Sunday, June 29, 2014

Simple Test / Check of Power Supply for Raspberry Pi

There are numerous blog posts and forums that discuss about the suitable power supply that Raspberry Pi can operate on. In layman's term, as long as your power supply can support 5V and 1A, you Raspberry Pi should operate properly. However, there are questions remain, for example:

1. How can we be so sure that our power supply we use can supply 5V 1A all the time?
2. Can the power supply still supply 5V 1A to Raspberry Pi if we have several peripheral connected?

Today I'm going show a simple method on how to check your power supply whether it is good enough to support RPi's operation.

First you have to know some basic info on RPi's operating condition. You can get them HERE or HERE. I'm using a Model B board, so according to the sites, the operating voltage is from 4.75V to 5.25V. Operating current is from 700mA to 1500mA. I don't have a equipment to measure current consumption for now. So I'm going to assume the power supply i will use later can provide current that RPi requires.

Next, you should have the following hardware prepared. Refer to list below:

  • Raspberry Pi loaded with Raspbian. (Refer to HERE for more info, if you haven't install Raspbian)
  • Power Supply (I'm using a smartphone charger, refer to HERE for more info)
  • Wireless LAN USB adapter
  • USB Keyboard and Mouse
  • LAN cable (Hooked up through router or computer)
  • Multimeter (To measure voltage across Pi)

I've set my Pi to boot up normally and do not boot to GUI, this should keep the Pi's processes to minimum so that i can get good reading on Multimeter. You can set the RPi to boot without GUI loaded by typing command "sudo raspi-config" in LXTerminal and select option 3 to choose booting without GUI. After you finish the configuration, enter "sudo shutdown -r now" to reboot to apply changes.

You should also enable SSH in raspi-config so that you can still control your RPi remotely. Refer to HERE for more info.

I've configure my RPi through raspi-config to use normal operating condition for its processor, ie no overclocking, frequency set to default 700Mhz and no overvolt.

I also configure RPi's config.txt file to make sure RPi is turning on HDMI port even without HDMI connected. I was away from my TV when i was doing this test. So i had to change the config.txt file to tell RPi to keep turning on the HDMI port. Refer to HERE on how to edit you config.txt file.

We are going to monitor the voltage across RPi under different setup to see whether the power supply is indeed within 4.75 to 5.25V when operating. To achieve that we are going to measure the board using Multimeter on TP1 and TP2. You can check out Figure1 below for the location of TP1 and TP2 on board.

Figure1: Location of TP1 and TP2

Here is a list of hardware configuration i tested and its respective voltage level when i boot up my RPi.

Hardware Configuration Measured Voltage Across TP1 and TP2
Normal Mode + WLAN + LAN 4.76V
Normal Mode + WLAN 4.80V
Normal Mode + LAN + USB Keyboard + Mouse 4.83V
Normal Mode + LAN 4.87V
Normal / Idle Mode 4.91V
Power Down Mode 5.03V

  • As i mentioned earlier, i just boot up my RPi and did not boot GUI. So basically my RPi is idling and do nothing. I call this state of RPi, "Normal mode".
  • Power Down Mode is where i shutdown my RPi and leave the power supply on. I achieve this by sending in command "sudo shutdown -h -P now". This is a rough estimation of the voltage level that my smartphone charger provides to my RPi.

Based on the Multimeter's reading that i get under different hardware configuration, the RPi is operating within 4.75V to 5.25V. So in this simple test we can conclude that the power supply used is capable of providing enough power to RPi under normal usage.You might notice the lowest voltage reading is 4.76V (very close to 4.75V lower operating voltage) where WLAN and LAN were turn on at the same time. So from this test you know you should avoid turning on both network at the same time. =)

Now you might ask, what is the accuracy of that multimeter, and how reliable this method is on rating the power supply? I would say, these readings are all estimation and it is not 100% accurate. This method can just give you an idea on how well your power supply perform, based on the specs given.

Ideally, regardless of what hardware configuration you use, voltage across the TP1 and TP2 should be always within 4.75V and 5.25V. If one of the hardware combination caused voltage across TP1 and TP2 drop below 4.75V, we can say it is either one of the hardware consume too much power, or the power supply is not capable of provide enough power for RPi to operate normally.

Here are some pictures on the measurement i get during the test.

Figure2: Normal Mode + WLAN and LAN

Figure3: Normal Mode + WLAN

Figure4: Normal Mode + LAN + USB Keyboard + Mouse

Figure5: Normal Mode + LAN

Figure6: Normal / Idle Mode (No other hardware connected)

Figure7: Power Down Mode (Measurement after shutdown)

I hope this post will be useful for you. Enjoy! Feel free to drop your questions in comment. =)

Disclaimer: Please use this site's info at your own risk. I am not responsible for any damage to your RPi or you. Cheers =)


No comments:

Post a Comment