1.) Introduction

Characteristics of Solid State Relays

- No mechanical parts

- Galvanic separation between control and load circuit by opto-coupler

- Semiconductor components like tnacs, thynstors, alternistors or MOS-FET's in the output

- Function comparable to electromechanical relays

Advantages of SSR's against Electromechanical Relays

- Nearly unlimited life expectancy

- Low control power, direct interface to microcomputer or PLC

- Zero crossing or random switching versions available

- No contact bounce

- No sparks

- No mechanical contact wear

- Insensitivity to shock, vibration and mechanical forces as well as severe environmental conditions

- GUNTHER thyristor SSR's are manufactured using DCB-technology (direct copper bonding) and are approximately 100 times more resistive to temperature cycles than conventional SSR's

2.) Switching Types

GUNTHER Solid State Relays are available in two different switching types

Zero Cross Switching (Z-type SSR's)

After switching on the control voltage the SSR switches through within the next zero crossing of the load voltage. This switching type is suitable for resistive, capacitive and slight inductive loads.

Random Switching (R-type SSR's)

After switching on the control voltage the SSR switches through without any delay. This switching type is suitable for inductive loads, e. g.  motors and magnet valves

3.) Protection Circuits

RC-Snubber

A RC-snubber limits fast load voltage changes (e. g.  caused by inductive loads) at the load terminals. Solid State Relays either with or without an integrated RC-snubber are available as listed in the technical data.

Diode

Solid State Relays for DC loads have no internal contact protection A diode or a RC-snubber for semiconductor protection must be connected externally and is recommended for inductive loads

Fuses

To protect Solid State Relays the use of semiconductor fuses is recommended. To determine the suitable semiconductor fuse the max load integral I2t is listed in the technical data for every Solid State Relay. The value of the semiconductor fuse should be smaller than the maximum load integral I2t of the Solid State Relay

Varistor

The varistor conducts overvoltages and protects the output semiconductor of AC-SSR's (triac, thyristor, alternistor) against destruction. The use of varistors is recommended - the suitable varistor type is listed in the technical data

With Reversing Relays WG A0 a varistor is always recommended, because with reversing inductive loads (such as motors) the blocking voltage of the thyristor is easily exceeded

In order to prevent unintentional contact with the terminals, a plastic protection cap for the Solid State Relays WG A5, WG 280, WG 480, WG A3, WG AO and WG F is available.

4.) Approvals

UL,CSA,VDE

GUNTHER Solid State Relays have been developed according to the regulations of UL CSA and VDE and are tested according to their requirements. Many of GUNTHER SSR's are already approved by these institutions, applications for approval for the remaining series are in process (see listed approvals in the data sheet)

CE-Mark

All chassis mounting SSR s WG A5, WG 280, WG 480, WG A3, WG A0 and WG F carry the CE-mark and comply with the EU low voltage directive 73/23/EEC. Compliance with other directives is not implied. The SSR's are components which may only be incorporated into a device which meets the requirements of relevant directives

5.) Cooling

When the Solid State Relay is switched on there is a voltage drop at the output semiconductor. The load current multiplied by this voltage drop causes power dissipation and thus a thermal rise in the SSR. Therefore it is necessary to use a heat sink to prevent damage to the SSR. A derating diagram for each SSR is given on the applicable data sheet. The following is an example of how to select a heat sink for a chassis mounted AC relay using these diagrams. The load current is 9 A and the ambient temperature is 50°C

Use heat sink with 2,5 K/W

Draw a vertical line in the left diagram from the desired load current (9 A) up through the curve.

b ) Where the vertical line intersects the curve, draw a horizontal line extending across both diagrams.

c ) The power dissipation is indicated at the left end of this line, 9 Watts in this case

d ) Draw a vertical line in the right diagram from the specified ambient temperature (50 °C) up through the horizontal line drawn in b 

e ) The intersection point indicates the minimum value of thermal resistance a heat sink must have to prevent damage to the SCR, 2,8 K/W in this case

f) The required heat sink must be rated at less than 2,8 K/W. Therefore select the GUNTHER heat sink rated at 2,5 K/W

Should the thermal resistance for your application fall below the line noted "without heat sink" no heat sink is required

DC chassis mounted SSR's have a slightly different derating diagram as shown on the data sheet. To find the required heat sink draw a horizontal line for the output current and a vertical line for the ambient temperature. The intersection point indicates the minimum value of the thermal resistance as in e. (above). Follow f. to select the correct heat sink

A heat sink cannot be used for PCB mounted devices, but derating curves are shown for them. Follow the steps above. If the intersection point falls above the curve in the right diagram you cannot use the relay for the application parameters you plotted

On-off cycles longer than one minute cause greater than normal temperature differences in a SCR. For these applications, derate the thermal resistance found in e. (above) by an additional 0,75. In the example above, a heat sink with a thermal resistance of 2,1 K/W is required. Therefore you should select the GUNTHER heat sink rated at 1,6 K/W

