Transformer for halogen lamps: why is it needed, the principle of operation and connection rules

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Inna Alekseeva
Last update: May 2019

Halogen lamps can be considered an improved version of the usual incandescent devices. They work the same way, but due to some features of the halogens they are more economical, durable and give a pleasant to the eye, but at the same time bright light.

Manufacturers offer two options for halogen lighting devices: high and low voltage. For the second to work correctly, a transformer for halogen lamps is required. We will talk about how to choose and correctly connect the specified device.

Why a halogen transformer?

Halogen lamps successfully compete with LEDs. Despite the best operational characteristics of the latter, it is halogens that often benefit, which is explained by their lower cost and, accordingly, affordability, as well as some features of the light beam of LEDs, from which eyes can get tired.

The main “trump card” of LEDs is operation without heating, which makes it possible to widely use them. Halogens have the same advantage, but only for low-voltage lamps. They can be installed in areas sensitive to high temperature. For example, in the ceiling luminaires.

But at the same time, you need to understand that halogen low voltage lamps can only work with transformers. The latter are necessary to convert the mains voltage to an acceptable indicator for the lamp. Usually it is 12 V.

In addition, the transformer protects the light source from power surges, overheating and short circuit, and can also provide the ability to smoothly turn on the light. It must be admitted that, on average, lamps with transformers last much longer. Although much depends on their quality.

Halogen lamp with transformer
Low-voltage type halogen lamps are not able to operate on 220 V mains voltage, therefore they need to be connected only through a step-down transformer

What are transformers?

Transformers are called electromagnetic or electronic type devices. They differ somewhat in the principle of operation and some other characteristics.

Electromagnetic options change the parameters of the standard mains voltage to characteristics suitable for operation low voltage halogen, electronic devices, in addition to the specified work, also perform current conversion.

Toroidal electromagnetic device

The simplest toroidal transformer is assembled from two windings and a core. The latter is also called the magnetic circuit. It is made of ferromagnetic material, usually steel. Windings are placed on the rod.

The primary is connected to an energy source, the secondary, respectively, to the consumer. There is no electrical connection between the secondary and primary windings.

Electromagnetic transformer
Despite the low cost and reliability in operation, a toroidal electromagnetic transformer is rarely used today when connecting halogen lamps

Thus, the power between them is transmitted only by electromagnetic means. To increase the inductive coupling between the windings, a magnetic circuit is used. When AC is applied, a terminal connected to the first winding forms an alternating-type magnetic flux inside the core.

The latter interlocks with both windings and induces an electromotive force or EMF in them. Under its influence, an alternating current is created in the secondary winding with a voltage different from that in the primary.

Depending on the number of turns, the type of transformer is installed, which can be up or down, and the transformation ratio. For halogen lamps, only lowering devices are always used.

The advantages of winding devices are:

  • High reliability in work.
  • Easy to connect.
  • Low cost.

However, toroidal transformers can be found in modern circuits with halogen lamps quite rarely. This is due to the fact that due to the design features, such devices have quite impressive dimensions and weight. Therefore, they are difficult to disguise when arranging furniture or ceiling lights, for example.

Toroidal transformer
Perhaps the main drawback of toroidal electromagnetic transformers is the massiveness and significant dimensions. They are extremely difficult to disguise if you need a hidden installation

Also, the disadvantages of devices of this type include heating during operation and sensitivity to possible voltage drops in the network, which negatively affects the life of the halogen.

In addition, winding transformers can buzz during operation, this is not always acceptable. Therefore, the devices are used mostly in non-residential premises or in industrial buildings.

Pulse or electronic device

The transformer consists of a magnetic circuit or an intermediate and two windings. Depending on the shape of the core and the method of placement of the windings on it, four types of such devices are distinguished: rod, toroidal, armored and armored.

The number of turns of the secondary and primary windings may also be different. Varying their ratios, get lowering and raising devices.

Pulse transformer
In the design of a pulse transformer there are not only windings with a core, but also electronic filling. Thanks to this, it is possible to integrate protection systems against overheating, soft start and other

The principle of operation of a pulse type transformer is somewhat different. Short unipolar pulses are supplied to the primary winding, due to this the core is constantly in a state of magnetization.

The pulses on the primary winding are characterized as short-term square-wave signals. They generate inductance with the same characteristic differences.

They in turn create pulses on the secondary coil.

This feature gives electronic transformers a number of advantages:

  • Light weight and compact.
  • High level of efficiency.
  • Ability to embed additional protection.
  • Extended operating voltage range.
  • Lack of heating and noise during the work.
  • The ability to adjust the output voltage.

Among the shortcomings, it is worth noting the regulated minimum load and a rather high price. The latter is associated with certain difficulties in the manufacturing process of such devices.

Rules for choosing a lowering equipment

When choosing a transformer for halogen type light sources, you need to consider many factors. It’s worth starting with two important characteristics: the output voltage of the device and its rated power.

