Basic Electrical Theory of a Quartz Watch

basic power theroy in quartz wtch

Written By Alex Hamilton

Alex Hamilton is a watchmaker, collector of fine watches and writer of all topics in the study of Horology.

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The biggest problem with the power in a quartz watch is that you cannot see it. That is why it can be hard for some people to understand it. For you to understand troubleshooting concepts for quartz watches, understanding the power supply in a quartz watch is essential. To make it easier, I will give you a simple analogy.

Basic Electrical Theory

In the picture above the pump pushes water from its outlet along the top pipe. It goes through the radiator and back through the bottom pipe to the pump inlet.

The pump will generate a certain amount of pressure and the radiator, adds resistence to the flow of water. Therefore, a given amount of pressure from the pump, will move a given amount of water flow around the pipes. As you increase the pressure from the water pump, the flow of water increases and if you reduce the pressure, the water flow will decrease.

Now, if you increase the resistance in the radiator, the water flow will decrease and if you decrease the resistance in the radiator, the water flow will increase.

As you can see, the flow of water will be determined by two things:

  • The pressure from the pump.
  • The resistance of the radiator.

With this I mind, lets look at the electrical circuit.

The Basic Battery Circuit

basic quartz watch electrical theroy

In the picture above, a battery has replaced the water pump and a light has replaced the radiator. The long bar stands for the positive terminal of the battery and the short bar represents the negative terminal of the battery. The electrical current flows out of the positive terminal and comes back into the negative terminal. A watch battery will generate a certain amount of electrical pressure. The light represents the radiator from earlier and will have a certain amount of resistance.

Just like in the water analogy, if you increase the electrical pressure from the battery, you increase the flow of electricity in the circuit. Therefore, if you increase the resistance of the light, you reduce the electrical flow from the battery through the circuit.

Electrical Units of Quartz Watch 

  • You measure Electrical Pressure in volts. The Symbol for volts is V. Most quartz watch batteries generate 1.5 volts of electrical pressure.
  • You measure Electrical resistance in ohms. The symbol for ohms is Ω.
  • You measure the Electrical current flow in amps. The symbol of amps is A

Their relation to one another is remarkably simple. A pressure of 1 volt, when applied to a resistance of 1 ohm, causes 1 amp of current to flow. Similarly, if you have 2 volts of electricity, applied to 2 ohms of resistance, it will cause 2 amps of current flow.

Just as you might expect, if you go back to an electrical pressure of 1 volt but double the resistance to 2 ohms of resistance, the current flow is now ½ amps. Pretty simple, right?

Multiples and Sub Multiples

As it turns out, 1 amp is way too much for a quartz watch. Most quartz watches only draw 1 millionth of an amp. That is not typo folks. I said 1 millionth of an amp. There are special symbols used for these micro measurements.

  • Mega (symbol: M) for a million
  • Kilo (symbol: k) for thousand
  • milli (symbol: m) for a thousandth
  • micro (symbol: µ) for a millionth

For a resistor of one thousand ohms, you would write it as 1 kΩ and pronounce it as 1 kilohm.

For a voltage of 3 thousandths of a volt, you would write it as 3 mV and pronounce it as 3 millivolts.

For a current of 5 millionths of an amp, you would write it as 5 µA and pronounce it as 5 microamps.

As you can see, quartz watches deal with ridiculously small amounts of current.

Magnetism

Most people are familiar with magnetism. There are just a few things to keep in mind as it relates to the power source of quartz watches.

  • Opposite poles attract (N-S), Like poles repel (N-N, S-S)
  • Some material can become permanent magnets.
  • Certain materials are magnetic but will not become permanent magnets themselves.
  • When you pass an electrical current through a coil of wire, you produce a magnetic field known as an electromagnet.

Hopefully now you have a basic understanding of how a basic electrical circuit works. In my next article in this series, I will be discussing how the Stepper Motor in a quartz movement use these principles.

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