The Seiko caliber VS22B is a solar-powered movement with a solar cell underneath the dial which converts light energy into electrical energy that gets stored in a capacitor (secondary battery).
Official technical documentation for this caliber was found as far back as April 26, 2019, and as recent as May 21, 2021.
The example movement in this post is signed S. Epson Corp. / VS22B / TWO JEWELS / JAPAN / 4 / 4SC(?)
Some of the topics covered in this caliber listing:
VS22A VS VS22B:
The base caliber number is VS22, the A, B, C, is a evolution update to the movement. The VS22A has official documentation as far back as 2012.
The two versions appear to be interchangeable. The main specs between the two are the same: size, jewel count, running time, charging times, hand sizes, stem part number, etc.
If you know specific differences, please comment below…
VS22 VS VS42:
There is a similar series of movements called the S. Epson caliber VS42. It is basically the larger sized version of the VS22. You may see brands offering solar watches in two sizes, often with these two movements. For example, Vaer offers a solar diver in 38mm with the VS22B, and the same style of watch (they look identical) as a 42mm with the VS42A.
Seiko claims that the caliber VS22B will maintain accuracy of +/- 20 seconds per month at normal operating temperatures of about 5C to 50C (41F – 122F).
The caliber VS22B is a solar powered watch with a manganese titanium-lithium rechargeable capacitor. It is not a normal battery. The number is MT920, or more specifically: 302324Y (or Seiko part number 4020581). Order one here
The chart below shows how long different lights sources can take to fully charge the cell in the VS22B. This ranges from 60 hours to 6 hours of constant light, depending on the light source type.
Can you overcharge the VS22B?
No, you cannot overcharge it, but be careful not to leave your watch on a hot windowsill or the heat could warp the dial (seen it happen before). In Seiko’s own words:
“If the secondary battery is charged more than predetermined voltage, over charge prevent function is operated to prevent the secondary battery deterioration and breakage.”
Solar Cell Notes:
When repairing or tinkering with a watch powered by the VS22B, always be sure not to touch or scratch the solar cell.
When designing a watch with this movement, keep in mind that the dial should be at least 30% transparent over the solar cell for effective charging capabilities.
When fully charged, the VS22B has an expected running time of around 6 months. When the power is low, the second hand will skip a second and move in 2 second intervals.
At the time of this post, replacement prices for the VS22B were found in the range of $26.90 to $33.29 USD.