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What kind of resistor do I need?

I have a wire going from the battery to led lights. Its putting out about 14 volts and I need to take it down to at least 10 volts so it won't blow the 20 amp fuse. I've looked at radioshack for resistors and I'm lost on which one I need because they go by watts and I don't know anything else about what I'm running.

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  • 9 years ago
    Favorite Answer

    First, let me say that if you have enough LED lights

    that you might blow a 20A fuse,

    you have an awful lot of LED lights!

    Resistors are rated by more than wattage.

    Of course, they are first, and most importantly, rated by their resistance,

    and, although they are rarely (if ever) marked for it,

    they also have a maximum voltage rating.

    In order to use Ohm's Law to calculate the resistance needed,

    you must know both the voltage to be dropped (which you do)

    and the current that will be drawn (which you may or may not yet know).

    You also need to calculate how much power the resistor will dissipate.

    The wattage rating of the resistor should be more than twice as much

    as it will dissipate in use (for example, if it will dissipate 0.33 watt,

    a 1/2-watt resistor would get rather hot; a 1-watt part would be more suitable,

    and a 2-watt one would be even better).

    One of the best things you can do is go to a library

    and find a Radio Amateur's Handbook,

    which is a good general reference for many principles of electricity and electronics.

    Any edition from 1970 to the present will do for most purposes.

    A good library will have several books on electronics

    in which you should be able to find useful information.

  • 9 years ago

    I have not fully understood your question but let me attempt to answer anyway.

    LEDs act as diodes, so you when you connect them in forward direction to the battery, they have certain voltage drop across them.

    So let us say you have series of LEDs, amounting to a drop of 4V. (14V -10V).

    Battery is also sourcing some current and there is a 20A fuse in series - which is kind of protection circut.

    So you do not want current to go beyond 20A, by keeping a resistor in series.

    Following is the calculation for you:

    10V drop across the resistor to limit 20A of current.

    Resistance value: R = V/I - ohms law = 0.5 ohms.

    power rating of resistor would be V*I = 200W.

    Wild Guess:

    But, I dont think you need 20As to be flowing through your diodes.

    I am pretty sure you may require < 1 or 2A.

    So, assuming you require 2A current.

    10V/2A = 5ohms -

    10 * 2 = 20W

    You may find more details about resistor

    www.resistor.in

    and where to buy,

    http://resistor.in/?q=node/24

    different types of resistors

    http://resistor.in/?q=node/16

    Let me know if this information helps. Else please give more details of what you want to do.

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