21V

21V refers to a potential difference of 21 volts. It is not a standardized mains voltage but a value that appears in various contexts in electronics and electrical systems. In practice, 21V can be a nominal or approximate operating voltage for devices, power adapters, or battery packs, and the actual voltage may vary with factors such as load, regulation, and state of charge.

In consumer electronics and tools, a label like “21V” is often used to indicate the general class of the device rather than a precise voltage specification. For battery-powered equipment, a 21-volt designation may reflect a marketing convention or a nominal range around 20 volts, even though individual cells and configurations can produce voltages somewhat above or below 21V depending on chemistry and how the battery is charged.

In power supplies and charging circuits, 21V can denote the expected DC output or the maximum input tolerance for a device designed to operate in a roughly 20-volt region. It is distinct from standard mains voltages (such as 120V or 230V AC) and from higher DC rails used in industrial settings.

Safety considerations for circuits labeled 21V follow general low-voltage guidelines: while it is well below mains voltage, there is still potential for shock, short circuits, or heat generation in high-energy battery packs. Proper insulation, handling, and adherence to manufacturer guidelines are advised.

See also: Voltage, Battery voltage, Li-ion, Power tools, Safety.