Why are High-Power Devices Not Designed to Run on DC Voltage?

Why Don’t We Use 120V DC, 230V DC, or 240V DC Instead of 120V/230V/240V AC for High-Power Electrical Appliances?

Most high-power appliances are designed to run on AC (Alternating Current) instead of DC (Direct Current) because AC is easier to transmit over long distances with minimal energy loss. In addition, transformers are used to step voltage up or down the level of voltage only work with AC. DC would require larger and more expensive components for switching, voltage conversion, and insulation. Hence, it makes it less practical for most of household appliances and industrial power distribution at high power levels.

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Obviously, high-power devices can operate on DC voltage just like they do on AC, but typically at a higher cost. Let’s see how and why this is the case.

12/24/36/48V DC vs 120/230/240V AC – Which one is Economical?

When it comes to electrical or electronic devices (especially household appliances) most countries following IEC standards (such as the UK, Australia, and many in Asia) supply 230V AC power, while countries following NEC/CEC standards (such as the United States and Canada) use 120V/240V standard AC power supply for residential applications.

Therefore, products operated at electricity are designed based on standardized electrical parameters. The manufacturing process involves numerous internal components that must conform to these standards. It’s also important to note that all electrical devices have operational limitations based on the ratings and applications.

Now, let’s consider DC voltage. The question arises: What should be the standardized DC voltage level? At what voltage should devices be manufactured?

For example, some small appliances, like fans or water pumps, are designed to run on 12–24V DC. So, can we apply the same concept to high-power devices such as, water-heaters, electric ranges, refrigerators, and air conditioners?

Technically, it’s possible! And standardization of DC voltage can be done. However, the limitations of electrical parameters become a major challenge. Let’s see why?

Example:

Electric power is the product of voltage and current:

P = V × I

Let’s say a 100-watt fan is running on 230V; it will draw approximately 0.43 amps. If we operate the same 100-watts fan on 120V AC supply, the current will increase up to 0.83 amps.

On the other hand, if that same 100-watt fan is designed to operate on 12V DC, it would require about 8.33 amps.

I = 100W ÷ 12 = 8.33A

To carry such high current through household wiring, significantly thicker conductors would be needed. For manufacturers, this presents serious design challenges. To counter this issue, they would need to use heavier windings, thicker conductors, and other components capable of handling higher current, which would drastically increase production as well as operation costs.

Just from this 100-watt fan example, you can see that the current increases about 20 times when running on 12V DC. Now, imagine the scenario for larger loads:

• A 400-watt refrigerator
• A 1000-watt electric iron
• A 1600 to 2400-watt air conditioner

Designing and operating these on 12V DC would be highly impractical.

In summary, DC systems are suitable only for low-power applications or makeshift setups (such as a DC ceiling or pedestal fan (typically 50–60 watts), or a cooler (up to 80 watts).

Furthermore, unlike AC voltage, DC voltage cannot be directly increased or decreased using a transformer.
Instead, it requires specialized circuitry, which adds complexity and cost.

This is why most electric appliances are specifically designed to operate on AC voltage.

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Why is it Impractical to Use 120V/230/240V DC instead of 120/230/240V AC?

As we know that at low DC voltages (such as 12V or 24V), the current increases significantly compared to 230/240VAC, which is why thicker conductors are required.

But this raises another question: What is the drawback of using 120V or 230V DC instead of 120V/230V or 240V AC?

There are several reasons for this, and the most important ones are as follows:

1) Issues of Carbon Brushes in DC Motors:

After World War II, there was a massive surge in industrial development. Industries rapidly expanded, and every sector required electric motors to provide mechanical energy.

At that time, DC motors were commonly used. However, because they relied on carbon brushes and commutators, they required frequent maintenance.

Additionally, carbon brushes produced sparking, which made it extremely dangerous to use DC motors in applications like fuel pumps or any equipment that handled flammable materials such as petrol/gasoline.

As a result, industries adopted induction motors, which are safer and more reliable, but they require AC voltage to operate instead of DC. This is one of the major reasons AC power became dominant.

2) Voltage Conversion

Another key reason is that in many industries, different devices operate at different voltage levels. The simplest and most cost-effective way to change voltage levels is by using a transformer. However, transformers only work with AC power, not DC. DC system requires expensive and special components (e.g. converters and rectifiers) to step up/down the level of voltage. This gave AC a major advantage in terms of flexibility and cost-efficiency in power distribution.

3) Economical AC Motors

AC power enables the use of three-phase supply systems, which allows three phase electric motors to be smaller in size and more economical to manufacture. This efficiency in motor design is another significant factor in AC’s widespread adoption.

Due to these reasons, that’s how AC power replaced DC in, residential, industrial and commercial applications.

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How High-Wattage DC Load is Managed in e-Bikes and EV?

The main point is not that high-wattage appliances are incapable of operating on DC voltage. They certainly can!. For example, motors used in electric bikes (e-bikes) typically range from 800 to 3,000 watts and are rated for various DC voltages such as 36V, 48V, 60V, or 72V.

Similarly, DC motors used in electric vehicles (EVs) generally range from 20 kW to 30 kW, with operating voltages often between 96V and 192V DC.

Now, consider a 3,000-watt motor in an e-bike operating at 72V DC. It would draw approximately 42 amps of current. To safely carry this high current, the system requires thicker wires and heavier components, which increases the overall cost.

In other words, a similar power system running on AC voltage would likely be more cost-effective due to lower current requirements and easier voltage transformation. However, in applications like electric vehicles (where batteries supply only DC) AC operation isn’t practical or feasible. In this case, the big issue is that we are unable to store AC power in batteries.

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