Thursday, September 3, 2015

Disassembling a hair clipper

After several years of use, my electric hair clipper (a.k.a. trimmer) finally broke. For that reason, I decided to buy a new one. When I saw that the prices were actually quite cheap, I got interested about how manufacturers are cutting down on costs.

The body of my hair clipper consisted of just 2 pieces of plastic and a mechanical switch connected directly to the internal board. A detachable part (not shown in the picture) with two blades oscillates from side to side driven by the internal DC motor and a fancy spring. The electronics are as simple as it gets with just a classic AC->DC rectifier whose output is connected directly to a Mabuchi FK-290PY-051100 DC motor (100VDC, 6800RPM without load).

The motor has a cam attached that allows transforming rotary motion into linear motion for moving one of the two blades.

The board's circuit diagram is a classic that any electronics hobbyist should know. The input wave (mains electricity) is a SINE with 100V amplitude and a frequency of 50Hz (Tokyo). The 1MΩ resistor is used to increase the input impedance (ideally infinite). Then, a 100nF/125VAC ceramic capacitor is used to filter out noise from the mains signal. The result is rectified through a diode bridge (i.e.: a full-wave rectifier), and then smooth out with an electrolytic capacitor in parallel (a low pass filter). The output voltage is 98,88VDC instead of 100VDC because of the forward voltage (Vf≈0.56) of 2 diodes. In sum, here is the bill-of-materials (BOM):
  • Resistors: 1x1MΩ, 1x150Ω
  • Capacitors: 1x100nF (125VDC), 1x4.7μF (160VDC, electrolytic)
  • Diodes: 4x1N4004-TP (Vf=~0.56)
  • Motor: Mabuchi FK-290PY-051100 (~4 dollars)
  • Camshaft
  • Blades
  • Spring
  • Plastic body
  • Power cord
  • Others: size attachments, oil, brush..
  • PCB
Conclusions: making profit from selling an electric hair clipper at about 2000~4000 yen looks quite challenging to me, unless you sell enough of them so that you can average out the cost of the initial mold for the plastic body and attachments. There are lots of brands competing in the market with completely different plastic bodies. I wonder if all of them are selling enough to compensate those initial costs.

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