Originally Posted by chev49
you are talking about a normally on solinoid, for those who dont know what that is. i think the cheapest ones start somewhere around 15 bucks or so. ..
Actually what you want to ask for is a continuous duty
unit. Continuous duty parts are designed to be on hours at a time to forever.
A solenoid actually designed for starter service might be what is called intermittent duty,
meaning it would be on for a short period of time to start the engine, and then turned off. Intermittent duty parts are not designed to survive being on all the time. But a starter solenoids might last, as battery charging current is a fraction of the engine start current. It would depend on the design of the activating coil windings if they could keep cool with constant current to hold the battery contacts together.
Relays and solenoids have their contacts in two classes:
Normally open (N.O.) contacts have no connection unless the relay is powered - what you want
Normally closed (N.C.) contacts are always connected unless the relay is powered
- what the parts man may think you want if you ask for "normally on."
Many relays and some complex solenoids have more than one set of contacts, and normally open and normally closed sets may be found on the same unit.
There can also be what is called a "common" (C) contact, which would connect to a normally closed contact until the relay is energized, and then connect to a normally closed one when power is applied. Automatic change-overs for AC gensets are like this. Usually, an RV shoreline is wired to normally closed contacts, the generator to normally open contacts, and the RV to common contacts which connect to one of the other two at any time. When the generator starts, its power is wired to energize the relay, disconnect the shorline's N.C. contacts, and connect the RV to the generator's N.O. contacts.