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INSIDE THE CAN
Build a high-voltage capacitor
Follow a high-voltage capacitor from wound sections to a sealed, oil-filled can.
The can is mostly a pressure-tight, insulating home for a stack of wound sections.
SERIES SECTIONS
Sharing the voltage
Each wound section is rated for a few kilovolts. Stack them in series and the voltages add.
High voltage comes from many sections in series, not from impossibly thick film.
INSULATION
Keeping kilovolts where they belong
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Pressboard
Dense, oil-soaked board between sections and between the stack and the case
Series links
Short connections from one section's end to the next
Floating foils
Some designs add series steps inside one winding with unconnected foils
Voltage sharing
Matched sections share the voltage evenly; a mismatched one is overstressed
Every boundary inside the can, section to section and stack to case, needs its own insulation.
CASES AND BUSHINGS
The outside of the part
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Metal cans
Welded stainless steel, or drawn steel or aluminium
Plastic cases
Lighter and insulating, for smaller parts
Bushings
Porcelain, epoxy or glass-filled nylon insulators that carry each terminal out of the case
Sheds
The ridges on a bushing lengthen the surface path so high voltage can't flash over the outside
The case keeps the oil in and the moisture out; the bushings keep the voltage off the case.
HOW BIG?
Energy sets the volume
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Defibrillator part
Hundreds of joules in something you can hold in one hand
Industrial and medical
Brick to shoebox size, a few hundred to a few thousand joules, a few kilograms
Big pulse-power cans
Suitcase to mini-fridge size, tens of kilojoules and up, up to hundreds of kilograms
Very high voltage
Tall columns with long bushings: voltage sets the length, energy sets the girth
At roughly 0.1–2 J/cm³, every extra kilojoule costs real volume.
UNIT 7 STUDY COMPLETE
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Ready for the Fab Challenge?
You've built a high-voltage capacitor from sections, insulation, series links, a can, bushings and oil.