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Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Well, success at last and better welds! Today I've added another van battery in series and found the reason the micro was resetting (the most ridiculous ground bounce I have ever created, due to not isolating the gate drive).
Added an opto-isolated gate drive arrangement with a logic opto and an old UCC37322 gate driver from the Tesla coil days. I had to modify the software so that the pre-weld pulse is now just 10mS with a 200mS delay before the main weld pulse. I've been using about 100mS to do the welds which is injecting a lot of heat in a very short time and creating some good welds. It needs to be good because the pack I'm making will be sourcing up to about 35A in use.
It actually got to the point where the whole thing became quite scary. The first time I used it with the second battery, I had a short piece of 2mm brass rod acting as a fuse. Well it went off like a firecracker (with a pulse length <100mS) and burnt through the kitchen stool.
No semiconductor or electronics failures which I'm happy about, but I've had to stop because the IGBT was getting too warm after several hours of use and I started to notice the weld quality decreasing.
Tomorrow will be a quick overhaul - sharpen the electrodes, charge the van batteries again, then finish up the pack and do some discharge tests on it up to full load. A thermal imaging camera would be really handy to check all the connections but I'll have to settle for measuring the voltage drop across each weld...
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Yay! Thanks for sharing. I have some welding (?!) multistrand thick cable here if you have a use for it: think it was an offcut from some audio project. PM me.
EDIT: B&Q have some 3 wire + earth low profile cable which might be suitable for a welding transformer.
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Battery tab spot welder advice
