Keeping The LiPo Smoke Where It Belongs

Nothing brings joy to a hacker’s heart like taking a cheap gizmo and making it useful. Over at [AndyHull] popped open some cheap LiPo battery power packs to see if he could power a Canon Powershot camera. The entire shebang would be left in the wilderness for photography so keeping it inexpensive was a big goal since it might be destroyed or lost.

The power packs [Andy] looked at have a TP4221 controlling the charge cycle for up to four 18650 LiPo cells connected in parallel. The controller also boosts the voltage to 5 volts for one or two USB ports while providing automatic shutdown if the LiPo cell voltage drops below 3.2v. Below that voltage the cells can be damaged and might possibly cause a fire.

The packs [Andy] used also had a torch output to drive an LED almost directly from the cells. That output is a nominally 3.8 V at 100 mA which is just what he needed to power the Canon Powershot. It could be used to power small micros or other low power devices.

The LED was removed and replaced by a connection to outside the pack. The torch output is triggered by two quick presses on a switch that was also replaced with a connector to allow remote control.

If you’re looking for powerful battery options, give LiPo a try and have a look at [Andy]’s LiPo battery safety issues post, also on For a broader LiPo overview, see this obsessive rundown of various batteries.





16 thoughts on “Keeping The LiPo Smoke Where It Belongs

  1. There is a bit cheaper option:
    1. Get an old laptop battery, disassemble it and check, what protection circuit it has. I’d suggest bq2040 of bq2060, or similar controllers with external EEPROM. Check cell voltages. You’d probably end up with few laptop batteries.
    2. Using datasheet and Arduino or other means to reprogram EEPROM to reset cycle counter.
    3. Replace the connector on board with some cables, solder to them a switch and buck converter or two to get required voltages. Also add socket for laptop charger.
    4. Select similar cells, recharge them, and optionally discharge back, if datasheet specified stat, connect them to the controller board.
    5. Put it back together.
    6. …
    7. Profit!

    1. Could make a nice power source. But doesn’t sound quite as compact and self-contained as the project presented.

      A tip: If you don’t have a way to equalize your batteries to within a few mV of each other before putting them in parallel, cut a square of unetched, double-sided PCB material that will fit between the battery and the spring terminal. Solder a 10 ohm 1/4W resistor between the sides. Insert that between battery and spring when putting the 2nd battery in the pack, let equalize. Repeat for the 3rd, and so on. Slow but very simple.

  2. One small correction to the HAD article, the 100mA LED output can power a small microcontroller, which in turn controls the camera. The camera draws up to 2A, so the microcontoller uses a FET or relay to power up the camera. The camera is fed directly by the LiPos.

  3. How exactly does over-DIScharging a lithium cell cause fire? What would start it, the LACK of energy???
    You are confusing overcharging (actual risk of SHTF) with over-discharging…

    1. Over discharging wont cause the fire, but it might put the battery in a condition where subsequent charging *may* be hazardous, so you are correct that the act of over discharging isn’t hazardous, however subsequent charging may be.

      It is possible to recover over-discharged lithium cells, if you know what you are doing, and the cell hasn’t been lying in a discharged state merrily growing internal lithium “fur” (needles of metallic lithium formed within the cell). You are welcome to experiment, but don’t say you weren’t warned. The manufacturers recommendation is don’t try it, but the hacker ethos says keep the fire extinguisher handy and you will probably be fine }:~)

        1. Overdischarge will always cause loss of capacity. It can’t be avoided. It will also increase both internal resistance and self-discharge rate. I never try to recharge cells that are below 2,5V. Those above I precharge with current limited to 0,1C until I get at least 3-3,2V on cell, then I recharge them normally. After that I wrap them in toilet paper, put in foil bag and put in freezer for 48 hours. After that I keep them in room temperature for few days, discharge them and recharge. This will “fix” chemistry a bit and decrease discharge rate.

        2. Take a look here… for a run down of failure modes and fires caused by mishandling of lithium cells (over discharge included).

          Their low internal resistance allows lithium chemistry cells to pump out some pretty hefty currents, but this also makes them much more prone to overheating than your average alkaline battery. It also means that damaged cells (due to overcharge/discharge chemistry issues, or physical trauma) are inclined to be unstable. A bashed alkaline will probably get hot and fizzle, but anything lithium will vent and possibly catch fire. The over discharged cell may present a hazard if paralleled up with a good cell too. The rapid charge in this case would almost certainly be spectacular.

      1. I’m not certain, but some things I’ve read suggest there may be no way to effectively extinguish a burning Li battery. Seems they might liberate their own oxygen. So the fire extinguisher may only be useful in the proverbial sense. If I’m doing something to a Li battery I know is risky, I just do it where I can safely let the battery burst and burn. And if that’s not outside to begin with, I make sure I have a plan to successfully transport it outside – while on fire – if needed.

    1. I didn’t check to verify your claim, but that’s not necessarily a bad thing. Charging to 80-90%, instead of 100%, can increase the lifetime of Li cells. I personally prefer that to what I see in a lot of my other cheap Li chargers, which charge too aggressively, and the batteries are dying early as a result.

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