External 24 Volts as the Power Source

External 24 Volts as the Power Source

As previously discussed, the Model 45 can be powered by a source of 24 volts DC. A “locking” 2.1 x 5.5 mm coaxial power jack is located on the back panel of the unit.

The center pin of the jack is the positive (+) connection. While the requirement for the external source is nominally 24 volts, correct operation will take place over a 20 to 28 volt range. The Model 45 requires 750 milliam- peres for correct operation. (Approximately 500 milliamperes of this current is used for the 2-wire party-line intercom power source feature.)

Included with each Model 45 is a universal mains input/24 volt DC output power supply. The power supply’s DC output cable has been terminated with a Switchcraft® S760K coaxial power plug. This “locking” type of plug correctly mates with the Model’s 45’s 24V DC IN jack. The locking feature is im- portant, allowing the external power source to be securely attached to the Model 45.

A detachable mains cord is used with the power supply’s 3-pin IEC 320 C14-type inlet connector. Included with each Model 45 is a mains cord with a North-American (NEMA 15L) standard plug on one end and an IEC 320 C13-type connector on the other. Units intended for use in other desti- nations require that the appropriate cord set be obtained from the dealer or distributor.

Using the Connected 2-Wire Party-Line Circuit as the Model 45’s Power Source

The connected 2-wire party-line intercom circuit can be used to provide the Model 45’s operating power. The acceptable volt- age range is 24 to 32 volts DC, with a re- quired current draw of 175 milliamperes. Note that for the Model 45 to be powered by the connected 2-wire intercom circuit

configuration DIP switch 1 must be in its on (up) position. Please refer to the Con- figuration section of this user guide for additional details.

Before blithely going ahead and powering the Model 45 with a party-line circuit, it’s important to review the possible pitfalls of this arrangement. First of all, compared to most intercom belt packs the Model 45 is a power “hog,” requiring the aforemen- tioned 175 milliamperes of DC current for operation. The other requirement is that the supplied voltage must be 24 volts or greater as measured directly at the Model 45’s 2-wire (PL) connectors. Whether the connected party-line intercom circuit can provide this much energy will depend on the characteristics of a specific installation. The relevant factors include the capacity of the intercom power supply, the number and type of connected user devices, and the length and type of the interconnecting cables.

The capacity of the intercom power sup- ply must meet or exceed the needs of the connected user devices, including the Model 45. It’s a good idea to perform a calculation of the total maximum current draw prior to attempting to install and use the unit. As a real-time confirmation often these power supplies have status indica- tors that can provide a direct indication of their ability to supply the connected loads.

In many cases the length and type (gauge) of the interconnecting cable will be the limiting factor as to whether the intercom circuit can provide adequate power for a Model 45. This is because the intercom circuit’s DC voltage will drop in direct relation to the length of the intercon- necting cable. And with the Model 45’s relatively large current draw this voltage

Model 45 User Guide	Issue Preliminary 2, March 2009
Studio Technologies, Inc.	Page 15