I am in the process of putting together my universal NiMh charger circuit, right now I solve one problem only to end up in another. I don’t have a proper schematic of the circuit so apologies for that, I plan on including it in my blog and completing a write up on it once everything functions with no issues.
The weakest link of my design is the SMPS half bridge power supply mainly because I am not good at power electronics but yet I desire a bulky transformer free design to feed controlled power to the battery in order to charge it.
I have attached a picture of the circuit to give you an idea about my layout and the strange problem I am experiencing and I hope maybe someone can enlighten me about the cause.
Ok so as I start up everything works normally, I start a charging process and nothing abnormal happens but as soon as I bring my hand closer to the microcontroller circuit board(as shown in the picture) my LCD becomes blank the relay that I have mounted on the controller board starts clicking fast and only after a reset things become normal again, so the erratic behavior is not the controller resetting but it malfunctions, atleast that is what it seems during this erratic behavior the LCD might or might not display random garbage characters.
Anyway the capacitor shown in the picture is a 2200uF output filter capacitor of the power supply, whenever I touch this capacitor by my finger and then try to bring my hand closer to the controller board in hopes to cause a malfunction, absolutely nothing happens, as if the problem wasn’t even there while my hand is close to the controller board and I lift my finger off the capacitor the controller board malfunctions instantly!, here I would like to mention that the SMPS only shares a common ground with the controller board and the controller board is powered off a small transformer and a rectifier setup feeding an 7805 regulator.
In order to further move in on the problem I touched one end of a wire on the top of the capacitor and touched the other exposed end of the wire with my finger and then brought my hand closer to the controller board and as expected everything worked correctly and the controller did not malfunction.
Later on I disconnected the SMPS and turned on the controller only and tested by putting my hand closer to the controller board and everything worked OK, so the problem IS the SMPS and its output noise, if I may call it, is being coupled to the microcontroller board via the supply wires ( as disconnecting them took away the problem).
Another important thing to mention is that while I touched the capacitor I was sitting on a chair and lift my feet off the ground to makes sure this isn’t some sort of an earthing issue, if that makes sense? so as long as I am touching the cap everything works fine.
If someone has faced such a problem before it would be great to have any input on this matter.