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Backing Up AC and DC Power in One Simple System

26 June 2018

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When it comes to AC devices, backing up power with an uninterruptable power supply (UPS) is well established. These range in varieties from consumer and office-oriented to industrial versions. Backing up DC devices is possible with some combination of rectifiers and batteries.

In many industrial and consumer uses, such as telecommunications, network equipment and rail signaling equipment, it is necessary to back up both AC and DC, either simultaneously or independently. Two-way radio communications central stations, like those used by police and fire services, is another place where a DC supply can be used. Here, a common DC supply can be used when charging batteries plus feeding many radios, while the computer equipment and base station equipment still requires AC

Backing up both AC and DC is more complicated with traditional equipment, which requires a combination of rectifiers, batteries and inverter technology working together. Although difficult, there are solutions to back up both AC and DC devices.

The Challenges of Backing up AC and DC

One possible solution is to use rectifiers to convert AC into DC, which charges and powers batteries and the DC load. From this DC source an inverter can convert the DC to AC to power and back up AC loads. This solution works well and is cost effective when there are more DC loads than AC loads to back up.

A second possible solution is to start with the same rectifier and battery backup for DC, but implement a traditional UPS for backing up the AC portion. This method works well when there are more AC loads to back up than DC.

While these two topologies of backup can work, they are less flexible in the mix of AC and DC power, and both come with negative and positive attributes.

With backup power, battery sizing is important and determines the battery amp hours — the backup device must also be able to meet the current demand. When the electrical load is fixed and not expected to change, the system can be sized accordingly.

It is difficult to size a backup system if the electrical load or mix of AC to DC might be expanded or changed. Such systems are often oversized for critical and high reliability to account for load variability, although this can result in reduced efficiency and higher cost, both in operation and equipment. One option is to use a modular solution to enable systems to be expanded.

Mixing and matching components to back up AC and DC will require equipment from multiple manufacturers. More components and more suppliers can mean more problems getting everything to work. This often means time spent troubleshooting, as well as complex maintenance and needing to keep different equipment as spare parts. Coupled with less reliability on critical equipment, it is obviously not the ideal solution.

A Flexible Solution for Electrical Backup

To solve many of the issues inherent in backing up AC and DC power together, the Sierra Power Converter was created. This module is available from CE+T Power and uses enhanced conversion innovation (ECI) technology to solve many of the issues resultant from backing up AC and DC power.

The power converter incorporates a natively DC buffer that takes the power where it is available and feeds the loads that need it. The energy is “mixed” in this DC buffer (capacitors) and therefore removes the need to precisely define the ratio between AC and DC loads. It eliminates the need for multiple pieces of equipment and the associated points of failure. This power converter combines the functions of a UPS (securing AC loads and charge batteries from an AC source), a rectifier (securing DC loads and charge batteries from an AC source) and an inverter (feed the AC loads using the DC source already secured with batteries). With this device, there is no single point of failure because everything, such as the transfer switch and inverter, is integrated.

Figure 1. Sierra Power Converter technical schema. Source: CE+TFigure 1. Sierra Power Converter technical schema. Source: CE+TA single Sierra module can provide 2.4 kW in any ratio of AC and DC power up to the maximum wattage. This fits in a form factor that is just 435 mm in length. For additional capacity, multiple modules may be used together. Just one Sierra Power Converter can provide up to 13 A of continuous single-phase AC power and 16 A overload for a brief time. The module can also be combined as a group of three or four in a power rack to secure three-phase loads and high amperages. Once a customer has chosen the load requirements, it is configured to meet the overall need. While the maximum load is set by the equipment, the ratio of AC-to-DC power can be changed so long as the load rating is not exceeded.

The Sierra has various modes of functionality for AC and DC input and output, as well as bi-directional modes to feed power back to the grid. The device is compatible with many different external battery chemistry, linked by the battery management system to provide backup. In the case of power backup, the Sierra Power Converter works similarly to a combination rectifier and converter combined in a single unit, as well as performing many other functions.

Uses for the Sierra

There are many typical uses for this kind of flexible power pack, as well as unconventional ones. One typical example is for telecommunication backup. Telecom and network equipment is often spread out, yet runs on both AC and DC power. This equipment is ever changing and growing as bandwidth increases and networks expand.Figure 2. The Sierra Power Rack system. Source: CE+T PowerFigure 2. The Sierra Power Rack system. Source: CE+T Power Additionally, the ratio of AC-to-DC power requirements may be ever changing, depending on the equipment.

Microgrids and storage solutions are new applications that are arriving more and more on the market. Storing the energy produced by renewables energies into batteries and optimizing the use of grid power to secure the whole load allows huge savings on energy bills. This also increases the autoconsumption rate (the use of the renewable energy produced). Reducing the cost for energy is possible with peak shaving capability and by purchasing the energy when the cost is low and selling it back when the price is high.

Figure 3. The Sierra Power Converter. Source: CE+T PowerFigure 3. The Sierra Power Converter. Source: CE+T PowerIn industrial settings, dedicated devices are excellent for three-phase balancing to account for harmonics and variable loads, which cause high power use. The Sierra Power Rack can replace this equipment. It works with three-phase power to balance and backup power.

For such a flexible device that can rectify and invert power in both directions, utilizing a battery can have many other uses. The Sierra Power Converter makes it simple to deal with all sorts of power situations, while fitting in a compact size that is easy to connect.


Simultaneously backing up both AC and DC power is traditionally a challenge that requires products from multiple manufacturers. With the Sierra Power Converter from CE+T, this job is done simply and easily. While not everyone may need this solution, it will benefit many industries like telecom, railway and networking, as well as other AC and DC backup applications. The Sierra Power Converter is the compact simple solution to the problem.

To learn more about the Sierra Power Converter visit its webpage, or contact CE+T Power directly.

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