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A relay that uses continuous, long-term current to the coil without normal switching operation will facilitate deterioration of coil insulation and characteristics due to heating of the coil itself. For circuits such as these, please use a magnetic-hold type latching relay. If you need to use a single stable relay, use a sealed type relay that is not easily affected by ambient conditions and make a failsafe circuit design that considers the possibility of contact failure or disconnection.
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Voltage going to the coil should be steady whether an AC or DC voltage. Noise can be introduced from external factors such as from the power supply powering the coil or from nearby equipment, which can sometimes cause issues regarding the set/reset pulse time of latching type relays. However, specifications differ for each, please refer to the relay’s individual specifications. If it includes ripple, the ripple factor should be less than 5%.
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If the relay has 2 coils, do not power them at the same time. When connecting coils of polarized relays, please check coil polarity (＋, －) at the internal connection diagram schematic. If any wrong connection is made, it may cause unexpected malfunction, like abnormal heat, fire and so on, and circuit will not work.
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If the coil voltage is equal to or greater than the maximum rated continuous voltage, the coil may burn or its layers short due to the temperature rise. Furthermore, do not exceed the rated usable ambient temperature range. Derating factors may have to be applied depending on environment and if operating at or near maximum values. The resistance/temperature relationship for copper wire is about 0.4% for 1 ℃, and with this ratio the coil resistance increases with temperature.
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Avoid excessive temperature fluctuations. Condensation occurs when the ambient temperature drops suddenly from a high temperature and humidity, or the relay is suddenly transferred from a low ambient temperature to a high temperature and humidity. Condensation causes the failures like insulation deterioration, wire disconnection and rust etc. The heat conduction by the equipment may accelerate the cooling of device itself, and the condensation may occur. Special attention should be paid when high temperature heating parts are close to the device.
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High temperature or high humidity levels or in atmospheres with organic gases or sulfide gases may cause a sulfide film or oxide film to form on the surfaces of the contacts and/or it may interfere with the functions.
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In terms of the packing format used, make every effort to keep the effects of moisture, organic gases and sulfide gases to the absolute minimum. A source of silicone substances (silicone rubber, silicone oil, silicone caulking compound, silicone-based coating materials, silicone based thermal pastes etc.) may emit volatile silicone gas (low molecular siloxane etc.) known as out-gassing, which is especially present in enclosed, high temperature, low pressure/vacuum, or humid environments. When silicone is used near a relay (or other switching mechanism), switching the contacts in the presence of its gas causes silicone to adhere to the contacts and may result in contact failure (silicone gas may penetrate into the inside of the relay through the plastic - in plastic sealed types, too). In this case, use a substitute that is not silicone-based. Otherwise, A hermetically sealed type sometimes referred to as “Sealed capsule type” is the only relay construction type protected for use around silicone being it is airtight and hermetically sealed.
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NOx Generation When relay is used in an atmosphere high in humidity to switch a load which easily produces an arc, the NOx created by the arc and the water absorbed from outside the relay combine to produce nitric acid. This corrodes the internal metal parts and adversely affects operation. Most relays to avoid use at an ambient humidity of 85 % RH or higher (at 20 ℃).
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Use the flux-resistant type or sealed type if automatic soldering is to be used.
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Although the environmentally sealed type relay (plastic sealed type, etc.) can be cleaned, avoid immersing the relay into cold liquid (such as cleaning solvent) immediately after soldering. Doing so may deteriorate the sealing performance. Cleaning with the boiling method is recommended (The temperature of cleaning liquid should be 40 ℃ or lower). Avoid ultrasonic cleaning on relays. Use of ultrasonic cleaning may cause breaks in the coil or slight sticking of the contacts due to ultrasonic energy.
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When switching inductive loads with a DC relay such as relay sequence circuits, DC motors, DC clutches, and DC solenoids, it is always important to absorb surges (e.g. with a diode) to protect the contacts. When these inductive loads are switched off, a counter EMF (electromotive force or electromagnetic field) of several hundred to several thousand volts develops which can severely damage contacts or circuitry and greatly shorten life. If the current in these loads is relatively small at around 1 A or less, the counter EMF will cause the ignition of a glow or arc discharge. The discharge decomposes organic matter contained in the air and causes black deposits (oxides, carbides) to develop on the contacts, this may result in contact failure.
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Known as “Icing”, condensation or other moisture may freeze the switch “ON” when the temperatures are lower than 0°C. This may cause problems such as fixing of the movable contact, operation delay, or interference of ice between the contacts, which may interfere with contact conduction.
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If switching of the mechanical relay contacts is synchronized with the phase of the AC power, reduced electrical life, welded contacts, or a locking phenomenon (incomplete release) due to contact material transfer may occur. Therefore, check the relay while it is operating in the actual system. When driving relays with timers, microcomputers and thyristors, etc., there may be synchronization with the power supply phase.
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As a guide, make the minimum pulse width in order to set or reset a latching relay at least 5 times the set time or reset time of each product and apply a rectangular-wave rated voltage. Also, please verify operation. Please inquire if you cannot obtain a pulse width of at least 5 times the set (reset) time. Also, please inquire regarding capacitor drive.
Source - Panasonic LQ Relays
Source - Panasonic Relay Cautions
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