Power supply/ charging

Deutschen Post electric vans in 1953-09-29 in Berlin. Electric vehicle batteries can be used to provide emergency electric power during power outages, to ensure that all necessary computer controlled functions in a house continue to operate.

Computer devices are dependent on electricity to operate. Increasingly, devices use battery storage/ power, to gain a temporary independence from the electrical power network. Various forms of small scale, local energy production (solar, wind) can even lead to a more permanent independence. However, not everyone is in a position to become permanently independent from the grid.

An electrical power blackout/ cut/ failure/ outage is the loss of electrical power somewhere in the network affecting the supply to an end user. These may be caused by faults/ damage at power stations, substations, transmission lines, short circuits, circuit breaker operation. A transient fault is a temporary loss of power, that is automatically restored once the fault is cleared. A brownout is a drop in voltage in an electrical power supply. Brownouts can cause operational problems. A blackout is the total loss of power to an area. They may last from minutes to weeks depending on circumstances. Rolling blackouts are planned blackouts that occur when demand exceeds supply. It rotates customers, so that at any given time some receive power at the required voltage, while others receive no power at all. Preventative blackouts are also used as a public safety measure, for example, to prevent wildfires around poorly maintained transmission lines.

Batteries in electric vehicles as well as solar panels are ensuring that there is always a minimal amount of electric power available, even if there is a grid related blackout. Circuits have to be designed so that electricity is not fed into the grid at these times, because that power could represent a hazard to people working on the lines to restore power.

Desktop and Tower computers

There are many different form factors used to make desktop and tower computers. These motherboard specifications determine dimensions, power supply type, location of mounting holes and ports. This ensures that parts are interchangeable over time. Two are especially important. The ATX specification was created by Intel in 1995, and is still the most popular form factor. Here the power supply offers several different voltages to meet the specific needs. These include +3.3 V, -3.3 V, +5 V, -5 V, +12 V and -12 V. There were and are attempts to offer just 12 V, but this reduces the selection of components available.

This type of computer has a power supply built into the computer case. It is suitable for power intensive assignments such as gaming or video rendering. Some can provide 500 W of power. The tower format is especially attractive if a large number of expansion cards are needed. One challenge with these is the need for active cooling. Fans can be noisy. The open nature of the case means that it will attract and accumulate dust, which will have to be cleaned at regular intervals.

The Mini-ATX family of motherboard specifications was designed by AOpen in 2005 with Mobile on Desktop Technology (MoDT). This adapts mobile CPUs for lower power consumption. With a simple but effective thermal design, it is suited for passive cooling, making it virtually silent. Manufacturing costs and overall operating power requirements are lower relative to active cooling designs. A DC-to-DC converter removes the power supply from the case, reducing system size. This type of computer is suitable for general use. The number of expansion cards is limited.


Almost all modern laptops use Lithium Ion (LiIon) batteries and use 19 V chargers. Each battery arranges LiIon cells in series. A LiIon cell has a maximum charging voltage of 4.2 V, although slightly more voltage is applied in practice. Voltage needs: One cell = 4.2 V; two cells = 8.4 V; three cells = 12.6 V; four cells = 16.8 V; five cells = 21 V. A charger uses switched mode power supply (SMPS) to convert the supply voltage to required voltage, sometimes using a boost converter (steps voltage up), but usually a buck converter (steps voltage down). A 19 V buck converter could charge up to 4 cells in series. When a LiIon cell is close to fully discharged it’s terminal voltage is about 3 V. A buck converter can accommodate this reduced voltage to maintain its charging efficiency, which can exceed 95 %.

Handheld Devices

There are three charger plugs in common use on handheld devices: micro-USB-B, USB-C and Apple Lightning. A cable will typically have a connector for one of these standards on one end, and a standard USB-A 2.0 connector on the other, that can be plugged into a charger, which – in turn – is plugged into a wall socket.

The micro-USB and lightning connectors will likely disappear in Europe, as the European Union has mandated use of a common charging connector, which will probably end up being USB-C.


As stated in an earlier post, USB originally allowed power to flow downstream from a Type-A connected device to a Type-B connected device. This situation has changed with the introduction of USB-C connectors, which combine A and B characteristics. It is not easy to see where power is flowing.

