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The aim of this guide is to see the different components that make up the device, and to understand their function, how they work independently and how they interact.
This page might be of interest as well!
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Hair dryers use a motor-driven fan and a heating element to transform electric energy into convective heat. The whole mechanism is very simple. The video (FR) shared in the introduction shows the general principle. You can find it, along with other videos, on Mozaik Education (FR).
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When you plug in the hair dryer and flip the switch, current circulates in the hair dryer. First, the circuit powers the heating element.
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In most hair dryers, the heating element is a bare coiled wire. In more expensive models, more sophisticated materials might be used, such as a ceramic coating entwined in tourmaline. The electric current then makes the small electric motor run, which powers the fan.
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The flow of air generated by the fan goes through the body of the hair dryer, above and through the heating element. When air flows on and through the heated element, the generated heat warms up the air by forced convection. Hot air flows through the extremity of the front nozzle.
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Hair dryers are mostly identical in their design and choice of components. The electrical/electronic part is more or less elaborate, but rather similar regardless of the model.
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The teardown view schema shows the different elements that make up most hair dryers: 1. Grid with a removable nozzle (not shown here), 2. Insulated support cone made of mica, which supports the heating resistor. 3. Heating resistor made of nichrome, 4. Diode bridge
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5. Air entry filter, 7. Fan blade, 8. Cold air button, 9. Speed switch, 10. Power supply cable
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Nichrome is a poor electricity conductor compared to copper wire. It gives the alloy enough resistance to heat up with the circulating current. It doesn't oxidize when heated. Other metals, such as iron, would quickly rust at temperatures used in toasters and hair dryers.
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As previously stated, each model uses a solution that varies depending on the brand. It would be difficult to study each one. We will focus on studying the circuit of a Philips SalonDry Compact. We find the same components in devices with variants, but the overarching principle remains the same.
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The overarching principle that we encounter in most hair dryers is the following: the device's power supply is 230VAC. This power supply goes through a switch with multiple positions. The switch makes it possible to vary the speed of the fan and the temperature of the hot air exiting the device.
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It's often coupled with a push-button that 'cuts' heating (absent on this model). Depending on the position of the switch, current is sent to one or several resistors. One of these is in series with a diode bridge, which powers the engine in direct current.
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The motor of the model studied is powered by between 12 and 17 VDC. At this voltage, it runs at approximately 20,000 rpm. Its reference number is RS-365S.
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Circuit diagram: when the switch is in position 0, no current flows.
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In position 1, the R3 resistor is powered, and the current (positive half wave) goes through the D1 diode, the engine, the D4 diode, then R1. The negative half wave does not flow through. The engine runs at half throttle and the resistor heats up ~by half.
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In position 2, R2 and R3 are powered. The positive half wave goes through D1, the engine, and D3. Then, the negative half wave goes through D3, the engine, and D2. The engine runs at full speed and the resistors heat up fully.
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Lastly, a thermostatic contact Th° is placed in the circuit to protect the device and the user, in the event of overheating.
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As an example, here is the circuit diagram of a different model. We find more or less the same components, mounted differently. They are connected to a switch with 4 positions: P0 = power off; P1 = medium speed and temperature; P2 = high speed and temperature; P3 = low speed and temperature.
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In position 0, the circuit is not powered. The hair dryer is off.
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In position 1, current goes through D1 which cuts a current halfwave, hence reduces the effective power. The temperature gets reduced.
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The current also goes through D2, which causes the same effect on the engine and on R3. The engine runs at medium throttle. R3 acts both as a divider bridge to power the engine, and as a heating element.
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In position 2, the current goes directly to diodes, R1 and R2. They fully heat up. Similarly, the engine runs at max speed.
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In position 3, the current no longer goes by R1 and R2. It only goes through the engine and R3, which still runs at full speed. Hence, R3 heats at its nominal speed.
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This setup includes a capacitor and a resistor connected in parallel to the mains input as a noise filter, as well as two coils connected in series with the motor for the same reason. There is also a thermostatic safety switch, Th°.
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Now that we are familiar with the functional aspects of our device and that we know its subsets and their functioning, we can proceed to repairs with the following tutorial: Hair dryers - Frequent issues
Now that we are familiar with the functional aspects of our device and that we know its subsets and their functioning, we can proceed to repairs with the following tutorial: Hair dryers - Frequent issues
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