Contactor
Sometimes used in EV Conversions
A contactor is an electrical device used for controlling power flow. A contactor is activated by a control input which is a lower voltage / current than that which the contactor is switching. Contactors come in many forms with varying capacities and features.
Contactors range from having a breaking current of several amps and 110 volts to thousands of amps and many kilovolts. There are highly specialised contactors which are as large as a small car and those which are almost subminature.
A contactor is similar to, but different from an electrical relay. Although commonly both use a magnetic coil to draw a contact closed a contactor differs in that it is designed to "break" a high current load - although relays are designed for switching loads on or off as well they tend to be of much lower capacity and are usally designed for both Normally Closed and Normally Open applications. Apart from optional auxillary low current contacts a contactor normally only has normally open contacts fitted.
Contactors are commonly fitted with overload protection to prevent damage to their loads. When an overload is detected the contactor is tripped removing power downstream from the contactor.
The Contactor is commonly represented electrically with the symbol K.
A basic contactor will have a coil input (which may be driven by either an AC or DC supply depending on the contactor design) and generally a minumum of two poles which are controlled.
Some contactors are motor driven rather than relay driven and extremely high voltage contactors often have arc suppression systems fitted (such as an inert gas surrounding the contactor).
Magnetic Blowouts are sometimes used to increase the ammount of current a contactor can successfully break. The field produced by the magnets in close proximity to the contact forces the arc produced while breaking current to flow through the field which is curved and a greater distance than the streight path between the contacts. The magnetic blowouts in the pictured Albright contactor more than double the current it can break from 600 Amps to 1500 Amps.
Sometimes an Economizer circuit is also installed to reduce the power required to keep a contactor closed. A somewhat greater ammount of power is required to initially close a contactor than is required to keep it closed thereafter. Such a circuit can save a substantial ammount of power and allow the energized coil to stay cooler.
- http://www.qsl.net/ki7cx/Coilrewind.htm - Instructions on rewinding contactor coils for different voltages.da:Kontaktor