Sunday, May 24, 2009

Cool (Laptop) Hack

I had to share the latest little hardware hack I did in the hope that it will be useful to others.

I have a laptop that, like many, gets a fairly warm hard drive with consistent (i.e. large build execution) utilization. Since I do a lot of that, I splurged on a targus laptop cooler like the one to the left.

The cooler is powered by USB, just plugs in and runs, and blows cold air over the bottom of the laptop. It works like a charm, bringing the temperature of both the HD and CPU way down to a very comfortable operating temperature even under extreme and consistent load. However, there were a couple of things I didn't like about it.

The primary one was the noise. Targus claims about 23 dB for the cooler - I am not sure if that is accurate, but either way it is still annoyingly loud when using it on your lap. Secondly it pumps out a lot of air, which is the point, but I wondered if it might be too much. Finally it does take its toll on the battery - driving 2 fans at full speed will do that. I appreciate the cooling, but not the fact that it appears to be taking more power than needed and turning it into noise. So I set about trying to hack it and fix the problems.

I thought about stepping down the voltage in a fairly efficient way, with some kind of clever electronic wizardry and even pulled an electronic engineer friend of mine into the problem, before I hit an embarrassingly simple solution.

Note: if you decide to try this for yourself, you are at the very least voiding your warranty on the cooling pad, reducing the cooling potential of the laptop cooler, and risking the whole thing not working at all afterwards. I point this out because I really don't want any messages along the lines of "I broke my laptop cooler and you owe me a new one" or worse "I broke my laptop when it overheated and now you owe me a new one". Assuming we have an accord, please read on.

So, what do you need for this hack?

You will need - a philips head screwdriver, a large flat head screwdriver, wire cutters/strippers, optionally a soldering iron, and some electricians tape. Also recommended is a multi-meter to make sure you have the right wires.

The principle (I warned you it was simple) is to re-wire the fans in series rather than in parallel. In the standard cooler, both fans are wired in parallel. This means both fans get 5v potential difference, running them at full speed, drawing twice the power of running just one fan, and making a fair amount of noise (including the occasional "fan mooing").

By connecting the fans in series, you are effectively changing the potential difference across each one to 2.5v. The eagle eyed among you will quickly note that the impedance of the fans might be different, resulting in one fan getting slightly higher voltage than the other when run in series, and I have no doubt that this is true - however for me at least they seem to spin at the same speed as each other after the hack, and the cooling is almost as effective as with both fans running at full speed. Also, the cooler is whisper quiet after the modification, and uses less power (approx half) as well.

Here are the steps:
  1. Peel off the 4 rubber spacers on the top side of the cooler. Under each you will find a philips screw.
  2. Unscrew all 4 of the screws, then use the large flat head screwdriver to gently prise apart the case. The top of the cooler is a little more reluctant to separate, so just work it gently on each side until it clicks apart.
  3. You will see two fans with black stickers in the center. Carefully remove the black stickers from each (be careful not to damage the delicate coil wires in the fan when you do this).
  4. When you peel off the stickers, you will see little solder points where the power comes into the fan. Grab the multimeter and work out on each fan which is +5v and which is common. In all likelihood the right contact (with the top of the cooler away from you) will be +5v and the left will be common on each fan, but it's a good idea to verify with a multimeter (if you don't have a multimeter, that's likely a sign that you should not be attempting this hack).
  5. Trace the common wire out from the fan on the left, and cut it about half way along its length to the switch.
  6. Trace the +5v wire from the fan on the right and cut it about half way along its length to the switch.
  7. Tuck the two cut wires from the switch safely out of the way inside the cooler case, You can cap them off with some electrical tape for extra safety, but most of all make sure they will not tangle in the fans.
  8. With the two cut wires from the fans, strip about half an inch at the end of each, twist them together and optionally solder them, then wrap them in electricians tape.
  9. Test the cooler - connect the USB power and both fans should spin. Hold your hand above each to make sure they are both blowing air upwards. If they are not both blowing, you have isolated and connected the wrong wires. Either try and find the right wires, or if this has scared you, reconnect them to the old wires running to the switch, put it all back together in the old configuration and pretend none of this ever happened.
  10. Assuming both fans are blowing upwards, you are done. Congratulations. Re-assemble the cooler taking care to route the wires internally so they won't tangle the fans or get trapped when you re-attach the top. You can choose to stick the black stickers back over the top of the fans, or leave them off like I did (I like the look, but now I have to be careful not to drop a staple or something in there that might cause a short). Stick the rubber separators back over the screws.
  11. Try it out.
I have found that the mod makes about 1-2 Celsius of difference only to the temperature at which it keeps the hard drive, and with a much quieter running noise and less power draw. It is unknown if there will be any long term damage to the cooler fans running at the lower voltage but I seriously doubt it. Overall my laptop is now quieter than without using the cooler, since the airflow stops the internal fan coming on under all but the most extreme load, and the cooler tray is almost silent.