The first should strictly correspond to the value of the operating voltage of the lamps connected to the device. The second determines the total power of the light sources with which the transformer will work.

Electronic transformer
There is always a marking on the transformer case, having studied which you can get complete information about the device

To accurately determine the desired rated power, it is desirable to make a simple calculation. To do this, add up the power of all light sources that will be connected to the step-down device. To the obtained value should be added 20% of the "margin" necessary for the correct operation of the device.

We illustrate with a concrete example. To illuminate the living room, it is planned to install three groups of halogen lamps: seven in each. These are point devices with a voltage of 12 V and a power of 30 watts. Three transformers for each group will be required. We will choose the right one. Let's start by calculating the rated power.

We will calculate and get that the total power of the group is 210 watts. Given the required margin, we get 241 watts. Thus, for each group a transformer is required, the output voltage of which is 12 V, and the rated power of the device is 240 W.

Both electromagnetic and pulse devices are suitable for these characteristics. When choosing the latter, you need to pay special attention to the rated power. It should be presented in two digits. The first indicates the minimum operating power.

You need to know that the total lamp power must be greater than this value, otherwise the device will not work. And a small comment from experts regarding the choice of power. They warn that the power of the transformer, which is indicated in the technical documentation, is maximum.

That is, in normal condition, it will give out somewhere 25-30% less. Therefore, the so-called “reserve” of power is necessary. Because if you make the device work to the limit, it will not last long.

Halogen lamp with transformer
For long-term operation of halogen lamps it is very important to correctly choose the power of a step-down transformer. Moreover, it should have some “reserve” so that the device does not work to the limit of its capabilities

Another important nuance concerns the size of the selected transformer and its location. The more powerful the device, the more massive it is. This is especially true for electromagnetic units. It is advisable to immediately find a suitable place for its installation.

If several users more often prefer lighting fixtures, divide them into groups and install a separate transformer for each. The explanation is very simple.

Firstly, when the lowering device fails, the remaining lighting groups will work normally. Secondly, each of the transformers installed in such groups will have less power than the total that would have to be supplied for all the lamps.Consequently, its cost will be noticeably lower.

Two options for connecting a transformer

Before connecting the step-down device, you must follow the layout of the fixtures, if there are more than two. In addition, you need to choose the installation location of the transformer.

The latter is done taking into account such rules:

  • Free access to the device must be provided, which is necessary for its maintenance or replacement.
  • If the transformer is located inside a confined space, the volume of the latter cannot be less than 10 liters. This is necessary to remove the heat generated during operation of the device.
  • The distance from the device to the nearest halogen lamp should not be less than 250 mm. This is to avoid unwanted additional heating of the light source.

Only after a place has been determined for the transformer and for the lamps, you can proceed with installation and connection.

Transformer Mounting
The correct choice of location for the installation of a step-down transformer is important. If it will be mounted in a confined space, the volume of the latter should be sufficient to remove the heat generated during operation of the device

In this case, two main options are possible, the latter can be modified and used to connect not only two groups of lamps, but also three or more.

Single Transformer Luminaire Chain

This option is considered optimal for four, maximum five light sources. If there are more lamps, it will best be divided into groups. Halogens are connected only in parallel. This must be taken into account when drawing up the scheme. Another important nuance.

It is necessary to place the lamps so that the distance from each of them to the transformer is approximately the same. This is necessary for the correct operation of the devices.

If there are wires of different lengths, the lamps will burn differently. The one with the shorter wire will shine brighter. A device with a long cable will burn dimly.

In addition, in the latter case, during the operation, heating of the wire is also possible, which is extremely undesirable. Experts recommend constructing the circuit so that the length of each of the wires extending to the lamps does not exceed 200 mm. In this case, the cable cross-section must be at least 1.5 square meters. mm

Single Transformer Circuit
In this way, a small number of lamps are connected. It is optimal to connect no more than five, otherwise you will have to install a high power transformer

There are output and input terminals on the transformer case. Primary are labeled as N and L or Input. This is an input located on the side of 220 V. It must be remembered that here the connection is through a single-key switch.

Further, the zero and phase wires of blue, orange or brown color extending from the distribution box are connected to the corresponding terminals of the transformer. Halogen lamps are connected to the secondary terminals of the Output or output of the lowering device.

For this, only copper wires with the same cross section are used. Important note. If for some reason the transformer terminals are not enough, install additional terminal clamps. They can be purchased at any specialized store.

Two groups of lamps with two transformers

Such a connection is optimal if there are more than five lamps. Groups can consist of the same number of lamps or different. It does not matter. The main thing is that for each a transformer is correctly selected. As in the option described above, it is worth starting with the implementation of the scheme.

When choosing the location of the lamps, similar rules work. That is, the length of all wires extending to them from the transformer should be approximately the same.

