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

You need power supplies almost in every project, because someone needs to deliver the energy for your project. 🙂

There are some things to consider. On the one hand, you do not want to put yourself or others at risk, and on the other hand, the built project should run successfully with it.

It is particularly important that the power supply has enough power to supply the project. On the other hand, you do not want to have any expensive giant power supply at home. Here, therefore, a compromise between price, electrical power and application needs to be found.

Which criteria you should consider is described in the following article.

In addition, the information contained on the data sheets of the power supplies are described. Often you do not have to buy a new power supply but can simply use the power supply of the old phone, children’s toys, etc.

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

Hints for our lovely english readers: Basically, many of the articles on Nerdiy.de are translations from the original german articles. Therefore, it may happen here and there that some illustrations are not available in english and that some translations are weird/strange/full of mistakes or generally totaly wrong. So if you find some obvious (or also not obvious) mistakes don't hesitate to leave us a hint about that in the comment section. 
Also please don't get confused, that instead of a "dot" often a "comma" is used as decimal separator. 🙂


Safety instructions

I know the following hints are always a bit annoying and seem unnecessary. But unfortunately, many people who knew it "better" from carelessness lost their eyes, fingers or other things or hurt themselves. In comparison, a loss of data is almost not worth mentioning, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Even the coolest project is worth no injury or other annoyance. https://www.nerdiy.de/en/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 shop via this link, Nerdiy.de receives a commission from the online shop or provider concerned. The price doesn't change for you. If you do your purchases via these links, you will support Nerdiy.de in being able to offer further useful projects in the future. 🙂


Requirements

Required material:
-none-

Required tools:
-none-


Sustainability

A key word that has been heard more and more in recent years is “sustainability”. In principle, it is about using old, already existing resources for new purposes. This is exactly what the knowledge in this article should help you with. Because if you can “decrypt” the symbols and data on your existing power supplies, you can continue to use them for new projects.

So you have to buy fewer power supplies, do not have to throw away as many power supplies and 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 (symbol: U) is inevitably determined by the circuit of your project. Often you need a certain voltage or a certain voltage range for your project.

For example, if you have a project that is powered by a USB port, such as one of the projects here on Nerdiy.de, then you need a power supply with a “typical USB voltage”, ie 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 gives the USB power supply is therefore in the range of 4.75V-5.25V.

Examples:
– Your circuit needs 12V: The power supply must also supply 12V
– Your circuit needs 5V: The power supply must also supply 5V. In this case, you can – at least the voltage concerning – also use a USB power supply.

Current

To find out how much power (symbol: I) has to supply your power supply, you must first – at least roughly – determine how much power your circuit needs. It is important that you do not accept the “normal case”. So the average power consumption. But the maximum case. The maximum case is in this context the case in which all consumers “consume” the maximum power.

To determine the maximum power consumption of your circuit, you must determine the maximum power consumption of all components used therein and then sum up these values.

The maximum current consumption of a specific component can always be found on the respective data sheet or measured with a measuring instrument. (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 a LED strip with 23 RGB LEDs. In addition, a Wemos D1-Mini is installed to control the LED’s. This means the maximum power consumption can be calculated as follows: 23×0.06A + 0.2A = 1.58A. So you should use a power supply that can deliver at least 1.6A. To be on the safe side, this value is roughly rounded up to 2A. So you’re on the safe side.

Instagram lamp:
The Instagram lamp uses two LED strips with a total of 35 LED’s. In addition, a Wemos D1-Mini is installed to control the LED’s. This means the maximum power consumption can be calculated again 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, this value is roughly rounded up to 2.5A. Even a 3A power supply would not be oversized at this point. 🙂

Power

The performance (symbol: P) is simply – in the DC-range – the product of voltage and current. On some parts, however, sometimes not the output current but only the output power is indicated. With this knowledge and the right formula you can calculate which power or which power 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 switching power supply or transformer power supply is actually no real (technical) criterion that you have to consider when selecting your power supply. When the power supply provides the required voltage and power, the switch and transformer power supplies are (mostly) electrically identical.

The big pro-argument for switching power supplies, however, is that they are often smaller/more compact and lighter than comparable transformer power supplies. That’s why the price goes along with it. Especially in the higher power range, switching power supplies are often much cheaper than transformer power supplies. But if you already have a transformer power supply you can of course use it.


