Use 12v fans for your ESC/motor...

[BrianG]

Even though I personally don't like to use fans, I can see their usage for those who push things too far (you know who you are!). But it can be difficult to find 5v-6v fans. But 12v fans of all sizes are pretty much at any computer store.

So, I thought I'd put together a little how-to for wiring up a 12v regulator so we can use 12v fans instead.

Parts list:

• LM7812 +12v linear regulator available at RadioShack.
• Mounting hardware for the regulator. This keeps the regulator tab from making electrical contact with the heatsink.
• Some type of heatsink. A piece of 1/8" thick aluminum works OK.
• Thermal paste. The generic stuff works fine too.
• About 3-4 feet of 20GA red wire and 3-4 feet of 20GA black wire.
• Heatshrink

Pictures are worth a 1,000 words so:



These are the parts I used. You can see the regulator mounting kit. Just a mica (I think) insulator and a flanged plastic washer to keep the regulator electrically insulated from the heatsink, yet thermally coupled. The aluminum heatsink is 1" wide x 1/8" thick x 2.25" long. A hole was drilled and tapped for a 3mm screw roughly in the middle. I also am using a piece of a heatsink from my spare parts bin.



The Artic Silver products I'm using. The "Ceramique" is a thick type of thermal compound (not adhesive) for the regulator. The thermal epoxy is to hold the finned heatsink to the Al slab.



You can see I put some compound on one side of the insulator and pressed it where it needs to go, and put some compound on the regulator. It's OK if you use too much as any excess will squish out (but can be messy).



I put the regulator in place and put the washer in the regulator hole so the flanged edge lays on top of the tab.



I used a 3M thread x 6mm long screw to secure it to the heatsink slab. Note the flanged washer position.



I thermal epoxied the finned heatsink on the end of the slab. Then I soldered the wires on the regulator. The center pin is ground. Make sure two ground wires go here - one from the batts and one to the load. Just strip the ends, twist the wire together, and solder it to the center pin. The leftmost pin is the input from the batteries. The rightmost pin is the 12v output. Then put some heatshrink over the connections. Also note the holes drilled on the side of the wire. The zip tie is a crude strain relief.



The finished part with some heatshrink over the whole thing. Make sure to keep at least half the heatsink uncovered, but make sure the regulator itself IS covered. Twist one ground wire (doesn't matter which one) with the input wire to go to your batteries. Twist the other ground wire with the output wire to go to your fan(s). That's it!

Now a little math. This is a linear regulator, so it will heat up. The amount of heat it produces is determined by how many cells you are using and the current drawn by the fan(s). Wasted power (as heat) = ( battery_V - 12v ) * fan_current. As you can see; high battery voltage and/or high current is going to create more heat.

As a test, I used a battery pack measured at almost 20v. I found a 12v 40mm fan that draws 0.07A, which is fairly typical. When I hooked up the regulator, the temerature went up to about 80 degrees F. This equates to 0.56watts wasted on the regulator: (20v-12v)*0.07.

I also found a high output large crossflow fan that requires 0.250A. This is wayyy bigger than needed to cool an ESC, but even so, the temperature only got to 108 degrees F. Wasted power was 2watts: (20v-12v)*0.25.

So, this setup will easily power a typcial 12v 40mm-60mm fan and barely get warm using up to 5s or 16ish cells. It will power 2 of these and get a little warm. Three, and the regulator starts getting toasty. If you use 4s/12 cells, the regulator will heat up less.

Hope this helps someone...