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if i have 3 resistors each 22 ohm, and i hook them all together, do i have 66ohm total resistance?

 
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In sieres yes

If you put them in parralle they dived by there squares

 
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Series=66
Parallel=7.33

 
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you can check that with an ohm meter

 
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this is why i couldn't be an electric engineer

 
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You can also get 33, by paralleling two (for 11 ohms), and putting them in series with the other.

--TMB

 
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Wow .. i just noticed I forgot all my electronics knowledge!

 
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lol so did i. most noob question ever but i had a feeling it added up, common sense i guess haha

 
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so are they in series or are they parallel? ans what are they for.

 
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well i'm being lazy. i have a gauge cluster with 30+ leds wired. 4 leds in series and each set of 4 wired in parallel. this is fine without resistors for 12v, but for 15v (running car) i need 68 ohm resistance on the power lead. and i should just go buy a single instead of sticking a bunch of 22 ohm together.

 
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lol probably best. help your cost be down when you make them too

 
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A 1/2 Watt resistor may run hot in that situation, You may need a higher Wattage rating.

Good info here ----> http://www.lsdiodes.com/shop/

 
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This is easy. Its the complex differiential equations that gets most people.
(I am not an EE but I am a Computer E student and so far the first 2 years are the same 'cept i get programming classes)

here are 2 ways to find resistor value of resistors in parallel:

say you have R1 || R2 (R1 in parallel with R2)

R[equivalent]=(R1*R2)/(R1+R2) This only works for 2 resistors
R[equivalent]=1/((1/R1)+(1/R2)+(1/R3)+...) Follow this pattern to add up any amount of resistors in parallel

Capacitors are the opposite:
In parallel C[equivalent]= C1+C2+...
In series C[equivalent]=1/((1/C1)+(1/C2)+...)


Hope that helped

 
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P=V^2/R...
so the power on the resistors are 15V squared 225 and divide that by 68 ohms...equals to 3.3W...this is the minimum power rating of your resistors..all combined....it will burn/turn black...

 
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P=IV too.

 
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i'm lost. i have bunch of 4 led series hooked in parallel. each led has forward volt 3.4v and 20ma current. Now hooked to a 12v the circuit is fine, but i need 15v since the alternator puts out more. according to what i've calculated, thats around 68ohm needed for 4 leds. i thought it wouldn't matter since everything else is in parallel. can't i just add 68ohm resistor to the beginning of the circuit?