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How many batteries are needed to light up this led button?

  1. Nov 7, 2015 #1
    Hello everyone,

    I am currently involved in a project where I'm building a pipboy 3000 from scratch. I'm close to finishing it and I wanted to take the extra step and make some functional/interactive buttons on it. I've been searching for led button switches to use for some of the buttons for the pipboy and this one was the best option I found all day (its the only one I found that ships here in the US and its the best fit; 8mm diameter button).

    I was hoping if anyone might be available to help me figure out how many (and what kind of) batteries would I need in order to make a circuit with the led button functional? I know the basics of electrics since I took automotive in high school and how to solder/build basic circuits, but I'm not too good in creating a circuit from scratch.

    Here's the ebay link to it;
    http://www.ebay.com/itm/IDEC-AL8M-A...924218?hash=item5d5b8cf9fa:g:qwsAAOSw~gRVuXhs

    The only useful information I think I found about this led switch is that its max capacity is 24 volts but I'm not sure if that's the led bulb circuit or the slave/power circuit. Here's another answer I received from another site, but I'm not sure if the info is accurate,

    "3vdc or greater, 20 mA current. You supply the external resistor based on maintaining 20mA. Vf varies between 1.7v and 2.2v depending on color, and If is the standard 0.02 amps. See page 3 of source. Two AA batteries in series would power it for a long time. If it was illuminated only 5 or 10 minutes a day, a single CR2032 coin battery would work

    R = (Operating Voltage – Vf) / If

    Source(s):
    https://www.idec.com/language/english/catalog/Switches/A8Series.pdf"

    bulb.png
     
  2. jcsd
  3. Nov 7, 2015 #2

    CWatters

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    The links don't work for me but ..

    If you used a 3V CR2032 the resistor you need would be either..

    R=(3-2.2)/0.02
    Or
    R=(3-1.7)/0.02

    Depending on the colour of led.

    A CR2032 has a capacity of about 200mAh so would power the LED for about 200/20 = 10 hours.
     
  4. Nov 8, 2015 #3

    meBigGuy

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    Gold Member

    A CR2032 cannot supply current at that level and meet its Ah rating. They are generally rated in the vicinity of 200uA. You can draw quick bursts at high currents, but then the chemistry needs time to recover. You might get a few minutes at 20ma.

    Here is a typical datsheet http://data.energizer.com/PDFs/cr2032.pdf
     
  5. Nov 8, 2015 #4
    Thank you CWatters and meBigGuy

    I messaged the owner but he claims not to have the information available from the manufacturer, but he affirms that the LED is colored yellow. Here's another updated response from another site,

    "This is a data sheet: http://www.galco.com/techdoc/idec/al8m-a11-y_cp.pdf
    This is other helpful info:http://www.lectrocomponents.com/pushbuttons/idec-al8m-a11-y-switch/

    You need a resistor of 39 ohms 1/4 Watt in series with two AA batteries or C or D, which ever is easiest for you. You may want to get a battery holder. The battery voltage will be 3V the LED Vf is 2.2V and the current is 20mA.
    This is shown at the bottom in the last table for a yellow LED."
     
  6. Nov 8, 2015 #5

    CWatters

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    Data sheet says Yellow LED is nominally 2.2V so yes the R you need for 3V would be..

    (3-2.2)/0.02 = 40R (nearest standard value is 39R).

    The power rating you need is tiny... 0.8 * 0,02 = 0.016W so not sure why they say you need 1/4W - perhaps because they are easy to handle so you could solder it direct to the pin on the switch if you wanted. 1/8th W would also be ok.
     
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