Relay Purpose ... ?

A relay is used for one of two purposes.

First: This is most common in automotive use... A remote switch sends a small current to the relay,, The relay can then switch a much higher current.

For example. 5 amps to the coil 100 amps to the starter (The Starter Solenoid is in fact a relay).

This also works when you are using a low current (power) transistor to switch a larger current (the blower motor on your furnace)

It can also be used for "Automatic transfer" two cases of this, One is the Auto-Transfer-Switch that selects either Shore Power or Generator power, the actual switch is a bank of relays.

or in a Magnnetek 6300 there is an isloator relay that isolates the battery and charger circuit from the converter circuit, a very bad design in my opinion.

But it is basically either a remote switch or a way to make a small current control a much larger current.

The most common failure mode is dirty/pitted contacts, followed by welded contacts and finally coil failure.

Hi 2ndhom,

Relays come in several types. Continuous duty and momentary are the most common. Most often in the house part of an RV the continuous duty type would be used.

They are just a big remote controlled switch.

2ndhom wrote:
I frequently read "check your relay" in threads here on the rvnet. I've read several Google explainations and still don't understand their function. In very simple layman terms ...... could someone explain? In my electrical bay they all look the same. Are they? Thanks.

on/off valve controlled by a small current and can be a long distance from the control.

Remote controlled switch

2ndhom wrote:
I frequently read "check your relay" in threads here on the rvnet. I've read several Google explainations and still don't understand their function. In very simple layman terms ...... could someone explain? In my electrical bay they all look the same. Are they? Thanks.

2ndhom,
Dale did a good, but technical job of explaining the function of a "relay". Well, in short, a relay does, just what the name implies. It "RELAYS" electricity from one point to another. It's nothing but a large switch. And, what you do, as Dale said, is use a small switch, to control, A LARGE SWITCH.

Many components need more power to operate efficiently or correctly. And, that means there's a need for larger wire to carry the current needed for those components. And, that also means a large type switch, to be able to handle switching such loads, on and off without damage to the switch. So, that switch, or "relay", is typically located under the hood or, any other place other than under the dash in the drivers compartment.

Then, there's a tiny switch, on or in your dash, that controls, that relay which, controls the larger current etc. to operate whatever high demand item it requested. Hope his and my explanation helps some.
Scott

A relay is basically just like a switch with added stuff to turn it on or off. There are two parts to a relay, a electric magnet and the switch part.

A relay can be used to switch something that has a heavy load such as head lights. A dashboard switch heavy enough to handle the power and not melt would be pretty bulky and wouldn't fit in the end of the turn signal.

So when you turn your head lights on a small switch sends low power to the relay coil which turns into a magnet that moves the switch to send power to the head lights.

Relays come in all shapes and sizes. The shore power transfer switch uses relays to switch between the generator or shore power. The engine starter solenoid is basically a relay. Be very careful swapping relays that may look alike. You really can't be sure the relays are identical unless you cross the model numbers. A turn signal blinker looks like a relay but works very differently. Swap it with a relay and you'll have lots of problems.

Did I confuse you more?