Newbie:Current and voltage draw through light bulb

Jan 31, 2007 5 Replies
M

I am fairly new to this and have several (simple) question:



I have a krypton flashlight bulb (markings on bulb say 4.8v .5A). The original flashlight that the bulb was removed from used 4 AA batteries.


  1. Wouldn't the 6v from the batteries be 'pushing' the bulb a bit and reducing its life?


  1. If I want to wall-wart power this bulb, what voltage wall wart would be recommended?

  2. Since most wall warts (unregulated) supply higher voltage than the sticker says, what method should I use to bring down the voltage to the recommended voltage (regulator, resistor, etc) (I remember once trying to do something similar to this project and using a resistor. Even though the resistor was a high wattage resistor it got REALLY hot)


  1. I think this question probably will have the same answer as #3, but if I want to dim the bulb what method would be recommended?



Thanks for you assistance


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J

For alkalines, yes, but at 1/2 an amp the internal resistance of the cells would drop the voltage somewhat, and as the batteries were drained the voltage would also drop. For NiCd and NiMH rechargeables I believe their "flat" voltage region is around 1.2V/cell, so that would work perfectly.
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H

When you draw .5 A from the batteries you wind up with 4.8 V (not strictly true but it works).

4.5 V.

Use a multi voltage unit, run at 3 V.

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J

5V ones are fairly common, use one of them.

5V ones are usually regulated :), or you could use a 4,5V unregulated one that'd probably be close enough.

to drop 0.2V at 0.5A you need a ideally a 0.4 ohm resistor, 0.39 will probably be will close enough, actually 5V would be close enough.

usually it's just easier to buy a nightlight,

Bye. Jasen

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M

be

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I

Thanks

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M

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Thanks

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