Hello, I have a question regarding the power supply of a single circuit. I have dismantled a simple 9 led torch and removed the circuit board with the 9 led's. I would now like to connect these with cables and a reed switch. The lamp should switch on when a magnet is close to the reed switch. Unfortunately I only have limited space for the power supply and normal batteries even aaa batteries would be too big for the available space. The only option would be button cells. The torch was powered by 3x1.5 V aaa batteries. The circuit does not need a long battery life 30 minutes is enough. Can I use button cells and if so which ones and how many? Many thanks in advance for any answers.
I've got a torchlight with 3 white LEDs powered by 4 buttoncells type LR44. How long it shines, I have no idea.
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3x1.5V button cells. Let us know which one you try, and how long it lasts.
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I's probably best just to try it.
As a rough estimate, check the mAh (milliamp-hour) ratings for the battery. I'd guess 20mA per LED so that's 180mA and a 100mAh battery would last a little over 1/2 hour. (And you could expect the LEDs to be dimmer, but not "dead".)
...In series, the voltages sum but the mAh rating remains the same as one battery (so the milliwatt-hour rating increases.)
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hello i have another question, i can't find a battery holder for 3x LR44 batteries online, only for 2 or 4. I would like to model one myself online and print it out with the 3d printer. I now have a question about how to wire the button cells. I have had very little experience with this. So in short, how do I build a battery holder?
many thanks for any answers 
A little late but I have a few of those 9 LED flashlights. They use the 3 1.5 volt AAA battery packs. Typical current draw is only 40 mA.
As to a LR44 battery holder? This holder holds 3 EA of LR 44 batteries delivering the 4.5 volts you want.
I am seeing plenty of them on Amazon including 5 packs and very inexpensive. Tabs you can solder to also..
Typical LR44 battery has Average Service Capacity( to 0.9 volts):120 mAh (Rated capacity at 4.7k ohms at 23℃)
So figure roughly 3 hours use with your 9 LEDs give or take.
Ron
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I have now found this battery holder to print myself: LR44 / AG13 Battery Holder by jeplans - Thingiverse
but I don't know how to wire it. Is it enough if I attach a cable to the - side and also to the + side or do the ends of the battery have to be connected somehow?
Look at the link I gave you. Make contacts as shown in the link. A few pieces of tin and a spring to maintain load tension on the batteries. You are stacking 3 each 1.5 volt batteries, yes, you need to connect to the batteries. Personally I would just buy one as shown in the link I provided but if you choose to roll your own have at it. Just make sure the batteries are spring loaded and you have good contacts (+) and (-).
Ron
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Thank you for your reply I would personally like to save myself the work and buy a holder directly as you suggested. However, I still need this before Christmas and I have not yet found one that arrives in time.
I have no idea where you are located. I am in the US and for me here is what I see:
FREE delivery Thursday, December 21.
Order within 7 hrs 3 mins
Arrives before Christmas
My wife uses Amazon Prime so when looking for stuff I start with Amazon. I would think these things are pretty common globally but I don't know where you are located.
Here is another example of roll your own.
I am finding plenty of examples of make your own and other distributors of what I linked to. I assume you have Google?
Ron
Yes thanks for the link this is very helpful I am currently in deurtschalnd I also find many battery holders unfortunately only some that do not arrive on time but I will now build a diy holder thank you very much.
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