Troubleshooting Power Supply and Electro Magnetic Field Issues in Electronic Access Control

Occasionally when installing access controls, things will not go the way you thought they ought to. Some call it a “bug” or a “ghost in the machine,” but your equipment is misbehaving. There are a number of possible reasons for this, and you...


Occasionally when installing access controls, things will not go the way you thought they ought to. Some call it a “bug” or a “ghost in the machine,” but your equipment is misbehaving. There are a number of possible reasons for this, and you need to determine exactly what breed of bug or...


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Occasionally when installing access controls, things will not go the way you thought they ought to. Some call it a “bug” or a “ghost in the machine,” but your equipment is misbehaving. There are a number of possible reasons for this, and you need to determine exactly what breed of bug or ghost you've got.

An accurate digital volt meter (DVM) is an essential tool for those involved in electronic access control.

 

POWER PROBLEMS

I prefer to clearly differentiate between power supply, which in my vernacular provides DC (Direct Voltage) and may also provide battery backup, and transformers, which step down a line voltage input to a low voltage output, usually 12 or 24 volts. Transformers can come in metal enclosures, or with wire pigtails, or in a wall-wart module. You should always use UL approved transformers and power supplies, and if the device is not supplied with a line cord, call in a licensed electrician to hook it up.

Power supplies are usually in metal enclosures, but are also available as separate modular components such as the regulator, rectifier and transformer, so that an advanced technician can create a custom setup for a particular application.

Depending on a number of considerations, it is typically preferred to use a separate power supply for your access control module and a separate power supply for your locking device.

 

Electronic access control problems can be divided into three basic categories:

1. Not enough power (to either the controller or the locking device, or both)

2. Excessive voltage drop in wiring

3. Wrong kind of power

You'll run into the “not enough power” problem when you're trying to operate too much equipment off a single power source, and the result is fluctuations in voltage level as the system is operated. It may be that your line voltage receptacle is not at proper level or you might not have selected the right power supply for the application.

When you overload a power supply, it can heat up: Obviously this is dangerous and must be avoided. Eventually excessive heating will result in a component failure in the power supply, a blown fuse or breaker, or a fire.

Overloading a power supply can also cause the power quality of the supply to suffer, which in turn can have a crippling effect on your system operation.

Excessive voltage drop occurs when the combination of the gauge and length of wire between the lock power supply and the electric locking device, and the power requirements of the electric locking device result in a drop in voltage at the locking device which results in the lock not operating correctly because it isn't getting adequate energy.

One typical problem will be when a valid credential is entered into the card reader or the REX (Request To Exit or also referred to as remote unlock) is activated, the door lock does not unlock for the time you programmed. Instead it will instead only momentarily activate, and then immediately relock.

TEST: When you disconnect the door lock and use a credential or the REX, the relay activates and times out properly. Remove the power and lock from the controller and place an ohmmeter on the contacts on the access controller you are using for switching the electric lock. The meter should also track as the relay changes state, and indicate pretty close to zero ohms in one position and infinity in the other. It depends on whether you're working with a failsafe or failsecure type locking device.

Electromagnetic locks are an example of a FAILSAFE locking device because if power is interrupted to the electromagnetic lock, it unlocks. A Von Duprin exit device with electric latch retraction is an example of a FAILSECURE locking device, because it has to be powered to unlock it, and if power is removed, it locks is a secure mode.

When you connect the lock directly to your lock power supply, the lock works properly; that is to say, it locks and unlocks when power is applied and removed. Assuming you did not bring the power supply over to the door or the lock over to the power supply for your test, and the power supply is in its permanent location, as is the door lock, then you are not dealing with voltage drop.

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