HowTo: Electronics - correctly dimension power supplies and understand their data sheet

You need power supplies in almost every project because the energy for your project has to come from somewhere. 🙂

There are a few things to consider. On the one hand, you don't want to put yourself (or others) in danger and on the other hand, you want the project to be built to be successful.

It is particularly important that the power supply has enough power to supply the respective project. On the other hand, you don't want to have an expensive, huge power supply lying around at home. A compromise must be found between price, electrical performance and intended use.

The criteria you should consider are described in the following article.

The information contained on the data sheets of the power supplies is also described. Often you don't even have to buy a new power supply; you can simply continue to use the power supply from your old phone, children's toys, etc.

Of course, you have to understand what voltage, current or power the potential power supply can deliver.

---

Safety instructions

I know the following notes are always kind of annoying and seem unnecessary. Unfortunately, many people who knew "better" have lost eyes, fingers or other things due to carelessness or injured themselves. Data loss is almost negligible in comparison, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Because even the coolest project is not worth injury or other trouble.
https://www.nerdiy.de/sicherheitshinweise/

Affiliate links/advertising links

The links to online shops listed here are so-called affiliate links. If you click on such an affiliate link and make a purchase via this link, Nerdiy.de will receive a commission from the relevant online shop or provider. The price does not change for you. If you make your purchases via these links, you support Nerdiy.de in being able to offer other useful projects in the future. 🙂 

---

Requirements

Required material:
-no-

Required tool:
-no-

---

sustainability

A keyword that has been heard more and more often in recent years is “sustainability”. In principle, this involves using old, existing resources for new purposes. This is exactly what the knowledge in this article will help you with. Because if you can “decode” the symbols and data on your existing power supplies, you can also use them for new projects.

This means you don't have to buy as many power supplies, you don't have to throw away as many power supplies, and you also save money and other resources. 🙂

---

Parameters of the required power supply

Voltage and voltage range (ripple)

The first important criterion of a power supply is the voltage. The voltage (formula symbol: U) is inevitably dictated by the circuit of your project. So you often need a certain voltage or a certain voltage range for your project.

For example, if you have a project that is powered via a USB port, such as one of the projects here on Nerdiy.de, then you need a power supply with a “USB-typical voltage” i.e. 5V+-0.25V.

The voltage range of a normal USB power supply is standardized. This must always correspond to 5V with a tolerance of +-0.25V. The voltage that the USB power supply delivers is in the range of 4.75V-5.25V.

Examples:
– Your circuit requires 12V: The power supply must also supply 12V
– Your circuit requires 5V: The power supply must also supply 5V. In this case you can also use a USB power supply – at least in terms of voltage.

Electricity

In order to find out how much current (formula symbol: I) your power supply has to deliver, you first have to - at least roughly - determine how much power your circuit requires. It is important that you do not accept the “normal case”. So the average power consumption. But that Maximum case. The maximum case in this context is the case in which all consumers “consume” the maximum current.

In order to determine the maximum current consumption of your circuit, you have to determine the maximum current consumption of all the components used in it and then add them up.

You can always find out the maximum current consumption of a specific component from the respective data sheet or measure it with a measuring device. (But it is often easier to take the value from the data sheet.)

Typical maximum current consumption:
1x RGB LED: 0.06A
1x normal/simple LED: 0.02A
1x power LED: 0.3-0.7A
1x Wemos D1-Mini: 0.2A

Examples:
WhatsApp lamp:
The WhatsApp lamp uses an LED strip with 23 RGB LEDs. A Wemos D1-Mini is also installed to control the LEDs. This means the maximum power consumption can be calculated as follows: 23×0.06A+0.2A=1.58. So you should use a power supply that can deliver at least 1.6A. To be on the safe side, round this value roughly up to 2A. This way you are on the safe side.

Instagram lamp:
The Instagram lamp uses two LED strips with a total of 35 LEDs. A Wemos D1-Mini is also installed to control the LEDs. This means the maximum power consumption can be calculated as follows: 35×0.06A+0.2A=2.3A. So you should use a power supply that can deliver at least 2.3A. To be on the safe side, round this value roughly up to 2.5A. Even a 3A power supply would not be grossly oversized at this point. 🙂

Performance

The power (formula symbol: P) is ultimately – in the track current range – just the product of voltage and current. However, on some power supplies sometimes the output current is not specified but only the output power. With this knowledge and the right formula, you can calculate what power or current your power supply must deliver. Because it applies:

Power = Voltage * Current
respectively
P = U * I

Switching power supply or transformer power supply

The question of whether a switching power supply or a transformer power supply is actually not a real (technical) criterion that you have to consider when choosing your power supply. If the power supply delivers the required voltage and power, switching and transformer power supplies are electrically identical.

