FAQ's

A relay is an electromagnetic device, within which an electro magnet is fixtured to cause controlled movement either by magnetic attraction or magnetic repulsion. Other hardware attached to the moving magnetic portion of the motor such as relay contacts will cause switching of electrical circuits.

The word “normally” refers to deenergized condition of the relay or the state of the relay when no power on the coil The second words “open” and “closed” refer to the position of the contacts at the deenergized condition.

We must express the load as a contact rating, which is the electrical load-handling capability of relay contacts under specified conditions and for a prescribed number of operations or life cycles.

Resistive Load: A resistive load usually consists of some sort of resistance in the circuit; e.g., heaters, resistors etc.

Inductive Load: An inductive load consists of a load created by a wire wound coil, such as in a relay, which uses a winding over a magnetic iron core. Breaking an inductive load is usually more severe than breaking a resistive load.

Motor Load: A motor load can be referred to as a rotating inductive load, generally with a high inrush of six times the normal load. The breaking of the load is much the same as a resistive load.

Lamp Load: The loads we normally concern ourselves with are tungsten filament lamp loads. Tungsten filament lamps when first turned on will draw an inrush current of 10-15 times of the steady-state current. The inrush is similar to a motor load inrush and is caused by the cold filament in the lamp. After the lamp filament has heated up, the current will drop to its normal level. Most tungsten filament lamp load ratings are 20% of a resistive load.

SPDT Relay : ( Single Pole Double Throw Relay) an electromagnetic switch, consists of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a) and one normally open terminal (87). When the coil of a SPDT relay is at rest the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and the normally open terminal (87) have continuity.

When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with the stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected. That is why we only sell diode relays, to those specifically requesting one.

SPST Relay: ( Single Pole Single Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30) and one normally open terminal (87). It does not have a normally closed terminal like the SPDT relay, but may be used in place of SPDT relays, in most places where only one thing needs to be switched.

Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes. We feel resistors are just as effective, for most automotive purposes, while maintaining the advantage of not being polar sensitive.

Anytime you want to switch a device which draws more current than is provided by an output of a switch or component you will need to use a relay. The coil of a SPDT or a SPST relay that we most commonly use draws very little current and the amount of current that you can pass through a relay common, normally closed, and normally open contacts will handle up to 40 amps. This allows you to switch devices such as headlights, parking lights, horns, etc., with low amperage outputs such as those found on keyless entry and alarm systems, and other components.