Apple power supply consists of a very thick, inflexible AC cable (wall outlet to converter) and a very thin, flexible DC cable (converter to computer):
Why? The currents through the cables should be comparable, right?
EDIT: the label on the converter says:
- input: 110-240V ~ 1.5A 50-60Hz
- output: 16.5V = 3.65A max
EDIT2: cf. ThinkPad power adaptor (typical cables, similar to hp/dell &c)
Which has a thicker (than Apple) DC part and thinner (than Apple) AC part and is rated
- input: 100-240V ~1.5A 50/60Hz
- output: 20V =3.25A
The characteristics seem to be similar – why are the cables so dissimilar in the ratio DC cable thickness / AC cable thickness?
EDIT3: cf. AC Adapter For System76 Pangolin (which has 3 wires – including earth – in the AC part)
It is rated similar to the above and has a thicker DC part and thinner AC part than the Apple cable.
EDIT4: Looks like Lenovo/ThinkPad cables are under-engineered, which explains the cable thickness discrepancy observed!
Best Answer
The size of the cables isn't due to the size of the copper conductor inside them - that's a fairly small part of the cable. Most of the bulk comes from the electrical insulation.
Electrical cable needs to be insulated so it doesn't short circuit. The higher the voltage, the thicker the insulation required.
Your thick mains power cord is insulated to withstand mains voltage. In your country, that's 110 VAC; in my country it's 230 VAC. On top of that, the insulation must withstand transient voltage spikes ("surges") - AS1660.3 specifies a multi-core flexible cable must withstand a 3,000V AC hi-pot test for five minutes, so the insulation must be thick enough to withstand 3,000V RMS or 4,200 V peak.
The thin DC cable, on the other hand, only has to withstand 12 VDC. There is not any chance of voltage spikes on this line because the design of the power supply won't allow them. There is minimal electrocution risk from 12 VDC. Therefore this cable doesn't need much insulation and it can be quite thin.
To emphasise the relationship between voltage and insulation thickness, you can get cables like this:
The copper conductor is relatively small relative to the overall diameter of the cable. Note the thickness of the insulation (the white material). This short off-cut of cable had no markings, but this is rated for at least 132,000 VAC and the insulation is thicker to match.