Triboelectrostatic separation of granular plastics wastes is a technology that is more and more employed in the recycling industry. The paper is aimed at characterizing the tribocharging of Polyvinyl Chloride (PVC), Polyamide (PA) and High Density Polyethylene (HDPE) granules on a vibratory feeder tray covered by a Polyethylene Terephthalate (PET) sheet, in order to evaluate the possibility of using this device in a continuous tribo-electrostatic separation process. A capacitive probe was used to evaluate the surface charge density on the PET sheet. When the tray of the vibratory feeder was grounded, the charge density at the surface of the PET sheet was found to increase slightly after every tribocharging experiment, while the charge of PA granules saturated at 2.6 nC/g. In the case of an isolated PET sheet, its surface charge density is rapidly increasing and tends to saturate, limiting the charge/mass ratio of PA granules at 1.4 nC/g. Similar results were recorded for other tested materials, proving the efficiency of the tribocharging on the PET tray of the vibratory feeder.