volts amps watts and ohms?

Question

attempting to add a resistor to a 12v .183 amp fan. I was using this calculator to reduce my 12v fan to 7v

http://www.blackfiveservices.co.uk/fanspeedcalc.php?Voltage=12&Current=0.183&Target=7

From the calculator it it says "Target resistance: 46.838 Ohms"
So from that I know what type of resistor to buy. Being close very close to those ohms right?

There is also the "Power dissipated by resistor" from the website cal. it says 0.534W
That is what I'm not sure of... what does that mean?? I know I need to worry of overloading a resistor. assuming that has something to do with it?

Found these online
http://www.ebay.com/itm/50-x-Resistors-24-Ohms-OHM-1-4W-5-Carbon-Film-/260803143144?pt=LH_DefaultDomain_0&hash=item3cb91425e8#ht_1262wt_905

with these work?
http://www.ebay.com/itm/50-x-Resistors-47K-Ohms-OHM-1-4W-5-Carbon-Film-/250840184468?pt=LH_DefaultDomain_0&hash=item3a673d7694#ht_1262wt_905

Answer 1

I would not use carbon film based resistors for any motor load particularly if you are looking to reduce voltage. What you really should be using is this



http://www.ebay.com/itm/7807-Voltage-Regulator-7-Volt-1-Amp-TO-220-Hard-Find-Type-/290731939118#ht_694wt_956





This is a 7 Volt Regulator, meaning 10-36 Volts go in and only 7 Volts go out.





Pin 1, Input = 12V + input

Pin 2, Ground = - input for both fan and power source

Pin 3, Output = 7V + output



This single transistor will outperform a carbon film resistor and offer something more consistent, accurate and desirable. Go with that.

Answer 2

Connected in series, the 24 ohm resistors in the first link will give you a 48 ohm resistance. (The power will be split across the two roughly equally.) Since your expected dissipation is over 1/2 watt, you'll be exceeding the 1/4 watt rating of the resistors. (It's close enough that you might be OK. It would be better to find a 47 ohm or 51 ohm resistor with a 3/4 or 1 watt rating to give you some margin.)



The second link is for 47K resistors. The K stands for 1000, meaning that the resistors are 47,000 ohms and definitely won't work for what you want to do.

Answer 3

the power would be watts, amps is currrnt, volts is voltage and ohms is resistance. the power would depend on the light bulb, like 45 watt or 60 watt.