Electronics help needed....simple maths

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altruistica

altruistica

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In an effort to sort my fan noises out on both my TASCAM MX2424 and the TASCAM MS-16, I've been experimenting with a 9V battery and 12V fans and a variable resistor :

https://www.youtube.com/watch?v=mOiP4SBjM10&feature=youtu.be

I want to know which Pot (variable resistor) I should buy given that I've just measured the resistance at the maximum resistance value (minimum fan speed) to be around 50 ohms. I don't really want to blow up my machines or wreck them in any other way, but the fan noise is driving me insane.

Thanks for any help offered.

Al
 
Hey.
1st up, the fans probably run at a certain speed for safety. Slowing them down isn't a great idea unless you have some way of being certain that they are cool enough.

Are they dirty, and is the exit path clear of wires etc?
Sometimes fans get loud over time because of built up dust or because the airflow is obstructed by something.

If you can't be certain about safe temperatures then a better approach would be to get bigger fans, silent fans, or a greater number of slower fans.

As a more direct answer, though, couldn't you just use a pre-made fan speed control unit?
They're available for computer case fans and graphics cards fans.
 
The fans are 24V (at least in the MS-16), so the computer fan control won't work.

What is the voltage driving the fan in the MX-2424?

Whatever came of my suggestion I made in your other thread of getting the p/n make/model/manufacturer of the fan in the MS-16, find the dB and air volume spec of the fan and then seeing if you can find two half-thickness 12V ultra quiet computer case fans, stacking them and wiring in series? It'll deal with the noise and voltage problem without any other mods, assuming the current fan is truly being driven by 24V.
 
Thanks for the replies guys.

The sole fan in an MX2424 is a 12V fan. What I find with manufacturers of all equipment that have fans in them, is that it seems like the designers do not figure in any cooling considerations until right at the end of the design process. I could list at least half a dozen products I've used in the past where the fan noise has made any recording impossible within the same space.......and yet the equipment still gets hot because the design and placing of the fan is incorrect. The MX2424 is a classic example of crap design where the fan is concerned. All the heat generated from the unit comes from the power supply at the front of the unit (behind the faceplate) and also some comes from the internal SCSI drive (which I'm hoping to replace with an SSD and IDE to SCSI bridge). The fan position is in the rear corner of the unit. You couldn't get further away from the heat source if you tried. Then the fan is positioned to blow air out of the unit (ie.sucking air out of the unit itself). This type of cooling I've found never works well and the unit is warm to the touch.

In the past I've fitted a fan immediately behind the power supply, blowing directly over the supply. The faceplate at the front remains cool to the touch because the fan is placed in the right position to cool. Because the fan is placed correctly, it can also spin more slowly. The Scythe S-FLEX fans I fitted to the MX2424 and SX1 units in the past were advertised as 'silent fans' and had a remarkable spec of 4dB. What I found though, was that there wasn't anything particularly special about 'silent fans'.......they were only silent because they were spinning at about 1/3rd the speed of a normal fan. Some of the S-Flex fans spun at 800RPM.

This is really the crux of my question and Cory why I never investigated the air volume spec of the fan out of the MS-16. I haven't yet looked into what is generating the heat in the MS16 and why that unit requires a fan, but if it's anything like the MX2424 then fan position is crucial and I might find a similar thing that I've found with the MX224....namely that fan position is more important than fan speed in cooling the components that you want to cool. The bonus of course is that you're reducing the noise of the fan itself.

This next bit deals with the MX2424 and the 12V supply.
In my video, I showed a fan specced at 12V / 0.09A being slowed down with a variable resistor (set at 50ohms) and a supply voltage of 9V (well really 7.92V as the battery is flat). Can I buy a variable resistor (ie. 'pot') that at its maximum resistance would be a certain value (in this case 50ohms) which would give the fans the minimum voltage (slowest fan speed) and was adjustable then, to give no resistance (ie fans at maximum speed)....the fans (possibly three as I'm going to fit an analogue card to the MX2424 which I believe generates quite a bit of heat too) all wired in parallel from the pot to the fans.

Maybe I just need to bite the bullet and try it.....

Cheers
Al
 
Beware of slowing computer fans with simple resistive droppers.

Yes, they may run nice and slowly* for days, even weeks until one day when they are perhaps dirty they fail to start because there isn't enough juice to "unstick" them.

You will know nothing of this until you are 9 10ths thru your killer milyon $ song and the PC crashes!

My new Asus build is very quiet but I had to buy a graph card for it (grrr!) and that got hotter than I liked so I bought a "Be Quiet" 80mm fan off 'zon and stuffed it under the card. The sink now barely gets above ambient and yet the fan is super quiet.

*I think fan noise is inherent, buy quieter fans, forking about with the supply does not seem to work IMO.

This is the chap! Be Quiet! Shadow Wings Fan PWM - 80mm [BQT T8025-MR-PWM]

And! (sorry) Electronics for motor control needs to be specific. The back EMF from even a small motor can blow transistors in mu secs!

Dave.
 
To make the fan in the MX2424 quiet, you just replace it with a Noctua NF-R8 80mm Quiet Case Fan.

Cheers
Alan.
 
Sorry Alan,

Never got round to thanking you for that.

I got round to dismantling the MS-16 today as it was blowing fuses.
I took this video of the fan position to reiterate my point about fans often being in the 'wrong place'.

https://www.youtube.com/watch?v=SnKuToMcMiw&feature=youtu.be

The cables were fully obscuring any cooling. I'm definitely going to fit some kind of retro-fit switch or pot to control the cooling....might even step down the power to use a 12V.

Al
 
Well OT, but,
I saw an example of very poor fan implementation a couple of years ago.
The old boy next door asked me to see if I could fix the charger for his electric scooter.
This was an metal box about a foot long and a bit bigger section than the 80mm fan at one end.
Tother end was a PCB about 60x60mm which had a 10mm black hole in it where some now unknown component had burned out, about 1/2 the board was SM components.
In the middle was a chunky transformer of about 150va. The stupid thing was, the fan drew in cold air and blew it over the transformer THEN onto the PCB! Had it been the other way I am convinced the PCB would not have suffered a burn out.

I emailed the company for a replacement PCB but was told none were available so the old feller had to stump up £116 for a new charger.
How "green" is that!

Dave.
 
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