High Voltage DC Contactor FAQ
Q: What is the difference between a relay and a contactor?
A: Usually, both of these terms refer to electromechanical switchgear, which operates on the same principle, where the coil is used to generate magnetic force and mechanically operate electrical contacts. Although the term relay is widely used in various industries for low and medium power equipment, the term contactor is more common in the high-power field. Contrary to the hinged armature design commonly used in relays, magnetic "motors" are typically achieved through a plunger in the center of the contactor coil body.
Q: The new generation of contactors can operate without the need for inflation. What are the advantages of non inflatable contactors? Will the inflatable contactor break?
A: In order to protect switch contacts and support rapid extinguishing of switch arcs, many contactors are filled with pressurized inert gas. Usually nitrogen or hydrogen gas is used, as well as SF6 (sulfur hexafluoride), mainly used for industrial applications. On the other hand, pressurized gas filling requires more effort in the design and manufacturing process to ensure reliable gas retention throughout the entire lifespan of the contactor. Due to the fact that such contactors essentially must be sealed, they also bear the risk of rupture when extremely strong arcs - in the case of high overcurrent or short circuits - generate excessive gas pressure in the contact chamber.
Q: What are the applications of high-voltage relays and contactors?
A: In hybrid and electric vehicles, high-voltage relays and contactors are commonly used for the following applications:
Main contactor: used for the positive and negative poles of traction batteries. The main contactor connects and disconnects the traction battery from the entire electric transmission system of the vehicle.
Pre charging relay: In order to protect the main contactor from excessive inrush current, the pre charging relay is used together with the pre charging resistor to charge the filter capacitor of the power inverter to 90-98% of the battery voltage.
Charger contactor: used to establish a connection between the battery charger and traction battery when the vehicle is connected to the charging station.
Auxiliary contactors: They control other electrical loads operated by high-voltage batteries in the vehicle. A typical example is the electric heater in the passenger cabin of an all electric vehicle, where no waste heat from the internal combustion engine can be used for this purpose.
In addition, automotive high-voltage contactors are sometimes used for fixed systems, such as DC charging stations, fixed battery storage systems, uninterruptible power supply systems, etc.
Q: What performance range can contactors be applied to?
A: BSB's contactor product portfolio includes heavy-duty products that meet the requirements of the most powerful battery electric vehicle with high peak power, as well as miniaturized products for low-power series loads and pre charging applications.
Q: What continuous currents can contactors handle?
A: Usually, the current carrying capacity is limited by internal heat dissipation and thermal management. The dissipated power increases the temperature of the internal parts of the contactor and transmits it to the outside. This external temperature rise determines the current limit that the contactor can be used for. BSB recommends that the final temperature of the contact terminal should not continue to exceed 150 ° C. The effectiveness of the cooling mechanism depends on the cross-sectional area or thermal resistance of the external connecting conductor, as well as the ambient temperature. Heat is transmitted to the environment through electrical connections. For a constant current, the system reaches a stationary state after approximately 3 to 5 minutes. Example: BSBC7-250 contactor and 50mm ² The busbar is connected and can withstand 250A at an ambient temperature of 85 ° C. For 125mm ² The busbar, this limit will be converted to 375A.
Q: What overload can contactors handle?
A: For peak loads of a few seconds, the heat transfer process is too slow and the terminal temperature cannot change significantly. Over a long period of time, an increase in temperature inside the contactor may cause irreversible damage. For example, the BSBC7-250 contactor can handle 1500A current for 20 seconds or 2000A current for 5 seconds. Please contact BSB Electrical for more information and support.
Q: What determines the efficiency of a coil? What are the requirements for coil drivers?
A: In order to separate high voltage, a large contact gap is required. In the open position, the holding spring holds the armature back in position to provide appropriate impact resistance. In order to overcome these high contact gaps and forces, it is necessary to generate high magnetic flux. In order to obtain the necessary force, the coil is designed to have a relatively low resistance. Therefore, the driver should be able to provide a current of up to 6A. This high current can only be used to close contacts, and then the current must be reduced to avoid overheating of the coil. Once the contact is closed and the armature is in a fixed position, the magnetic flux required to keep the armature in place will be reduced by an order of magnitude. This reduction in coil power can be achieved through external energy-saving devices or internal boost/hold coil configurations.
Q: What is important to operate a contactor with an external energy-saving device?
A: After the online loop is powered on, the operation of the external economizer should start for at least 100ms. For pulse width modulation (PWM), BSB recommends a minimum frequency of 20kHz. The minimum value of the generated oscillation coil voltage should always be higher than the specified holding voltage. For the shutdown operation, the response time of the mechanical system depends on the external terminals of the coil. Therefore, the PWM driver should terminate in a way that does not slow down contact opening. Link to data sheet BSBC7-250 main contactor. The coil resistance varies with the temperature of the coil. The magnetic force only depends on the coil current. If PWM is set to a specific coil voltage level, these thermal changes must be considered. In order to minimize the thermal load of the system, it is preferable to control the coil current to ignore the influence of temperature.
Q: What is the significance of operating contactors with boost coils?
A: The booster electronic device applies full coil voltage to a single booster coil for a limited time. When a voltage is applied, the pulse immediately begins. If the necessary pull-in voltage is not reached within the gate time of the boost electron, the contactor will not close. Therefore, it is necessary to achieve the minimum pull-in voltage within 50ms. The termination of the coil is completed using an 80V Zener diode. An additional terminating diode can be installed in parallel. The termination voltage should be Vz>33V to maintain a short drop time.
Q: Why is load polarity important for contactors?
A: The breaking ability under high voltage is achieved by using a magnet placed perpendicular to the contact terminal. Both terminals are connected internally through a bridge. When the contact bridge moves away from the fixed contact, two arcs are generated. In the forward current direction, the magnet deflects the arc to the outside, resulting in rapid arc extinguishing. In the direction of reverse current, the arc may merge at the center, resulting in a decrease in breaking capacity.
Q: What should I do if I need bidirectional disconnection capability?
A: In the case of using two contactors in a circuit, they can be arranged as one in the forward direction and one in the reverse direction. When two contactors are opened simultaneously, the combined breaking ability is significantly better compared to a single contactor in the forward direction.
Q: What should silicone materials be considered when using unsealed relays or contactors?
A: The use of silicon containing materials or their derivatives can affect the normal function of electrical contacts. Due to the energy in the arc of the switch contact, volatile silicon molecules are converted into silicon compounds that deposit on the contact surface and form an insulation layer. Therefore, BSB ELECTRICAL strongly recommends thorough testing of the expected contact compatibility of silicone. Please contact BSB Electrical for more information and support.
Q: Does BSB provide a solution for applications above 1000VDC?
A: According to insulation coordination requirements, solutions up to 1000VDC can be provided. In addition, BSB has currently developed a solution that complies with IEC 60664 and is suitable for 1500VDC voltage levels. For more information, please contact BSB Electrical.
Q: How should the coil driver be protected from the transient impact of contactor coil shutdown?
A: The best solution is to use a Zener diode in parallel with the coil driver.
Q: Are there any prompts for installing the busbar to the contactor?
A: Please consider the maximum allowable torque to avoid any misalignment between the busbar and contactor terminals to ensure uniform interface pressure. BSB recommends using conical spring washers. When installing cable lugs, ensure that the cables are free and not pinched.