In discussing another matter with Johannes at Excito, I included some pictures of the fan modification I did on the B3 and he asked me to post them here. Semiconductor life is dramatically improved with cooling and I am always concerned about this and willing to spend some time and effort if needed. In my case, I had about 15W inside a closed case (the B3) and this was more than I was comfortable with. The standard Excito design is quite good. Excito tells me that they have a failure rate that is very low, confirming that for most applications, the design is appropriate. The air cooling I have done here is beyond normal requirements but may be considered if you are a cooling nut (like me), planning very heavy use or want to assure maximum system life. The approach I took was influenced by a desire to minimize modifications to the B3 and minimize the time required while achieving a high level of cooling capability that would accommodate any disk changes or high use of the system that I might want to do in the future. My modification consisted of:
Remove the front panel (it is glued on) and drill it with 2 holes to mount it on the fan enclosure.
Remove the back panel and cut 2 slits in it for the escape of cooling air. This is the most severe part of the modification. I cut these slits with a Dremel using a metal cutting disk (carefully from the back). I cut it on top and bottom for both disk and motherboard airflow, being careful to leave all original labeling.
Carefully remove the disk and circuit board, tap 4 holes (4x40) in the B3 case front (in existing case channels like the ones Excito tapped for the screws holding the rear panel on).
Cut and drill the fan enclosure for the fan, exhaust hole and mounting to the B3 case, and other apparatus.
Optically redirect light from the status LED. In my case, I decided to mount the B3 front panel on the side of the fan enclosure and carefully mount, fit and adjust a small piece of fiber optic cable to redirect the light to the original B3 plastic light “window”. (http://www.jameco.com
#171272 10' fiber optic cable for U$5.95). This allows me to slip the enclosure cover on and off with the LED “window” stopping in front of the fiber optic and take the motherboard in and out with the status LED stopping in front of the fiber optic.
Cut and fit the EMI screening and add a removable fan air filter.
Fit everything in the modification, replace the disk and circuit board and assemble.
To make mounting screw access easier, I mounted the fan enclosure on the B3 front with 1/2” below the bottom of the B3 case, then added 1/2” “feet” to the back end of the B3. To maintain EMI shielding, I used some galvanized steel screen (1/8” square grid) between the fan and the fan enclosure and shaped and slip-fit into the air exhaust slits.
The simplest method you could use to address heat would be to place an external fan blowing on the case. This would have a signifficant effect. If you are concerned about noise and fan life, you can add a 1-3W potentiometer (depending on the wattage of your fan) in the 12v side of your fan wiring. See the following for one discussion on this: http://www.bit-tech.net/modding/2001/12 ... _control/1
In my approach I used a linear voltage regulator which has become sort of a standard for me in doing this type of thing. Another simple method is the use of a single bipolar or FET transistor for the voltage control. Search Google for examples. If you want a simple off-the-shelf controller, search Google shopping for things like “12v dc motor speed controller” or “12v fan speed controller” for many fairly inexpensive products. Here is an example of a simple 6-12v (U$6.99) fan controller, this one designed to mount in a standard PC case slot, but I presume it could be easily modified to include in your controller enclosure. I expect it is a single FET and is biased to force a minimum 6v on the low-end: http://www.xoxide.com/sunbeam-pci-fan-controller.html
In my approach, I added two 12v power jacks (add another if you want for an external eSATA disk), an on-off switch, an 80mm fan and filter, a linear voltage regulator and potentiometer for fan speed control, and a pair of jacks for voltage measurement of the fan voltage, all in a standard 6” x 4” x 5” aluminum enclosure. On the front of the fan enclosure I added an LED and trim pot (for LED intensity adjust) for “Power ON” status. I used a 1k ohm resister into a 5k ohm trim pot then through an LED for 2ma to 12ma adjustment for different ambient light conditions.
