Contactors & Solenoids
Not a lot of an EV’s components could seem to match the importance of a contactor. Defined to be primarily as the device that clicks the circuit “closed” alive, a contactor will allow for a high voltage circuit to operate smoothly and without a hitch. The standard contactors today are magnetized just to make sure that when there’s an emergency, you can just simply turn the key off and the contactor pops open the main circuit, rendering it “dead”.
A closer look at an EV’s contactor would reveal that despite the fact that it doesn’t appear to be the most important element in an electric vehicle, contactors are critical for the vehicle’s complete safety. Without the use of contactors, which act as a heavier-duty version of a relay, there would be no switch power to the loads that run through an EV. The power is being supplied by an EV’s traction battery and without such component, it would hardly be possible for anything else in the engine to run as they’re intended.
A contactor is important for another reason: it acts as the switch for the EV’s motor drive, heating and cooling systems, the DC/DC converter and all the 12V loads that draw more than a few amps from the traction battery. If you’re having a bit of confusion about how these contactors differ from relays and solenoids, we should mention here that contactors, relays and solenoids are just the core names of the electromechanical switch used in any type of EV. The definition and names for such EV elements will depend more on the type of power rating and industry/application used.
We must add here that contactors are sometimes termed to be the high-power device built with a limited number of “poles” or individual switches (one to three most commonly), and will eventually offer a single “throw”. On that note, there may be a bit of confusion comparing solenoids from contactors. Despite being an obsolete term, a solenoid may be referred to as a descriptive term used for modern contactors and relays, as they refer to what can be called as an electromagnet operating a plunger.
Another important aspect of contactors is the type of circuits they usually encounter when installed with circuits. These three major types include resistive, capacitive or inductive in nature. Most of EV’s motors today are inductive in nature, so it may make sense to acquire a contactor that fits this, which, for example, will select between forward and reverse operation of a series DC or a 3-phase industrial motor.
One should pay special attention, too, in checking if the input to any switchmode power converter is capacitive in nature. Otherwise, there’s a large risk of contact welding upon closure if the capacitance is not fully charged up to near the same voltage as its own supply. That said, there are mechanisms to boost the performance of such contactors. One of these ways is to increase the DC power rating of such contactors through the use of magnetic blowouts.