New Gadget - No More TO-220 Finger Burns

26 Nov 2014

After a conversation with Mark (mcb1) about how I was always burning my fingers testing TO-220 devices, I decided to try to do something about it. The problem is I get excited when an idea comes to me so I take some short cuts and usually do not heat sink my TO-220 devices on the breadboard. Once in test mode, I worry that I am over heating them and then here comes the burning part. I grab them with my fingers and ouch. Today I gathered up some materials and set about building a couple of Do It Yourself heat sinks with temperature warning. Now since this is a very high tech web site you might expect at least a little high tech. Unfortunately you have me as a guide and I always try to follow the dictates of KISS **.

Here are some of the raw materials that I will need for this project.

The Brass strip is 12.5mm X 90mm X 0.8mm. It was sold as 1/2 inch X 3.5 inch X .032 inch but, don't worry, I converted it to real units of measure. We will talk about the other two items here after we bend the brass piece to fit our needs. I want to make it look like a little "Money Clip". I will fold it at the 5mm point from either end but first I will make a lip at the end of the 4mm section. I want this clip to slide over a TO-220 case and the lip allows the clip to easily open. Here are three pictures of the finished Clip.

I now have, at the very least, a simple heat sink that can be added to my hastily made mockups on the breadboard. The addition of a little silicon lubricant also makes for better heat conduction and dissipation. But wait, we are not through yet. We are going to add the liquid crystal indicators that we have stolen from the Duracell Battery and the Jacks Pan Cake Syrup. Here are some pictures of the finished clips.

As you can see the heat from the TO-220 causes the liquid crystals in the battery test plastic to reflect yellow light. This will warn me that the clip is hot. Unfortunately, while a good proof of concept the indicator strip is triggering just above 30 degrees C. I would prefer to see it trigger about 50 degrees C.

The hot indicator from the bottle of pan cake syrup also triggers around 30 degrees C. In both of these examples I was running a cheap NPN BJT with about 1.6 Watts of dissipation required. If I make more of these I am going to get some digital liquid crystal temperature strips that run as high as 100 degrees C. This will not only let me know when my components are getting hot but also when they are getting too hot.

Finally since I was there with camera in hand I took a picture of the bench. I know there have been rumors and speculation that there might be some correspondence between clean benches and empty minds. Here is proof the mind is only partially empty as long as I continue to try to replenish each day the information that leaks out over night.