Relay

Just trying to understand what and why we use 5 pin relay for why cant we just use 4 pin relay instead of 5 pin relay what is making the difference in this system?

5 pin relays are often used as they are the more commonly found type of relay, and are usually cheaper. If you can do the job with a 4 pin relay, then there is not reason that you cannot use it.

The basic four pin is a solinoid power on, relay out on. Solinoid power off, relay out is off.

The basic five pin has an out that alternates with the other out. I don't recall the designations, off hand, but it's something like 87 and 87a for the two outs.

There are some applications where it's useful to have the relay turn off when the solinoid is on, and vice versa, or it makes it easier to change between two outputs using the same relay and a simple toggle switch to the solinoid - such as changing between pumps, switching between high and low beam headlights, etc.

Hi Gord,

The 5 pole with the 87 and 87a output pins is typically called a changeover relay, these can also be had with diode or resistor protection on the 85 and 86 pins.

Relays with both output pins labeled as 87 are dual output relays, these can also be had with diode or resistor protection on the 85 and 86 pins. The dual output relays can be had as a normally open or normally closed configuration, where the normally open relays need the activation circuit on the 85 and 86 pins to be energised to make the circuit, and the normally closed have a circuit that is broken when the activation circuit is energised.

I was trying to keep it simple for him, Steve - I agree there are many different relay types, depends on what one's application is.