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A battery solenoid is a one designed for exclusive use with a direct current (DC) power supply. The term is somewhat of a misnomer though as a DC solenoid doesn't necessarily have to run from a battery and can be driven by any suitably-rated rectified DC supply. The battery solenoid differs little from alternating current (AC) types, both sharing most physical characteristics, applications, and output configurations. The main difference between the two types is the absence of a shading coil on the battery solenoid coil. This coil is designed to reduce the “chattering” in AC solenoids caused by the zero voltage points in the AC wave form and is not necessary in a DC solenoid.
The solenoid is certainly one of the most widely used of all the remote activation devices. A study in simplicity, the solenoid is cheap, efficient, and capable of producing surprisingly powerful output motion. Their simple efficacy centers around the fact that the solenoid generally consist of only two parts, one of which being a non-moving part. A static wire coil is wound onto a hollow cored bobbin with a moving metal plunger located near the entrance to the hollow. When a suitable electric current is applied to the coil, a magnetic field is formed around it that attracts the plunger, pulling it into the inside of the core, supplying the solenoid's output motion in the process.
The battery solenoid is, in most respects, identical to those designed to operate with AC power supplies. The only difference between the two is the addition of a shading coil on the coil's AC devices. This is simply one or two windings of the coil shorted out in such a way as to shift the current phase relation by 90 degrees in that section of coil. This supplies just enough magnetic retention force to prevent the plunger from continuously moving out of the coil, or chattering, each time the AC voltage cycles through its zero-volt point. The battery solenoid is designed to work on a DC supply that has a constant voltage level so that a shading coil is not necessary.
This characteristic of solenoid operation means that a device designed to work with an AC supply can be used with DC power, but not the other way around. In truth, a battery solenoid may be used with an AC supply, but will constantly chatter and eventually overheat, and, if left long enough, may suffer irreversible failure. This point requires careful attention when choosing solenoids for AC applications.
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