Virtual1
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- Nov 19, 2017
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Yeah the pics are nowhere near good enough to tell for sure, but the MC34063 is a pretty common SOP-8 IC for buck-down regulation, that's very likely what they are using. The nearby cap and inductor for the buck are about the expected size for it too, but it's not really rated for 2A continuous without some thermal management (heat sink or other additional cooling, good airflow / venting at the very least - and there are no vents up there) Especially for a battery that may take 90 minutes to charge. It looks like each of the three bays has its own set of regulator circuitry. They did demonstrate a thermistor in the battery and that's absolutely necessary, but they also need to have thermistors up in the enclosed regulator area, preferably one in the middle of each of the buck circuits by the MC, to shut it down in case the regulator starts to overheat. I doubt their circuitry currently allows for shutting down an individual bank though, so there's a non-trivial amount of re-engineering to be done there.
If you run something like that over its continuous duty cycle (but still below its absolute maximum) for too long in an enclosed area with no ventilation, heat starts to build up and temperatures rise, which increases resistance, which causes more heat to be produced. "Thermal Runaway" happens when things rapidly spiral up and out of control, and the scorching in the pics looks very much like what I would expect from a TR event. Speculating further, (and we know how that can go!) it looks like they are shutting down the output of the battery when an overcurrent is detected from the battery to (collectively) all three regulators, maybe with something as simple as a polyfuse. That won't protect you if a single battery is on charge and it its regulator runs away, because by the time you're drawing enough current to trip it, you're probably already on fire. This is because it has to allow enough power through to run three regulators, and so it won't trip until at least enough power is flowing to run more than three regulators. (ie over triple its rated power) And that'll light up a single regulator nicely.
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