Pfaff and Svanberg multiplier

Multiplier prototype

A curious multiplier of electrical charge using four insulated metal plates with a complex sequence of manual operations appears in the book by Daguin [54], with a summary description and without reference to origin:

P. A. Daguin, "Traité Élémentaire de Physique," 1856.

It works in a way similar to Péclet's condenser, with one of the plates split in two for convenience and symmetry, and changing the roles of the plates periodically. The same operations can be repeated with the three plates of Bennet's doubler, if one manages to keep track of the long sequence of operations. Some investigation revealed that the first description of this device was presented by Svanberg in 1846, and published in the "Report of the annual meeting of the British Association for the Advancement of Science in 1847 (pp. 31-32): The description is the same of the book.

Report of the BAAS, 1847.

The operation is best described by the figure below, that shows two triplication cycles, starting from a configuration where the capacitor a-b is charged (0), as described in the texts above. The full triplication cycle (1)-(5) does not require the repetition of position (0), and so requires five manipulations, as seen, after the first that requires six. The sequence of operations is easy to remember, with plates c and d, and then a and b, being alternately grounded by a touch, starting at the upper plate. Three touches produce duplication, five touches triplication, seven quadruplication, and so on.

Sequence of operations.

In January 2011 I built one to see how it behaves. It was made with four 13 cm wood disks covered with thick aluminum foil, with acrylic plates glued to them for insulation, supported by plastic HDPE rods and with thin PVC tubes for handles. A curved brass rod interconnects the two lower plates. Everything can be disassembled for storage.The size of the disks is just enough to produce visible sparks and significant shocks when the device is fully charged. A larger device would be quite disconfortable to operate due to the shocks. The maximum voltage appears to be around 15 kV, limited by leakage around the spark shields.

A video, showing the manipulation following the sequence shown above: Starting from discharged plates, after four triplications the electroscope balls separate, indicating about 500 V. The full charge appears at the lower plates when both upper plates are removed.

Created: 28 January 2011
Developed and maintained by Antonio Carlos M. de Queiroz.

Return to Electrostatic Machines