Understand datasheets

Each power supply now contains a data sheet that is either glued or stamped in the housing plastic. This data sheet then always contains information on the permitted input voltage, output voltage, power and often other additional information.

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

A general information about the information on the data sheets:

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


Power supply of a printer

In the following you see the power supply of an old printer. These types of power supplies have the advantage that they can supply different voltages and currents. But the design is usually very specialized on the particular printer.

Detail view of the data sheet without notes.

1. “INPUT: 100V 50 / 60HZ 82VA”:
Indicates (in combination with the underlying INPUT line) that the input voltage (INPUT) must be in the range between 100V and 240V. This large valid input voltage range is due to the fact that the power supply can be used both in 120V power grids (e.g., North America, South America, Asia etc.) but also 230V (e.g., in Europe, Russia, Asia). These are the typical voltages for the electricity grids in the world. The indication “50/60 Hz” indicates, on the one hand, that the input voltage should be an alternating voltage. Furthermore, this indicates that the power supply comes with the different power frequencies of 50Hz or 60Hz clear. The last indication “82VA” indicates to which power the power supply unit absorbs at maximum. Normally, a power in watts (unit symbol: W) is specified. In this case, however, “VA” is indicated, which indicates that it is an AC power in this case.

2. “OUTPUT: 32V 0.75A 24V 0.5A”:
This indicates that there are several output voltages. The first corresponds to 32V and can deliver 0.75A. The second corresponds to 24V and can deliver 0.5A. Both voltages are DC voltages which can be seen by the symbol that looks like an equal sign of which the lower bar is 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 to all potentially live parts. Additional information can be found 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 audit companies


Open / closed frame power supplies

Open or closed-frame power supplies are often supplied in the form of an open or closed metal frame. They are perfect for mounting in the case of a device (such as a monitor). Because of the very specialized application, they also often provide multiple functions (e.g., standby voltage or more voltages in general).

1. “Input: 100-240V ~ 50-60Hz 1A”:
Indicates that the input voltage (INPUT) must be in the range between 100V and 240V. The indication “50/60 Hz” indicates, on the one hand, that the input voltage should be an alternating voltage. Furthermore, this indicates that the power supply accepts different power frequencies of 50Hz to 60Hz. The last indication “1A” indicates which maximum current is drawn from the mains.

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 fire, replace only with exact type and rating of fuse, 1.6A, 250V.”:
This information indicates that there is a device fuse inside, which in the case of a defect should be replaced by a new one with the specified information.


Plug-in power supply with transformer

Plug-in power supplies are largely defined by the fact that the power supply units are integrated in the plug housings. There are plug-in power supply units with transformer and plug-in power supply units as switching power supplies (see below). Plug-in power supplies with a transformer are usually easily recognized by 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 close to cubic.

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 the frequency 50 Hz. Since this power supply is a transformer power supply – and not a switched-mode power supply like the two previous power supplies – its input voltage range is limited to a fixed value. The output voltage is directly dependent on the input voltage.

SEC: 10V ~ 7V
Indicates that the output voltage is an AC voltage with an RMS value of 10V. The maximum output power here is 7VA. The output power is given as apparent power. So it is not to be equated with the active power in watts. As an estimate one can assume a maximum active power that is “somewhat” lower than the apparent power.

3. Symbols of various audit companies

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

5. Symbol with two nested squares:
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 to all potentially live parts. Additional information can be found in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung

1. NETWORK: 230V ~ 50Hz 0.1A
Indicates that the input voltage (mains = mains side) must be 230V. The indication “50 Hz” indicates that the input voltage should be an alternating voltage with the frequency 50 Hz. Since this power supply is a transformer power supply – and not a switched-mode power supply like the two previous power supplies – its input voltage range is limited to a fixed value. The output voltage is directly dependent on the input voltage. The figure 0.1A also indicates that the power consumed by the grid is 0.1A.

2. OUTPUT: 5Vdc 800mA
Indicates that the output voltage is 5V and can deliver 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 indication: Note that this power supply is temperature-protected up to a maximum of 115 ° C. At 115 ° C in the power supply a fuse is triggered to protect the power supply and possibly downstream consumers.
Symbol with two entwined rings and a “shield”:
This symbol indicates that the relevant power supply meets the criteria of a safety transformer. More information can be found again in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Sicherheitstransformator
Symbol with two nested squares:
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 to all potentially live parts. Additional information can be found 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 of the test centers of Norway, Finland, Sweden and Denmark.

