Assa Model 34 - Manual (Page 18)

Rev. A.5, 8/03 Page- 15
wires, while observing correct polarity. The lock, however, automatically detects whether it is
receiving 12 or 24 volts and draws the correct amount of current for that voltage (the current is
twice as high when the lock is receiving 12 volts than when it is receiving 24 volts). The model
32 series has separate models for 12 and 24 volt operation.
It is good practice to use power supplies with 1/3 extra capacity beyond the current
requirements of the load. This greatly reduces the possibility of heat induced power supply
failure and also allows for future expansion. Power supply cost is a small fraction of the job cost
and should not be skimped on.
Switches may be wired as necessary between the Magnalock and power source. Internal
circuitry eliminates inductive kickback, so neither electromechanical switches nor solid state
devices will be damaged by arcing when the Magnalock is shut off.
3.3 AVOIDING POOR RELEASE CHARACTERISTICS
One of the exceptional features of Magnalocks is near instantaneous release. This is
particularly valuable when the lock is being switched off and the door is being opened at the
same time as occurs when a switched exit device like Securitron’s Touch Sense Bar is being
used. Two separate wiring errors can however cause Magnalocks to release slowly (in one or
two seconds) and this is annoying.
The first problem is connection of a reverse diode in parallel with the lock's power input.
This is often done to suppress inductive kickback from a coil such as a relay coil or solenoid.
Magnalocks already have internal inductive kickback protection, so addition of a reverse diode is
pointless. The diode does act to "recirculate" current flow through the magnet coil and thereby
considerably slows release. A diode should never be connected as shown in Figure 14.
The second problem is when any load is operated in parallel with the Magnalock. A good
example would be adding an incandescent lamp in parallel with the lock so that the lamp would
be illuminated when the lock is powered. The lamp acts like a resistor and allows current
recirculation which will greatly slow lock release time. When you want to add a resistive load in
parallel with the lock, you must put a forward diode in series with the resistive load. This
will block recirculation and restore quick release. Correct practice is shown in Figure 14 below.
A special case exists when you use an LED connected in parallel with the Magnalock (to
show that the Magnalock is on for example). This does not slow release as the LED does not
allow recirculation but the limited recirculation energy will eventually burn out the LED. LED’s
are susceptible to even a tiny amount of reverse voltage. Therefore add the forward diode as
you would with an incandescent lamp (see Figure 14) to extend the life of the LED.
FIG. 14: WIRING CONSIDERATIONS TO AVOID SLOW RELEASE
MAGNALOCK
RED
BLACK
NEVER CONNECT PARALLEL
REVERSE DIODE AS SHOWN
MAGNALOCK
RED
BLACK
USE A FORWARD DIODE WITH ANY PARALLEL
RESISTIVE LOAD SUCH AS A LAMP
3.4 WIRE GAUGE SIZING
If the power supply is distant from the lock, voltage will be lost (dropped) in the connecting wires
so that the Magnalock will not receive full voltage. The following chart shows the minimum wire
gauge that will hold voltage drop to an acceptable 5% for different lock to power supply
distances
. Proper use of the chart assumes a dedicated pair of wires to power each
Magnalock (no common negative). Note that a Magnalock operating on 24 volts is a much
better choice for long wire runs as it has 4 times the resistance of a 12 volt installation. Also
note that the correct calculation of wire sizing is a very important issue as the installer is
responsible to insure that adequate voltage is supplied to any load. In multiple device