Re: Wiring LEDs together

On 30 Mar 2007 10:57:31 -0700, in sci.electronics.design "alokw"
<alokwadh@xxxxxxxxx> wrote:

Hi all,

I have a quick question that should be simple to answer.
I have 54 LEDs that require 3.4 V DC with a maximum of 30 mA that need
to be wired together.
I have 9V batteries to power them.

I did the calculations and ended up wiring them in series of 2 LEDS
with an 82 ohm resistor for each pair and hooked up the end to a
single 9V battery. With the 27 pairs, it was suppsed to draw 810 mA.

When I switched it on, everything was dim. I didn't think about how
many mA the battery could provide.

My alternative idea is to wire 2 9V batteries together and wire 55
LEDs in series of 5 LEDs with a 39 ohm resistor with each series. This
*should* draw 330 mA. Right?

I think this will work, but want to verify it with you people that
know what you're doing before I buy more 9V batteries and new
resistors. I just want all the LEDs to be as bright as possible.

Thanks for your help!
forget about PP3 9V batteries, they are unsuitable.

From the Duracell MN1604 data***:

Rated capacity 580mAH.
At just 25mA load the volts drop to about 7.5V in ten hours, and you
want over 10 times this current


martin
.