# Modding Fan controllers and the heatsinks

Discussion in 'Modding' started by mookboy, 25 Sep 2002.

1. ### mookboyBRAAAAAAP

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OK, basically I am following this guide to make myself a nice Rheobus using the LM317/T voltage controller chips.

All I want to know is how hot are these things expected to get with a single 80mm case fan running off each of them? I've got some nice neat heatsinks stuck to them (not a chunky as those in the above guide...) and I'm worried they may not be sufficient. Some pre-fab'd kits I've seen have huge heatsinks on em.

Anyone know?

2. ### D3monWhat's a Dremel?

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myself and my bro have just built a fanbus each but not as normal...
4 switches to control the fans and a single pot and lm320 so that we can either run 12v or variable volts ...
we bolted a small hs with a 45mm fan fixed at 5v to the regulator and can draw up to 2 amps safely thru it without it going bang it would probably be ok without the fan but was just something else to play with

3. ### mookboyBRAAAAAAP

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Yeah I'm thinking about putting it all in an enclosure and adding an exhaust and intake Sunon 40mm fan but how small do mean by 'small' when u describe your HS?

4. ### linearMinimodder

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Well, if you run your fans wide open mostly, you won't need much of a heatsink.

You can calculate exactly the heat that will be generated:

P = I * (Vs - Vl) where
P = power dissipated as heat
I = current delivered to the load (add up your fans currents)
Vs = source voltage (12V)
Vl = load voltage, which will vary

As you dial the fans down, the voltage term will increase, but the current delivered to the fans will as well (although it won't be a linear relationship necessarily).

The real thing to design around is how much load you present to the controller--one more fan could mean you need to upgrade your heatsink.

Check out cpemma's sterling page on this topic if you're hungry for more detail. He walks through a complete thermal design.

5. ### D3monWhat's a Dremel?

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the 45 mm fan is screwed thru th normal fixing holes straight on to th hs so i suppose th hs is approx 50x50x10mm total height of all 3 parts is probably no more than 25mm..
I'm not going to stick a tape measure in there as it is all running at th mo

6. ### KipsterWhat's a Dremel?

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Hi there.

Ive recently made a 4 & 6 channel Bus Using LM317Ts and they dont break any sweat running a single 80mm Fan

However im using each one to drive a 120mm fan and they do get hot, without a heatsink (as i didnt have any at the time ) but its been running for about 3 weeks now and they are hot to touch - I added a resistor in series with the pot so at switch on and the pots at Min setting the fans start. I just used the example cct with the datasheets.

Heres the 6 Channel one with HS fitted, each channel runs 2 80mm fans.

the 4 channel one fits behind a 3.5" plate & 6 channel behind a 5.25" Plate

7. ### KipsterWhat's a Dremel?

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Also just finished a proto of a decent fan speed indicator

Now to design it and get a board or two etched.

Note the bargraph display in the bottom left, sorry pics are bad quality.

8. ### mookboyBRAAAAAAP

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Excellent replies guys! Thanks!

I just finished all the basic wiring and soldering and ran a quick test on a gutted Pentium 233 system (mobo, cpu and psu only!) and it ran a 60mm Ystech at full speed and really slowed down almost at a stop without making the HS's noticabley warm. So i tried adding an old triple fan bay cooler aswell from the same single molex and it did make the heatsink alot warmer altho not what I would call hot (ie I didnt flinch away when I touched it).

Running sans HS's made laugh tho dude. I've been stressing none stop about whether it can take the load and that made me feel alot better. I guess I don't have anything to worry about with just a single 80mm fan on each rheo/LM317.

Thanks again!

9. ### KipsterWhat's a Dremel?

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Theyve got "Internal Thermal Overload Protection" Whoo Hoo, So i guess youll never have to worry / me as well

10. ### linearMinimodder

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Kipster, those are some clean looking boards you made. Nice work and welcome to the forums. (Edit: I See now you registered last year!)

I'm recalling a review of two different commercial baybuses, one based on LM317 and one based on transistors, TIP31A. (a forum member wrote the review, but I don't remember who.)

The conclusion was that the transistor design was better--it put out more volts at the top end.

But later on he found out what happens if you short the output. A LM317 survives that typically, but a transistor won't. And ditto on the thermal protection, it doesn't exist for the transistor design.

11. ### KipsterWhat's a Dremel?

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Hi,

Thanks.

Yep the 317s are hardy little chaps and cheap too, Ive ran 4 80 mm fans off one for hours at min speed and although it was burning hot it didnt give up.

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