If the relay is used at an ambient temperature exceeding the operating temperature range, the performance of the relay may be degraded and the life may be dramatically shortened.
 

The permissible maximum applied voltage of a given relay coil changes with ambient temperature. The coil temperature rise (the self-heat temperature, i.e., the applied-voltage-dependent portion) is the difference between the permissible temperature specified by relay design and the operating temperature.

Refer to the coil voltage vs. temperature derating characteristics in the Technical Documents for this value. An example is shown in Fig. 5.

The permissible temperature of relay operation is determined mainly by the coil wire and plastic materials used. In the case of the NEC Miniature Signal Relays, the standard specification is set at 120°C.

As the applied coil voltage increases, the operate time becomes shorter. However, the bounce in the make contacts becomes longer, increasing the contact opening or closing frequency. This may affect the life of the contacts.
 

When the temperature of the relay has risen due to heat generated by the coil being energized, the relay may not operate if the coil is de-energized and then immediately re-energized. This is because the coil resistance increases due to heat, causing the current to fall when applied voltage remains constant. This phenomena is called a hot start. This occurs when the operating temperature is high, and a voltage lower than the specified coil voltage is applied. It is necessary to refer to Technical Documents to know in advance the must operate voltage at a given temperature in order to prevent this phenomena.
 

In some circuits, the relay must not operate at a certain voltage or release at a certain voltage. Contact World Products for a product specification outlining non-must operate and holding voltages.
 

The relay will not operate correctly if coil drive waveform gradually increases and decreases. The voltage must instantaneously rise and fall as a pulse.
 

This voltage may damage the relay driver transistor, therefore a diode should be connected in parallel with each coil. With a single coil latching type relay a diode cannot be used because the current direction of the coil inverts, a transistor with sufficient reverse breakdown voltage should be used instead.
 

Inductive loads, such as solenoids and electromagnetic clutches produce a large energy discharge when the contacts open. A Zener diode should be connected with the drive transistor to prevent damage.

When a diode is connected in parallel with the coil, the current in the coil diminishes gradually when the relay releases. This may slow down the opening of the normally open contacts thereby increasing their wear.
 

If the contacts are opened or closed frequently with a high current load, repeated electric discharges may cause contact metal deposition or damage to the contact spring. When frequently switching a high current load consult World Products for technical data.
 

If the coil is energized for long periods of time the coil temperature may rise. This promotes the generation of organic gas within the relay. This can cause trouble with contact stability. When using a circuit that requires the coil to be constantly energized, consider the possibility of using a latching relay. Latching type relays do not require constant energy to hold the same operating state as the non-latching types.
 

When the same power source is used for both the load and relay drive circuits, care should be taken when switching a load with a high inrush current such as a lamp load. The source voltage may drop if the power source capacitance is small resulting in a case where, the relay may release or an oscillation phenomenon occurs.

Power source capacitance or a smoothing circuit should be added to prevent this phenomenon.