Variable resistors or voltage regulators?

LeperousDust · 7 Feb 2006 at 13:10

I have 6 fans each in 3 PC's that sit in a cupboard out the way in my loft conversion, acting as a mass storage server, and firewall/antivirus/router, and webserver. I can't help but notice the noise they make, it isn't much but its driving me up the wall whenever i'm quiet in that room.

I'm going to knock up a little fan controller ghetto style because these computers aren't seen, now to control the fans.... going completely off topic i've just had a wasp fly up here :confused:

it IS february isn't it?!... can i get away with just using variable resistors, or will i need variable voltage regs?

mc_bob · 7 Feb 2006 at 13:22

Variable resistors will be fine.
Do a google for 'Baybus' and youll get a better idea.

MC_Bob

LeperousDust · 7 Feb 2006 at 14:25

Wow, all knowledge of GCSE electronics has failed me, i've got an input of 12v and i'd like a variable output, buy a pot will do me find, but how do i work out what value pot i need to give me a nice even resistance. The fans are 0.2A for the record, i'm absolutely useless, and i can't be bothered finding croc clips to mess about and work out what i need

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sinister_stu · 7 Feb 2006 at 15:45

Right... I should probably be able to answer this, what with my Masters in Electronic engineering. Unfortunately, 7 weeks of temp office work has turned of my brain to sponge.. but i'll hazard a guess that its not too important what the value of the pot is. I'd just get a 5k pot and see what happens, the impedance of the fan will be negligible compared to the pot (@0.2A this will be 60 Ohms) so that shouldn't cause any problems, you'll probably just find that you can't turn the fans off with the pot.

Then you need to take into account the power dissipated in the pot and make sure the rating of the pot is high enough to cover this (P = IV)

LeperousDust · 7 Feb 2006 at 17:37

Thats my problem i've just fell accross my local electrical store's pot's are all under 2watt's max, when my fans running at 12v (well max) will be using 2.4w and my pots will fry won't they?

Arg nothing is ever simple, if i knew all these fans i bought would have caused so much trouble i would have bought other fans! :mad:

I've got a few 120mm fans that use less than ONE watt!

sinister_stu · 7 Feb 2006 at 21:04

The power of the fan isn't the power being dissipated by the pot, so you're probably ok. Another equation for power - P = V^2/R - so divide 144 by the value of your pot, and that will be the rating of the pot you require. I doubt the power will be anywhere near a Watt. As an example, a 5k pot at 12V will dissipate about 30mW.

LeperousDust · 7 Feb 2006 at 22:10

Well looking at it differently then, my fans are 0.2A and the only variable voltage regs i can find are 0.1A or 150mA! The pots all have max watts on so i thought i'd try and convert no doubt i've missed something though.

These fans i've bought seem to eat power and be horrbily inefficient, but that would probably explain why they where so cheap

. Poo

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I might just buy one of the pots and vol regs and just leave both running for 24hours maxed out see if either melts or gives up.

LeperousDust · 8 Feb 2006 at 18:13

Ok bought a few pots today, 1k, 4k7 and 10k just to check which one would give me the nicest scope. Tried the 1k and as soon as i turned it up it popped i nice flame came from somewhere (???!) and then it stunk my room out. So i guess my fans are drawing too much through it

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I'm looking into buying a few multi gang switches and coupling them with two fixed voltage regs (as they can handle the power draw). Just switch between off, 5v, 7v and 12v. Its just a pain cause i'd have to wire each one up for each fan, there are 4 (or 6 if i include both power supply fans too which i may) in each case i'm looking at, and there are 3 cases!