• Episode Weld: A New Hope

    CriptasticHacker • 09/23/2024 at 01:09 • 0 comments

    The other issue with the cheapo (er - expensive) online pre-built welders is that they are lower voltage. Usually only 3.7V parallel Li-ion or Li-Po are used.

    Fortunately, they sell 12V standalone board alternatives:

    These are actually quite nice, with more modes than the other one. They refer to power readings as "gear" modes in the description usually (this has 6).  And while it has one bulk capacitor, it's quite small.
    What would happen if I hooked up a massive 1 Farad capacitor to this?  That would give me a lot more discharge current :)  Maybe I could use a AC power supply then?


    I tried this at first with my old spot welder, but it didn't work. Even with massive 30A and 40A supplies, it simply wasn't enough current to do welding without tripping the supply safety limits.  Whoa.

    I wondered, what can I use around the house?
    And then it dawned on me: my old wheelchair batteries!  They no longer move my ass for half a dozen city blocks, but they still pack a punch!  Do they have enough juice for spot welding?

    This would be amazing, since I have to replace them every two years anyway.  It would be so nice to find a use for them, instead of letting them go to waste.


    Some testing proved that yes - they have more than enough power with the added capacitor!  So much in fact, I can't use it beyond "gear 2" or I will melt a hole in the nickel strip!

    But nothing about this setup was safe. There is no case for the welder, no protective covers for the probes (which create a spot weld when touched), and no way to transport it.

    A little 3D printing and wood working was in order :)


  • Spot Welding Done Wrong

    CriptasticHacker • 09/23/2024 at 00:58 • 0 comments

    Li-ion batteries are essentially large hunks of metal; they cannot be soldered easily..  Even if they could, it's actually quite bad for the cells to absorb that much heat. It degrades their lifespan.  So we need a tool that can deliver an instantaneous powerful spark to connect some nickel strips - and thus the other cells - to eachother to form a battery pack. That is, we need a spot welder!

    It is also a good idea to use some top insulating paper for the positive terminals, and plastc frames around the cells.  I 3D printed my own, since I had some (very uncommon) AA-sized Li-Ion cells:

    Now there are spot welders on the market of course.  Even ones for hobbyists doing the kind of recycling work described in this project.

    The problem is, these "portable spot welders" usually die after the first few months, because the battery capacity isn't large enough to keep on delivering those massive surge currents for welding.  

    I bought one, but it died after less than six months.  And it never worked that will begin with:

    It looks like such an ideal starter kit! but I was left very disappointed.
    It's time for a better solution ---

  • Lithium Batteries and Greenwashing

    CriptasticHacker • 09/23/2024 at 00:01 • 0 comments

    This project was born out of a desire to recycle batteries.  Specifically, 18650 Li-ion cells.  These are by far the most common batteries in the world today, although LiFePO4 is coming up through the rear due to their lower cost and widespread adoption in more recent electric vehicles.

    If you're into battery hacking, you've probably seen these around.  They are everywhere.  They are in laptop batteries, e-bikes, phone power banks, e-scooters, modern wheelchairs, home appliances, - you name it.



    and why is that?   Well, these overcame the memory-effect of Ni-mH batteries, the darling chemisty of the 1990's.  Before that, it was Ni-Cd (Nickle-Cadmium).  But what makes Li-ion so special?

    Lithium is the lightest solid element on the periodic table.  It only has 3 protons in its nucleus.  So if you can add an electron to ionize it- then you have the lightest conducting solid known to humans.  This is the promise of Li-ion (Lithium Ion), as it's weight to power ratio is the very best of all battery chemistries.  It also does not have the "memory effect" of older chemistries, so it does not need to go to zero percent before recharging.

    In fact, letting these batteries drop to zero is very bad for them.  This old wives tale of "let it go to empty before recharging" is a fallacy I combat in every conversation I have with the layperson on battery care.

    (please note, I'm not a chemist or physicist!)

    So what are the drawbacks?
    First, Li-ion cells are prone to explode under certain condititions.  If cells fall below 2.9V (and then gets recharged) or it gets recharged over 4.3V, very bad things can happen:

    Hoverboards and vape pens are one example of many stories where these powerful batteries go up in flames.

    This can be due to a number of factors, but the most common are lack of (or failing) protection PCBs and overdischarge/overcharge.

    In order to be safe to use, there needs to a be a monitoring circuit attached to the battery pack.  This circuit (the SOT-23-6 above) is usually hooked up to 2x N-channel FETs.  Any number of FETs can usually be connected in parallel for higher current.  The circuit checks the voltage level and turns off the FETs (which act as solid state on/off switches) if the voltage is too high or low, or the current is too large.

    Not all monitoring ICs are created the same.  The best ones incorporate a sense resistor to measure current and also use an extrnal NTC thermistor to keep an eye on the temperature of the cells.  If they sense an error, the FET gates go low and there is no longer a conductive path for the battery pack to reach the load.  Some will incorporate a nice thermal fuse as an additional safety.


    Sounds nice, doesn't it?   But what happens if the error is temporary, or a user disconnects the pack to make a DIY cell?


    In most consumer lower-expense systems, the protection PCB will be de-activated until the correct cells are reconnected and a charger is plugged in.  The "dumb" hobby RC chips work this way.

    However, the stuff in more expensive equipment is different.

    This is essentially an e-bike battery used for a power wheelchair.  It has a microcontroller - essentially a mini computer- as well as a very fancy BMS (battery management system) chip.  It monitors the entire lifespan of the battery - how many times it has been charged/discharged (cycled) since the factory, every time a voltage threshhold is reached, it's temperature over time, and much more.  It sends all this data to an onboard CPU in the bike / wheelchair controller and also gives an authenticity serial number over the data bus.  Whoa!


    Modern laptops do the same thing.  And they usually use a family of TI (Texas Instruments) chips beginning with "BQ" to do this:


    what SUCKS about this, is that these chips have essentially a "suicide" mode.  The...

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