stupid question

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Z1P2

Joined Mar 19, 2004
1
ok, forgive me for asking this, but I'm not an electronics guru... yet. On my car, my rear turn signal is approximately 45 watts, I want to splice into it to add some led blinkers on the mirror, but I'll need to drop the power, would putting a 5w resistor on the new circuit after the splice burn it up? Thanks
 

Dave

Joined Nov 17, 2003
6,970
Yes that would work, however I have never heard of a 5 W resistor!! Resistors are expressed in Ohms and disipate power (Watts or W) according to the voltage across them and the current through them.
 

mozikluv

Joined Jan 22, 2004
1,437
:) :rolleyes: :D :) hi Z1P2,

your heading says "stupid question about resistor wattage" now what is stupid about your question. i would consider a guy/gal stupid if he/she does not ask the question. there are only 2 kinds of person in this forum, one who is short of knowledge on a certain aspect and the other is of more knowledge of that certain aspect. so, pls. don't belittle your question, we are not all perfect. ;)
 

jatmi

Joined Mar 21, 2004
6
Originally posted by Dave@Mar 20 2004, 06:05 AM
Yes that would work, however I have never heard of a 5 W resistor!! Resistors are expressed in Ohms and disipate power (Watts or W) according to the voltage across them and the current through them.
awwwwwwww contrair!
resistors are most definatly rated in power dissapated as well as the ohm value ;o)
 

Dave

Joined Nov 17, 2003
6,970
Originally posted by jatmi+Mar 22 2004, 08:32 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (jatmi @ Mar 22 2004, 08:32 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Dave@Mar 20 2004, 06:05 AM
Yes that would work, however I have never heard of a 5 W resistor!! Resistors are expressed in Ohms and disipate power (Watts or W) according to the voltage across them and the current through them.
awwwwwwww contrair!
resistors are most definatly rated in power dissapated as well as the ohm value ;o) [/b][/quote]
Not traditionally, there not. They have a maximum power rating, but they are not generally called an "x" Watt resistor.

Anyway welcome to the forums :D
 

beenthere

Joined Apr 20, 2004
15,819
The bulb wattage has no bearing on your application. All you need to do is to limit current through the led(s). Assuming one led, subtract the led junction drop - about 1.5v- from the source voltage. That's your battery, which is 13.6v. You get 12.1 volts. Normal led current is 10 - 20 milliamps. Use R = E/I, and you see that a 1000 ohm (1K) is good. Anything above 1/4 watt will be ok. The power a resistor dissipates is the product of the voltage dropped across it and the current passing through it. 12 volts times .01 is 120 milliwatts. The duty cycle is also anout 50%, so the resistor cools off a bit even when operating.
 
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