What is an electronic ballast?

What is an electronic ballast?

Published:19 Mar 2021

What is an electronic ballast used for?

High pressure sodium (HPS), metal halide (MH) and ceramic metal halide (CMH or LEC) HID lamps cannot be connected directly to a power socket, they would not light up. These lamps need a device that allows them to start up with an initial high-intensity discharge and they then maintain a voltage that is different from that of the power grid.

What types of ballasts are available in the market?

High pressure sodium lighting has required ballasts since the 1930s. Magnetic ballasts have always been used, but electronic ballasts have been with us for more than a decade.

Electronic ballasts are available as independent components that can be adapted to lighting systems, or they may be integrated with professional lighting equipment such as technical grow lights.

Electronic ballasts are also available for CMH or LEC lamps, which unlike the above, are low-frequency, with a light output of between 400 Hz and 800 Hz.

The most common powers for magnetic or electronic ballasts for use in horticulture are: 250 W 400 W 600 W 750 W and 1000 W for HPS and MH and 315 W 630 W and 945 W for CMH.

What are ballasts made of?

There are 2 ballast technologies: magnetic and electronic or digital.

Magnetic ballasts are mainly formed by an electric coil and a starter, and are less efficient.

Electronic or digital ballasts work by modifying the electrical frequency with electronic components.

How do electronic ballasts for grow lights work?

Magnetic ballasts are more rudimentary and less efficient. They have a coil for creating a magnetic field in order to obtain the voltage required by the lamps.

On the other hand, electronic or digital ballasts achieve the same goal by modifying the lamp output frequency.

They both require the lamp to be started up with a discharge of over 2500 V (normally 5000 V) and then they keep the lamp on, supplying a voltage that is different from that of the power supply.

Their main function is to start up and stabilise the lamp.

At what frequency does a ballast work?

Magnetic ballasts depend on the power supply frequency, which is generally 50 Hz in Europe, Australia, Asia and 60 Hz in the USA. The ballast must be designed for a specific frequency and 60 Hz ballasts must not be used in 50 Hz connections or vice versa, as the magnetic principles on which they are based must be calculated for a constant frequency. The power supply frequency will be the same as the one received by the lamp.

Electronic ballasts depend on the manufacturer’s design. These ballasts normally permit connection at 50 Hz or 60 Hz without this affecting their operation, whereas the frequency received by the lamp is completely different. To obtain an optimal performance in high pressure sodium and metal halide lamps, a frequency higher than 50 Khz is recommended, equivalent to 50,000 Hz for CMH between 400 Hz and 800 Hz.

Electronic ballasts vs. magnetic ballasts: differences and advantages

A magnetic ballast is limited by the magneto-electric effect it uses in order to work. Its main and only advantages is its price, but this is not justified as its performance is extremely low.
An electronic ballast has many advantages that justify a higher economic investment that will be quickly amortised.

Output frequency.
Plants use energy in the form of light to perform their photosynthesis process. If the light flow flickers, the process of transforming light into glucose to perform the photosynthesis will be interrupted and not be smooth and continuous.
An electronic ballast has a high frequency output, which provides a practically continuous electricity flow towards the lamp which is transformed into uninterrupted energy for the plants.

Power control.
A plant does not always need the total lamp intensity. The first phases of development require a lower intensity. Electronic ballasts permit the control of the output power, thus reducing the light intensity of the lamp, which leads to a lower energy consumption. In energy cost terms, this is one of the reasons justifying the difference in the cost of the equipment compared to magnetic ballasts.

Voltage stabiliser.
Although not all electronic ballasts have an adequate voltage stabiliser in their design, this is one of the main differences if we compare them to magnetic ballasts.
It is impossible to precisely control the voltage received by a system, as this depends on many factors related to the supply company and the system.
However, if the voltage received by the magnetic ballast is lower than normal (which is quite common), the power supplied to the lamp will be much lower, and thus the plants will receive less energy and, naturally, their productivity will also be lower.

This does not occur in an electronic ballast with an adequate voltage stabiliser. Fluctuations in voltage are offset by increases in intensity so that the lamp always receives the same power, without the electrical alterations of the grid affecting productivity.

Supply quality.
The electricity supply quality is considerably improved, as electronic ballasts correct the power factor, thus preventing contamination of the power grid red when there are large greenhouse installations. Furthermore, the transformation stations are not harmed, and it is not necessary for the supply companies to inspect the electric lines.

Security measures.
The different security measures implemented in their electronic design means, among other things, that the lamps can be switched on in conditions in which magnetic ballasts could not.
For example, when high pressure lamps heat up, due to micro-interruptions in the power supply, a magnetic ballast cannot switched the lamp on again immediately. This gives rise to excess power consumption during several minutes which may even cause the disconnection of the safety switches, making it necessary to operate the system manually. In addition, the constant attempts to switch it on, various times per second in several minutes, reduce the lifespan of the lamp.

An electronic ballast always switches on the lamp at the first attempt.

How to choose a ballast for grow lights?

Unfortunately, choosing an electronic ballast to guarantee the best results is no easy task, as there are many factors to consider. The most important and easiest to identify are as follows:

Input voltage.
Not all brands have electronic ballasts with good voltage stabilisers in their electronic design.

