Durakool, a manufacturer of power switching components based in Copthorne, UK, has launched a first-of-its-kind automotive plug-in relay for automotive and industrial applications that features advanced magnetic arc blowout technology. Despite an additional magnet, the DG82M still fits standard Micro-ISO sockets, making it ideal for industrial vehicles transitioning to electric power and higher voltage systems.
Optimized for DC switching, it can handle up to 3A@110VDC for 100,000 cycles and 7A@110VDC for 20,000 cycles. It is one of three new products launched by the company. Another is the DE40, a high-performance miniature PCB power relay engineered for demanding applications in EV charging and photovoltaic systems. Completing the trio of launches is the DHVC300, a state-of-the-art automotive contactor designed for high-voltage DC applications.
“These new products represent a significant leap forward in relay technology,” said Carlos Mendes, product manager. “The DG82M, DE40, and DHVC300 are not just incremental improvements – they are transformative solutions that address the complex challenges faced by our clients in the EV and industrial sectors. By combining advanced technologies like magnetic arc blowout and high-performance materials, we are enabling our customers to push the boundaries of what is possible in electric and hybrid vehicle design, as well as in critical industrial applications.
Blowout Magnets – What They Are & Why Use Them?
The rise in demand for electric vehicles, together with introduction of lithium based batteries and the popularity of alternative energy sources such as photovoltaic panels has led to increased requirements to switch ever higher DC voltages, explains Durakool in a presentation available on its website and highlighted here. For example, the domestic car once used 6VDC batteries (in the 1950’s) and this increased to 12VDC and 24VDC in trucks. Now, 48VDC (mild hybrid) systems are in relatively common use in cars and commercial vehicles. Hybrids and pure EV’s are now working with 400VDC and even as much as 1000VDC. Many smaller vehicles, such as forklift trucks, that once used 24VDC or 48VDC are using 72VDC or higher battery voltages.
But this is not new, there were electric cars before internal combustion engine cars and there were DC motored electric railway locomotives pre-1900. In fact, up until Henry Ford introduced the Model T, electric cars were more common than IC engine vehicles in the USA.
The one big problem facing anyone switching a high current DC load is how to turn off the arc which is generated when the switching contacts open. By comparison, switching AC is easy, the arc is self-extinguishing every time the waveform crosses zero which happens several times, depending on the AC frequency, whilst the contacts open and move apart.
For a DC load, the only way to turn the switching arc off is to have a contact gap big enough that the arc eventually goes out as it cannot sustain itself. This requires a big device to do the switching (big gaps require distance and therefore big coils to move contacts long distances). So, over time, a number of techniques have been developed to safely extinguish the DC switching arc. One of the earliest ideas was to use a magnet to extend the arc distance (or “blow out” the arc). The magnet could be a fixed magnet or an electro-magnet and is still in use today. This technique enables a smaller DC relay or contactor than otherwise would be possible.
What has changed is that companies like Durakool, which have a long history in DC switching technology, are using magnets in ever smaller relays to extend the relay’s DC switching capability as well as in new, special, contactors to switch higher voltages up to 1000VDC or more.
So, how does the magnet work? Most electrical engineers are familiar with Fleming’s ‘Right-Hand Rule’ which determines the direction in which a current will flow when a conductor moves through a magnetic field. It is the basis for generators, but its corollary is Fleming’s ‘Left-Hand Rule’ which determines the direction of movement of a conductor if a magnetic field is applied across the conductor. This is the rule which applies.
The switching arc is the conductor with a current flowing through it with the actual medium being the plasma between the opening contacts; and the magnetic field is applied from external magnet(s). These magnets are positioned to deflect the arc away from the opening contacts and as a result, stretch the apparent contact gap to the point where the arc is no longer self-sustaining and goes out. In the diagram, the arcs are deflected outwards (F).
The main disadvantage of using magnets for arc quenching is that it polarizes the relay or contactor’s terminals – the current must flow in the correct direction for the magnetic field of the magnets to deflect the switching arc in the correct direction. If the current flows in the reverse direction, the arc will be deflected incorrectly which might lead to failure of the relay or contactor, or, at the very least, reduced switching life. You can see in the example above that if the current flows in the opposite direction, the arcs will be deflected inwards and might not be extinguished, or, stay in place long enough to damage the contact surface.
The examples so far show magnets in contactors which have a double break configuration as standard. With relays there is usually, but not always, only a single fixed contact and a single moving contact. Here there is usually enough space to fix only one magnet and, due to the reduced size, care must be taken that the magnetic field does not interfere with the coil operation, whilst also ensuring that the arc is deflected in a safe direction.
Established in 1935 to manufacture switching devices for power generation in industrial & power automation systems, Durakool has evolved to become a leading manufacturer supporting switching, resistive and sensing for power electronics, industrial electronics, automotive and telecom applications. See www.durakool.com.
