The invention relates generally to electrical relays, and more particularly, the invention relates to a circuit and a method for wetting relay contacts.
Electromechanical relays are used in many applications. In some applications the relays are used for switching of currents and/or loads. However, in some applications, the relays are used only for isolation of the voltage or for an additional level of control for security. These isolation-type relays include circuits, sometimes referred to as dry circuits, having loads that are not opened or closed by the contacts. Instead, current may flow through the contacts after closure and before opening, but the contact does not directly control the load. The relay contacts simply control power to another device that in turn controls the load.
In circuits where the relay is not used for switching of the current, over time, damaging chemicals, such as, oxides and hydrocarbons are formed on the relay contacts. The build-up increases the contact resistance which can cause a voltage drop and/or heating of the contacts. Additionally, with continued build-up of chemicals, the relay may maintain an open circuit even when a relay is energized and should close.
Currently, many circuits are designed without any compensation for chemical build-up. On the other hand, some existing circuits, which are designed to prevent or diminish the chemical build-up on the contacts, use additional costly components, such as relays, capacitors and resistors to pre-charge the contact when closing the relay. This is commonly called “wetting” the contact. What is needed is an inexpensive, yet efficient circuit or method of wetting contacts.