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RSS >  9 V battery what resistor
wiechu #1 10/01/2018 - 18h31

Class : Apprenti
Posts : 2
Registered on : 09/01/2018

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Hi all
Im building my first free track and Im complitely noob when its comes to watts , volts , ohms etc. I have those 3 led

http://uk.farnell.com/osram/sfh485p/ir-emitter-880nm-5mm-radial/dp/1212738 a
nd I would like to connect them to 9v battery so any one know what kind of resistor should I use. I found one resistor in my drawer and its a 30 ohm 1/4 watt and im just wondering if thats enough .
Thank You
Stormrider #2 14/01/2018 - 13h29

Class : Légende du Forum
Posts : 466
Registered on : 02/01/2013

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this setup will only work for a very short time and will end in smoke.With that resistor there will flow a current of 300mA.For those leds it is to much.A current between  50mA and 75mA is what you need.If you want to stick wihh that 9v battery you need a resistor value between  180 ohm( 450mW) and 120 ohm(675mW).

Just make it easy for yourself and take a look at this.
http://forum.free-track.net/index.php?showtopic=1856#11461

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