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Conductors, AC and DCWhat's the difference between AC and DC?
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Conductors and insulators
- A voltage is put across a circuit or load. Current flows through it.
- A conductor is any material that allows current to flow through it. Good conductors (copper, aluminium, most metals) have low resistance.
- An insulator is any material that doesn't allow current to flow. Good insulators (plastics, rubber, wood, glass) have very high resistance.
A cable uses both: copper conductors to carry current, and PVC insulation and sheath to keep it where it should be.
DC and AC
Direct current (DC) flows in one direction at a steady level. The three most common sources:
- a battery of cells
- a DC generator
- electronics, using a rectifier, which converts AC to DC
A battery produces pure DC as long as it has energy left in it.
Alternating current (AC) constantly reverses direction, following a sine wave. The UK mains is AC at 50 Hz, which is 50 complete cycles a second. AC is what the grid generates and what transformers need.
The 230 V we quote is the RMS (root mean square) value, not the peak. The peak is RMS ÷ 0.707, about 325 V on a single-phase supply, and 325 × 0.707 brings you back to 230 V.
- Rectifier
- Converts AC → DC. Your phone charger has a small bridge rectifier inside the plug to charge the DC battery from AC mains.
- Inverter
- Converts DC → AC. Solar panels produce DC, and an inverter turns it into AC for the home.
If DC isn't fully smoothed you get a rectified waveform: humps that stay on one side of zero, because the current never reverses.
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