The number of rotation with VK depends upon the quantity of the thing to be charged. Up to 2 ltr of liquid or 2 kg of solid can be charge with simply 15 to 20 slow rotations. If the quantity is more than 2 ltr or 2 kg increase the rotation according to quantity.
This Water Charging method with examples will give you more insight about rotation.
You can learn in this video how to charge different quantities of water or things by VK rotations: Simple & Easy Ways to Charge Drinking Water Using VK.