ups double post

 

The voltage at the end of a circuit (the negative pole of a battery) will always be 0. So, in your case. when you connect 1 LED, it would have to swallow all 9 volts. If you connect 2 LEDs, the voltage accross each one will be 4.5V. If you connect 3 LEDs, the voltage accross each one will be 3V and so on.

Most types of loads, including LEDs, can only handle some maximum voltage before they get damaged. So what to do if when you have a 9V battery and a bunch of LEDs that can handle 2V tops? You keep connecting them in series until each has to only deal with a safe portion of energy.

It is not a good idea to drive LEDs at their maximum, the brightness won't be significantly increased and they would age faster, becoming dim in the process. Let's go for 1,5V per LED.

Now how many LEDs should we connect in series so that each receives 1.5V? Well 9/1.5 = 6. Most people would use 5 LEDs and a resistor for the last 1.5V. I would use 6 LEDs and no resistor.

All that being said, I've made IR torches for filming in darkness... normal LEDs are too much hassle. You can get the 5W high power kind for a dollar on ebay / aliexpress. They run on 1.5 - 2V too so you can hook one to a single AA battery and don't have to worry about any resistors.

 

©-©-©-© R
©-©-©-© R
©-©-©-© R
©-©-©-© R
©-©-©-© RR
Thats the way i have my leds
© - leds
R - resistor

 

You may use the LED calculator here to help you calculate the LED resistor value.

©-©-©-© R
©-©-©-© R
©-©-©-© R
©-©-©-© R
©-©-©-© RR
Thats the way i have my leds
© - leds
R - resistor

You may use the LED calculator here to help you calculate the LED resistor value.

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

Allen

 

Dunno.what to punch in

 

Prob frying ur heads with questions. A 12v battery pack (8AA batteries), how many ir leds could i attach to it the maxium i mean an how many resistors

 

Do you mean, how many parallel strings? The more you add, the less battery life you will have since each will draw the same current from the battery. You could keep adding them up to about 1/2 amp total current without too much trouble. Beyond that, you need to know the specifications of the battery. Too much total current may damage it.

Also note that the voltage will sag as the current draw increases, so you may reach a point where adding more strings does not increase the overall amount of light produced.

 

I agree, it's that simple; too many lights and not enough battery.

20 LEDs at 300mW each is 6W. A typical 9V battery might provide 400mAh to your lights until the voltage has sagged so far it will no longer work. If it really maintained, say, 8V (it won't), that would be 3.2W•hrs or about one half hour at 6W. Ten minutes is a little short, but not at all surprising.

The batteries may have some useful life left in them for other uses, though.

If that's a PP3/6F22 I'm surprised the OP gets 10 minutes! The individual cells in those are *TINY*.

IWHT the appropriate number of AA cells at least, and rechargeable Ni-Mh would certainly work out a lot cheaper.

 

if u look to bottom of list like the purple colour is uv leds i got if i run on 12v battery pack 8xAA what resistors can i use an how many