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Circuit board heat Trouble. Answered

Full disclaimer, I am still learning and at my current skill level I am essentially following a picture book showing how to hammer a nail then emulating it, Hope that analogy paints the picture correctly. Now for the problem! I have embarked on a journey of growth and learning, in said adventure I took a personal challenge of building something and hopefully learning in the process. Needless to say I did learn, some lessons more painfully than others (soldering Irons are HOT *Sigh*) but I am at an impasse.

You should see attached (hopefully) one schematic and two photos.

The schematic correlates to the board of course.

The next two are of the silkscreen on the board (empty) and the board upon "completion". If you notice in the empty board photo I have drawn your attention to a specific area, the area in question. In this area there seems, during testing, a decent amount of heat build up. Now this may be normal, I do not know. The device calls for the use of three Protected 18650 Lithium Batteries (3.7V I believe). I attempted to do a continuity test with what I thought was under voltage, in hindsight, I'm not sure whether the power cells are in series or parallel so perhaps I was not under? anywho that is when I noticed the heat in that area.

I hope I have illustrated my predicament enough for a solid enough understanding, If not I apologize. Please ask any information you require. 


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Best Answer 6 years ago

It would help to know what this device is suppose to be. But after spending about 20 minutes poring over the schematic i see it's a PWM motor control module. Which of the 2 chips is heating up the most. The one on the right is basically a set of 4 switches. The one on the left is the chip that is generating the PWM signal. It should be the main culprit other than the 7805 which will produce more heat than anything else on the board. If you had the batteries wired in series then you where feeding the system about 11V. If they where in parallel then it was only getting about 3.7V. Either way you won't hurt this thing. The 7805 basically sits between the batteries and everything else. It's designed to take any voltage from about 7.5V to 35V and regulate it down to the 5V the rest of the system needs. If it was only getting 3.5V then the regulator isn't able to do much and this won't work. So the only real heat issue you will have to worry about is the 7805. Keep the batteries away from the component side of the board so it gets plenty of airflow. If you get too worried about it slap a heat sync on the 7805. That is what the tab with the hole in it is for.