Home & workshop Conversions
12V amps
Voltage
V
Load power
W
Power factor
DC has none — leave at 1Current 5 A
60 W ÷ 12 V
Fuse at 125% 6.25 A
In milliamps 5,000 mA
Equivalent resistance 2.4 Ω
A = W ÷ 12
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320 × 100
At 12 volts, amps are watts divided by twelve. A 60 W load pulls 5 A; a 500 W inverter load pulls 41.7 A. Twelve volts is why vehicle and van wiring is so much thicker than mains wiring for the same power.
How to work out 12 V current
1 Enter the load in watts.
2 Read the current, and the 125% figure for fuse selection.
3 Size the wire for that current over the round-trip length.
4 Fuse close to the battery, not close to the load.
Twelve-volt systems punish inefficiency twice. The current for a given power is nearly twenty times what the same load would draw at 230 V, so cable has to be far thicker; and because voltage drop is a percentage of only twelve volts, even a small absolute loss is a big proportional one. A 0.5 V drop is 4% at 12 V but 0.2% at 230 V. That is why serious van and boat installations move to 24 V or run high-power appliances on their own short, heavy feeds.
Questions
8.33 A. At 24 V the same load is 4.17 A, and at 230 V just 0.43 A.
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300 × 250
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