I was wondering whether someone may be able to shed some light here. I have an old Oxford bantam transformer welder. Its one of the ones with a fourth terminal on it for battery charging supposedly. I was just wondering how this was setup within the welder? How is the current and voltage regulated and how is the DC formed? I assumed it's rectified the single phase input but does it have any methods of smoothing the high frequency output of the rectifier (i.e. capacitors, chokes etc)? Is the voltage accurately regulated or is it a bit high and risk boiling batteries if you're not careful? Not planning to charge batteries on it, maybe see if I can use it for a booster. Mainly just want to know how it works as I don't want to go about taking the heavy top off the welder!