The big pro argument for switching power supplies, on the other hand, is that they are often smaller/more compact and also lighter than comparable transformer power supplies. This goes hand in hand with the price. Switching power supplies are often significantly cheaper than transformer power supplies, especially in the higher power range. But if you already have a transformer power supply lying around, you can of course use it.

---

Understanding data sheets

Every power supply now contains a data sheet that is either stuck on or stamped into the plastic of the housing. This data sheet always contains information about the permitted input voltage, output voltage, power and often other additional information.

Unfortunately, these data sheets are often not uniform, which is why it is sometimes difficult to interpret these data sheets and understand the information. That's why a few power supplies and their data sheets with explanations are listed below. This should provide an explanation for every symbol or information. If not, just write it in the comment section. 🙂

General information about the information on the data sheets:

The information there is always maximum information. So if it says that a power supply can deliver 1A, then of course it can also deliver 0.2A or 0.5A. But not 1.1A.
The same also applies to performance information. If the data sheet states that a power supply can deliver 50W of power, then - in most cases - it can of course also deliver 10W, 20W or 45W.

Power supply of a printer

Below you can see the power supply of an old printer. This type of power supply has the advantage of being able to deliver different voltages and currents. The design is usually very specialized for the respective printer.

1. “INPUT: 100V 50/60HZ 82VA”:
Indicates (in combination with the underlying INPUT line) that the Input voltage (INPUT) in the range between 100V and 240V must lie. This large valid input voltage range is because the power supply can be used in power grids with 120V (e.g. in North America, South America, etc.) but also 230V (e.g. in Europe, Russia). These are the typical voltages for the world's power grids. On the one hand, the specification “50/60 Hz” indicates that the input voltage should be alternating voltage. This also indicates that the power supply also works with the different network frequencies 50Hz or 60Hz comes clear. The last entry “82VA” indicates which one The maximum power the power supply absorbs. Power is usually given in watts (unit symbol: W). In this case, however, “VA” is indicated, which indicates that the power in this case is AC power.

2. “OUTPUT: 32V 0.75A 24V 0.5A”:
This indicates that it multiple output voltages gives. The first corresponds to 32V and can deliver 0.75A. The second corresponds to 24V and can deliver 0.5A. Both tensions are DC voltages which you can see from the symbol that looks like an equal sign with the bottom line dashed (see 3.).

3. Symbol for DC voltage and pulsed DC voltage

4. Name of the power supply

5. CE mark

6. Symbol for reinforced or double insulation:
This symbol indicates the protection class of the power supply and symbolizes protection class II. Devices of protection class II have reinforced and double insulation for all potentially live parts. You can also find additional information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung

7. Various other symbols from various testing companies

---

Open/closed frame power supplies

Open- or closed-frame power supplies are often delivered in the form of an open or closed metal frame. They are perfect for being installed in the housing of a device (e.g. monitor). Due to the very specialized application they often offer several functions (e.g. standby voltage or generally several voltages).

1. “Input: 100-240V~50-60Hz 1A”:
Specifies that the input voltage (INPUT) must be in the range between 100V and 240V. On the one hand, the specification “50/60 Hz” indicates that the input voltage should be alternating voltage. This also indicates that the power supply can also handle the different mains frequencies of 50Hz or 60Hz. The last information “1A” indicates the maximum current that is drawn from the supply network.

2. “Outputs:
+5V dc 3.70A: Output voltage from +5V to a maximum of 3.7A
+12V dc 0.60A: Output voltage from +12V to a maximum of 0.6A
-5V dc 0.05A: Output voltage from -5V to a maximum of 0.05A
+5V Trickle dc 0.1A”: Pulsed output voltage from +5V to a maximum of 0.1A

3. “CAUTION: For continued protection against risk of fire, replace only with exact type and ratings of fuse, 1.6A, 250V.”:
This information indicates that there is a device fuse inside, which should be replaced with a new one with the information specified in the event of a defect.

---

Plug-in power supply with transformer

Plug-in power supplies are largely defined by the fact that the power supplies are integrated into the plug housing. There are plug-in power supplies with a transformer and plug-in power supplies as switching power supplies (see below). Plug-in power supplies with transformers are usually easy to recognize because of their relatively high weight. This is because these power supplies contain a transformer, which is usually very heavy. In addition, the housing shape is often almost cube-shaped.

1. PRI 230V ~ 50Hz
Indicates that the input voltage (PRI=primary (winding)) must be 230V. The indication “50 Hz” indicates that the input voltage should be an alternating voltage with a frequency of 50 Hz. Since this power supply is a transformer power supply - and not a switching power supply like the previous two power supplies - its input voltage range is limited to a fixed value. The output voltage is directly dependent on the input voltage.  

2. SEC: 10V ~ 7VA
Indicates that the output voltage is an alternating voltage with an effective value of 10V. The maximum output power here is 7VA. The output power is given as apparent power. So it cannot be equated with the active power in watts. As an estimate, one can assume a maximum active power that is “slightly” lower than the apparent power. 

