Submitted by peter on

A Raspberry Pi powered by Intel? In this case, the Intel based notebook is the power supply and could be the model for a portable Pi.

Who?

You have a notebook computer and a Raspberry Pi device. You want to show off your Pi in a cafe with no mains power sockets anywhere near the table. Or power is available but you want to carry less equipment by leaving out the Pi power block. Here are ideas for you.

You are travelling across country by car without a massive trailer to carry power bricks and everything else. Here ideas around minimising the load when you have a notebook and a Pi.

When?

When there is no mains power. When your backpack is full before you pick up the Pi power block. When there is one mains power socket and you need two or more. When an organisation provides a hall for a meeting but nobody can switch on the power to the building.

Where?

You might be in a barn or at a barbeque. On stage in a public hall with heaps of power points if only someone had extension cables. A car in a remote area. A tent. A cabin when the power fails.

Why?

Mains power for your power supplies is often not available or not reliable or switched off in a mains power cabinet with no access or too far away even with extension cables. If something is battery powered and has USB ports, like a notebook, those USB ports may run a Pi and a portable screen.

With more effort, preparation, and testing, you can use a notebook screen for the Pi instead of lugging a separate screen.

Way?

You can power a Raspberry Pi device and some portable screens from USB. Some notebooks have plenty of USB power. There are a variety of connection options. My examples here use a Pi 500 as that has the heaviest power requirement.

The HDMI output from the Pi can go into a television if there is one in the premises and it has power and you can access a HDMI input. You may need a very long HDMI cable and they often fail with some televisions.

You may be able to unplug the TV, plug in a double adaptor, plug an extension lead into the double adaptor then use a power board and power supplies from the power board. For this approach, you need a backpack full of cables and adaptors and you may crash into the limit of the HDMI cable length.

There are HDMI cables up to ten metres but the signal from the source many be too weak for the cable length or cable quality plus the TV might not handle weak signals. You need the highest quality cables for anything over 2 or 3 metres. My high quality 5 m cable works from my notebook to some screens and fails with other screens. My excellent quality 10 m cable works from my desktop with a powerful graphics card to a professional screen but only at 2K, not 4K. If you cannot test the configuration before use, you need a plan B.

The HDMI output from the Pi can go into a notebook size LCD screen running from a USB port, a configuration I use. My portable screen is an Acer and is exactly the same as their higher quality large notebook screens. There is a USB Type C input for power and it works easily from a typical USB Type C 5 volt 3 amp output. The screen drops in brightness when used from a USB 3 socket with power limited to about 1.6 amps.

The USB 3 specification says a USB 3 Type A socket provides 0.9 amps and many computers have two of those sockets next to each other. In my experience, if you use only one socket out of the two, you can use the combined 1.8 amps. My portable LCD screen can run with the lower amperage but the backlight dims to the point where it is difficult to read. You would use it to show something to one person but not a group.

The screen output can can be copied via VNC and similar protocols across a network connection to the notebook screen, a setup requiring more work and of less use.

  • The setup of VNC and equivalents is difficult. You have to work hard to make anything appear then work harder to make the Pi automatically boot into the right configuration.
  • The connection can be slow to the point where you cannot demonstrate animations at the maximum rate a Pi 5 or 500 produces.
  • You can show the Pi screen on the notebook but not at the same time as anything on the notebook for a comparison. The comparison is limited to half a screen each.
  • Ethernet and WiFi connections chew up power, driving the Pi 5/500 power usage up to the maximum 3 amps from a USB Type C connector. You then have to muck around with PD, USB Power Delivery, and the Pi 5/500 requires an uncommon setting.
  • VNC style connections require different software across each operating system and most options are not well supported. You have to test carefully with whatever OS is on your notebook.

When you need more than 3 amps into a Pi 5/500, the official Pi 5 power supply is much easier than the options. Give up on tricks and plan ahead to have mains power, even if it means a big battery.

