Following up on last week’s newsletter covering the battery master switch we look
at the solenoid.
The solenoid is a large heavy duty relay. It is basically an electric switch - when
power is applied to the coil it uses an electro magnet to close the contacts. These
contacts are large heavy duty contacts similar to the contacts in your starter motor
and can carry very high current.
Solenoids are used in starter motor circuits but are not the continuous duty type.
Continuous duty solenoids can be kept energized for extended periods, even days or
weeks at a time. This makes them ideal for battery isolator and accessory circuits,
they are simple and are still a preferred method of battery isolation for ‘old school’
The continuous duty solenoid has two main functions:
1) Battery isolation – Used to link or disconnect batteries.
2) Equipment switching – Used as a main power switch to accessories.
Battery isolation can be done with 3 types of isolators. a) Master Switch. b) Heavy
duty solenoid / relay. c) Smart Isolator also known as a VSR (Voltage Sensing Relay)
or Electronic Isolator.
Note: Diode Isolators are not recommended as they have a substantial voltage drop
and batteries do not fully charge.