Understanding the Function and Wiring of 1N4007 Diode in Electric Strike Circuit

Hello,

I install a combination lock (code and proximity cards) with an electric strike in the external door of the house. The manual states that they recommend connecting a rectifying diode to the circuit, as close as possible to the electric strike, because without it it can cause interference, in the worst case causing a restart or suspension of the lock.

The power supply supplies the code lock and the electric strike with a direct current of 13.8 V. The electric strike can operate with both direct and alternating current.

My question is: what is this rectifier diode for, what is its function? On wikipedia I read that it is mainly intended for rectifying alternating current, which does not occur here. Can it be omitted? If not, how to properly connect it to the circuit? I was supplied with one piece of 1N4007 diode with the lock. It looks something like this:

Where is the plus and where is the minus?

The diode is used to eliminate the high voltage induced on the electric strike coil. You mount it parallel to the electric strike coil with the line towards the contact to which the power supply plus will be connected.

When controlling inductance from semiconductor circuits, a diode is given to eliminate / limit the voltage peak, among others dangerous for the controlling transistor.
Almost every scheme with a relay has such a diode, parallel to the relay windings, in terms of direction it is reversed.

I'm not judging this case, I'm speaking generally

EDIT I'm surprised that it's optional (with a round marketing formula that it's better, but it doesn't have to: a blown transistor is disruption may occur ), should be in the driver.
What, on the other hand, I explain to myself that optionally it can be set up differently, including for alternating current (but I guess the lock is universal, the driver is not???)

Where is the plus and minus?
The diode conducts from the black side to this white stripe. (translating pathologically) From the anode to the cathode.
But in your case, as mentioned above, the diode should be connected in reverse to the power supply. It discharges the coil when it is disconnected from the power source.
@Edit
I have attached an oscillogram for illustration.
Blue color means that the power is connected, purple voltage on the coil.
When disconnecting the power supply, you can see a large peak of 46V (probably from 5V).
Unfortunately, I do not have an oscillogram how it looks with the diode attached, but it eliminates the above-mentioned case.

I suggest the author to read how the coils behave in the event of a power failure.
They just reflect the magnetic field like a generator, the direction of the voltage is opposite to the supply voltage and the diode will work here, it will simply short this impulse.
As a colleague wrote earlier, without a diode, the control element, e.g. a transistor, will be damaged.

Thank you, these answers explained a lot to me!