how can I power 30 IR leds comes from TV remote by a 3.6volt cell phone battery. the LEDs are 1.5 volt.
The answer depends on how they are wired. If wired in parallel yes, in series not. In a parallel circuit all of the LED's together draw 1.5v in your case. So 3.6v will work with a resistor. However the current, AKA amperage draw is added for each one. for example if one LED draws 30mA, that will be multiplied by the number of LED's 30mA x 30 LED's = 900mA this is important in determining battery life. It would be beneficial to do a search for LED parallel and LED serial circuits to better visualize this. I also included a couple of example images. Now we come back to the question that steveastrouk asked, "How long for?" That comes down to capacity of your battery. For example a fully charged 1000mAh battery will release 1000 milliamps of current at a specific voltage for one hour before it is discharged. so for our example above. If your LED circuit draws 900mA, a fully charged, properly maintained 1000mAH battery should last a little over an hour. Check out this battery life calculator. It is meant for RC flight time but it works for any application. http://www.scoutuav.com/2011/05/12/calculate-flight-time/
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then what resistor should I use ?
Check out Ledcalc.com You will need to know the battery voltage, and the LED voltage, and amperage draw for one LED. Put those numbers into the boxes on the website along with how many LED's you have and it will give you a resistor value and suggest a diagram for the circuit
Which LED. How long for.
If you wire them in parallel you will need a resistor. I use http://ledcalc.com/
If he puts 30 in parallel with that battery, he's not going to get much current per LED. I don't know the output resistance of a coin cell, but its not especially low.
I don't use a coin cell.It's a cell phone Li-Ion battery.
I had a cheapo 29 led flash light with 3 AAA's in a holder. I went to a thrift store & wiped them out of TV remotes. I took out all the IR LED's from the remotes, then changed them out one by one until I had 29 IR LED's installed. Interesting because you don't know if it is off or on, and you have to hide it for people don't play with it & leave it on. I checked it out with my night vision, and it is not that bright, I am definitely going to have to increase the voltage, by adding a couple more batteries in series, so that is the tricky part, getting them nice & bright without over doing it & ruining the whole project.
The next part 5 to 30 ma. So for 30 IR LEDs in parallel you need 150 ma to 900 ma. And for 30 IR LEDs in series you need 45 volts to 180 volts. The .6 volts should not be a problem. This is only if you are lucky and all your LEDs are 5 ma and 1.5 volts. Two in series and 15 parallel the circuit would be would be 3 volts and 75 ma. My LG cell phone battery is 3.7 and 800 mah it might work for 2hr before the battery didn’t have enough power to support the circuit. See my Instructables:https://www.instructables.com/id/Ghost-Busted/https://www.instructables.com/id/Photo-Components-Testing/https://www.instructables.com/id/Liner-Counter/
Hey good call on the two serial circuits. No resistor required. I think your answer was more what the asker was looking for. I may have went overboard with info.
It would be helpful to know the amperage draw of the LED though.
It would be helpful to know the amperage of the LEDs as I said earlier 5 ma up and 1 volt up. Salvaged IR LEDs are hard to get the data on simply because they don’t have part numbers. Go to this page.http://www.maxim4u.com/ Search these IR LEDs. IR333 IR383 QED234 TSAL6400 This one I got from Radio Shack runs on 5 volts 150 ma.
Wow 150mA. That's no joke there.
Yea and on the battery he wants to use maybe 30 minutes on six LEDs.
That being said. Another valid question would be will they be on continuously like a flashlite or in bursts like a TV remote control. If it were in bursts it might not be too bad depending on how long / how often the burst.
He has to be doing ether one of two things night vision or light setting a resin.
I thought about the NV thing. But I didn't know about the resin thing.
Most are UV like the fillings in a dentist office but there are IR resins also.
How long for ?
It depends on the current draw of the circuit compared to the mAH capacity of the battery.
Precisely. That's why I ask the question.
My guess would be that the author of the question would like them to last for as long as possible with the battery specs already given. It doesn't appear from this question that he wants to know what type of battery will last a given amount of time. Of course I only assume that because he states that he already has a battery in mind.