How do DC Contactors Work?

DC Contactors are comprised of a high current switch and a solenoid in a single enclosure. The switch provides the desired function, to turn current flow on and off. Trombetta DC Contactors provide a robust and economical means to switch high currents in low voltage DC circuits. These DC contactors are suited for applications involving voltages up to 48VDC. Current capacity varies by family with inrush capacity reaching 800 amps and continuous carry capacity reaching 225 amps for the larger units.


Accurately matching a DC contactor to an application requires proper attention to a number of details that define conditions of operation. These generally fall under three major divisions of voltages, currents and environmental factors. Adequate definition of an application specification can be a challenging task. Significant effort in creation of the application specification is justified because its' accuracy is of critical importance in achieving satisfactory durability and longevity with the most economical design. Trombetta can provide expert assistance in this most important activity.


• Addressing voltages must give consideration to the voltage being switched by the contacts and the voltage applied to the coil. These voltages need to be defined not only in their nominal condition but also at their extremes. Voltage is often a very dynamic parameter affected not only by system design but also by state of maintenance and dynamic parameters such as the current load imposed on the system at any given moment.


Coil current requirements for the solenoid portion of the DC contactor, after brief review, typically are not of significant concern because the device controlling coil current is found to be more than amply rated. Usually consideration for current focuses on the current to be switched by the DC contactor.


Environmental considerations need to address operating temperatures, especially the extremes, humidity, exposure to splash and spray of contaminants and what those contaminants might include, as well as shock and vibration parameters.


DC Contactors FAQs

What is the Mechanical Life Expectancy of a contactor?
Trombetta's contactors are rated for Electrical life only. Mechanical life expectancy is always greater than electrical life. Electrical life ratings determine the useful life of the contactor.
What is the worst type of load to switch?
Inductive (motor) Loads First, Capacitive Loads Second, Resistive (light bulb) Loads are the most forgiving loads to switch.
Why do you offer 2 types of contact material?
Generally speaking, copper is cost competitive and is good for switching loads but can have corrosion issues when used with resistive loads (i.e. no inrush). Silver is more expensive, however it resists corrosion and is good for low and high current switching.
In a Static Power System, why do we need to size the coil voltage above the nominal rating, i.e. 24VDC/48VDC?
In a normal Static Power System, we need to take into account the "maximum battery equalization charge voltage" whereby if the nominal system DC voltage is at 24VDC, the maximum coil voltage will be around 30VDC. If the system nominal voltage is at 48VDC then we would size the maximum coil voltage at 60VDC. The reason for this is to alleviate any potential for premature coil thermal runaway. If using the product in a charging system please contact Trombetta.
What is the maximum carry current rating of the Trombetta DC contactor product line?
  • Bear - 225 to 300 amps
  • Metals - 125 to 300 amps
  • Plastic - 100 to 200 amps
  • HP Plastic - 200 amps
  • PowerSeal - 150 amps
  • RP - 75 to 125 amps
  • Defender - 200 amps (resistive) or 100 amps (inductive)
  • Contact Product Support for mixed loads
What are Magnetic Blowouts?
Rare Earth Magnets molded into the top cover which produce magnetic fields which act on the main contact arcing, thereby extinguishing the arc outwards. This is particularly true in the case of "Inductive Loads".
Are the high current contacts polarity sensitive?
The contactors without blow out magnets can have any polarity on the high current contacts. Types with blow out magnets need to be wired up with the higher potential at the terminal marked with a + sign on the top cover. This is necessary to ensure that the blow out magnets push the arc out of the contactor.
How do you install a DC contactor?
Please refer to the instruction sheet for the specific product. The instruction sheets are found under the product section and under each product.
What is the torque rating for mounting hardware on the studs?
The torque ratings are stated on the product label.
How do you determine if a contactor is operating correctly?
One way is to determine if the Nominal Coil Resistance is at the right level.
  1. From our literature on the web site (products/contactors) determine the Nominal Coil Resistance.
  2. Get an OHMS meter that reads to milliohms (less than one ohm)
  3. Connect the 2 leads to the 2 small studs/spades (To get an accurate reading, the contactor needs to be at room temperature and not recently energized).