Mixed voltage?

[smusno]

Hi.

Smusno here.

Some of you might have seen my progress in the space/si-fi section.

Anyhoooo, I have a question.

Im running 2 circuits for my Voyager. 8 white LED's, all on 100ma resistors. All powered up by 4 AA batteries @ 6v.

I have 2 feet of Modelers Brand LED tape. Of which I want to run 9 in each engine, 3 behind the main deflector.

Now, here is where I shall start to confuse myself..........

I have had to buy a 9v battery, as the 6v circuit is not enough to kick in the blues. And I want to ultimately run all the blues, 2 red LED's (190ma resistors) for the bussards, and 2 white LED's (100ma resistors on the 9v circuit.

By making sure the resistors in the the line properly, will they handle the 9v power source properly? Or will they just fizzle and die?

(I intend an independent line to the power supply for each of the lighting units)


Clear as custard.

HELP :-*

 

[Grendels]

First if you go to this website:

http://led.linear1.org/led.wiz

It will tell you what resistors you need for which led. Remember that White LED's are 3.2V and that red are 2.2V. So you cannot use the same resistors on these. At 9V you will need 330 Ohm for the white and 390 Ohm for the red.

For six volts the white LED's will need a 150 Ohm resistor. I would cut the number of AA batteries down to two and drop the resistors. Then you have a 3V system, and no need for resistors at all.

One other problem. Each AA battery will supply 2700mAh of power. Since each LED consumes 20mA of power, a AA battery will power a single LED for 135 hours. So for a 3V system using two AA batteries and your 8 LED's the batteries will last for (2*2700)/(8*20)=33 hours. Not bad.

The problem is the 9V battery. It will only supply 565maH or power. One LED will drain that in 28 hours. So if you use your array with 21 blue LED's, 2 red, and 2 white the circuit will consume 500ma of power. The 9V led will only last one hour, and then you will have to change it. Now I am not taking into account the resistors in the circuit they will also consume power. A 330 Ohm resistor at 9V will take 3mA and you will have about 25 of them so that is an additional 75ma of power. That means the battery will last less than an hour.

One other problem as the battery drains, the voltage will drop and your LED's won't light up as well. So I suspect that the 9V battery will last about 20 minutes max.

I would get a wall plug for it. Here in the states, you can find them on Ebay pretty easily and most second hand stores have tons of them for cheap. Look for a 9 V and make sure it will supply more than 600ma. Most wall plugs list this on them. Here is a link and a picture just in case you don't know what I am talking about:

http://en.wikipedia.org/wiki/AC_adapter

 

[smusno]

thanks big G

ill have to do a minor think about this, as the Modellers Brand LED's need at least 6 volts to power them.


Possibly, the future would be to buy a multi voltage "wall wart" adaptor and power the whole lot at 6 volts.



The only reason I put the 9V battery on at all, is the batteries wouldn't power up the MB lights at all!

(and i was impatient, and wanted to see them alight!)



To the electrical shop!!

 

[Grendels]

Your welcome, I would just do the whole thing in 9V and use a wall wart.

Glad I could help!