Document # MAN0001 Issue 4.29 Page 30 of 34
Power Supply Maximum Loads
The 12V DC supply should a have a capacity to run the electronics and locking device but also
current limit suitable for the cable being used. For 7x0.2mm cables, this would be approximately 1A
but check with your cable supplier.
Lock Suppression
It is important to check that the locking device is suppressed. Any electromagnetic device will
produce a Back E.M.F when power is removed. This can interfere with and even damage other
electronic equipment. Most good locking devices will already have suppression fitted. If not, you
should fit an appropriate suppression device across the coil.
In the case of solenoid operated locks, a flywheel diode will do. Connect the cathode to the positive
and the anode to the negative terminal of the coil. The diode will need to be rated at the full
operating current of the coil.
Do not use a diode for a mag-lock, as this will cause an excessive delay to the release of the
door. A MOV or VDR is a far better choice. Polarity is not critical, but make sure the rated voltage is
greater than the normal operating voltage of the lock.
A more detailed explanation of Back E.M.F. can be located at our website here:
https://progeny.co.uk/back-emf-suppression
Lock Cable Volt Drop
Figure 3 shows how the voltage at the locking device varies with cable length and core size.
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