Solid State Relay in Gujarat, India.

Frequently Asked Questions


Solid State Relays(SSR) a relay with Isolated input and output whose functions are achieved by means of electronic components without the use of moving parts- NARM(USA) It is a static Switch.


Their construction is different. No coils , armature and metal contacts. Functionally both do the switching function but are noiseless, arcless switches.


Initial cost is high, but in the long run, it works out economical due to long life.


May be 3-4 times for the lower currents and 2 times for higher currents (this comparision is with standard makes).


SSR's are highly reliable, consumes less power, switching can be controlled electronically,can be operated in harsh environment.


Yes they are avaible in 'NC' configuration.


No. Technical limitaions inhibit this configuration.


Series and Parallel connections are possible, but is not recommended by ERI as the characteristics of the semiconductors vary from one device to other.Higher voltage can be achieved by connecting the o/p two SSR's in series.


Good Question! Normally this is a misunderstanding.The relay cannor give any o/p on it's own. It is only a switch , which can operate using the external power supply.


You can switch Resistive, Inductive and Capacitive loads.


Resistive loads: Lamps, Heaters, resistors etc., Inductive loads: Motors, Solenoid coils, transformers, magnetic clutch etc., Capacitive loads: Capacitors, Power capacitors etc.


Make sure to use an external heat sink for load current more than 3 Amps. Apply heat sink compound to he base of the SSR before mounting it on the heatsink.

What is the soft-start function?

The soft-start function is a function that gradually increases Solid-state Relays output using phase control until it reaches 100%. It is applicable to Solid-state Relays with AC outputs and allows a smooth startup by suppressing the starting current.
This function is effective for applications with motors and halogen lamps.

What is the difference between phototriac and photocoupler isolation for the G3NA Solid-state Relay?

The applicable output load voltage range is different.
Solid-state Relays with a zero cross function using a photocoupler can operate with a small input current because they have very good coupler transmission efficiency.
Photocoupler Input Current Phototriac Input Current
The input current for a phototriac is greater than that for a photocoupler, but that doesn't necessarily mean it must be a selection criteria for the type of Solid-state Relays. Other parameters can be used as a basis for selection.

Does the input current change for Solid-state Relays with a wide rated input voltage?

In Solid-state Relays which have wide input voltages (such as G3F and G3H), the input impedance depends on the input voltage and changes in the input current. For semiconductor-driven Solid-state Relays, changes in voltage can cause malfunctions in the semiconductor, so be sure to check the actual device before usage.
This is not the case for Solid-state Relays with DC inputs that use a constant current input method (such as G3NA and G3PA).

Why is a switching time lag necessary for the forward and reverse operation of a three-phase motor?

The forward and reverse operation of a three-phase motor is conducted by switching two phases. If the Solid-state Relays for forward and reverse operation are switched ON simultaneously, a phase short-circuit will result through the two Solid-state Relays, causing the Solid-state Relays to breakdown.
Also if the forward and reverse Solid-state Relays are switched over immediately, both Solid-state Relays could become ON at the same time because the Solid-state Relays reset time varies by up to a half cycle, which would cause the Solid-state Relays to breakdown.
When an Solid-state Relays is turned OFF, counter-electromotive force may be generated from the motor and cause a malfunction. If this occurs, it is necessary to increase the time lag between switching.
Make sure that there is a time lag of at least 100 ms.

What is counter-electromotive force (surge)?

Counter-electromotive force is the voltage that arises in the reverse direction when the switch is set to OFF with an inductive load using a coil. As shown in Figure 1, flux is generated when voltage is applied to the coil.
When the switch is set to OFF again, there is no more flux, but the coil's self-induction action causes counter-electromotive force to be generated in the direction where flux remains. A very high voltage is generated because the switch is already open and there is no place for the power arising from the coil to escape to.
Counter-electromotive force may cause contact wear and element damage. Use caution when using coil loads. As shown in Figure 2, both the power supply voltage and the counter-electromotive force will be applied to the open switch.

We think a Solid-state Relay (SSR) is faulty. Can a voltage tester be used to check an SSR to see if current is flowing?

No, that is not possible.
The voltage and current in the tester's internal circuits are too low to check the operation of the semiconductor element in the SSR (a triac or thyristor). The SSR can be tested as described below if a load is connected.
Connect a load and power supply, and check the voltage of the load terminals with the input ON and OFF. The output voltage will be close to the load power supply voltage with the SSR turned OFF. The voltage will drop to approximately 1 V with the SSR turned ON. This is more clearly checked if the dummy load is a lamp with an output of about 100 W.
(However, the capacity of the lamp must be within the rated range of the SSR.)

