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wiring up variable resistor

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DeathONator

Member
Joined
Nov 21, 2002
Location
Colorado, USA
Ok, I feel retarded. I'm wiring up the radioshack 25Ohm 5W variable resistor. I'm using it w/ my 172mm sanyo denki fan (.48amp X 12V).

In an article here at overclockers.com, Joe says: "All you do is clip the black wire on the fan, attach one end to the center pole and one end to either of the side poles; insulate with shrink wrap and you're all set to go."

I'm sure this makes sence to people who already know what their doing but I don't get which wires he's talking about. I don't just wiring up both the 12V and ground wires from the fan to the resistor because then how would I be getting the power for the fan?!?

Thanks for setting me strait... once you do!
 
Ahh, yes that makes sence. I have to remember !DC voltage! you don't need a ground there!

Now I don't have any shrink wrap, and I don't really want to use electrical tape... hmm I'll have to look around the house. What do you guys use?
 
You don't need the resistor to be grounded... that is what I meant.

I have taken two spare molexi; one male, one female; wired them together w/ the 12V GROUND line. Then put a wire on each of them in the 12V slot. Now all I need to do is solder both sides of the 12V to the resistor and shield it. Then plug them in to my fan and PS molex.

My fan is going to take 5.76W. The resistor is suppose to take 5W. Is the resistor going to fail on me?
 
DeathONator said:
Ahh, yes that makes sence. I have to remember !DC voltage! you don't need a ground there!

Now I don't have any shrink wrap, and I don't really want to use electrical tape... hmm I'll have to look around the house. What do you guys use?

A hot glue gun works well for insulating low voltage items that don't draw enough current to get very hot. Squirt a big dollop on the connections and let harden. Very simple and quick for small things.
 
Deathonator,
Make sure you watch that rheo carefully as it will most likely get very hot. You stated it was a 250 Ohm/5W and you are using it on a fan that draws 5.76W at peak. If you can, it might be more beneficial to pick up a 10+W rheo for this application as you don't want anything to fry!

Just a suggestion. be careful and have fun!
 
Thanks for your concern Lord-MiL. I was wondering if it would be a problem. But will it only be a problem when I have it dialed down below say 1/3? I don't plan on having the dial under 1/2. But yes I should probably buy a 10W one and use this one for an 80mm.
 
Well, I'm not 100% sure (I don't finish my EE/CE degree for a few more years!) but it will most likely get hot no matter where you have it set. Now whether it will get hot enough to damage itself or your case is something I can't tell you.
You are correct in assuming that it would be hotter the lower you set it as the rheo will be disipating more power, however the fan is always going to draw .48A and since the fan is in series with the rheo, that amount of current will be flowing through no matter what.
Your rheo is rated at 5W, I have always assumed that is the maximum power that it could handle flowing through it, not the maximum it could dissipate.

Hopefully someone who has finished a little more education will come in and set us straight.
 
DeathOnator no problem you won't burn the res with overpower.
However you have to check if it can withstand the current 0.48A.

That res won't see much more power than around 2W during use but the current when you use it around 1-6 ohms must be checked up.
 
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