An option is to buy several USB power banks. Find ones with a guaranteed 5 volts 3 amps output. Use one for the Pi and a separate one for the LCD screen. Stick to a HDMI connection. If you need WiFi for one part of your demonstration and a USB 3 disk for another part, leave the disk unplugged when using WiFi and switch off WiFI when using the disk. That will keep the peak power usage below 3 amps, down around 2.5 amps.

Always use the same power banks and USB cables for each device. A marginal/cheap power bank may heat up when producing the maximum power then switch down to a lower output. Most power banks show 2 or 3 sockets with each one capable of delivering 3 amps but down in the fine print, they say the maximum combined output across all the sockets is only 3 or 4 amps, a good reason to buy 2 power banks for two devices.

A slightly longer USB cable may have too much resistance. A lower quality cable can have numerous limitations. Test the USB cable supplying power to the Pi 5. Run a light workload with WiFi on and a USB disk plugged in. You will push up near the limit of 3 amps. Now run a heavy workload with network and disk activity. You should push past the 3 amp limit and get low power warnings. An inferior cable will fail before you start the heavy workload.

Worth?

Whatever you choose, test before you need it as that will save you from wasting the time of everyone waiting for your presentation. Prepare and test a plan B.

You might pack a second backpack with power boards and extension cables for those cases where there is a mains power socket. A third backpack might have power banks and a portable LCD screen for those locations with no mains power. You walk in with your regular backpack and the mains power backpack. if there is no power socket, or the power is not working, return that backpack to your car and grab the power bank backpack.

Power boards and extension cables are cheap. Good power banks are expensive. Portable LCD screens are expensive. USB cables can be cheap but good reliable ones cost more. I research the expensive items carefully before buying.

For USB cables, I used to buy USB 3 back when USB 3 was all you could buy but I had to throw out half of them as faulty, no matter how much I spent on the top brands. USB 3.1 enforced some compliance and quality checks before the product could be labelled USB 3.1. I now buy only USB 3.1 or later and only from shops with a good returns policy.

With good planning and testing, you will not have a failure, just, perhaps, a delay while you switch from plan A to plan B.

What?

The Raspberry Pi 500 needs power from a USB Type C cable. I powered the Pi through a USB 3 Type C – Type A cable plugged into a USB 3.1 Type A socket in my Intel based notebook. The notebook has two Type A sockets next to each other and the Pi can draw the power allocated to both, 1.8 amps, if I am not using the other socket. The Pi 500 boots ok and runs programs successfully when booted from a microSD card with power usage around 0.7 amps for just moving the mouse, down to nearly 0.4 amps at idle then up to 0.9 amps during moderate program activity.

The maximum power output from that Type A socket will be reduced if the adjacent socket is drawing power for something like a USB disk. Each Type A socket is supposed to provide 0.9 amps and some USB disks peak at 1.1 amps or more, leaving only 0.7 amps for the Pi. The Pi 500 is most likely not receiving enough power to run applications while plugging in a USB disk as the plugging in produces the biggest peak.

In a notebook with USB Type C sockets, the Type C sockets should provide 3 amps. Some computers are wired in a way where a pair of Type A sockets can supply 3 amps. You have to check your computer. When there is more than one set of USB sockets, test each set for 3 amps output then test the output when all the sets are used. Test with the mains charger unplugged as many notebooks are set to limit power usage when not supplied with mains power.

The Pi 500 has Micro HDMI output for a screen. I have an Acer notebook style screen accepting Mini HDMI input. I have several Micro HDMI to HDMI cables from 1 metre to 2 m. I also have a short extension cable with Mini HDMI male to a HDMI female socket. I add the Mini extension on to a full HDMI - Micro cable to create a Mini to Micro cable.

I looked at buying a Mini to Micro HDMI cable as connecting two cables limits the cable length compared to one dedicated cable. I did not find a suitable cable. The two cable combination works for my current Pi ~ screen combination so I stopped looking for a better cable. At some stage, I will test using adaptors and my 5 metre HDMI cable.

