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Why I'm currently using 18650 batteries

A project log for ZeroPhone - a Raspberry Pi smartphone

Pi Zero-based open-source mobile phone (that you can assemble for 50$ in parts)

ArsenijsArsenijs 10/20/2017 at 15:507 Comments

So, there are a lot of questions about my battery choice. ZeroPhone is known to work with LiIon batteries that have 3V-4.2V voltage range, so both 18650 cells and pouch cells will work (though some chemistries, such as LiFePO4, are not yet supported). So, why not decrease the thickness of the phone by using some kind of pouch cell by default, as opposed to bulky 18650 cells?

The main problem is - I don't actually have control over which batteries others will use, I can only suggest. Lately, lithium batteries are really hard to ship, so when I send ZeroPhones, best I can do is include a holder of some sorts. So, the kind of holder that I include (and assembly instructions which I include by default) is going to the way I can make I suggestion. Currently, I include a holder for 18650 batteries, and instructions are also tailored to these. It's done for multiple reasons:

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  1. 18650 are the easiest to source. Sourcing is an important thing here - even if I send out a fully assembled ZeroPhone, the recipient still has to source batteries (since, again, I can't ship those without getting the shipping cost up). With pouch cells, you'd need to source one that fits into 4x10cm dimension (so that it doesn't stick out the ZeroPhone outline), has enough capacity and the right connector. Do I want to subject somebody to this sourcing process when it's all that stands between a working and a non-working ZeroPhone? No way. 18650 cells are easy to get from vape shops, regular online shops, and even harvest from laptop batteries - the latter is where I got all my 18650 cells from.
  2. 18650 standard size and resulting capacity average. With 18650 cells, you know you're getting about 2000mAh of capacity in one in the medium-to-worst case, you know the length is 65-67mm, the diameter is 18mm + 1mm for isolation, and these things won't change significantly, so you don't have to mod a ZeroPhone case for your battery before printing it, you don't have to worry about finding the right one among many because even the worst ones will likely still fit the requirements.
  3. Price. 18650 cells are ubiquitous, and they're cheap. Especially compared to pouch cells - I can get 18650 batteries in my hometown for 3.5EUR/one, and pouch cells start from 10EUR/piece (those are not even quite suitable ones). And then, there's harvesting!
  4. Safety. It's much harder to pierce a 18650 battery, they have venting mechanisms built-in and they're really unlikely to burst in flames - unlike the pouch cells, which are much easier to pierce inadvertently, and they will react violently, and they don't quite have a venting mechanism - they'll just inflate, until they crack the case they're in, or, worst case, get pierced by something.

Having said that, I know that thickness of ZeroPhone has to be reduced, and there are safety precautions that can be taken. So, I welcome everybody that'd like to mod their ZeroPhone to accept a pouch cell instead of a 18650 bank, and I'll eventually provide both instructions and materials for such a mod (namely, JST pigtails and something that could be inserted between back board and the battery to prevent damage.

[TODO: insert a photo of experimental ZeroPhone with a pouch cell here, just need to take it]

Discussions

sunny wrote 10/16/2018 at 00:49 point

I have a ideal, I can design a plastic box to protect battery,then fixed it to backpcb with 3mm screw 

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Ember Leona wrote 10/15/2018 at 06:04 point

I need to learn how to make a battery charger work. Maybe I can take one apart.

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Arsenijs wrote 10/15/2018 at 13:14 point

Which kind of charger are you interested about, and what's the purpose?

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Ember Leona wrote 10/20/2018 at 10:11 point

Well I am interested in using [diodes] a mosfet or transistor directly with a usb cable and creating a driver to trigger a "battery pack effect" in the circuit there is no on/off switch other than controlling the 5v output via usb commands perhaps there is a variable resistor controllable by usb. on  ubuntu I am trying to learn evtest command or something to learn how drivers and data signals work in general. I ve had this simple project for a long time now and no one seems to help me so far. vibrochat.com I thought this would take a coder like 2 minutes to implement a mechanism for *poke in chat to control usb 5v output. I later want bobble head webcams and kinetic statues (basically paper clip and motor) I waited a month for AAA to AA adapters to attach to the USB cable. I am still waiting for RCA plugs for my Scratchbox project.

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crasch wrote 10/13/2018 at 06:35 point

Speaking for myself, I prefer 18650 batteries.  I like the fact that I can easily replace the batteries with freshly charged batteries easily, and immediately.  

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schadenfreude wrote 10/21/2017 at 20:19 point

what runtime do you get from 2x 2400mah 18650 batteries?

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Arsenijs wrote 10/24/2017 at 16:20 point

About 20 hours on 2x~2000mAh from normal usage (playing MP3s 24/7, too). It's bad alright, but I have my hopes high due to the fact I don't have any power optimizations in place yet. So, I aim to decrease power consumption enough to allow using only one 2000mAh battery for a day - which should allow for using ~2000mAh pouch cells, and make it last for almost two days with 2x18650.

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