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Engineer Kerry D. Wong is not any stranger to the operation of spot welders, having transformed elements from an previous microwave oven into one — however was curious as to how a extra skilled design labored, so set about dismantling a preferred pocket-sized mannequin.
“I constructed a spot welder with an previous microwave oven transformer (MOT),” Wong explains. “Since then, I’ve used it in lots of my tasks together with utilizing it to make a battery financial institution. Whereas that spot welder does a wonderful job, it is extremely cumbersome, so this time round I acquired a commercially out there battery powered spot welder and wished to see how effectively it really works.”
The chosen welder: The BIFRC DH20, a compact battery-powered unit that comes with interchangeable welding suggestions. In addition to being significantly moveable, the DH20 has a function lots of its rivals lack: Fairly than manually triggering the welding course of, it detects when the information are involved with the fabric and robotically powers up.
“The DH20 has 9 selectable welding durations, and the waveform consists of two separate pulses: A pilot pulse that’s roughly 11ms in length which is used to pre-weld the supplies collectively,” Wong explains, having verified its operation with an oscilloscope. “The secondary pulse which is delayed by 3ms , it’s used to finish the weld. The width of the secondary pulse is selectable and might chosen from 30 ms to 150 ms at an interval of roughly 10 to fifteen milliseconds per step.”
An oscilloscope revealed simply what the totally different welding modes change within the unit’s operation. (📷: Kerry D. Wong)
From there, Wong took the unit aside — discovering 4 MOSFETs wired in parallel, thick copper wires to deal with the excessive present, an STC 15W404AS 8051-based microcontroller with voltage measuring analog to digital converters, and a useful 5V USB output — letting the unit double as an emergency USB battery financial institution.
“The Lipo battery is mounted on the reverse aspect of the PCB. You’ll be able to see that the battery is soldered straight onto the PCB and the safety circuitry will not be on the battery terminals,” Wong notes. “That is because of the giant pulse present required throughout regular operation. So excessive warning must be taken when the circuit board is faraway from the chassis.”
The complete tear-down is on the market on Wong’s weblog, whereas a companion video has been printed to YouTube.
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