solar relais info


Innovation and leading-edge product development have always been a hallmark of ZETTLER Group’s engineering competence. During recent years, this has been particularly evident by our leadership role in providing component solutions in the field of Alternative and Renewable Energy and by developing special electromechanical switching devices for these types of applications.

As solar and other alternative energy technologies continue to grow globally, ZETTLER New Energy division is committed to supporting customers in renewable energy industries around the world, with first-class engineering and new product design, and by leveraging ZETTLER Groups worldwide production and distribution resources.

ZETTLERs industry-leading electromechanical ‘new energy’ components are designed for use in solar inverters, electric vehicle charging devices, or any similar applications requiring high loads to be switched and carried.

Solar Relays Overview

Power inverters are an integral part of any solar energy system, converting DC power output coming from solar panels into AC current that can be fed into a commercial electrical grid or into an off-grid local electrical network. In the interface to the power grid, electro mechanical relays on the AC side of the inverter play a critical role as switching devices and to provide necessary safety ‘circuit-break’ functions.

The ‘ZETTLER Advantage’

As photovoltaic (PV) power applications proliferate from micro-inverters, to string inverters, to commercial and even utility-scale PV systems, we have continually expanded our line of solar relays. These state-of-the-art ZETTLER components have been successfully integrated into many inverter applications by market-leading manufacturers of PV systems since many years.  Today, ZETTLER’s product line of AC circuit Solar relays spans across an extended range of product characteristics:

  • covering PV inverter applications from under 20kVA to over 100kVA,
  • handling continuous currents from 1
  • 2A to as high as 200A and
  • max. switching currents ranging from 12A to 100A, and
  • featuring min. contact gaps from 1.5mm to 4.6mm.
Since its inception, ZETTLER NEW ENERGY SOLUTIONS product design and engineering staff has proactively anticipated the PV inverter industry’s desire to replace space and power consuming, relatively expensive contactors with increasingly smaller and more energy and cost efficient PCB relays.

ZETTLER Europe was one of the first companies to have successfully developed and produced a 35A and 50 A PCB solar relay (AZSR235/250) with a footprint of just 25mm x 40mm and the capability of handling 2 x 35A (50A) at a holding power of only <100mW.

As pertinent safety standards such as IEC 62109, UL 62109 and DIN VDE V 0126-1-1 gradually evolved and internationally converged, additional capabilities of solar relays deployed in solar inverter applications became necessary to fulfil ever higher isolation requirements, which – in turn – continued to raise the bar, especially with respect to wider contact gaps.

For example, for inverters deployed at altitudes from 3000m of up to 4000m above sea level, contact gaps of at least 2.32mm became a standard requirement.


Equally importantly, as the demand for higher kVA capacities of solar inverters continues to expand, higher continuous and maximum switching currents need to be accommodated by relays used in these applications.

Here again, ZETTLER has remained at the forefront of these developments and, in close cooperation with its inverter producing customers, has engaged in the development of 80A, 120A and 200A solar AC relay products.

Some of these developments required completely innovative design approaches, as not all relays can be structurally modified to achieve widening contact gaps, while handling ever increasing current flows and also being capable of accommodating demanding, and sometimes arbitrary inverter-design driven specifications.

ZETTLERs 200A AZSR1200 solar relay is a perfect example.

In close cooperation with one of our leading PV inverter industry customers, and with a great amount of research and testing, ZETTLER has developed a patent-pending contact system that works without the otherwise usual contact springs and is able to effortlessly overcome the reset force, or to move it in the first place.

In the AZSR1200 the conventional contact spring was replaced by several highly flexible copper strands that are suspended from a ‘gallow’-shaped device, requiring little to no initial spring tension. Only negligible amounts of friction and the elasticity forces of the copper strands have to be overcome to move the 200A contact into its operating position.
This approach allows peak operating and holding power performances to be achieved; with a low holding power of only 0.6W (also suitable for PWM), this 200A PCB relay has entered a dimension that was hardly imaginable just a few years ago.


ZETTLER AZSR1200 contact system

An additional significant advantage of this innovative contact configuration is the avoidance of contact welding risks that are often associated with short circuit currents in conventional contact spring solutions. The magnetic force between parallel contacts springs, created by short circuit currents, usually pushes the contacts apart and causes them to open which frequently leads to contact welding and relay damage.

With the AZSR1200 contact system the opposite occurs: the stronger the surge current, the more the contacts are pressed together. Even temporary short-circuit currents of up to 3000A, therefore, would not pose any welding risks for the relay contacts.

An equally innovative engineering approach was applied in the development of AZSR180, a single pole AC side 80A solar relay that features a thermally conductive copper bridge, riveted directly behind the contact studs of two movable parallel contacts. This patent pending ‘thermal bridge’ allows the two parallel contact springs to be thermally ‘connected’ which, in turn, provides for a more even-leveled distribution of any excessive heat between the two contacts that can result from a significantly uneven distribution of currents carried in one vs. the other contact. Uneven resistances and currents in parallel relay contacts are not uncommon.

Even in the highly critical instance of a total failure of one of the two parallel-connected contacts, in which one would be completely isolated while the other would have to carry the entire current in a severe overload condition, the ‘thermal bridge’ of the AZSR180 will prevent the extreme overheating of the latter contact that would inevitably result in the destruction of the entire relay.


The above mentioned design elements of both the AZSR1200 and AZSR180 relays have also been combined in our most recent development, the AZSR1120 solar relay, a single pole AC side 120A relay that requires only about 40% of the volume space of the 200 A solar relay, yet still performs with very favorable, low self-heating characteristics.

These are just a few examples for ZETTLERs approach to finding innovative and intelligent engineering solutions for our partners in the solar inverter industry.