Recommendations for controlling different types of loads

i3 Engineering controllers are designed to manage a variety of engineering systems in the house - HVAC, lighting, water supply, security and more. Accordingly, controllers must work properly and safely with different types of devices. But not always, having read the technical characteristics of the end devices, it is easy to choose a proper controller for the task.

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For example, this label says that the consumption of this lamp is 20W. Manufacturers of controllers offer to switch such lamps by means of a relay output with a switching current of 5A. Very simply, we can calculate that the current consumption will be equal to 20/220 = 0.09A, which is much less than the proposed value of 5A. But in fact, after a few switches, the relay contacts may just stick and stop working. Why? Let's find out together. 
All manufacturers always add something like "5A of resistive (active) load" to their equipment in small font, or put an asterisk and do it on the last page. What is resistive (active) load?
There are 2 types of electrical loads in this world: active (or resistive) and reactive.

Active (resistive) load is, for example, heating devices that can be considered as a resistor with a certain resistance, and after the passage of current through it, electrical energy is converted into heat. An electric kettle, electric boiler, towel dryer or ordinary incandescent lamp are typical examples of such a load. The maximum current consumption of such devices during start-up can be significantly higher, it is called starting (or inrush) current. For example, incandescent lamps at the time of switching on consume current 10-12 times greater than the nominal, i.e. in lamps with a power of 200 watts, the starting current will be somewhere 9-11A. If you have such equipment, you can safely take values ​​from the catalogue and, simply taking into account the starting current, which is also specified in the catalogue, choose a device with a proper switching relay.

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Current change when switching on active (resistive) load

What to do with our LED lamp of only 20 watts, why will it fail the relay at lower power? There is another type of load - reactive.


Reactive loads are of two types: 
 Inductive load - devices with electric motors (fans, vacuum cleaners, power tools, pumps, etc.) or with power transformers (power stabilizers, old appliances, audio equipment).

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Voltage change when switching inductive load on and off

● Capacitive load - all LED lamps and fixtures, almost all household and computer appliances, modern power supplies and devices in which they are used. In such loads, inrush currents can reach gigantic values (hundreds of times greater than the nominal value).

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Change of current at switching of capacitive loading

As you can see from the graphs, when you turn on the device, the current sometimes reaches values much higher than the advertised nominal value, for example, a normal 20W light bulb at start consumes about 15-20A.

How to control different types of loads

As mentioned earlier, the current of our LED lamp at startup reached almost 20A, which is much higher than the value specified on the relay 5A, so it failed. i3 Engineering is very concerned about the correct connection of end devices to our controllers, so we decided to write a few recommendations for you.
Each of these types of devices has its own connection features, and the differences between them are manifested when turning them on or off. This imposes certain conditions on the characteristics of the power elements of the controllers.

Active loads (heaters) are usually characterized by high power consumption (more than 500W). When switched on, the current may exceed the rated current several times for a short time. It is most convenient to switch ON such devices by means of the relay.

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Another type of active load is LED strips connected directly to the controller outputs. Dimers based on MOSFET transistors are provided for proper control and the ability to change the brightness.

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Inductive loads are characterized by a slightly higher starting current (for motors 2-5 times higher than nominal). Another feature is that when you turn off the energy of the magnetic field accumulated in the windings, causes an instantaneous increase in voltage at the power terminals. Because of this, they should be turned on and off with more powerful relays. However, it is desirable that the contacts have a protection circuit based on varistors or RC-links to avoid the formation of sparks when opening.

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But switching on devices with capacitive load without taking into account the peculiarities of their operation can end in failure of the control device. It's all about the very large starting current that occurs at the time of switching on. As we noted at the beginning of this article, this current can in some cases be more than 200 times higher than the rated current.

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There are several ways out of this situation:
1. Use only high-quality relays with a high allowable starting current. Exactly as used in all Atom series controllers.
2. Use controllers with power elements based on triacs or MOSFET transistors, which not only provide silent load switching, but are more reliable and durable than relays. We recommend the Atom Helium or Hydrogen controller with ACD or ACD + interchangeable modules.
3. Use a relay with a large switching current (10 or 16A) and a large allowable starting current. For example, it is convenient to use Atom Ferrum or Carbon controllers.
4. Use magnetic starters (contactors) or intermediate relays to connect powerful lighting devices. In this case, the best solution is to use an Atom Argon or Argon + R12 controller.
5. Use high-quality equipment with reactive load compensation schemes. That is, such a device when turned on has a starting current close to the nominal.
6.Some manufacturers of electrical equipment have begun to manufacture devices to protect the contacts. These are devices for mounting in the switchboard, which are designed to limit the starting current and thus protect the contacts of the relay from damage when turned on.

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