Look at this beast! It’s a dual run capacitor for a central air conditioning condenser unit…this starts the compressor motor and keeps it turning. “Dual run” means it’s really two capacitors in a single package, with three terminals. The size of a soda can, this one’s rated 40 and 5 microfarads at 440 volts. Let’s call it the Widowmaker.
Widowmaker replaces this old cap that was shot and puffy. It’s a $15 part, versus the A/C repair guy who wants to upsell everything. The how-to instructions were free on YouTube, where there’s no shortage of well-meaning but not-always-safe advice. For example: most were discharging these caps with a screwdriver, when you really should use a large power resistor! This is in addition to all the other safety precautions one should take when dealing with house wiring, like the One Hand Rule and Assume Everything Wants to Kill You.
When going the D.I.Y. route, always go a bit further and find safe and trusted sources, take the extra steps. Especially with something like Widowmaker here.
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I remember at TMRC (Tech Model Railroad Club at MIT) we had some 160,000 uf capacitors. In fact we had six, mounted in a wooden box and wired in parallel. We referred to the box as our One Farad capacitor (not exact, but within 5% tolerance). I think it was rated for a lower voltage, but still quite dangerous if you don’t know what you’re doing. The One Farad capacitor was used for several minor hacks while I was there.