Will 48V Power Replace 24V in Industrial Systems?

EVのバッテリーシステムの図
Most industrial control systems run on a 24VDC supply rail. This voltage was chosen for several good reasons; it is high enough to power valves, solenoids, and relays, low enough to be considered safe to touch under SELV regulations, and it is a standard lead-acid battery voltage, making it easy to implement redundant supply back-up systems. However, as power demands increase, 24V systems become less efficient, especially over longer cable runs, because the higher current leads to significant cable losses.

If the DC supply voltage is increased from 24V to 48V, the total current is halved and the cable losses are quartered. This means that four times as many loads could be powered from the same supply cable.

The main reasons why 48V was not chosen as a standard industrial power supply voltage instead of 24V were that 48V lead-acid batteries were simply too big and heavy, and it was harder to find DC/DC converters and regulators that could operate from such high input voltages. Even 24V supplies are often dropped down to an intermediate bus voltage of 12V to supply point-of-load converters that power low-voltage 1V/2.5V/3.3V circuitry.

RECOM power modules showcasing increased DC supply voltage from 24V to 48V


How GaN and Automotive Trends Are Making 48V Practical

Recently, there have been two developments that have changed the game plan and made 48V supplies significantly more attractive.

The first game-changer is GaN HEMT. This is a new type of switching transistor that can switch much faster than silicon-based technologies. If a 100kHz DC/DC buck converter is used to efficiently step down a 48V supply to 1.2V, the mark-space ratio will be 40:1. Add a load regulation capability of 1%, and the switching transistor must cope with a PWM signal with less than 2.5ns jitter. This is at the limit of conventional switching regulator technology, but well within the specification of GaN transistors, making 48V-to-1V converters a practical possibility.

PWM control signal of a 48V-to-1V buck converter

PWM control signal of a 48V-to-1V buck converter
マイルドハイブリッド電気自動車の図
The second game-changer technology is mild hybrid electric vehicles. A mild hybrid is like a standard car with a fuel-burning engine and a 12V lead-acid battery but also includes an extra 48V lithium-ion battery and an electric drive.

The 48V battery can be used to power the car purely electrically for the first hundred meters or so after moving off, allowing a smaller and more efficient engine to be used without affecting acceleration. This also means that in heavy stop-go traffic, the fuel-burning engine will not be running. Thus, automotive manufacturers can meet the latest energy efficiency standards for urban traffic conditions without having to redesign the entire vehicle.

The 48V battery also allows for higher peak electric loads than a 12V system, so the air conditioning, power steering, and turbocharger can all be electrically powered at will and not constantly absorb power by being mechanically connected to the engine. With optimized control algorithms, the overall efficiency of the vehicle can be significantly increased.

What this all means for industrial applications is that 48V lithium-ion batteries will soon become mass-produced, low-cost items. As lithium-ion batteries are also more compact and lighter than equivalent lead-acid batteries, they are ideal as back-up supply storage elements for 48V systems.

The major difference between a 48V lead-acid and 48V lithium-ion storage battery is the allowed voltage levels. The traditional telecom power standards for a 48V input DC/DC converter supply are based on old lead-acid battery chargers with an 18–75V output voltage range. Lithium-ion battery packs must not be overcharged nor deep-discharged to avoid cell damage.
The limits are defined in the LV148 norm:

48V lithium-ion storage battery
LV148 48V Lithium-Ion Voltage levels:

48V Lithium-Ion Voltage levels
Therefore, a DC/DC converter designed to operate from a 48V supply with Li-Ion back-up does not need to cover a 4:1 input voltage range. A 3:1 input range (20–60V) is perfectly adequate. Furthermore, the old telecom standard allowed input voltages of up to 75VDC, which exceeds the Safe Extra Low Voltage (SELV) limit of 60VDC. If an industrial installation can be made SELV, there are significant savings in cabling, installation, and equipment costs, which is why Power-over-Ethernet (PoE) is limited to 56VDC, for example.

Optimizing Industrial Power Systems with 48V Solutions

In conclusion, a DC/DC converter that operates over a 3:1 input voltage range of 20–60V will cover 48V lithium-ion battery voltages, well-regulated (±10%) DIN rail standard power supplies of 24V, 36V, and 48V, and PoE supply voltages.

RECOM offers the RS3-Z series, a miniature 3W DC/DC module with up to 3kV isolation for the new 48V supply standard. Regulated output voltages of 3.3V, 5V, 9V, 12V, 15V, ±3.3V, ±5V, ±12V, and ±15V are available to power a variety of sensors, monitors, ADCs, DACs, and isolated data buses from a 20V–60V supply. The converters are sealed against moisture and dirt, operate from -40°C up to +85°C ambient temperature, and are UL and EN certified, making them ideal for industrial power applications.

RECOM also offers a range of single-phase AC/DC DIN rail mounted power supplies with 48V outputs at 120W, 240W, or 480W output power. The units can deliver up to 150% over-power to supply high start-up loads and can be paralleled to increase output current. They are fully UL/IEC and EN certified for use in industrial applications.
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  Series
1 RECOM | RS3-Z Series | DC/DC, THT, 3 W
  • 2:1 and 3:1 wide input voltage ranges
  • 1kVDC, 2kVDC and 3kVDC isolation
  • UL94V-0 package material
  • Continuous short circuit protection