Type of DeliveryCurrentVoltagePower
Low Power USB 3.0150 mA5 V0.75 W
High Power USB 3.0900 mA5 V4.5 W
Battery Charging 1.25 A5 V25 W
Standard USB-C3 A5 V15 W
Power Delivery 1.0 Micro-USB3 A20 V60 W
Power Delivery 2.0/3.0 USB-C5 A20 V100 W

One of the most common devices needing power to operate are external drives. For example, Western Digital My Passport external hard drives that feature 2.5 inch drives, are powered by the computer, using a USB Type-A connector for data and power. In contrast, Western Digital My Book external hard drives feature 3.5 inch drives, that also come with a USB Type-A connector for data, but with an AC adapter with wall socket plug for power.

USB Battery Charging defines a charging port, which may be a charging downstream port (CDP), with data, or a dedicated charging port (DCP) without data. Dedicated charging ports on USB power adapters can run attached devices and battery packs. Charging ports on a host are labelled such.

In the computer world, one is perpetually in a transition period. There is always something newer and potentially better, and something older but tested and, hopefully, more reliable. Thus, a Western Digital G-Drive comes with three cables: USB-C to USB-C, USB-C to USB-A and a power cable that attaches to an AC power adapter. For computers that can provide power over a USB-C connector, only the first cable is needed. For computers without USB-C power, this first cable connects the AC adapter to the G-Drive, with the second cable connects the G-Drive to the computer.

Power over Ethernet (PoE)

With domotics (smart houses) becoming increasingly popular, it is becoming increasingly advantageous to install and use Ethernet cables to ensure devices are able to communicate effectively. While some switches only provide data transfer, many switches offer power, using one of the many Power over Ethernet standards.

There are two different approaches to providing power. Power sourcing equipment (PSE) that provide power on the Ethernet cable, typically a network switch, is called an endspan or endpoint. The alternative is an intermediary device, a PoE injector, also referred to as a midspan device.

A powered device (PD) is any device powered by PoE. One common device is a room controller which has sensors collecting data about a room, and actuators such as a solenoid capable of opening and closing a heating vent. In the future many computing devices should be able to receive power directly from an Ethernet cable.

PoE is expected to become a DC power cabling standard, replacing individual AC adapters in a building. While some are concerned that PoE is less efficient than AC power, others argue that it is a better solution because a central PoE supply replaces several/ many AC circuits with inefficient transformers and inverters, compensating for any power loss from cabling.

Standard 802.3af Type 1at Type 2bt Type 3bt Type 4
Power at PSE15.4 W 30 W 60 W 100 W
Power at PD 12.95 W 25.530.0 W 51 W 71 W
Voltage at PSE44.0–57.0 V50.0–57.0 V[50.0–57.0 V 52.0–57.0 V
Voltage at PD 37.0–57.0 V42.5–57.0 V42.5–57.0 V41.1–57.0 V

Inductive Charging

Inductive charging involves wireless power transfer, using electromagnetic induction to provide electricity to portable devices. The most common application is the Qi wireless charging standard. Devices are placed near an inductive pad. There is no need for electrical contact with a plug, or for devices to be precisely aligned, for energy transfer. Advantages of wireless charging include: corrosion protection and reduced risk of electrical faults such as short circuits due to insulation failure; increased durability, because there is significantly less wear on the device plug and the attaching cable; No cables; Automatic operation.

There are some disadvantages: Slower charging, devices can take 15 percent longer to charge; more expensive because of drive electronics and coils in both device and charger; there is a certain inconvenience cause by an inability to move a device away from its pad, while it is being charged; there is an assortment of incompatible standards that not all devices support; devices get hot when charging, and this continued exposure to heat can result in battery damage.

The Qi standard is supported on devices fro Apple, Asus, BlackBerry, Google, HTC, Huawei, LG Electronics, Motorola Mobility, Nokia, Samsung, Sony and Xiaomi. Released in 2008, the Qi standard had by 2019 been incorporated into more than 160 handheld devices.

Uninterruptible Power Supply

An uninterruptible power supply (UPS) provide electricity to an attached device if the main supply becomes unavailable. The duration of this protection varies. This is particularly important for desktop and server devices that do not have built-in batteries, in contrast to those with batteries, found in handheld devices and laptops. Even if a UPS is designed for mission critical equipment, it can be nice to have in a residence. Perhaps the most important device to connect is to a UPS is the router, to allow communication outside the residence. The local internet service provider (ISP) should have the rest of the network protected with their own UPS. What they actually provide varies.

Data or voice communication with a handheld device on cellular network can be the most effective way of communicating in an emergency situation, during a blackout. This is because the cellular base stations should have their own backup power sources, allowing them to operate normally.

Surge Protection

All electronic devices should be protected against surges = situations where voltages increase above specified levels, even if just for one or more seconds. Surge protectors can prevent this form of damage. This is probably best provided by having surge protection built into the circuit-breaker box.