HI i new to all this . i need help please . i would like to try and build a with ir leds and 9 volt battery , how ever the pp3 9v rechargeable is 8.4 volts. how many leds and what size 3mm 5mm or 10mm can i run of the battery that would last couple of hours or . and what resistor i need please , would be so grate full thank you

 

Welcome to AAC!

How many LEDs would you like, what is the part number, how long do you want the circuit to operate, and what are the specs for the battery in question?

 

A PP3 isn't a great choice because of the low capacity. You'll be able to put 2, maybe 3 LEDs in series. That string will draw maybe 50-100mA (it depends on the LEDs) and will make only a small amount of IR light. Hardly "night vision" unless you're up close to it. I don't know if you'd get a couple hours even with just one string, and I think you'll want several strings to get an appreciable amount of light.

 

hi i look on the internet , there a home made one 54 leds work of a pp3 battery or there 6 leds 10mm leds works with a pp3. i just confused. more leds will be better i think . i haven't got a clue what size what ma etc . thats why i asked ps polaroid make one 36 led run of a 3.7 volt battery

 

haven't got a clue what size what ma etc . thats why i asked

It would help if you gave the part number for the battery. I searched for PP3 batteries and everything from alkalines to lithium came up.

A 9V battery is compact, but capacity is relatively low; even to AA batteries.

54 LEDs with that type of battery won't have a long run time. For 2 in series, times 27 in parallel; current draw (assuming 20mA) will be 1A. That wouldn't give you hours of run time. You'd be lucky if you got an hour.

 

• Low power consumption
• Voltage: 1.5V~1.6V
• Current: 20-25 mA
• Peak(pulse): 700mA
• Power: 200mW
• Wavelength: 850nm

what this mean about this is for 20 leds. its 1.5 volt for one led or 20 will run of 1.5 volts

 

So what is your goal? No matter what you do, there will always be a tradeoff between luminance and battery life. You have to specify either the luminance or the operating time. Then you can optimize the other with an efficient circuit.

You'll likely want a constant-current boost converter to take the place of a simple current-liming resistor. This will be more efficient and will maintain brightness as the battery discharges.

An obvious question is, why not just buy one? You will probably not save money building your own.

 

So what is your goal? No matter what you do, there will always be a tradeoff between luminance and battery life. You have to specify either the luminance or the operating time. Then you can optimize the other with an efficient circuit.

You'll likely want a constant-current boost converter to take the place of a simple current-liming resistor. This will be more efficient and will maintain brightness as the battery discharges.

An obvious question is, why not just buy one? You will probably not save money building your own.

if i can get good hour or 2 with good luminance that be good please

to buy one they around £38 upwards . i can make less then £10

hi it ok i work it out myself ,thank you