BasicB-003-019-009
What is a safe method to discharge power supply filter capacitors?
D
Answer
Basic radio theory
Type
A
Allow time for bleeder resistors to discharge the capacitors
B
Use an insulated wire with alligator clips on each end
C
Use a long screwdriver with an insulated handle
D
Use an insulated shorting stick with an inline resistor
Answer Notes
High-voltage power supplies often contain large filter capacitors that can store lethal amounts of energy long after the equipment is turned off and unplugged. The safest active way to discharge them is using a specialized insulated shorting stick equipped with an inline current-limiting resistor.
While power supplies are usually designed with 'bleeder resistors' to passively drain the charge over time, these internal components can fail silently. Relying solely on them is a major safety risk.
Using a standard screwdriver or a plain piece of wire to short the capacitor will cause a massive, instantaneous discharge. This violent spark can weld the tool to the terminal, spray molten metal, and destroy the capacitor.
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Where should the chassis ground terminals on all station equipment be connected?
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On mains-operated power supplies, the ground wire of the AC line is connected to the power supply chassis. What protection does this provide if a fault occurs in the power supply?