4. Symbol with a minus and a plus in a circle:
This symbol indicates the pin assignment of the connector. This has an inside and an outside pole. The innermost (which is connected to a dash with the circle containing a plus sign) is in this case connected to the positive pole. The outer pole is therefore the negative pole or the ground.


Plug-in power supply as switching power supply

Plug-in power supplies as switching power supply are often much lighter and more compact than plug-in power supplies with transformer. Even with these, the entire power supply technology is integrated into the connector housing.
The advantages over power packs with transformers are also that they are cheaper, with the same power are often more compact and lighter, and also often suitable for different networks (which makes it easy to use this type of power supply even when traveling to other countries).

Detail view of the power supply without hints.

1. INPUT: 100-240V ~ 50 / 60Hz 9W
Indicates that the input voltage (INPUT) must be in the range between 100V and 240V. The indication “50/60 Hz” indicates, on the one hand, that the input voltgae should be an alternating voltage. Furthermore, this indicates that the power supply is okay with the different power frequencies of 50Hz or 60Hz. The last indication “9W” indicates which maximum power 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. In summary, this information is given as an indication of the degree of protection. The letters “IP” always stand for International Protection. Only the following codes give information about how strong (or weak) the device is protected. The first code stands for protection against foreign bodies and the second code for protection against contact. Further information can be found in the corresponding Wikipedia article: https://de.wikipedia.org/wiki/Schutzart

4. Symbol with two entwined rings and a “shield”
This symbol indicates that the relevant power supply meets the criteria of a safety transformer. More information can be found again in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Sicherheitstransformator

5. “transistor symbol”
This symbol indicates that this power supply is a switched-mode power supply.

6. Symbol with a crossed-out wheelie bin
This symbol indicates that this power supply must not be thrown in the normal “household-rubbish”.

1. AC / DC
Indicates that the power supply is expected to have an alternating voltage (AC) on the input side and converts it to a DC voltage in the output side (DC).

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

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

4. Symbol with two nested squares:
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 to all potentially live parts. Additional information can be found in the very detailed Wikipedia article: https://de.wikipedia.org/wiki/Schutzklasse_(Elektrotechnik)#Schutzklasse_II_/_Schutz_durch_doppelte_oder_verst%C3%A4rkte_Isolierung

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


Additional information

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

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


I hope everything worked as described. If not or you have any other questions or suggestions, please let me know in the comments. Also, ideas for new projects are always welcome. 🙂

Fab

P.S. 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 appreciate it that I share these information with you, I would be happy about a small donation to the coffee box. 🙂

Buy Me a Coffee at ko-fi.com

3 comments

  1. Hallo Fabian,

    cooler Artikel, war mir auch nicht klar, was für einen bunten Zoo an Netzteilen es gibt. In dem Abschnitt “Steckernetzteil mit Transformator” ist mir aber was aufgefallen: Da steht unter dem Bild “2. SEC: 10V ~ 7V”, auf dem Netzteil steht aber “2. SEC: 10V ~ 7VA” – was glaube ich heißen soll, dass das Netzteil 10V Wechselstrom mit maximal 7W leistet oder?

    Viel Erfolg noch mit Deiner neuen Website,

    Christoph

    1. Hey Christoph,
      Danke für den Tipp! Du hast absolut recht. Habe den Teil korrigiert. Da habe ich wohl etwas geschlafen beim Schreiben. 😀

      Danke und Beste Grüße
      Fab

  2. Hi Fab,
    vielen Dank für diesen tollen und ausführlichen Artikel. Besser erklärt als jedes Schulbuch 🙂
    Gerade die unterschiedlichen Beispiele & Fotos sind klasse.
    Vielleicht kannst du ganz oben beim Teil “Schaltnetzteil oder Transformatornetzteil” noch schreiben, dass du weiter unten die Details erklärst. (Ist zwar eigentlich klar, aber ich bin da schon ganz wibbelig vor Interesse geworden und habe quergegoogelt, was denn jetzt was ist 🙂 )
    Schönen Gruß
    Paul aus Aachen

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