What kind of applications can Power MOS FET Relays be used for?

1.Applications where it is not known whether the load connected to the relay is DC or AC.
Example: Warning output for a robot controller
2.Applications with high-frequency switching of loads, such as for solenoid valves with internally, fully rectified waves, where another type of relay (e.g., G2R General-purpose Relays) would need to be replaced frequently.
Power MOS FET Relays have a longer lifetime than other Relays and so the replacement frequency is lower. The terminals of G3RZ Power MOS FET Relays are compatible with those of the G2R-1A-S and so these models can be easily exchanged.
Note:Be sure to confirm the input voltage, polarity, and output capacity.
3.Applications with high-voltage DC loads.
To switch a 100-VDC, 1-A load with M2XP General-purpose Relays or equivalent is required. With G3RZ Power MOS FET Relays, however, switching is possible with this size of relay.
4.Applications where otherwise a Solid-state Relays would be used with a bleeder resistance.
The leakage current for Power MOS FET Relays is very small (10 μA max.) and so a bleeder resistance is not required.

What should be done about surge-absorbing circuits for AC-load Solid-state Relays?

Measures against AC Switching Solid-state Relay Output Noise Surges
1.The Solid-state Relay has a built-in snubber circuit to smooth out a sudden rise in voltage. If there is a large voltage surge in the output-side AC power supply, the snubber circuit will not be sufficient to suppress the surge, and overvoltage will damage the output elements.
2.The following models have a built-in surge-absorbing varistor:
G3NA, G3S, G3PA, G3PB, G3NE, G3J, G3NH, G9H, G3DZ (some models), G3RZ, G3FM
3.Be sure to take measures against surge when switching an inductive load with an Solid-state Relay that does not have a built-in surge-absorbing element. (Refer to the following figure.)
Note:A separate varistor with a surge resistance higher than the built-in varistor must be mounted externally if influence is possible from noise that is not completely absorbed by the built-in varistor (surge resistance: 700 to 1000 A).

What is bleeder resistance?

Bleeder resistance is resistance connected in parallel with the load so that the load current appears to increase in order to correctly switch microloads.

Why do Solid-state Relay load Relays sometimes hum?

Leakage current flows when the Solid-state Relay input is OFF. If a small Relay is driven, this Leakage current may cause the Relay coil to become slightly energized, which results in a humming sound being produced.
Insert bleeder resistance in parallel with the Relay coil to eliminate any humming. The same effect as bleeder resistance can also be obtained by connecting multiple Relay coils in parallel or connecting the Relay coil in parallel with another load.

What is the zero cross function?

The zero cross function causes the Relay to turn ON when the AC load power supply approaches 0 V to suppress noise generated when the load current rises suddenly.
There are two types of noise: noise on power lines and noise emitted into open spaces. The zero cross function is effective against both types of noise.
A very large inrush current flows when lamps and similar equipment are turned ON, but the zero cross function causes the load current to always flow from a point near zero so that inrush current can be suppressed more compared to Solid-state Relays that do not have the zero cross function.
Ideally, the function turns ON near 0 V, but restrictions in the circuit configuration cause it to operate within the range of 0 V ±20 V. This voltage is called zero cross voltage.

What is a snubber circuit?

A snubber circuit is a circuit consisting of a resistor (R) and a capacitor (C) that prevents faulty ignition from occurring in the Solid-state Relay triac by suppressing a sudden rise in the voltage applied to the triac.

Can Solid-state Relays for DC loads be connected to a negative power supply?

Connections can be made in any of the configurations shown in the following diagrams.
If the load has positive and negative terminals, match the polarity of Solid-state Relays when connecting it.

Can a DC load be used with Solid-state Relays for AC loads?

No, it cannot be used. The element characteristics of Solid-state Relays will not allow it to reset if a DC load is used.
Explanation : Solid-state Relays for AC load switching use thyristors and triacs as output elements. By turning Solid-state Relays input ON, the output can be turned ON, but simply turning the input OFF doesn't mean that the output will be turned OFF. This is because Solid-state Relays have a characteristic that it stays turned ON until the load current becomes zero regardless of the absence of input signals into Solid-state Relays. The DC current will never become zero, therefore it will not be reset.

The Solid-state Relay (SSR) is too hot to touch. Does it have any trouble?