An electricity supply company does not normally give the exact voltage, there are usually voltage fluctuations within a higher or a lower margin. For instance, if the supply contract says 230V, the voltages actually received may be between 210 V and 245 or even much lower. This depends on many factors: the distance to the transformation station, the quality of the electrical wiring in the supply area, the power line capacity or even the quality of the customer’s installation.

The higher the electronic ballast operating voltage range (impossible in magnetic ballasts), the better it will adapt to electrical fluctuations, stabilising the efficiency and performance of the installation and plant productivity and controlling exposure to voltage fluctuations in the grid.

Power factor.
The perfect power factor is 1. The technical characteristics of an electronic ballast with a good power factor may include a PF (power factor) of > 0.99. Those with a PF of >0.9 or >0.8 need to be improved in this respect.

A professional installation must not contaminate the power grid by correcting an excessively high power factor with electronic ballasts.

THD or Total Harmonic Distortion.
High frequency electronics have many advantages in terms of producing low-cost, compact, efficient equipment. However, one of the most difficult aspects to control is contamination in the form of the harmonics transferred to the installation, which causes the tripping of circuit breakers in the presence of a THD higher than 10%. In such cases, it may be offset by creating groupings with a lower number of electronic ballasts per circuit breaker.

Output frequency.
The output frequency is the frequency at which the lamp operates. In 230 V lamp ballasts, the frequencies must be >50 Khz, while in 400 V lamp ballasts they must be >80 Khz, or in the case of CMH or LEC technology lamps, between 400 Hz and 800 Hz.

Output voltage.
High pressure sodium or metal halide lamp ballasts are supplied in 2 different output voltages:
Normally 230 V for up to 600 W.
Normally over 400 V for more than 600 W.
This is the most common standard in the market.

These V values do not correspond to real voltage values, as the nominal operating voltage of 230 V lamps is around 110 V and that of 400 V is around 250 V. So there is no need to take these V output values are real voltage values, this is only a way to distinguish between them.

It is important to choose the right lamp for the right ballast and vice versa. Some companies manufacture lamps and ballasts of 1000 W in 230 V, but this is very unusual. Similarly, there are companies that manufacture 600 W lamps and ballasts of 400 V.

For 600 W powers, a few years back, there were enormous differences in light intensity between 400 V lamps and 230 V lamps, but nowadays these differences have disappeared, and it is more common to find 230 V lamps for 600 W.

For 1000 W lamps normally used in professional lighting, the standard is 400 V which gives a higher performance.

Power switch.
It is always important to reduce be able to reduce electricity consumption. For this reason, it is interesting to adapt the light intensity on the plant during the growing phase. An electronic ballast must permit power control.

Control connection.
More advanced and innovative electronic ballasts permit connection to a control device in order to control all the ballasts of an installation through a controller. This allows the control to be centralised, in which switching on, off and power control is programmed from a single point, thus making it faster and easier to manage the system.

Improved ballasts for plants

These adapt better to the needs of the system and plant, but mainly, they have a greater voltage stabilisation range and are made with lasting electronic components and usually have longer warranties, as the manufacturer puts its trust in the excellent engineering and quality control.

Installing a grow light ballast

Location
It is important to choose an adequate location for installing any ballast. The technical features of the ballast must give the ambient temperature range for which it has been designed. The limit is normally between 30ºC and 40ºC, and so a ballast should never be installed on the lamp or reflector where it receives the heat of the lamp directly or indirectly.

Distance from the lamp
Most brands permit installations where the distance between the ballast and lamp may be more than 10 metres, but it is important to consider that the frequency, voltage and intensity from the ballast outlet to the lamp will not be the same as those of the ballast inlet.

It is advisable for the ballast to be as close as possible to the lamp, every metre of cable is very important. Considerable power losses may occur at distances of more than 5 metres.

The installation of centralised ballasts where there are great distances between the ballasts and the lamps is not recommended. They will work but this is not the best method because of the power losses caused by this type of installation.

Connection
The installations must always be executed by qualified, authorised personnel, in accordance with local installation regulations.

It is important to ensure the correct dimensions of the electrical wiring cross-section where the ballasts will be connected, and it is even more important to ensure that the recommended cross-section of the cable between the lamp and the ballast, which is 3×1.5mm².

Install the reflector to the chosen location

Secure the ballast in place
If a mural installation is elected for the ballast, it must be in a vertical position to favour air convection, optimising the passive cooling. It can also be installed in a horizontal position.

Connect to the appropriate wiring in accordance with local installation regulations.

Use the power cables supplied with the ballast, or connect them to the power socket with the wiring with a cross-section that is sufficient for the necessary power. It is always important to connect the earth wire correctly and make sure that the installation is properly earthed.

Install magnetothermal switches and circuit breakers in accordance with local installation regulations.

Connect the equipment and select the nominal power for the first 100 hours of operation. This must always be done in new lamps during the first 100 hours, otherwise the lamp lifespan will be considerably reduced. Once the first 100 hours have passed, the selected can be controlled.