Help!

StarvinMartin · Post by **StarvinMartin** » Mon Nov 06, 2006 3:24 pm

I'm going to attempt to light my PL 1/350 Refit E, and will be using a 12V DC supply with a mixture of 1.8 and 2.8 volt 3mm LEDs, all rated 20mA, broken down as follows:

12 x 1.8V (6 LED x 2 series lines, and 68 Ohm R in each line)
20 x 2.8V (4 LED x 5 series lines and 47 Ohm R per line).

I'm not planning to blink any of the lights (I'm not that clever!).

My question is:

Can I just create the 2 arrays, one for the 2Vs (and one for the 3Vs, and connect them in parallel to each other as shown above, or would I need to adjust the arrays?

macfrank · Post by **macfrank** » Mon Nov 06, 2006 3:44 pm

Have you used the LED array wizard? You can play with your array parameters until you get one that is simple to build.

Frank

StarvinMartin · Post by **StarvinMartin** » Mon Nov 06, 2006 3:55 pm

macfrank wrote:Have you used the LED array wizard? You can play with your array parameters until you get one that is simple to build.

Frank

Each of the two arrays I've listed above was created using the array wizard, and I'm satisfied that they will work fine on their own. It's when I put them together that I'm worried about. When operated independantly the 2.8V array draws 100mA, with the 1.8V array drawing 40mA.

Will this change if I run both arrays in parallel? I don't think it will, since I think it will just draw a total of 140mA from the power supply (draining a 12v battery pack a little faster or giving me a higher electricity bill if I use a DC mains adapter!)

However, I'm the first to admit my inexperience here, so I was looking for someone to confirm or correct my thought processes.

jwrjr · Post by **jwrjr** » Mon Nov 06, 2006 11:22 pm

There's a 'gotcha' in play here. Is your 12 volt power supply really putting out 12 volts? AC adapters that are not the 'regulated' variety generally have an output at 25% higher than the rated voltage open circuit, decreasing to the rated voltage when fully loaded. Best to make sure that you don't overdrive your leds under ANY circumstances.

StarvinMartin · Post by **StarvinMartin** » Tue Nov 07, 2006 1:21 pm

Thanks for the advice. I didn't know that. However, I've got a variable voltage adaptor. so I'll probably set it to 9V, which should keep me under the 12V even taking into account the 25%.

Failing that, I might just use a 9v battery and change the design of the arrays to reflect the reduced voltage.