Heat sinks

The available GUNTHER heat sinks are listed on pages 43 - 45. All of them are assembled with 35 mm snap-on-rail mounting and should be mounted in a vertical position. Furthermore it is very important that air circulation is not impeded

Conducting Paste

The Solid State Relays should be mounted with conducting paste between the heat sink and the SSR baseplate to ensure maximum thermal conductivity. Firm mechanical mounting is very important

Overvoltages

The voltage across the semiconductor in the output of the SSR may not exceed the rated blocking voltage. Overvoltage protection is integrated in some SSR's as listed in the technical data. All AC-SSR's have a RC-snubber in the output. Moreover, varistors or further RC-snubbers can be switched parallel to the output, if needed (see also protection circuits)

Overloading Through Excessive Currents The current through the SSR must remain within the specified limits. It is important to note that the inrush current can often drastically exceed that of the nominal current, e. g. with motors 5-10 times and with lamps 15 - 20 times higher current. The choice of the SSR should be made with reference to these criteria

7.) Parameter Definition Control Voltage Range, Turn-Off Voltage. The listed control voltage range indicates the operating input voltage. Below the turn-off voltage the SSR must be switched off. Between the minimum control voltage and the turn-off voltage the range is not defined

Input Resistance, Control Current

Inside most SSR's constant current sources exist which operate the opto-coupler. This means that the input resistance changes continuously over the control voltage range. The maximum control current is listed for the maximum control voltage

Load Voltage Range

The listed load voltage range indicates the operating voltage for proper operation of the SSR

Peak-Off State Voltage

Maximum peak voltage on the load terminals to prevent destruction of the semiconductor component

Off-State Leakage Current

This current flows through the load terminals during the off state of the SSR

Load Current Range

The minimum and maximum continuous load current with appropriate cooling of the SSR

Surge Current

Maximum current for a defined duration of one sine half wave without destroying the semiconductor component.With the maximum surge current the chip reaches the maximum junction temperature in this time. In the technical data the maximum surge current (valid for one sine half wave at 50 Hz) for every SSR-type is listed

Maximum Load Integral I2t Value indicates the necessary semiconductor fuse for contact protection

On-State Voltage

Effective voltage drop over the load terminals with control voltage on and maximum load current

Off-State (static) dv/dt The maximum allowable rate of voltage rise across the output terminals

Turn-On Time The maximum time duration until the output is switched on

Turn-Off Time The maximum time duration until the output is switched off

8.) GUNTHER Solid State Relays SSR's for AC Loads and PCB Mounting

WGA4..

This type offers high component density on the PCB with a maximum load current of 2 A

WGA8...

This series is especially developed for PCB mounting with very small dimensions and load currents of 3 A or 5 A. There are SSR's with 600 V peak-off state voltage (load voltage max 280 V AC) as well as types with 1200 V peak-off state voltage (load voltage max 530 V AC) available. Moreover the WG A8 are available in zero cross switching (Z-types) for resistive and capacitive loads or in random switching (R-types) for inductive loads

WG A5...... (Hockey Puck Housing)

This relay is especially suited to switch resistive loads as in heaters and lamps

WG 280 ..... (Hockey Puck Housing)

This relay is designed to switch inductive loads like electric motors and valves (R-type) as well as resistive loads like heaters and lamps (Z-type). High current devices up to 90 A are available

WG 480 ..... (Hockey Puck Housing)

For switching applications in three phase systems the GUNTHER SSR series WG 480 offers excellent reliability due to high noise immunity (maximum peak-off state voltage 1200 V) and extremely good dv/dt characteristic. Some types have internal over-voltage protection (see data sheets) This relay is available in both Z- and R-types

WG A3 .... (Maxi Puck Housing)

This series is able to switch three phase loads with one control signal up to rated line currents of 45 A and line voltages up to 480 V AC. The WGA3 has high noise immunity (maximum peak-off state voltage 1200 V) and internal overvoltage protection which becomes effective at approximately 1000 V

WG AO .... (Maxi Puck Housing)

This series is recommended for electronic motor reversing in three phase systems Load voltages up to 400 V AC and load currents up to 45 A can be switched A built-in interlocking circuit with a typical change over switching time of 60 ± 20 ms prevents simultaneous switching-on of forward and reverse functions and prevents a short circuit between two phases.An LED indicates the forward and reverse function

WG F8 ...

The WG F8 are for PCB mounting and DC loads and have a MOS-FET in the output. This series is suitable for resistive, capacitive and inductive loads. With inductive loads a protection circuit like a diode or a RC-snubber is recommended

WG F .... (Hockey Puck Housing)

The WG F are for chassis mounting and DC loads and have a MOS-FET in the output. The electrical data are the same as for the WG F8, but with a higher load current