Connection of two groups of halogen lamps
So two groups of halogen lamps are connected. Each of them uses its own transformer, but the switch is common to both

This can be difficult to do. Then you need to make some adjustments. You need to know that for wires made of copper with a cross section of 1.5 square, namely it is recommended to use them in this case, the optimal length varies from 150 to 300 cm. Energy will be transmitted to such a distance with minimal loss and without interference.

Sometimes this length is clearly not enough. In this case, you will need to select a larger wire section. For a distance of 300 to 400 cm, a cable with a cross section of up to 2.5 square meters is selected. mm If an even greater length is expected, which is undesirable, a special calculation should be made and a suitable section determined according to a special table.

The connection of each of the transformers and groups of lamps to it is carried out similarly to the method described above. That is, the zero core from the junction box is connected to the zero terminals of the transformers.

The phase core from the switch is connected to the phase cables of the lowering devices. Theoretically, this way you can connect more than two groups of fixtures, but each of them has its own transformer.

Important note. A separate cable is laid for each of the lowering devices, and they are connected exclusively inside the junction box. Some "craftsmen" prefer to connect the wires somewhere under the ceiling, but do not use the power distribution box.

This is a serious mistake, contrary to the PUE, where it is written that each of the completed cable connection sections must be provided with free access for inspection, maintenance and possible repair. Therefore, the only correct option is to connect in a junction box.

Halogen backlight
In the process of creating a halogen backlight with a large number of lamps, it is important to correctly calculate the number of lighting groups and the location of the transformers for each of them

Experts emphasize that if it is supposed to connect a group consisting of a large number of lamps, it is possible to place a junction box between the lamps and the output of the transformer. This is especially true with a lack of terminals on the step-down device or with restrictions on its placement.

Choosing this option, you need to know that at the same power, the low-voltage circuit passes more current than the high-voltage circuit. Based on this, an accurate calculation is required to determine the cross section of the wire. It is produced by calculating the total current strength.

We illustrate with an example. Seven 12 V of 35 W light sources must be connected via a transformer. Lamps are mounted through the distribution box in parallel. Necessary to find out wire cross sectionto be laid between the distributor and the output of the unit.

To do this, first multiply the number of bulbs by their power. Then the resulting value is divided by the operating voltage. We get approximately 29 A. This is the current strength that will pass through the low voltage wiring.

Using the table of dependence of the wiring cross section on the operating voltage presented in the PUE, we determine the appropriate wire size. In our case, it will be at least 4 square meters. mm As you can see, the load is quite large. Perhaps it makes sense to divide this group of lamps into two more.

Halogen lamp connection diagram
If you connect a two-halogen switch when connecting two groups of halogen lamps, you can get the opportunity to control each of them individually

When mounting two groups of halogen bulbs through a transformer, two types of switches can be used. If you put a single-key model, then both groups can turn on / off only at the same time. If separate control of groups of lighting devices is required, a two-key switch can be installed.

Recommendations of practitioners

Practicing electricians often face the need to install low-voltage halogens when the wiring has already been completed and has been successfully operated.In this case, it is far from always possible to carry out parallel connection of the lamps to the transformer without a cardinal wiring alteration.

In order to minimize costs, experts recommend in this case to connect each lamp with its own transformer. As a rule, it will be small in power and size of the device.

If this seems wasteful, you can put in the luminaires instead of low-voltage high-voltage halogens of 220 V. But in this case you will have to equip them with a soft starter. Or as an option, if the design of the lamp allows, you can replace the halogen lamps with economy-class LEDs.

With landmarks halogen picker for the device of the lighting system will familiarize you with an article that thoroughly analyzes all sides of the issue.

Halogen backlight
The ability to adjust the light intensity attracts many. Most electronic transformers are supplemented with the ability to reduce input voltage, which allows you to adjust the brightness of halogen lighting

Very often, it is planned to control the intensity of lighting, for which purpose it is added to the general scheme Dimmer. You need to know that most pulse transformers are not designed to work together with a dimmer.

Since the latter adversely affects the operation of the electronic converter, this ultimately significantly reduces the life of the connected halogen lamps.

For this reason, the toroidal electromagnetic transformer is the best option for working together with a dimmer. And one more remark.

Electricians strongly recommend not to forget about the maintenance of already installed lowering devices. It is optimal to conduct a routine inspection every six months with a performance check. If problems are identified, the device is repaired or replaced.

Conclusions and useful video on the topic

Video # 1. Let's get acquainted - Osram transformers:

Video # 2. How to connect the transformer:

Video # 3. All you need to know about transformers for halogen type light sources:

Low-voltage halogen lamps are a practical solution for arranging recessed lighting. They are considered a budget analogue of LEDs, significantly surpassing them in the quality of the emitted light.

The main difficulty in using low-voltage halogens is the need to connect a step-down transformer. However, if everything is done correctly, lighting devices will serve for a long time and without problems.

Have experience connecting a transformer for a low-power halogen bulb? Do you know the technological subtleties that are useful to site visitors? Please write comments, share useful information, publish photos in the block below.

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