====== Relays ======
Electrical relays are devices used to **turn relatively heavy loads on/off**.  They are //triggered by small amounts of power// from an external source (usually a switch operated by the user) but //can pass larger amounts of power// to the load.  This reduces the cost and physical requirements of the switch and can help automate some processes.
A typical setup looks like this:  switch (and house power) --> relay --> load
The most common relay campers are exposed to is the solenoid for [[electrical:12v:alternator|charging house batteries from the coach's alternator]].  When the vehicle is turned on power activates the solenoid and connects the house and vehicle electrical systems.
Relays are also useful for powering loads from [[electrical:12v:lvd|LVD]] or [[electrical:solar:charge_controller|Charge Controller]] LOAD outputs.  This allows powering larger loads than the controller is rated for. 

Common uses:
  * battery isolation when [[electrical:12v:alternator|alternator charging]]
  * [[electrical:12v:lvd|low voltage disconnect (LVD)]]

===== normally open vs normally closed =====
Relays come in two basic types:  
  - **Normally Open (NO)** - the output circuit is open/incomplete when the relay is resting.  No power flows.  The controlled device is **off** until the relay is triggered.  //This is usually the default.//  
  - **Normally Closed (NC)** - the output circuit is closed/complete when the relay is resting.  Power flows.  The controlled device is **on** until the relay is triggered.
===== latching relays =====
Normally it takes power from the trigger source to operate the relay.  A latching relay, however, moves from position to position and locks there even when power is removed.