Empeg cooling fan installation

Although it probably isn't necessary to install a cooling fan, I've seen the temperature of my empeg go over 55°C. The operating range of the disks (spinning and being read) are 5°C (41F) to 55°C (131F), so I felt that a cooling fan wouldn't be a bad idea.  Even if the temperature doesn't reach 55°C in normal conditions, it's best for the player to run as cool as possible.  I prefer 41°C over 53°C any day, even if 53°C is within specs.

The cutout in the top lid of the empeg allows for the installation of a 40mm fan, as found in older PC's.  I glued the fan to the lid with double sided tape.  There are holes for screws, but unfortunately they interfere with the car mounting sled. 
At first, I simply hooked the fan up to the power supply input, but it was too noisy, even in the car I could hear the fan whine.  I tried a resistor in series with the fan, which reduced noise quiet a bit.  The downside is that the fan doesn't run at full speed and I was afraid it wouldn't cool well in extreme conditions. 

I replaced the resistor with a thermistor, but that didn't give good results either.  There simply wasn't enough change in resistance to control the speed (I think the current through the thermistor must have heated it up, lowering the resistance, increasing current again etc). 

I then built a circuit with a L200CV voltage regulator along with the thermistor.  The output voltage is adjusted by the thermistor in the control potential divider.  The theoretical output of the L200CV, Vout = 2.77 (1 + R2/R1).
According to the data sheet, the dropout voltage between pins 1 and 5 is under 1.5V.  In the car (14.4V), this should net me up to 13V at the fan. 

I experimented a bit with various thermistors and got good results with a 470 ohm thermistor (R1) and a 680 ohm resistor (R2).   Heating it up and using the formula above, I calculated the values in the table below. 
The last column is the voltage at the fan as I measured it.  The maximum voltage seems to level out at 12.8V, which is less than what the data sheet promised, but still more than enough (after all, the fan is rated at 12V only).  It turns off under 5V BTW.

Above 10V, the fan starts to get noisy, so if you want to reduce it's speed, replace R2 with a 1K ohm trimmer pot.  To lower the speed, lower R2. 
If you want the fan to be inaudible, you'd need to keep the voltage at about 6V.  You could also enlarge the holes in the top lid because they create a lot of turbulence. 

This graph (thanks Genixia) shows voltage versus temperature for various values of R2, based on the resistance / temperature values in the table above.  The real values will obviously level out at about 12.8V.
For example, with R2 = 400 ohm the fan will be very quiet, but it'll level out at about 10V only.  It's probably more than enough to get decent cooling though.

In the schematic, Vin comes from the fan pin on the motherboard (there's actually 2 pins, but they both give power so only one is used).  I tried using a connector on that pin, but it was too high and interfered with the hard disks.  I simply soldered a wire to the pin (the red wire in the picture). 
Ov goes to the ground screw on the motherboard just next to the fan pins.  Pin 5 (Vout) of the L200CV goes to the fan.  The other wire of the fan goes to the same screw on the motherboard.

Here's the thermistor, the nice (and unusual) thing about it is that it has a mounting screw, which makes installation very simple.

I decided to install it in the corner of the hard disk mounting bay.  Although in the pic it may look as if it interferes with the shock absorber, in reality it doesn't.
BTW, to make room for the fan, the drive cables need to be folded underneath the drive bay.

Another shot of the thermistor.  The wires are routed underneath the drive bay, to the back of the empeg.

I didn't use a circuit board, but soldered the 2 capacitors and the 680 ohm resistor straight onto the legs of the L200CV. 

Since the fan is only 0.6 Watt, the L200CV doesn't need any cooling.  I just covered the whole with heat shrinking tube and tie wrapped it to the wires in the back of the empeg.  Looks almost stock .

For home use, I installed an on-off switch.  I prefer to have the fan on, but if the noise bothers me, I just turn it off.   In the car, the player gets much hotter so I always leave it on.
There's a security slot on the back corner which served my purposes just right (I didn't even knew it was a security slot, I thought it was an unused cutout for a switch).  I had to drill one little hole on the side to mount it. 

When refitting the top lid, the capacitor on the back of the display interferes a bit with the fan .

Remove the top screw of the display and loosen the bottom screw (on either side). 

Seat the rear of the lid and let the front rest on the display. 

Now gently pull the lid to the front and seat it.  The display will move a tiny bit to the front, but you shouldn't need to stress it.  I wouldn't use a fan thicker than 10mm as it is a tight fit as it is. The capacitors on the back of the display couldn't be in a worse place ...

To test the effectiveness of the fan, I put the empeg on top of my monitor.  Not very scientific, but good enough for me.

I let it sit until the temperature stabilized, which was at 53°C. 

I switched on the fan (see, that's why I installed that switch ) and the temperature dropped to 50°C in about 2-3 minutes.  After 25 minutes, it had dropped to 43°C!  An hour later it had even dropped further to 41°C!!

The voltage at the fan at this point was about 10V, a reasonable trade-off between temperature and noise.  On my desk, the fan was still very audible, but when I put it in the car, I could barely hear it.  With the engine on, I couldn't hear it at all.  With a 12°C temperature drop, I think I can call this experiment successful, don't you ?

Hmm, in an ideal world, Hijack would be able to disable the fan in home mode ...

Parts list:
12Volt fan 25mm fan (25*25*6 mm)  
L200CV voltage regulator
220 nano farad capacitor
100 nano farad capacitor
1K ohm trimmer pot
470 ohm thermistor

remark: I use 25*25*6mm fans as the cutout in the lid is 25mm.  These fans are hard to find but a 25*25*10mm fan will do too.  It even is possible to fit a 40*40*6 fan but it's obviously bigger than the cutout in the lid.  I haven't tested a 40*40*10mm fan but according to what I read on the empeg forum, it should fit too.  It gets awfully thight though.

update:

I replaced the 680 ohm resistor with a 1K trimmer pot, set at 600 ohm, which makes the fan practically inaudible in house.  I used a 25 turn trimmer as it fits nicely in the back of the empeg, just next to the white connector (with double sided tape).  Each turn is 40 ohm, so should the need arise, it's easy to adjust as well.  I removed the switch as it's no longer needed now. 
 

Adjustment is done through one of the existing cooling holes.

Empeg player installation

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