Raspberry Pi Forums

Hi there!

Just unboxed my Pi this past weekend, I'm building a portable media center for my dad, so I'm loading it up with Grateful Dead, Pink Floyd, and some of his other favorites. I've also got some radio stations and Live TV on there now so he'll be able to watch the NASCAR races and whatever other shows he wants.

So my setup is with the Pi 3, the official 7" Pi touch screen, and the WD 314 GB Pi drive so far. I have it all working great so far on Kodi.

I would love to be able to make this thing portable, so my dad can take it outside and work around the house or on the cars with it, so I figured I'd try hooking it up to my phone battery pack (https://www.amazon.com/ZeroLemon-SolarJ ... B00NIOGKL8). Everything works, but I noticed Kodi had a little rainbow square locked in the corner. I thought nothing of it, until I read about it on the undervoltage forum here (view ... 29&t=82373). I combed through that forum and it didn't really answer the questions that I have.

So for starters, what are the consequences of under-powering the device, besides having that little square on the screen? Can I damage the device? Everything seemed to be working fine, I had it on the battery for about 4 hours to futz around and play a movie and it did so flawlessly.

If I am truly under-powering my device, what kind of battery setup would be recommended to run the Pi 3, the official 7" Pi touch screen, and the WD 314 GB Pi drive all hooked up together?

Ideally, I'd like to get this 26800 mah Anker Power Core or something similar to take care of it (https://www.anker.com/products/B1372014). This would be the simplest setup for me and my dad to use. I'm a mechanical engineer, so the hands-on, hardware stuff I've got down to a T, but not so great with software or electronics. I'm sure I could figure out how to rig something together, but since I got a C in Circuits (C's get degrees, right? ) I would much rather use a plug-and-play solution like this if it's available. I've read on other forums that these battery packs can power the Pi itself, but with the other peripherals plugged in, am I coming up short?

Thanks so much! If anyone has found a case for my combination of devices, that would be a great find, if not, I'll probably end up building a custom one!

petebrusch wrote: So for starters, what are the consequences of under-powering the device, besides having that little square on the screen? Can I damage the device? Everything seemed to be working fine, I had it on the battery for about 4 hours to futz around and play a movie and it did so flawlessly.

The low voltage indication tells you the 5V is low. Low voltage will have more effect on things plugged into the USB port that are powered by the port, such as wireless dongles, keyboard, mouse, flashdrive, etc. They will be experiencing low voltage, and some things, especially wireless items don't take to it very well. If the 5V drops too low and the regulator can't maintain it's 3.3V the Pi will crash, freeze, or reboot. But other than possible file corruption from the inadvertent shutdown it won't harm the Pi.

Ideally, I'd like to get this 26800 mah Anker Power Core or something similar to take care of it (https://www.anker.com/products/B1372014).

It seems that it provides two ports, each capable of 2.4A, so you'd have more power available than with your current unit.

The problem is going to be finding a cable with a USB on one end, and a microUSB on the other that has large enough conductors so you don't get too much voltage drop. Those are usually "data" or "phone charging" cables with #30AWG or #28AWG conductors and not really intended for "power" usage. If you're charging a phone, tablet, etc, it will still charge even if you have a voltage drop of a half volt or more. But the Pi will give you a low voltage indication if you're below ~4.65V. So just about any USB cable will work to charge your phone or other device, but you need something a bit more substantial if you want to maintain something near 5V with 1A or more being drawn by the Pi. That's likely why you're seeing the low voltage indication on the unit you're using now, the supply may be adequate, but you're dropping a lot of voltage in the cable.

Example:
Take a typical USB cable with connectors on each end, #28AWG conductors, and a common length of 1 meter (39")
At 5V and a 1A load that cable will drop .39V and you'll only have 4.61V at the Pi, and a low voltage indication will appear. Increase the load to 1.5A and the voltage drop increases to .58V and you'd only have 4.42V at the Pi. It doesn't matter if your power supply is 2A, 10A, or 50A, the voltage drop comes from resistance in the conductors between the Pi and the power supply.

Using a cable with #18AWG conductors, same 5V, same 1A load, and the voltage drop is only .038V and you'd have 4.962V at the PI. Increase the load all the way to 2A and the voltage drop is still only .077V and the Pi would have 4.923V

To summarize, if you want to maintain pressure (voltage) you need a large enough pipe for the flow (current).

Thanks JimmyN, that makes a lot of sense. I really like your pipe analogy, that makes a lot of sense to me. I'll have to see if I can find a better cable, then hopefully I'm good from there.

The best cable of that type (USB to usbMicro) that I've seen is the Anker Powerline+. I haven't found any actual specs and Anker only says "Thick gauge wiring and reduced cable resistance", but they never state what the actual conductor size is in their Powerline cable. And I haven't bought one yet to cut it open and see what's in there, but it is on my "to do" list. The 1' cable is only 4.99 on Amazon, which is really reasonable since the jacket is kevlar fiber with a 10,000 bend lifespan. In my experience Anker does make good quality cables.

They have 10', 6', 3', and 1' lengths. I'm confident the 1' cable would work well, the short length would cut voltage drop to a third of a 3' cable just by being only 1' long. The 3' would probably work too, but without knowing the actual wire gauge to calculate voltage drop that's just a guess right now.

JimmyN wrote: I haven't found any actual specs and Anker only says "Thick gauge wiring and reduced cable resistance", but they never state what the actual conductor size is in their Powerline cable.

I'm not sure how accurate this listing is - but it appears to have specs:

I really like the Anker products, I bought a battery and a speaker from them for this device. I'm basically building it to replace the Milwaukee boombox he carries around the house, he loves it but it uses the same batteries as his cordless drills, which you think would be convenient, but there's no option to plug the thing into the wall! Plus this device I'm building will be internet enabled and have all of his music and streaming capabilities on it, and much simpler to use than his smart phone.

So I did a little experimenting last night using a 3 inch micro USB cable. I discovered that I will get the low voltage warning no matter what by using the cables I purchased with my WD Pi drive. It's a strange custom cable that they made specifically for the drive, so I wouldn't be able to find a substitute. It takes one micro USB power in, and splits it to the drive and the Pi, with a data transfer USB in the middle:
http://store.wdc.com/store/wdus/en_US/D ... d.70262300.

I decided that the best way to do it for my application is to eliminate the Pi drive, as I simply don't need 314 GB of storage for my dad's music, so I purchased a 128 GB flash drive that's still much more than I require (He only has 50.6 GB of Grateful Dead ). It'll help me with packaging this thing too. Once I did away with the hard drive, I could run it on the battery pack with the short 3" cable no problem. I bought what looks to be a good quality 6" cable, so I'll give that a shot and hopefully I'll be good from there. I'm starting to plan out a case, I'll definitely post my results when it's finished!

Thanks again for your help!