Magnetic connectors: When plug and socket...find each other by themselves

29.10.13/XNUMX/XNUMX | Author / Editor: Simon Grüneberg (N&H Technology) / Kristin Rinortner (Market & Technology)
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New ground was broken in connector technology with self-locating magnetic connections. The article describes the advantages and possible uses of this connection technology.

Magnetic connectors consist of spring contact pins and a magnetic connection system. Due to the implementation of the spring contact pins, the contact is not created by plugging the pins into a socket, but by touching the contact pins with the contact points.

The contact points are soldered to the circuit board in the device. The advantage of this technology is the high functional reliability with a very high number of cycles of up to 10.000 reattachments.

The strong permanent magnet consists of a neodymium-iron-boron alloy (NdFeB) and ensures a quick, shock- and vibration-resistant as well as self-guiding connection or easy disconnection of plug and device.

The magnetic force can be customized using different magnets. The N&H Technology connector shown in the lead image uses a magnet with a magnetic strength of N48 and a flux density of 430 mT ±35 mT.

Magnetic connectors are used in the field of power and data transmission, for example in battery charging stations and battery compartments of electronic devices, especially in communication devices such as smartphones, tablet PCs and laptops.

The magnetic release mechanism prevents the device from being damaged by a fall if the cable is pulled unintentionally. With a computer, this can prevent the power socket from breaking out and possibly causing a loose contact.

Applications PC, battery charging stations and household appliances

But this type of safety mechanism has also proven itself in household appliances. Pulling on the cord of a kettle can cause severe scalding from hot water if it falls over. This danger can be avoided by using a magnetic connector. An application is also conceivable in the fields of medical technology.

With magnetic connectors, the contact between plug and socket does not take place via mechanical locking, but by touching spring contacts, which are brought together and held together by magnets. In addition to good functional reliability, this concept enables a high number of mating cycles. Significant advantages are self-detection, ie mismating is ruled out by magnetic coding, as well as the so-called tear-off function, which prevents damage to the connector if it is unintentionally disconnected. The connectors are also characterized by high vibration resistance, good cleanability and customer-specific configurability.

A wide selection of spring contact probes allows for custom configuration of magnetic connectors for a variety of devices.

The structure of magnetic connectors

Structure of a spring contact
Structure of a spring contact

A spring contact probe consists of three parts: a plunger, a spring and a pin sleeve. As standard, the piston and pin sleeve are made of brass and the springs are made of stainless steel. Other materials such as beryllium-copper alloys or phosphor bronze are optionally available to meet the requirements of special applications. The plunger and barrel are coated with gold because this material has excellent electrical conductivity and offers a high level of protection against corrosion and oxidation.

The pin sleeve and the piston are usually first double-coated with a layer of nickel of 1 to 2 μm and then with a layer of gold of 0,1 to 1 μm. The spring is made of stainless steel or steel with gold or silver plating. Here, too, other application-specific noble metal coatings of the piston (nickel, rhodium, etc.) and layer thicknesses are possible. Depending on the material and internal structure of the spring contact probe, currents of up to 10 A per pin are possible. This is a decisive advantage, especially for the charging time of high-performance batteries. The charging status can be displayed by integrating an LED in the connector assembly. Additional USB 2.0 or HDMI 3.1 connectors can also transmit HF signals quickly and reliably.

The properties of the magnet connectors

The contact resistance of a spring contact probe is <100 mΩ. Depending on the material, a long-term range of use up to temperatures of 150°C is possible. The contacts can be integrated into the magnetic connector in different numbers and configurations. For example, multi-row solutions are also possible, especially when high currents are to be transmitted. There is no maximum number of spring contact pins in a connector, but the pin spacing varies depending on the size and performance of the spring contact pin. A possible pin spacing (pitch) is 2,54 mm, for example.

The spring force also varies between 25 and 400 g depending on the type of spring contact. A minimum spring force of 60 g is recommended for signal transmission and 110 g for power transmission. The magnetic connectors can be designed in any plug shape and also for waterproof solutions up to IP67. N&H Technology from Willich also offers the development of magnetic connectors complete with integrated cable. The trend towards increasingly narrow and design-oriented construction of communication devices makes the integration of standard connectors difficult. Spring contact probes can also be ordered in very small designs. The smallest standard spring contact probe is 2,1 mm long. The arrangement of the contact pins in the so-called right angle design is particularly space-saving, as contact can be implemented in a very small space.

Development and manufacture of magnetic connectors

The development and production of magnetic connectors is more expensive than that of conventional connector solutions. However, this innovative system is often viewed by consumers as added product value and thus gives companies a competitive edge.

The magnetic connectors and the integrated cables are RoHS-compliant, and the cables are halogen-free. The Willich company offers customers a comprehensive full service, which usually begins with product development.

As a system supplier with its own technical know-how, the company from Willich is pursuing the strategy of optimizing the entire input system and assembly.
Thanks to the cooperation of German and Chinese engineers in Willich and a branch in Shanghai, the company knows the procurement market in Asia very well and can show customers various solutions and deliver competitive products - and that according to European quality standards.

The bias design for less signal interference

Design variants of spring contacts
Design variants of spring contacts

With this design, the end of the piston is beveled at an angle of up to 18° and thus installed in the pen sleeve. This ensures 100% contact of the plunger with the pin sleeve when the spring contact pin is actuated. This significantly reduces signal interference due to vibration.

The bias design is built into almost all spring contact probes with a length of 3,5 mm or more. For smaller designs, the so-called back drill design (Figure 3) is used. In order to achieve the spring force required by the customer, the spring used in this design is longer than the hollow piston.

Ball for current carrying capacity over three amps

If there are high demands on the current carrying capacity (>3 A), the bias design is supplemented by the so-called 4P design. If the plunger and the pin sleeve of a spring contact pin do not connect properly at high currents due to insufficient lateral forces, the pressure spring can overheat.

In order to prevent this, the previous three components of a spring contact probe (piston, pressure spring and sleeve) are supplemented by a stainless steel ball as the fourth component in the 4P design. This ball is integrated between the piston and the compression spring.

The result of this construction is an increased spring force, which guarantees a firm connection between the piston and the sleeve. The current flow is directed to the sleeve via the stainless steel ball.