Powering a Zero and Scroll pHAT with a battery

(Sorry if this is the wrong category, but it’s the closest I could think of).

Hi all, I’m working on a project which uses a headless zero with attached scroll pHAT, which I want to power using a (rechargeable) battery. The problem is that I know so very little about power consumption or how anything like that works, that I have no idea what I should be using.

Can someone point me in the right direction please? Thank you.

You can get 16000mAh batteries designed for recharging mobile phones for about £20.

Running the Zero on it’s own (estimating 100mA consumption) would be no problem for a battery like that (160 hours theoretically). Not sure how much the scroll pHat increases the power consumption though.

How long do you want to be able to run the Zero for before having to charge the battery.

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I’m using them to build a couple of awards for the second anniversary party for a tech community site I run in Birmingham. As such, because they’re just toys, essentially, as long as I get a good few hours out of it, then I’d be happy.

You probably don’t need anything nearly as beefy as I suggested then! Anything designed for charging mobiles should do tho, not sure about your standard AAs etc. Maybe someone with a Scroll pHat can weigh in with an answer on power consumption?

Having taken a look on Amazon, I see they do a line of AmazonBasics Portable External Battery Chargers, which may well suit my needs.

Looking at the photos, I see they all show as being 5 volts (which I’m guessing is what’s needed for the Pi?), and a range of amps (as shown below), but have no clue what that actually means.

Are any of these unsuitable for any reason? Cheers.

PS, for anyone that’s interested, here’s my rough idea for one of the awards:

The power usb connector would be built into his foot, with just the contact exposed for plugging into the pi (making it practically invisible), with the wires possibly fed into his back, or down into a stand on which he can sit (containing the battery).

The LEDs would be used to scroll a message across the screen (maybe the name of the award, along with the description, and name of the winner). I’m not too fussed about it being an open circuit board (it’s for a tech community after all), but I should probably put some type of diffuser on it, to avoid going blind.

Yeah 5V is fine, and 1 amp should be ok for the Pi Zero assuming the Scroll pHat doesn’t draw too much (which depends on the brightness) - for the bigger brothers 2 amp supplies are normally recommended. I’d expect to get a few hours out of a 2000mAh battery at least. Unless someone has some power consumption data on the scroll hat, it might have to be a case of try and see!

For my Unicorn Hat I just use a piece of paper (printed black with white letters) taped over the front, diffuses quite well.

I made a pin-badge with a pi zero and a scroll pHat, for the Raspberry Pi Birthday event, and I used one of these to power it with. It lasted most of the time I was there with juice to spare when I got home (so easily a few hours). If you like, I’ll completely charge the power bank and plug in my badge to see exactly how long it goes on for before it dies.

USB power banks are usually really easy to take apart, so if you wanted to have the connector in the foot and the battery in the body that shouldn’t be too hard. Make sure you insulate everything though - I don’t think having your award going up in flames would be great!

Looking at the picture, I think glowing eyes are also necessary!

I hope that helps.

If you weren’t mad keen on dismantling a power bank, you could use a micro USB extension cable like this one to put the micro USB port on the foot, and have the power bank hidden away in the body.

I used a right angle USB cable on my badge so that it was as low-profile as possible. One thing to be aware of with the USB power banks is that some of them require you to push a button to start the flow of electricity, and some just automatically start when you plug something in. I don’t know how they cope with something plugged into them whilst they’re charging either, so you might want to consider that.

That would be handy, thank you. I plan on turning off as many non-vital functions within the Pi (such as, I understand you can disable HDMI, etc…) which should help the duration, etc…


Haha, I wholly agree - although I think that’s a little outside my ability level.

That’s actually an excellent idea.

Useful advice, thank you. I’ll pick up a power bank and see what happens.

I’ve plugged in my scrolling badge, and I’ll let you know when it dies. Good idea to turn off non-vital functions, although I don’t know if you’d see a noticeable increase in real-life use. The power bank I used (linked in my first post), definitely requires you to push the button before it’ll turn on, but I also have one of these ones (now discontinued), which just turned on when something was plugged into it, which is much more useful in embedded applications like this because you can just get a USB cable with a switch like this one, and have the switch accessible.

TBH, the idea of being able to turn it on (and off?) via a button sounds like a useful feature, so long as the button is in an accessible location.

Based on your recommendation I’m going to get one of the Anker PowerCore+ minis. My only issue now is figuring out how to disguise it. Maybe put it into a box, which the toy sits on? Or maybe a mini backpack (although I fear this one will be too small).

Any ideas? How did you do it with your pin badge? Do you have any photos?

I don’t think the button turns it off, just to activate the power. Some batteries will probably have an on/off switch though.

Could you put it inside the toy? Perhaps do some surgery on it and hide it inside. You could even leave an opening with self-adhesive velcro or magnets or something on it to get to the battery, hence solving the charging issue. Alternatively, having it inside some kind of podium which it sits on is a good idea.

That backpack has a mini 170pt breadboard inside it, which from the pictures looks like it nearly fills it up. They’re about 6cm long, so that’s not big at all. You might be able to get a battery which is small and fat if you look around.

For my pin badge. I had a mini mint tin which I put the Pi Zero in. I cut a hole in the top for the GPIO header to stick out of, and the Scroll pHAT plugged in whilst holding the Pi in the tin. The lid of the tin just slides onto the back of the badge (over the Pi Zero shown in the second photo), and was magnetic so I just magneted it on to my clothing, although I could have easily glued a pin onto the back if I wanted. The cable went from the tin into my coat, and down to a battery in my pocket, so the battery wasn’t even in the badge. This probably isn’t too helpful for your project, but I’ve attached pictures anyway (right angle cable not shown in pictures).


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This is an option, as I think the battery might just fit inside (I may need to give him a hat or something, just to extend his height - although this could act at the aforementioned opening for charging, turning it on, etc…)

…only, I’ve never performed surgery on a toy before - I don’t even know where I’d start. I guess I should get a craft knife, as well as a needle and some thread.

I guess you’d find where it was sewn up and then cut the thread there. You could use stick-on velcro or sew it back up to fasten it shut. I like the hat idea too.

I’ve tested it, and it lasted about 11½ hours on the Anker slim battery. Not bad!

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At most the Scroll pHAT should draw about 180 to 200mA. This is full brightness with all LEDs lit. At 50% brightness it’s around 70-80mA. At 25% brightness it’s around 40mA.

  • 100% - 200mA
  • 50% - 80mA
  • 25% - 40mA

simple-text-scroll.py scrolling the words “Hello World” seems to draw a maximum of about 65 to 70mA on full beans.


That figures.

3350 mAh on the battery / 11.5 hrs = 291.3 mA of current. The Pi Zero draws about 100 mA, it says here, which leaves just under 200mA for the Scroll pHAT.

What sort of savings can I expect by disabling non-essential parts of Raspbian and/or the Pi itself? And will it be worth it?

I’ve not spent any time looking into this yet, but I understand you can disable the HDMI, et al. for some savings, but how much of a difference is it likely to actually make?

Tho’ batteries aren’t 100% efficient, so you’re probably looking at more like (3350 * 0.7) / 11.5 - 100 for about 100mA for the Scroll pHAT as Phil says.