The VL-PJ02 contact protection module is designed to protect the contacts of switches and relays from damage when connected to the power grid with capacitive loads that have significant starting currents. Such loads include: impulse power supplies, LED lamps, drivers for LED strips or modules, fluorescent lamps with chokes and starters, and so on.

The circuit of the touch switch is designed for 5 amps. It contains a relay that closes and opens the electrical circuit. The problem is that some electrical appliances consume a huge amount of current when turned on. For example, a miniature 4-watt LED bulb can consume 30-40 times more than usual for a fraction of a second when turned on.

To demonstrate this, we purchased a professional oscilloscope, assembled an electrical circuit with a current transformer to record the moment the luminaire is turned on, and saw something very interesting.

Starting current

In the photo above, we see the moment when a cheap Chinese 5W light bulb is turned on! One cell equals 10 amps, and as can be easily seen, the graph reaches 30A. For those who are far from circuitry, let's say it simply: at the moment of power supply, the 5W bulb consumes 30A x 220V = 6600W for a very short period of time! The current quickly drops, and the consumption decreases to the stated 5W. But what if 10 such light bulbs are connected?

As a result, the switch circuit and delicate contacts of the relay switch module cannot withstand such a load and may stick together (a small spark occurs at the switching point, similar to welding), after which the light cannot be turned off.

Why do Chinese and other unscrupulous manufacturers do this? It's simple, they save on simplifying the electronic circuit. In an apartment without a smart home, there is no relay, and the function of switching the electric circuit is performed by a wall switch. Even if its contacts "stick" at a high starting current, a strong hand of the owner will not even notice as it pulls the contacts apart. But it's a different story for a miniature relay module, which is not endowed with such strength as an adult human hand.

Starting current of a high-quality lamp

In this photo, we see the starting current graph of a high-quality Osram light bulb, which is significantly more expensive than its Chinese counterpart. As we can see, the manufacturer not only made sure that the bulb shines brightly, but also that it is safe for the electronics associated with it.

If this is true, why don't the automatic circuit breakers in the apartment work?

It doesn't work because the pulse is very short. To trigger the automatic circuit breaker, a pulse with a duration of 8 to 15 milliseconds is required. The pulse when turning on the lights is much shorter in duration.

The use of the contact protection module allows:

- increase the service life of electrical equipment;
- prevent false activation of automatic switches.

Application

It covers all production cycles in industry and households where it is necessary to protect switch contacts and executive relays from high starting currents.

Principle of operation

When the voltage is applied, the contacts of the built-in relay are open. The current is limited by the built-in series resistor. After a fixed time (100 ms delay time), the relay contact closes and the full current is supplied to the load. The contact protection module does not affect the operation of the load afterwards.

What to do if you've already purchased cheap light fixtures? Devices that provide "soft start" come to the rescue, which allow limiting the current at the initial moment and preventing expensive relay modules from failing.

The device is installed before the load in the 220 volt network, in the break of two phase and neutral wires (in series with the load).

Starting current using the soft start module

In this photo, we can see the result of using a soft starter. We see the same "Chinese" product, where the starting current dropped by more than 3 times.

Wiring diagram VL-PJ02

Based on the above, do not skimp on light bulbs so that you do not have to risk your equipment or spend money on additional devices caused by this parasitic effect.