Addictronics

About twenty seconds after testing my new 150watt,12v car power inverter, I knew something had to change. The built in fan was entirely too loud and I instantly came up with several ways of changing that.

• Put a resistor on the fan power to slow it down and make it quieter.
• Put a variable resistor so I could adjust the power level for better cooling.
• Get rid of the fan and see what happens.
• Add an external heat sink to take the heat load out of the case.

I finally decided on the latter of the choices as it is the quietest and safest combination. I figured that the fan was there for a reason and just getting rid of it would turn out to be a disaster. So my first step was to try and find a small heat sink that I could use to cool the inverter. Here is the location of the screw holding the inverter together.

Next I had to pry back four tabs that held the two sides together. I suggest using a knife for this task. And here is the case disassembled with the LED status light still glued to the lid. Also you can see the aluminum “heat sink” inside the case that the external heat sink will transfer from.

I found a heat sink lying around my room but it was still far to big so I hacked it down to size with my grinder.

Next I cut the leads holding on the fan, making sure to insulate them from each other afterwards.

My Dremmel tool is out of commission at the moment, so I had to use my grinder to murder the plastic case to allow the heat sink to pass through. Here is the final result.

After gluing the heat sink in and putting thermal paste heavily on both it and the small heat sink inside the case, I reattached both sides back together and pushed the heat sink hard in to make contact with the metal inside the case. The glue I used to hold in the heat sink was not dry yet so now it will be seated in the proper position.

Now that I have reached my destination (4hrs of driving) I can say that the heat sink is not near large enough to passively cool the inverter by itself. I am planning to re-insert the fan back into the casing, but adding a small resistor to knock it down from 12v to about 9 or even 7. Also I will add a small switch (PB or Toggle, I don’t know which yet) to allow the noisy fan to be turned off if it is powering small loads. My laptop charger says it only draws 65watts, and it is a 150watt inverter, so I had planned for it to not be under much of a load. I guess I was wrong.

One thing I learned that is good is that when the inverter overheats the beeper that I almost cutout will beep about once every five seconds. This informs the nearest passenger to either remove it or duck. When I get back to my workshop I’ll fix the known problems, hopefully not finding any more one the way home, and post some pictures later.

After reinstalling the fan I discovered that the heat sink I added now hits the top of the fan. This prevents the case from closing back together. My plan to fix that is to grind a notch off of that side of the heat sink.

I added an 100ohm resistor to the fan in order to shut it up some. It worked quite well and I decided not to put a switch since it is now quiet.

I also decided to help the now slower fan out by cutting down on air resistance. I carefully bent some of the capacitors out of the way, and rearranged how the LED wire bent into place. Then I cut out some of the plastic on either side of the case where the vents are and added some soft foam next to the fan to prevent a circulation inside the case. I have noticed a tremendous improvement in airflow and am quite happy with my hack.

It has now been several months since I finished this project and the inverter is still working great.