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 Electric feel

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Electric feel
« on: Jan 17, 2016, 02:11 PM »
Okay so I'm fooling around with some lighting and light up switches and such. If my power source is 9 v and the LED is rated at 3 but already has a resistor connected should I attach a second resistor just in case?

And second if I only want to attach a light up switch, does the switch need a resistor between it and the battery?

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Re: Electric feel
« Reply #1 on: Jan 17, 2016, 03:58 PM »
It depends on the value of the resistor and the data of the LED. Assuming it's an average LED with 20mA you would need a total resistance of 300 Ohm if you want to connect it to your 9V power source. So in case the already existing resistor is smaller than 300 Ohm you need to add another one until you reach at least 300 Ohm in total.

Does "light up switch" mean an illuminated switch? In this case you need to know the data of the LED or light bulb inside, most times it is the same as the working condition the switch is designed for. For example: in a switch that can handle 230v it is quite likely that the light inside needs 230V. If the switch is designed for 9V or slightly more, there shouldn't be a problem, but if it's lower you will need a resistor. (I would refer to the data sheet to be sure)
Or if you mean the switch to light up the LED from before you don't need anything else.

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electriFi - Mando Electronics English / German
Re: Electric feel
« Reply #2 on: Jan 18, 2016, 02:46 AM »
Its an illuminated switch that goes in a car.

And I double check the LEDs they are rated for 6v with the resistor that's already on there so I'm just going to add one more that I have that's rated at 3v and that will be okay yea? For a 9v battery pack? I still haven't figured out Ohms but...yea

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Re: Electric feel
« Reply #3 on: Jan 18, 2016, 05:13 AM »
The switches for cars are usually rated for 12V as far as I know. If there is a lightbulb inside you might be lucky if you try it at 9V but it wouldn't be as bright as at 12V.


Instead of adding a resistor you can add a LED in row rated at 3V with the same current the other LED is rated for and you have your circuit working with your 9V pack.

If you want to add a resistor instead here is how you can find out which one you need:

The resistance (R) measured in Ohm is defined by voltage (U) devided by current (I):

R=U/I

now you have your LED+Resistor with a voltage of 6V let's call it ULED your supply voltage is 9V (U0)
the additional resistor (Radd) you'll need calculates by:

Radd=(U0-ULED)/I

The only thing you need to know now is the current "I" the LED is working with, as I wrote before most LEDs I use are designed to draw 20mA.
In this case you would need:

Radd=(9V-6V)/0,02A=150 Ohm


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electriFi - Mando Electronics English / German
Re: Electric feel
« Reply #4 on: Jan 18, 2016, 02:04 PM »
You totally just blew my mind LOL  :o :o :laugh: :laugh:

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Re: Electric feel
« Reply #5 on: Jan 18, 2016, 03:35 PM »
I'm sorry, I'm not good at explaining.
Summed up I would say:
If you do not have the data sheet for your LEDs and the switches try

1. to connect the switch directly to your 9V supply
2. to add a 3V (and 20mA) rated LED or a 150 Ohm resistor to your 6V LED before connecting it to the 9V supply

That's what I would try.

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electriFi - Mando Electronics English / German
Re: Electric feel
« Reply #6 on: Jan 18, 2016, 03:46 PM »
Okay we're on the same track.  :D Its okay you just know the more technical functions of these things. And I'm all Barney style over here LOL

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