As the thread title implies, does anyone here know how many LEDs (with the appropriate resistor) can you hook up to a single 9v battery? If you hook up more than a few, does the battery just drain quicker? Or does it affect the light output of the LEDs? I'm figuring that the more LEDs you use, you should probably adjust the resistor, but let's assume that I'm Carson Dyle (:)) and I'm just going to hook up 15 LEDs with the same resistor in place as if I were only hooking up a single one. Any problems you can foresee?

I'm concerned about fitting more than one 9v battery through the Flying Sub rear door, but I've also created a bit of a monster with the lighting - lots of LEDs.

Thanks in advance,

Gene

Gene; I can't help with the voltage issues, but you'll play hell trying to get more than one 9v batt in that tunnel. You'd have to stack em on top of each other, and it's tricky just trying to get one in and out.
How about a wall wart?...a remote power source, depending on how much power you will need according to the electrical gurus.

Steve

If you hook them up in series with one resistor at the head of the string the voltages add so using a figure of 3 volts per LED on average you could light 3 LED's. Lighting LED's in parallel requires a resistor for each LED but the amps add up. So you could light more LED'S. Typical 9V batteries provide 500-800 mA. Each LED used about 20 mA so figure about 25-30 LED's. The more LEd's the faster the battery will run out of juice of course.

If you hook them up in series with one resistor at the head of the string the voltages add so using a figure of 3 volts per LED on average you could light 3 LED's. Lighting LED's in parallel requires a resistor for each LED but the amps add up. So you could light more LED'S. Typical 9V batteries provide 500-800 mA. Each LED used about 20 mA so figure about 25-30 LED's. The more LEd's the faster the battery will run out of juice of course.


Excellent info - thanks. Any other downside beyond the quick drain on the battery? Any permanent damage to the LEDs?

Gene

Type your stuff in here and it will even draw you a map!

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

Type your stuff in here and it will even draw you a map!

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

I've seen this array wizad. It's excellent. I like that you can have several strings of LED's in series connected up in a parallel array. Sort of the best of both worlds.

I think that site should be stickied in every modeling forums "Model Lighting" section!

Just be careful when you use the wizard to input good values for whatever LEDs you plan on using. White are around 3v, but red, green, and yellow, are less.

It's better to use a bigger resistor than you actually need than too small. You can also reduce the brightness if desired by using a higher resistance. Test using a breadboard before soldering!

Here's a table I grabbed from this website (http://www.kpsec.freeuk.com/components/led.htm). If you buy from a place like eLED.com (http://www.eled.com/Default.asp) they publish complete specs, otherwise this table is probably close enough:

Note that red LED's like 1.7 volts. (they max out at about 2.1V)


Standard Red 30mA 1.7V
Standard Bright red 30mA 2.0V
Standard Yellow 30mA 2.1V
Standard Green 25mA 2.2V
High intensity Blue 30mA 4.5V
Super bright Red 30mA 1.85V
Low current Red 30mA 1.7V

Excellent info - thanks. Any other downside beyond the quick drain on the battery? Any permanent damage to the LEDs?

Gene

LED's when the battery drains will get "dim" only to a certain point. Then they stop working abruptly (unlike light bulbs that get dimmererr). Not really a downside but consider this when lights stop working; try replacing the battery first.

Gene,the board that comes with the Voodoo Efx FS Kit has 24 ports.With the proper risistors thats how many LEDs you can run from a 9V.I have 14 in mine.alex

Gene,the board that comes with the Voodoo Efx FS Kit has 24 ports.With the proper risistors thats how many LEDs you can run from a 9V.I have 14 in mine.alex

Yes, that may be, but you have forgotten that it is my quest to over-engineer, over-complicate, and over-think all that I do. Translation - I didn't buy a kit or plan anything out. I just started sticking LEDs in there till I wound up with about 14. I say "about", because I'm not done. :thumbsup:

Gene

There should be no damage to the leds by under juicing them. It's pumping too much in that kills them. It's scary when they abruptly stop working, but take one out of the chain and they;ll light again.

But yah, for rough math, figure each led drinks 20mA. Give or take a few mA. So 4 leds at 80mA on an 800mA batt means you get ~10 hrs. 800mA gives ~1hr. 8000mA would be... 6mins?

As long as your resistors are geared for the 9v power, you can stuff 1000 leds in there and still get a ~1 min of life on the 800mA example. :hat:

PS I've got some old fashioned red leds that suck down 75mA each, so there are always exceptions to the rule. I just throw them in until they don't light, then up the mA of the power source to compensate (if I have one on hand, otw it's tough decision time).

PPS Adding cmos drains a few mA off the top as well.