3. Symbols of various testing companies

4. Symbol with three circles and a rectangle:
This is the symbol that indicates that this power supply is a toy transformer. You can find more information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Spielzeugtransformator

5. Symbol with two squares lying one inside the other:
This symbol indicates the protection class of the power supply and symbolizes protection class II. Devices of protection class II have reinforced and double insulation for all potentially live parts. You can also find additional information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung

1. MAINS: 230V ~ 50Hz 0.1A
Indicates that the input voltage (NETZ = mains side) must be 230V. The indication “50 Hz” indicates that the input voltage should be an alternating voltage with a frequency of 50 Hz. Since this power supply is a transformer power supply - and not a switching power supply like the previous two power supplies - its input voltage range is limited to a fixed value. The output voltage is directly dependent on the input voltage. The indication 0.1A also indicates that the current drawn from the supply network is 0.1A.

2. OUTPUT: 5Vdc 800mA
Indicates that the output voltage is 5V and can supply a maximum of 800mA. In addition, the output voltage this time is a DC voltage.

3. Various symbols:
House with arrow: Only suitable for use inside a building.
Rectangle with temperature information: Please note that this power supply is temperature protected up to a maximum of 115°C. At 115°C, a fuse is triggered in the power supply to protect the power supply and any downstream consumers.
Symbol with two intertwined rings and a “shield”:
This symbol indicates that the power supply in question meets the criteria safety transformer Fulfills. You can find further information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Sicherheitstransformator
Symbol with two squares inside each other:
This symbol indicates the protection class of the power supply and symbolizes protection class II. Devices of protection class II have reinforced and double insulation for all potentially live parts. You can also find additional information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung
The remaining symbols:
Test marks from the test centers of Norway, Finland, Sweden and Denmark.

4. Symbol with a minus and a plus in a circle:
This symbol points to the Contact assignment of the connection plug. This has an internal and an external pole. In this case, the inner one (which is connected to the circle containing a plus sign with a line) is connected to the positive pole. The external pole is therefore the negative pole or the ground.

---

Plug-in power supply as a switching power supply

Plug-in power supplies as switching power supplies are often much lighter and more compact than plug-in power supplies with a transformer. These also have the complete power supply technology integrated into the connector housing.
The advantages over plug-in power supplies with a transformer are that they are cheaper, often more compact and lighter with the same performance and are also often suitable for different supply networks (which means that you can often simply continue to use this type of power supply when traveling to other countries).

1. INPUT: 100-240V ~ 50/60Hz 9W
Specifies that the input voltage (INPUT) must be in the range between 100V and 240V. On the one hand, the specification “50/60 Hz” indicates that the input voltage should be alternating voltage. This also indicates that the power supply can also handle the different mains frequencies of 50Hz or 60Hz. The last information “9W” indicates the maximum power that is drawn from the supply network.

2. OUTPUT: 15V 5.4W
Indicates that the output voltage is 15V and the power supply can deliver a maximum of 5.4W of power.

3. “IPX4”:
This information indicates the protection against contact and the dust and water resistance of the device. This information is summarized as information about Protection class called. The letters “IP” always stand for International Protection. Only the following numbers provide information about how strong (or weak) the device is protected. The first number stands for protection against foreign bodies and the second for protection against contact. You can find further information about this in the associated Wikipedia article: https://de.wikipedia.org/wiki/Schutzart

4. Symbol with two intertwined rings and a “shield”
This symbol indicates that the power supply in question meets the criteria safety transformer Fulfills. You can find further information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Sicherheitstransformator

5. “Transistor symbol”
This symbol indicates that this power supply is a switching power supply.

6. Symbol with a crossed out garbage can
This symbol indicates that this power supply must not be disposed of with household waste.

1.AC/DC
Indicates that the power supply expects an alternating voltage (AC) on the input side and converts this to a direct voltage (DC) on the output side.

2. INPUT: 100-240V AC
Specifies that the input voltage (INPUT) must be in the range between 100V and 240V. Unfortunately, no permitted input frequency range or power consumption is specified.

3. OUTPUT: 5V 1A
Indicates that the power supply outputs an output voltage of 5V and delivers a maximum current of 1A.

4. Symbol with two squares lying one inside the other:
This symbol indicates the protection class of the power supply and symbolizes protection class II. Devices of protection class II have reinforced and double insulation for all potentially live parts. You can also find additional information about this in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung

5. Icon with a house and an arrow pointing to the inside of the house
Only suitable for use inside a building.

---

Further information

https://www.code-knacker.de/elektro.htm

https://www.iso.org/obp/ui#iec:grs:60417:6190

---

Have fun with the project

I hope everything worked as described for you. If not or you have questions or suggestions please let me know in the comments. I will then add this to the article if necessary.
Ideas for new projects are always welcome. 🙂

PS Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you think it's cool that I share the information with you, I would be happy about a small donation to the coffee fund. 🙂