Raspberry Pi Power Supply Test

The Raspberry Pi does not come with its own power supply. It’s up to you to provide one and make sure it functions within the designers’ parameters in order to make sure you’re getting enough stable power. In order to help you make your choice I have run a few simple tests of my own to guide you to a decision on which power supply to use and to show you how you can perform a test on your own power supply.

Power Supplies

I have four different power supplies available to test right now.

  1. Griffin SP5Q-NA, Output: 5V, 1A (upper left)
  2. Apple A1265, Output: 5V, 1A (upper right)
  3. BlackBerry PSM04A-050RIM(NY), Output: 5V, 700mA
  4. Belkin F5U415 Swivel Hub, Output: 5V, 2.5-2.6A

At first glance you may be leaning toward the Belkin hub but you need to realize that there are no specifications printed on the hub itself about the supplied voltage and current via the USB ports. I was also unable to find them anywhere online so we will just have to wait for the test results.

Before we get to the test results I need to quickly describe my testing method. I performed three tests on each power supply. The first test consisted of booting the RPi with no other cables or devices (audio, USB, network) attached. This was to allow me to see the voltage at system idle. The second test was to check the voltage with a network cable attached to the Ethernet port to see how much of a voltage drop we would see. The third test was performed after the RPi had been given the shutdown command and I was ready to disconnect the power.

Raspberry Pi - Model BI used my DMM for the voltage measurements. I set the dial to 20DCV and touched the positive (red) lead to the TP1 test point on the RPi. TP1 is located next to the capacitor just behind the power port on the RPi. I then touched the negative (black) lead to the TP2 test point between the GPIO header and the composite video port.

The Raspberry specifications call for a power supply that can supply 5V with a +/-0.25V variance. The results that fall into this range (4.75V-5.25V) will be shown in green. Anything outside that will be show in red. If the result is within 0.02V of either end of the range, the results will be shown in yellow.

The first power supply I tested was the Apple A1265, the power supply that came with my iPhone 4S. The cable I used was the 40-inch USB sync cable supplied with my retired BlackBerry Tour.

Test 1a: Running idle w/o data connections: 4.86V
Test 1b: Running idle w/ only Ethernet connection: 4.82V
Test 1c: Completed system shutdown, power still on: 5:00V

Now to test power supply #2, the Griffin PSM04A-050RIM(NY). For this test I used the BlackBerry sync cord used for the Apple USB adapter.

Test 2a: Running idle w/o data connections: 4.84V
Test 2b: Running idle w/ only Ethernet connection: 4.81V
Test 2c: Completed system shutdown, power still on: 4.96V

Now for the BlackBerry PSM04A-050RIM(NY) AC Charger.

Test 3a: Running idle w/o data connections: 4.97V
Test 3b: Running idle w/ only Ethernet connection: 4.94V
Test 3c: Completed system shutdown, power still on: 5:09V

Finally, the Belkin Swivel Hub.

Test 4a: Running idle w/o data connections: 4.59V (this reading fluctuated down as far as 4.42V)
Test 4b: Running idle w/ only Ethernet connection: 4.52V
Test 4c: Completed system shutdown, power still on: 4.93V

Now my rankings work as follows, by using the rated voltage as a zero point we add one point for each 1/100V the other readings are off by. As in golf, the lower score is the better score.

PS1: Griffin – 1a) 14, 1b) 18, 1c) 0 – 32 points
PS2: Apple – 2a) 16, 2b)19, 2c) 4 – 39 points
PS3: BlackBerry – 3a) 3, 3b) 6, 3c) 9 – 18 points
PS4: Belkin Hub – 4a) 41, 4b) 48, 4c) 7 – 96 points

Therefore, my final ranking for these four power supplies are as follows:

  1. 18 points – BlackBerry PSM04A-050RIM(NY), Output: 5V, 700mA
  2. 32 points – Griffin SP5Q-NA, Output: 5V, 1A (upper left)
  3. 39 points – Apple A1265, Output: 5V, 1A (upper right)
  4. 96 points – Belkin F5U415 Swivel Hub, Output: 5V, 2.5-2.6A

Hopefully this article has been helpful to you. If it has then please leave your comments.

Later,
Keith

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2 responses to “Raspberry Pi Power Supply Test

  1. Hello and thank you Keith for your very helpful article. I just ordered the model b and I was concerned about the power requirements. I have three of the Blackberry adapters lying around so I got lucky I guess. Do you think that the Blackberry power adapter will give me enough juice to power a USB nano WiFi Realtek RTL8188CUS? Thanks again.

    • I don’t have any specs on that WiFi dongle but I think the Blackberry power supply will provide sufficient power to support it if you are running in a headless configuration. However, if you are planning on using it along with a keyboard and mouse then I recommend connecting all the USB devices through a powered hub. Let me know how things go.

      If you are using a keyboard and monitor and running in command line mode only you may be able to get away with running the WiFi dongle and keyboard at the same time but you’ll likely be running right on the edge. And don’t expect to be able to hotplug the WiFi. In my experience, plugging in the WiFi after the OS is booted will cause a spontaneous reboot. Using a powered USB hub will help you avoid that.

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