I'm new to electronics and wiring, and wonder if a 15 ohm resistor will drain a 1.5v battery (specifically a Duracell Alkaline AA) in a reasonable amount of time to a super-intense white LED.
Does anyone know if this will work?
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2\$\begingroup\$ Could you please draw a schematic? I don't understand what you are asking. Data sheets are great too. \$\endgroup\$– TheNoonMooseNov 13, 2014 at 18:54
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2 Answers
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Assuming you mean a 1.5V battery with a 15\$\Omega\$ resistor in series with a white LED, no it will not drain the battery very fast at all. You will get something approaching the shelf life of the battery (could be years).
Unfortunately, the LED will also remain quite dark, as they require about 3V to operate.
answered Nov 13, 2014 at 18:56
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\$\begingroup\$ So now I actually built the circuit, but as you said, it's not draining at all. Do you recommend any electronic that could drain the battery? \$\endgroup\$– JoeyChorNov 14, 2014 at 17:48
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\$\begingroup\$ If your goal is to drain the battery, just connect the resistor across it and put the LED in your pocket. \$\endgroup\$ Nov 14, 2014 at 17:51
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Presumably your proposed schematic looks like this:
simulate this circuit – Schematic created using CircuitLab
If you build the circuit and measure the voltage across the resistor you can use Ohm's Law to calculate the current drawn. Or if you have a V-I plot for the diode you could use a load line analysis to calculate the current drawn analytically. Either way, you can use the current drawn to calculate the shelf life using Duracell's datasheet for its AA batteries (which can be found here). It includes plots for service life based on constant current consumption.
Unfortunately, as @Spehro Pefhany has pointed out, a white LED usually requires a voltage drop in the 3V range so the current consumption will be very low and the battery will last a long time. You could stack two or three 1.5V batteries to get around this problem. Since the batteries are in series the same current would be drawn from all of them.
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\$\begingroup\$ I have tested the battery, and to my surprise, it hasn't drained in a reasonable amount of time. I did try to add more batteries as to your suggestion, but there seems to be no difference \$\endgroup\$– JoeyChorNov 14, 2014 at 17:50
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\$\begingroup\$ @JoeyChor Did you measure the voltage across the resistor and calculate the current through it? Once you've done that you can look up the expected life time in the datasheet I linked to. Unless the LED is drawing on the order of 100mA the life time will be more than a day. \$\endgroup\$– Null ♦Nov 14, 2014 at 17:56