The Acer screen requires power through a Type C USB socket and I use a Type C to C cable for power out from my notebook Type C socket. The screen works but stays dull as if not getting enough power for full brightness. I will test with different cables as the socket could be capable of providing more power but some of my cables are the rubbishy USB 3 standard, not the revised, improved, and mostly fixed USB 3.1 standard.

Mains power backpack

The alternative power backup I would set up is for mains power. I would have a separate backpack for those situations where mains power is available but is rarely in the right location. The pack would contain the following.

  • A double adaptor so I can unplug whatever is plugged into the nearest mains socket then replace that item so it continues working but now I can plug into the other side of the double adaptor.
  • A 10 metre mains extension cable as you can easily need that length. You might need more when you have ot run the cable around the edge of the room.
  • A role of masking tape, gaffer tape, anything removable, so you can tape down the cable where people walk.
  • A power board with six sockets. One for the Pi 5/500. One for your screen. One for your notebook so you can look up problems. One for the sound system when someone walks in carrying one of those little toy amps. One for a desk lamp because some rooms have poor lighting. One spare to plug in a phone charger because idiots with a phone charger will pull out your Pi power supply to get a hit of juice for their iPhone.
  • A second power board if you can fit it in. Place it where you were going to put the double adaptor. This will provide several sockets for people with iPhone chargers. You can get a power board with six sockets plus a socket on the back of the plug, giving you five spare sockets after you plug in the original device and the extension cable.
  • A torch is useful when a mains socket is hidden under furniture.

Power Delivery

You will see PD or Power Delivery mentioned everywhere. USB cables can deliver power to devices like keyboards using just regular USB wires. PD requires separate thick wires for higher amperage. There is a PD chip in the USB cable to switch to the other wires when needed. If your device, the Pi 5, the cable, and the power supply have matching PD, everything works.

The Pi 5 and 500 run with a standard USB type C at 3 amps then switch to 5 volts at 5 amps using PD. 5 volt 5 amps is not a normal USB PD setting. Most cables and power supplies will not understand the request. Use an official power supply or keep the Pi under 3 amps by not using things like a USB disk and WiFi at the same time.

Some power supplies can provide 5 or more amps without PD and the Pi can be set to accept 5 amps without using PD. There are discussions online. I do not use that type of power supply.

The official Pi 5 power supply has the cable built in so there is no need for a separate PD chip in the cable. The official supply starts at 5 volts with 3 amps then switches to 5 amps. There are a large number of devices switching to 6 amps instead of 5 amps, making a PD setting of 6 amps the better choice for compatibility. Neither is specified in the USB standard as published back when the Pi people were planning the Pi 5.

If you do need 6 amps, for handling an NVMe SSD through the PCIe connection plus USB disks, you may need a different configuration. My Pi 4 based file server uses external USB 3 disks of size 3.5 inches as the bigger disks have better speed, more capacity, and external power. A Pi 5 can add heaps of disks using externally powered hubs and disks.

When you move to externally powered hubs, you can add monster WiFi and other devices without adding to the Pi 5 power usage. Some externally powered USB hubs have USB type C input which means that can run from a power bank. You need to test under load to make sure everything maintains full voltage.

There are a heap of projects for running Pi based systems from car batteries. I looked at off the shelf options and they are all expensive. The DIY, Do It Yourself, projects are mainly aimed at Lithium batteries which are expensive when you need more than trivial power and are a fire hazard. By the time you power a Pi 5 or 500 plus a screen, spill proof lead-acid batteries are a better choice. The wiring for use and for charging is, in Australia, mostly ready made for the outdoors market and there are always parts on sale at big discounts.

The portable power choice then becomes multiple power banks, which are on sale some of the time, versus a bigger battery pack from a car/caravan/camping supply store. If you can run everything from power banks, the good brands are a safe choice as the charging circuitry is built in and unlikely to fail plus there are enough brands for price competition. Just make sure you can avoid depending on PD.

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