Why is the input and output wattage of a welder different?

Question

For instance a welder can have a 200 amp output at 18 volts, but has an input at 20 amps and 240 volts, making wattage input 4800 and output 3600. What explains that loss in wattage?

Obviously these numbers are absolutes. However, if you physically measure the amps and volts at input and output, these are actual/real numbers. In this case you aren't consuming more energy than you are creating, there is a 1200 watt loss. Where does the loss occurr?

Answer 1

A transformer reduces the input voltage. In a perfect transformer, the output power would equal the input power. However, since no transformer is perfect (winding resistance, inductance, core permeability, etc.), none can be 100% efficient. The power is lost through electrical and magnetic resistance, which creates heat. Your welder example would be a 1200 watt heater ;)

Toroidal transformers are more efficient than the standard E-I lamination types. Toroidal ones are used in audio and high frequency power supplies.

Answer 2

Science has determined that you can't get more energy out of a device than you put into it. Voltage and amperage can change but the energy (power [watts}) will be the same or less.

In reality, you are likely to get less power of a device than you put into it. Heating losses, resistance of the wire, inductive resistance, capacitive resistance, hysteresis etc.

If you've ever seen the inside of a welder you'd see lots (and I mean LOTS) of copper windings. That much wire has a lot of resistance. Transforming 20A @ 240 volts uses up some of that power (hysteresis). In all, the losses of power in the device, be it a welder, a radio, air conditioner, etc. explain the difference.

A power loss of about 25% may seem high but for an arc welder it appears to be about right.

Answer 3

The input and output ratings are maximums, not absolutes.

That, and the law of conservation says you can never create more energy than you consume.

Edit:
Unless you are simply pulling these number out of a hat, rather than off the dataplate of the welder, then the numbers are maximum ratings, not absolutes.
As explained, you cannot create more than you consume, a welder has a huge transformer, and a lot of that energy loss is converted straight to heat (which is why the larger units are fan cooled).

Answer 4

If you are talking about the welding machine that is like a stepdown transformer then the power loss was only in the core of the transformer. But this is too much that made your machine heating more. But if there is a rectifier or SCR then the input and output will not definitely match.

Answer 5

Power(P) = Current(I) *Voltage(V). Power is in units of Watts. A transformer is the device that makes this all possible. It is the same concept as power generation to your home, and the power supplied to any electronic device.

Answer 6

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