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Relay arcing can be avoided using RC snubber circuits.

Snubber Circuits to Prevent Arcing in Relay Contacts

Which of these topologies is the most effective in preventing relay contacts from sparking and fusing? We discuss the many types of snubber circuits using resistor/capacitor, diodes, and varistors in detail.

Relays that control DC loads are often ideal when they have a diode snubber; relays that use RC components or work with resistor and capacitor networks come in second. However, a varistor or RC network tends to be the most efficient in an AC circuit.



The CR type Snubber is one sort of surge suppressor.

Circuits of both DC and AC can use this type. When using the relay to supply the AC voltage, the load impedance must be lower than the RC circuit impedance. Current will start flowing to the inductive load through the snubber as soon as the contacts open.

Consider that the release time of the relay contacts will be lengthened if the load is a motor or solenoid.

How to Choose the Capacitor and Resistor Values

For each 1 V of contact voltage, you can select a resistance value between 0.5 and 1. Since these numbers depend on a variety of variables, such as the load characteristics and variances in characteristics.

By doing experiments, you may confirm the values for R and C.  When the contacts are opened, the capacitor prevents discharge, and when they are closed, the resistor stops current flow. Therefore, selecting a capacitor with a dielectric strength of 200 to 300 V is advised.

Choose a capacitor with no polarity for an AC circuit.
Connect the snubber across the contacts rather than the load if there are any questions about the capacity's ability to stop arcing at the contact when utilising high DC voltages.

Snubber for diodes

When a diode is parallelly coupled to an inductive load, the electromagnetic energy contained inside it is channelled as current through the diode. The resistance from the load then causes the current to dissipate as Joule heat. The contact release time increases in circuits of this type.

How to Choose a Diode

This kind of suppressor uses a diode parallel to the induced load. Due to the diode, the electromagnetic energy trapped in the inductive load will reverse and dissipate as heat.

Compared to the RC network type, this form of suppressor lengthens the release time more.

The explanation is that an ideal diode has a forward current that is greater than the specified load current and a reverse breakdown voltage that is more than 10 times the circuit voltage.

As a result, it guards against excessive arcing when the contacts open.

Snubber diode type, diode +Zener

The circuit will shorten the time it takes for the relay contact to disengage when a Zener diode and a diode-type suppressor are connected in series. This frequently occurs when a diode's release time is extremely slow.

Additionally, this kind of suppressor is better for a DC network than an AC circuit. The breakdown voltage of the Zener diode is roughly equal to the supply voltage in terms of magnitude.

Snubber-type varistor

Both AC and DC circuits can be used with this style of suppressor. By utilizing the constant-voltage characteristics of the varistor, the varistor circuit prevents a large voltage from being transmitted over the contacts.
Additionally, the release time is comparatively longer with this kind of circuit. When the varistor is connected across the load with a supply voltage of 28 to 48 V, it can operate effectively.

For efficient suppression, you must connect the varistor across the contacts if your supply voltage ranges from 100 to 240 V.

How to Choose the Type of Varistor

You must first ensure that the cut-off voltage VC is multiplied by 2 in order to choose a decent varistor. If the value exceeds 1.5 times the supply voltage, more testing is required.

Remember that raising the VC too high will impair its efficiency and prevent it from effectively cutting off high voltages.

Surge suppressors should not be used with the following systems.

The configuration is quite effective at reducing arcing if merely a capacitor is attached across the relay contacts. The large electrical charge that the capacitor stores when the contacts are open, however, causes the current to flow to the contacts once more when they are closed. This will eventually lead to contact welding.

Another configuration allows connecting the capacitor in parallel and across the loads. This set up is particularly effective in minimising relay contact arcing during opening. On the other hand, instant contact welding might eventually happen because the charging current to C drives into the contacts while they are closed.

Switching a DC inductive load is typically thought to be more challenging than switching a resistive load. But with the right contact protection circuit, it is possible to attain the same degree of efficiency with both kinds of load.








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