A simple needle-plate charger with a gap of 16 mm for unipolar charging of silver nanoparticles in an air stream has been developed and manufactured. The charging efficiency and particle electrostatic losses of the designed charger were evaluated at various applied voltages and aerosol flow rates. With an increase in the applied voltage (corona discharge current) and the aerosol flow rate at a constant applied voltage, a decrease in the charging efficiency and an increase in the total losses of aerosol particles are observed. A charging efficiency of 43% with 38% electrostatic loss was achieved at a voltage of 8.1 kV (5.5 µA) and a flow of 10 L/min.