Although when the maximum current flows in the rated range, the temperature of the SSR reaches around 80 to 100 degrees, it is not abnormal.
However, pay careful attention to the heat loss. In general, when the ambient temperature is high, the value of switchable load currents decreases.
Switching elements in the SSR such as TRIAC, Thyristor and power transistor produce heat by having residual voltage (voltage lost inside a semiconductor when it turns ON).

Why is the minimum load current for most Solid-state Relays specified at 0.1 A?

For triac and thyristor output elements to stay ON, a small amount of current flow (called the holding current) is required. Considering the added effect of the ambient operating temperature, the output element may not be able to stay ON if the load current is less than 0.1 A. This may cause oscillations to appear in the output, or for it to not turn ON at all.
Solid-state Relays typically have less than 10 mA or leakage current at 200 V. To prevent the leakage current from causing load reset errors, the reset current is estimated to be at least 10% of the rated current, and the minimum load current is specified at 0.1 A.
For example, if a load with a rated current of 50 mA is used and the OFF leakage current is 10 mA, the load current would be 20% of the rated load. Depending on the load, this may cause a reset error.
Power MOS FET Solid-state Relays do not require a holding current, and feature small leakage currents. The minimum load current required for Power MOS FET Solid-state Relays to operate normally at 200 VAC is 100 µA.

Is it possible to connect Solid-state Relays in parallel?

Yes, it is.
Solid-state Relays are connected in parallel mainly to prevent open circuit failures.
Usually, only one of the Solid-state Relays is turned ON, keeping the other Solid-state Relay in the OFF state, due to the difference in output ON voltage drop between the Solid-state Relays. Therefore, do not connect two or more Solid-state Relays in parallel to drive a load exceeding the capacity of each Solid-state Relay. Otherwise, Solid-state Relays may fail to operate.
It is not possible to increase the load current by connecting the Solid-state Relays in parallel.
However, if an ON-state Solid-state Relay in operation is open, the other Solid-state Relay will turn ON when the voltage is applied, thus maintaining the switching operation of the load.

What is the relationship between the leakage current and the load voltage?

The leakage current increases proportionally with the load voltage. Refer to the following graphs.

What are the characteristics of a triac and thyristor?

Triacs and thyristors can switch the flow of an electricity supply. Solid-state Relays use this function to switch AC power. Solid-state Relays that switch AC power thus have the characteristics of triacs and thyristors.
They are different from power transistors or power MOS FETs, because they are semiconductor devices they cannot turn themselves OFF. They can be turned ON with a gate signal to supply current but simply turning the gate signal OFF will not stop the current. The element will remain ON until the current flow reaches zero.
This is an important aspect that must be considered to ensure safety in the system design, as well as the fact that semi-conductors are susceptible to breakdown caused by short-circuits.

What is the equation for calculating the heat radiated by Solid-state Relays?

The amount of heat radiated by Solid-state Relays can be found using the following equation.
Heating value P (W) = Output-ON voltage drop (V) x Carry current (A)
For example, if a load current of 8 A flows from G3NA-210B Solid-state Relays, the following heating value will be obtained.
P = 1.6 V x 8 A = 12.8 W

What is the difference between the input rated voltage and operating voltage for Solid-state Relays?

Rated voltage : The voltage that serves as the standard value of an input signal voltage. The voltage must be within this range.
Operating voltage : The permissible voltage range of an input signal voltage. The applied voltage may fluctuate within this range. Voltages outside this range cannot be used.

Solid-state Relays Output Short-circuit Malfunction 2: What cause an Solid-state Relays output to short-circuit?

An overcurrent flowed through the Solid-state Relays output and damaged the output elements.
Possible Causes :
1.A short-circuit occurred due to condensation, deterioration of load insulation, temporary short-circuit, or human error.
2.Solid-state Relays were connected to a load with high inrush current, or the current flow within the circuit configuration exceeded the rated withstand surge current for each Solid-state Relays.
3.A surge voltage was caused by the load power supply, or other loads connected to the load power supply line.
4.Solid-state Relays were used for an extended period of time in an environment subject to temperature increases.
The rated ON current depends on the ambient operating temperature, type of Solid-state Relays, and whether it has a heat sink. (Refer to information on the load current vs. ambient temperature rating for each Solid-state Relays.)
The heat radiation efficiency depends on how the Solid-state Relays were mounted to the control panel. (Refer to information on mounting Solid-state Relays.)

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