Which power supply to use for Raspberry Pi?

Thread Starter

nightcrawler218

Joined Dec 24, 2012
26
As far as the official specifications are concerned an rPi can be powered with supplies from 5V to 12 V. Typical current for 5V supply is 2A. Total power required for an rPi is 10W roughly.

I have two power supplies (5V, 2A) and (10V, 1A)
which one to be used so that the pi dissipates less amount of heat while in operation?
Why?

If in a given scenario, one has a blackbox with a power requirement of 10W irrespective of Voltage & current (lets assume the voltage bracket is 5V to 12V and current bracket is 1A to 3A) then which power supply you would go for? and why?

Any clarification shall be appreciated.

Thanks.
 
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MisterBill2

Joined Jan 23, 2018
6,359
I am not familiar with the power requirements of that board, but given that processors typically run on 5 volts or less, the 5 volt supply makes sense and the ten volt supply does not. Reducing the voltage with increasing the current will require some sort of active circuit and the efficiency is always less than 100%, and that is power wasted as heat.
IT would be making the decision a lot easier by providing the exact power requirements of the system.
 

LesJones

Joined Jan 8, 2017
2,671
The two Raspberry Pi's I have only support being supplied with 5 volts. The origin Raspberry Pi via a mini USB connector, The Raspberry Pi 2 via a micro USB connector.I have justlooked at the specifications for the Raspberry Pi 4 and that only supports being powered from 5 volts.
I reply to you question in post #3 Reading the datasheets or specifications of any device is a good place to start.

Les.
 

danadak

Joined Mar 10, 2018
4,057
Cascaded regulators waste energy. The overall efficiency is the product of the efficiencies
in the cascade. So if 10V supply has a 90% efficiency and the 10V to 5V also 90%, then
overall efficiency is .9 x .9 = 81%. Thats wasted energy which shows up in the form of heat.

Also reliability is reduced over a single regulator, preferably switched, that takes raw DC
and creates the 5V supply. Single regulator solution has less components, therefore greater
reliability.

Also make sure your USB cable for power to the Pi is a quality cable. There are a lot of cheap
cables out there that drop V due to wire gauge inadequacies in the cable.


Regards, Dana.
 

MisterBill2

Joined Jan 23, 2018
6,359
Any suggestions on how to think while solving such problem statements? Where to start from or which theories need to be re learned?
OK, and a good question indeed. The fist step would be to learn what voltage the actual system hardware uses for operation. That may be as simple as reading the specifications, or it may require studying the actual hardware, locating the model number of the various IC devices, and determining what the manufacturer recommends as the supply voltage. Or it may be found by examining the circuit diagram, either block or actual schematic. That ought to at least provide the same part numbers without needing a good magnifier.
After finding the required voltage, determining the required current capability for the power supply can be a challenge, although often that is stated in the system specifications. The main downside in having excess capacity beyond what the system needs is size and cost of that excess capacity. As long as the voltage is correct the load will only draw what current it needs.
If only the wattage is given, then once the voltage is determined, it is simple to calculate current. Watts divided by volts = amps.

Hopefully this explanation is useful.
 

MrChips

Joined Oct 2, 2009
21,377
For a definitive answer you can examine the circuit schematic of the particular model and board you have.

What supply voltages are required on the board?
What voltage regulators are being used? Are the voltage regulators linear or switching regulators?
Linear regulators required some overhead voltage. You want to keep the overhead to a minimum to minimize wasted power and heating.

As far as I can see with a quick examination of an rPi 3 Model A+ Revision 1.0 circuit schematic,
the components on board require 3.3V and 5V.
All regulators on board are switching regulators.
Incoming voltage to the board is +5VDC.

In conclusion, the correct power supply voltage is 5VDC.
 

MisterBill2

Joined Jan 23, 2018
6,359
For a definitive answer you can examine the circuit schematic of the particular model and board you have.

What supply voltages are required on the board?
What voltage regulators are being used? Are the voltage regulators linear or switching regulators?
Linear regulators required some overhead voltage. You want to keep the overhead to a minimum to minimize wasted power and heating.

As far as I can see with a quick examination of an rPi 3 Model A+ Revision 1.0 circuit schematic,
the components on board require 3.3V and 5V.
All regulators on board are switching regulators.
Incoming voltage to the board is +5VDC.

In conclusion, the correct power supply voltage is 5VDC.
OK,Mr Chips has verified that my process, as suggested, works. The detailed analysis method DOES work.
 

Reloadron

Joined Jan 15, 2015
5,512
From our friends at the Raspberry Pi world. I suggest you read this because as can be seen the current demand can vary based of course on what the thing is doing? Which model? And it helps to have an understanding of typical bare-board active current consumption, maximum total USB peripheral current draw and recommended PSU current capacity based on model. While they mention a 5.1 volt supply they all run just fine on a 5.0 volt supply.

Ron
 
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