Custom Powerbank In Compact Form Factor

The wide availability and power density of 18650 lithium-ion cells have made them a good option for everything from electric cars to flashlights. [Theo] needed a new power source for his FPV drone goggles, so he designed his own power bank with a very compact charge controller.The narrow PCB slips in between the cells

While [Theo] could charge the batteries with an RC battery charger, he preferred the convenience of one with a standard 5V micro USB input, and wanted battery level indication to avoid having the FPV goggles die unexpectedly mid-flight. When four 18650 cells are held in a cube arrangement, a 8x8x65 mm gap is formed between the cells. In this space [Theo] was able to fit a custom PCB with a micro USB jack, 1.3 mm power jack, BQ25606 charge controller, TPS61085 boost converter, and ATtiny MCU with LED for battery level feedback. The charge controller also allows 5V devices to be charged via USB, while the boost converter outputs 9V via the 1.3mm jack for [Theo]’s FPV goggles. Everything fits inside a nice compact 3D printed enclosure.

The project was not without hiccups. After ordering and building the PCB he discovered some minor PCB layout mistakes, and realized the boost converted could only output 600mA at 9V, which was not enough for his more power-hungry googles. He plans to fix this in the next version.

We’ve seen custom power banks in quite a few shapes and sizes, including one that runs on power tool batteries (which probably also have 18650s inside) and one that has just about every output you could want, including AC and wireless QI charging.

28 thoughts on “Custom Powerbank In Compact Form Factor

  1. Honest question, from a place of complete ignorance:
    Is it safe to have the charger enclosed in the battery pack like that? I saw that the chip he picked has battery charge and thermal protection so maybe it’s okay, but don’t lithium ion batteries like to explode if they get too hot?

    1. Its a very valid concern – but it should be fine in this case. My initial thought was it was too small and going to be toasty in there, but it looks like it will remain regulated.

      If you try to draw or sink too much current, such a compact form factor will be a hindrance. But the parts being used should stop short of burning fireballs of lithium.

      Many batteries do have part of the charger in the pack – think cordless tools for instance, probably a little more sophisticated than this… But as a V1 I can’t see a huge errors not already picked up on, and it looks safe enough to me that I’d use one and more challenging, let the less technically minded friends and family use one too.

      However for myself if I need something like this I think I am more likely to just use a powertool battery and some voltage regulators for whatever I want to power – Both less effort to create and probably cheaper overall, as the battery has many other uses especially if you make your cordless tool battery your standard, so its not quite as limited as this and the price of the battery isn’t really applied to just the one project.

      1. I’ve torn down quite a few powertool battery packs to scavenge cells. Most are not as sophisticated as this project, let alone more sophisticated. Plenty of really dodgy engineered to a price point battery packs out there.
        Agreed that flexibility is nice, but this is a case of the person having a very specific need, and fulfilling it with a custom design. Fits in the pocket of not going to be fulfilled with off the shelf power tool battery packs.

        1. Interesting – I’ve only torn down a few, from my own or friends tools and they have all be pretty complete on the battery balancing and protection, with more effort put into thermal management. But as they have come from ‘pro’ and ‘Prosumer’ level tools perhaps I’ve had a better experience – certainly not a huge amount of it though. The only cheaper pack I’ve taken apart was a NiMH or maybe NiCad from my first cordless screwdriver (well technically a drill but it didn’t really do drilling that well) and that was pretty trash on the inside, but its a less touchy battery chemistry and a dirt cheap tool…

          I agree entirely this design fits the builders needs well – though for me if you pocket isn’t big enough you should add bigger pockets! More and larger Pockets are always good – does help that I’m tall and broad so my pockets are bigger than most just to stay in scale.

      2. The printed battery case is problematic. Commercial packs are made of flame-retardant materials with a glass transition above the maximum working temperature. 3D-filaments usually contain no additives to prevent burning drops and have a low glass transition temperature (PLA at 60°C).

  2. Could someone point me to a good information source for building an overdischarge protection circuit for a 6-series 18650 pack? I’m looking to use Kobalt 24V batteries to power DIY tools….

    The battery management board in the pack only seems to take care of charging, but not low-voltage cutoff. I’m sure the data output contains the voltage reading as well as temperature and balancing info, with the overdischarge cutoff circuitry built into the tool itself. Unfortunately, I don’t have any equipment capable of reading the data output, and my attempt at reading it with a uC wasn’t successful…

    Thanks in advance for any help.

    1. I know Harbor Freight’s WARRIOR Lithium drills have a charge controller inside the pack, and a discharge protection in the drill lock-on plate. You could do way worse than tearing down one of those

      Source: I looked myself

      1. I get using TL431-based solutions in general-purpose low-voltage cutoff applications, but when it comes to single-LiIon cell applications, there’s just no need? There’s much better and cheaper solutions, i.e. DW01 (or even FS312 for a much healthier 3V cutoff) with FS8205A FET, which is super popular and known to work.

        You can design your own small board with these two chips, or just buy some “single-cell protection circuit PCB” boards off eBay… or even take any old LiIon battery that you’re about to throw away, get the protection circuit off it and reuse it for something else.

        There’s really no need for bodging together your own analog solution when you can get something that works, gives you guaranteed overcurrent, overcharge and overdischarge protection, and works reliably even with large loads.

    2. If you’ve got any older electronics books, circuits collections or magazines, much the same principles are employed in automotive battery savers or starter battery isolators for RVs, camping trailers/caravans or boats. Their cutoffs are going to be in the 12-13V range, but should give you insight on design of circuit for other voltages.

      1. I’m in US. I checked eBay, but mostly what I see are unbranded. Reputable online shops are selling branded one at $5+ EACH, plus shipping. That’s really expensive, IMO. That has got to be a better source.

          1. Thank you! 40 brand named recycled battery for less than $40 shipped seems like a good deal. Some disassembly, desoldering is needed but I think it is worth it.

        1. I see what you mean, yeah. I prefer LiIon batteries because 1) they’re easy to source from all kinds of electronics (laptops, smartphones, tablets etc.) 2) they have really high capacity 3) charging them is quite easy with TP4056 and the like 4) 1s configuration is comfortable to use – the voltage is decent (steps up easily to 5V and down to 3.3V) and you need neither temperature regulation nor balancing to get there 5) lifetime is good and replacements are easy to find, 18650 standardization helps, of course.

    1. Oh, also, vape shops are usually a decent place to get 18650 batteries, as long as they’re selling brandname ones. The batteries for vaping have to be super reliable because they have to be able to give large amounts of current and not blow up while doing so, so as long as the vape shop owners have a bit of sense in their heads while they’re ordering batteries for resale, you’re probably going to be just fine going with vape shop batteries – but if you want something non-overpriced and in larger quantities, check out nkon, for sure.

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