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| The original welder |
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| I discovered in the course of developing this welder that it was much easier to control high voltage, low current power, than high current power. This is the philosophy behind this device, which uses a variac to control the high voltage input to the welding transformer. The variac does not change the waveform shape of the power supply, it only changes the voltage peak. The weakness of this system is the amount of current that the variac can tolerate - the device pictured here can handle 5 amps only. This is OK for 230V mains - 4 amps is drawn during welding - but for 120V mains, the variac would have to handle 8 amps. This would be an extremely expensive unit. The welding transformer itself was custom made. Motor/coil rewinders or transformer manufacturers will perform this service, or you may be able to get one by asking around. I have found that a 300VA unit will perform OK while welding 18ga stainless, but 500VA is probably necessary for 16ga. Note: an undersized transformer will work, but will age and fail relatively quickly. If you hear a buzzing noise, that's the laminations shaking. Over time, the vibration will cause the coil winding insulation to wear through and fail, ruining the coil. The welding itself happens over a narrow range of voltages between 4.4V ac and 5V ac. The exposed electrodes do not threaten safety. Tight control of this voltage is necessary, otherwise incomplete or burnt welds happen. This is also the reason that a microswitch was incorporated in the primary side of the welding circuit, to allow precise control of welding time. The circuit itself is as follows: Inlet - fuse - primary appliance switch - microswitch - variac - welding transformer primary - return to neutral. The fan is connected in parallel. If you are keen on building one of these, be warned that there is an enormous amount of time, labour and money involved, as well as a safety risk. It took six months to build this in spare time, quite a few hundred dollars, and it also got me my first mains-rated shock. PLEASE DON'T GET ELECTROCUTED WHILE TRYING THIS STUFF OUT. If a basic arc welder is available, that'll do the job just as well, provided that it has a rapid-acting welding current on-off switch like the microswitch I have mentioned. Certainly it'll be cheaper. I'd mentioned the idea of commercially producing these welders and selling them to a few people. I got enthusiastic responses, so I took the next step. |