Wiring LEDs in series with chaser?

[miamimac]

I would like to know how to wire 3 x 3 sets of 4 LED's hooked up in parallel to a chaser. they would be powered by 8xaa batteries (12v). can I wire the 3 sets in parallel and the 4 LED's in each set in series with a chaser? so that every 4th LED lights up then the next... I would like to have 3 strings of this configuration hooked up to the battery for a total of 36 LED's. And is there enough power to have all the lights on at the same time, if so how would I wire this into the setup The LED's would be 3mm x 3.0v x 20mA. which resistor/s should I use. I am looking for the easiest/cheapest way to do this.

 

[audioguru]

8xAA battery cells make 12V only when they are brand new. The voltage will quickly drop to 9.6V as they are used then drop slower to below 8V.
Assuming you want the LEDs to still light (but dimmed) when the battery has dropped to 9V then you cannot have three 3V LEDs in series and in series with a current-limiting resistor.

Another problem is that NOBODY makes a 3V LED (but expensive high power LEDs are tested and "binned" into certain voltage groups).
LEDs have a range of voltages maybe from 2.7V to 3.3V. Some will be 3V but some will also be 2.7V and 3.3V or anywhere in between. Buy thousands of LEDs, test the voltage of each one, sort them then use only the ones (if there are any) that are 2.7V.

 

[alec_t]

Buy thousands of LEDs

...or else use only 2 in series per chain.

 

[WTP Pepper]

Use a constant current source instead of a resistor.