# eli5 Why are 110v transformers so physically heavy?

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For instance, a computer inputs 230v and is capable of splitting into various lower voltages and remains light?

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A transformer will have two or more “windings” of copper wire around an iron core. In simple terms, the ratio of the windings on the “primary” side- where power is applied- to the “secondary” side, where power is taken out, will determine whether the voltage goes up or down. If the secondary has fewer windings than the primary it provides lower voltage but can drive higher currents, and if it has more windings, higher voltage at lower current.

If a transformer is large and/or heavy it’s probably intended for either very high voltage on its output or high current on the output with a lower voltage- microwave oven transformers are an example of this, and do both at once.

A large transformer is going to be heavy simply because it has a solid iron core and lots of copper wire around it- if it’s handling large voltages and/or current, that’s necessary to keep it from burning up from the heat it generates.

A computer power supply will be a bit smaller, but will usually have a transformer in it- just not a really massive one like in a microwave. So they weigh a lot less.

Edit: If you specifically mean why a 110v transformer is heavier than a 240v one, it could be that the 110v transformer is intended to generate similar power at its output, but because at lower voltage that means more current (ohm’s law), it needs to be heavier to handle that higher current load.

The size of the transformer depends on two things: maximum power and AC frequency. The grid (both 110 and 230 V) has very low frequency (50 or 60 Hz), so powerful transformers must be big and heavy, if they want to plug directly into the grid.

But modern switching power supplies do not plug transformers directly into the grid. They convert the grid AC into 110/230 V DC, and then back into AC, but with a much larger frequency (~10000 Hz). That allows them to use small transformers.

The 110 V or 230 V is irrelevant to the problem. In fact, many 230 V switching supplies can work with 110 V as well – they will automatically regulate the output voltage. For ex., my laptop supply says “INPUT: 100-240 V, 50-60 Hz”. So both 110 V and 230 V are within its working range.

The required size of a transformer decreases with the increase of the frequency it is used with.

A straight-to-wall 50/60hz transformer is a big frickin chunk of metal.

A computer PSU or phone charger first converts the wall voltage to DC then uses a transistor bridge to turn it into 10,000-1,000,000+ Hz AC (sort of – this subject is complex). The transformer can be quite small and light then. It converts back to DC on the other end.

Lots of copper. Cooper is dense. Dense is heavy.

A transformer works by having two coils. One that’s powered and produces an electromagnetic field. The other at a set distance so that it can take in the electromagnetic field being generated and produce a current.