What is alternative current (VAC) and direct current (VDC)?
Usual ways to identify direct current are V-, VDC and DC. It is produced, for example, by batteries and power supplies. A voltage between the poles is generated and it makes the current remain constant along the time while flowing through the circuit and always in the same direction of movement.
A graphic representation of the electrical current signal into a graph would be as follows:
Alternative current can be identified as V ~, VAC or AC. It is generated in power plants and power supplies. In this type of current flow changes direction at 50 or 60 times per second (50Hz or 60Hz frequency) varying along time waveform (see chart). This kind of current is the one used in houses or industry.
As the graphic shows, the signal goes through 0 V (volts) 2 times and 2 times through the maximum voltage. The speed at which the wave is generated is so fast, that it is not noticeable, except by the blinking of fluorescent tubes (stroboscopic effect) and the buzz so characteristic of the VAC electric strikes.
The two main advantages of alternating current are its relatively economic transformation of voltage and lower power loss to carry the current over long distances.
How to know the kind of power that is being used?
DORCAS advises both installation and test being done by a professional, as safety is essential.
There are two ways to identify the kind of current, using a tester or by identifying the way it works.
– Using a tester.
First, plug the tip from black cord (-) to COM and the red one (+) to VMA.
– Put the knob in the position of current (V-). On the screen it will appear the kind of current being measured, in the case of a battery it would show 1.5 V. If the cords are connected opposite way of the battery voltage, it will show 1.5V.
Electric strikes adapted to this type of voltage are prepared to receive power for a long period of time, usually activated by switches and its power consumption is low. By contrast, generally they are not good at opening doors if it is applied pressure.
– Put the knob in VAC (V ~). On the screen it will show the current being measured permanently.
Electric strikes adapted for this type of voltage are prepared to receive power only for a short period of time, usually activated by buttons and their power consumption is medium / high. They usually are the best choice for situations where the door or users press towards the opening direction.
– Checking the installation.
– If the electric strike makes a buzz when it is activated, the installation is working with alternating current. On the contrary, if the sound heard is a dull thud an then silent even under electricity supply, it is direct current.
Why do I have to install a power supply?
Applicable law in force prohibits the installation of door openers with direct access to electricity network it should, inter alia, any electricle bypass could shock the user when he touches the door handle. Therefore only the installation below 48 V is allowed. DORCAS has a wide range of power supplies and electric strikes adapted for each type of voltage.
The electric strike emits a noise permanently
The installation was made with an AC power supply instead of a DC one. In the case the kind of current is the right one, it is possible that the element that cuts electricity is a conventional switch instead of a push button, or the access control is not set up correctly.
What is a delay action mechanism?
Delay action mechanism in an electric strike allows access to the door after a single electrical impulse, although this access does not have to be necessarily immediate. That is to say, the door stays unlocked from the time it is electrically fed until one user goes through the door.
In Dorcas have several categories of delay action mechanism for automatic function depending on the internal construction of the door opener:
– Traditional delay action mechanism (A) allows the door to remain open until access occurs. This way of working is made possible by a bolt on the front of the electric strike that is activated after an electrical pulse.
– Sliding delay action mechanism (Ab) is a new integrated feature into some of the most innovative DORCAS electric strikes. The bolt is replaced by a piece which moves integrally inside the adjustable flex jaw when it is adjusted according to the door latch. It allows the function to work effectively anywhere in the regulating range of the flex jaw.
– Built-in delay action mechanism (Aa) allows the electric strike to perform the delay action without any external mechanism or additional part, thanks to its internal construction. A brief electrical pulse for the proper work of this version is recommended.
What is it and how to install fail safe electric strike?
Fail safe function or 512/524 works using direct current and works in an inverted way, that is to say, stand by position of the electric strike is unlock. On the contrary, when it is electrically fed, it locks, as a result, the door gets closed. In case of a power failure the door changes to unlock position allowing to pass through it. This kind of function is recommended for escape routes in case of a fire emergency.
It works with a direct current power supply either 12 VDC or 24 VDC. Keep in mind that the more distance there is between the power supply and the electric strike mechanism, the greater the voltage drop is. For this reason it is suggested the power supply to be near the electric strike.
It must be installed with a switch or pushbutton inverted type (when pressed, the current is cut). If installed with access control, it has to be set to work inverted. If this feature is not available, it is needed to install a relay to regulate the flow of current to the mechanism directly from a power supply.
A replacement of an electric strike was done, however, the new one does not work properly.
The most common situations are:
– The electric strike to be replaced has a low consumption coil (many ohms) and the new one has a higher level of consumption, possibly more than the power supply or access control are able to provide.
– Actually, what the installation needs to be changed is not the electric strike, but the power supply, as it is what has stopped working properly.
– The new electric strike has a different setting and must be regulated. In that case it is recommended always to use the flex jaw version.
After some time working properly, the electric strike stops working
The most common reasons are:
– The electric strike has been recently installed, has few ohms (high consumption) and has been electrically fed for a long period of time, which has made it to become deteriorated. To identify it quickly, the electric strike smells like sour as it is burnt.
– The power supply has stopped working correctly.
– There is some dirt inside the electric strike which produces it doesn´t work properly.
How to install an electric strike with an access control?
It depends more on the access control, the type of electric strike and its function. The instructions of the access control must be carefully read. Install on the electric strike wiring a diode or varistor included with the access control (in case it is not internal).
Usually access controls intended to provide low power. In this case it is compulsory to install low consumption electric strike (412 or 512).
If it is needed to install an electric strike with enough power to open easily, even if pressure is applied on the door, there must be installed a relay that will be operated by the access control to activate or deactivate the lelectric strike using a separated installation ( electric strike using a wiring, access control using another wiring, electricity to the electric strike supplied from the relay).
The strike gets unlocked when the door gets closed
It is produced usually in a rim installation door in which a delay action and low-power strike has been installed.
Having the frame little anchorage, it absorbs all the impact of the door when closing, this causes both the frame and the mechanism vibrates producing an internal movement among the components of the mechanism. Because of this movement the delay action mechanism can be activated unlocking the door consequently.
To solve the problem improve the door attachment, regulate the door closer so that it does not slam, or use a non-energy-saving strike so that the internal springs are stronger and absorb correctly the vibration.
An electric strike with delay action mechanism is working as a normal one.
The most common reasons are:
Flex jaw is not regulated enough and the latch does not press the bolt.
Flex jaw is so much regulated that the latch gets stuck between bolt and flex jaw.
The electric strike has been installed too outward the door and the latch stands on the axis of the bolt instead of pressing it.
Is it possible to lock the door using a key?
There are two main kind of faceplates, with or without a hole for latchbolt.
If the lock has a bolt, the face plate which must be used need to have a hole for the bolt. When choosing the faceplate, it is needed to check the measurements of the lock in order to make it matches the hole with the bolt and the latch with the electric strike. Thus, when installing and the bolt gets out, it will be set to the faceplate.
Dorcas have a wide range of faceplates to match every kind of lock.
In the case the faceplate doesn´t have any hole but the lock has a bolt, the faceplate must be changed to enable the use of the bolt, otherwise can not be locked by using a key.