual resistors as seen in the second picture.

Yes you have series and parallel correct as are your estimated run times. Either ay you wire them, as long as they have the proper current limiting resistors for either configuration, they should be about the same brightness.