I considered smaller fans (like 1-3 30mm or 1-2 40mm) to better fit the size of the B3 case. This would have required more miniaturization, possibly building a custom enclosure, possibly more difficulty in redirecting the status LED, reduced air flow (or more noise) from smaller fans the lack of a air chamber, so I decided upon the larger case approach. Using an external case for the electronics is also possible but I did not want to deal with a second case and I had the space with my placement needs so I went with the larger fan and enclosure incorporating all electronics etc. into one package that was fairly easy to build.
Any amount of air flow would be very helpful. You could consider one (or two) 40mm fan(s), mounting all electronics (switch, speed control, etc.) in an external enclosure, with one power jack from the control to the fan(s). This would require making a B3 front plate replacement that would accommodate the fan(s), power jack (on a stand-out bracket) and drilling a hole for LED visibility. The plate would need to be thick enough to allow for countersinking the fan mounting screws (to not protrude into the B3 case) and should be conductive for EMI shielding. The existing front plate would be ideal. This plate is glued on and the “B3” lettering is also glued on and can be popped of with light pressure using a chisel. You could carefully drill the plate for screws to go into holes you tap (4x40) into the existing case channels. Cut a hole(s) for the fan(s), drill and countersink for fan mounting screws and the power jack bracket (that you must make). This would allow for the use of the existing status LED “window”. A fan air filter and EMI shielding should be provided. With a quick look I found 40mm air and EMI filters at http://www.newark.com
(parts 21M7155 and 56P2964). There are others, but this should get your thinking started. I expect that this approach would be fairly simple, clean looking and allow for a smaller “footprint” that may be better for your placement needs for the B3 (but requires an external case for speed control and switch, etc. or doing clever miniaturization and construction to get everything on the front plate).
A word about power. I took the fan power from the B3 power supply. I added a switch to turn on the power for the fan and the B3. I do not know the sensitivity of the power needs for the B3, however, it is important to add a ceramic capacitor (0.1 uF or greater) across the switch to reduce switch contact bounce possibly causing confusion to the B3 motherboard. By-the-way, the following jack and plug parts are compatible with the B3 jack and power module plug: http://www.jameco.com
parts 28760 and 151555 (standard power connectors, 2.1mm center pin, 5.5mm barrel diameter, 10mm barrel length).
The voltage regulator I used was an LM2941. This unit has a very low dropout voltage (0.1 volt at low current), however it is only good for 1A (very adequate for this need). You could use a standard LM317T (1.5A), LM350T (3A) or LM338T (5A) but these give you a dropout voltage of from 1 to 2.5v depending on the unit and the current (maximum fan voltage of 10.5v to 11v which should be adequate for this project unless you are using small fans, then I would recommend the LM2941). One or two fans will not be a problem, but if you use higher current in some other project, you must be concerned with heat-sink needs. I use the LM2941 in such fan speed applications because it allows me to crank the fan voltage up to 11.8v or 11.9v with a 12v input, great on computer case fans where I may have a need for the higher speed. For resistor values on the voltage regulator, I always use values that will prevent adjusting the low-end voltage below 5v or 6v for fans (I run my B3 fan at about 6v which is very quiet and with an 80mm fan gives very adequate air flow). This is important since you may adjust it below 5v and the fan will not start (some fans will not start below 6v), so you think it is nice and quiet (which it is) because it is not on (this could be bad - ruin your whole day). So, here is a set of resistances that will work for all the voltage regulators I have mentioned. Use 1k ohm from the adjust pin to ground, 3.3k ohm from the output to a 5k ohm potentiometer and the output of the 5k ohm potentiometer to the adjust pin. This will give you a calculated fan voltage range of 5.5-12v (with a 12.1v input). The final range will depend on variation in resistor actual values. For the LM2941, the 1k ohm from adjust to ground is required, it can be different for the other regulators (where you recalculate the remaining resistances from the specification formula). Just for completeness, (you can get this from the voltage regulator specifications) the remaining parts needed are 0.1uF (50v or more) from input to ground and 100uF (25v or more) from output to ground.
Below are the pretty pictures of what I built (3 here and 3 in the next post).