I'm an electronics newbie trying to learn about the subject through tinkering, and my current project is a capacitive discharge welder for welding on battery terminals. I thought I'd better have someone take a look at my schematic before I fry a bunch of expensive components.
Basically, I have a foot pedal which tells an Arduino when to (briefly) turn on an H-bridge made of beefy n-channel MOSFETs hooked up across a big 33mF 100V capacitor that I plan to charge to 30V. The alternating current produced by the H-bridge energizes a transformer which greatly steps down the voltage and steps up the current for welding through some copper electrodes.
The things I'm most concerned about are:
- I have a separate 5V supply for the Arduino because I have a vague sense that it would be a bad idea for it to share a common ground with the big power capacitor. I'm not sure how electrically stable an electrolytic capacitor is when you dump all of its energy all at once. Is this a valid concern? Will separating the Arduino from the rest of the circuit with the optocouplers actually help anything?
- Related to the previous question, I'm concerned about having to tie
GNDAdirectly to the negative terminal of the capacitor (
-BATT). Is there a better way to do this? Could my current design result in damage to the rather expensive MOSFET driver?
- Are there any flyback diodes or bypass/decoupling capacitors or anything that I should add? I have no sense at all for where such things would be advisable. I added the 0.1 microfarad capacitor between
GNDAbecause I saw it on the datasheet for one of the ICs, but I don't know if it's really necessary. Is there anything I can do to better protect the $20 (each!) MOSFETs I'm using?