What Is a Watch Mainspring and How Does It Store Energy?

The Energy Source

The mainspring is the coiled spring inside your automatic watch that stores energy. It is the power source for the entire movement.

How It Works

1. The rotor winds the mainspring through the gear train
2. The mainspring stores energy as it coils tighter
3. Energy is released slowly through the gear train
4. The balance wheel uses this energy to oscillate

Power Reserve

The power reserve is how long the mainspring can power the watch. The NH35 has a 41-hour power reserve.

What Affects Mainspring Life

• Over-winding modern springs have slip clutches
• Temperature extreme heat can weaken the spring
• Age springs weaken over decades

Frequently Asked Questions

Can I replace just the mainspring?
Yes, but it requires special tools. Most watchmakers replace it during a full service.