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?
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
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?
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.
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
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
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.
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!
Theyve got "Internal Thermal Overload Protection" Whoo Hoo, So i guess youll never have to worry / me as well
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.
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.
With or without heatsinks? My rheobus has now mutated into some hideous hybird. It now has a mini-toggle switch for each rheostat and it is completely sealed inside a project box from Maplin, with a pair of ickle fans scrounged from a baycooler on the back of the box to provide a thru-draft. Should have it finished this weekend provided I don't think of anything else to add to it....
