So I’ve always recommended the Heltec kits as a good entry-level kit but I can’t anymore due to issues with the USB->UART chips in them. What I originally chalked up as a mild annoyance has now proven to be a safety concern.

I’ve had 11 of them total. Of those, two had the USB->UART chip fail within the first week. Everything else still worked, so I was able to repurpose them as “repeaters” and manage them over LoRa. Firmware updates were a brute since I had to crack them open and use an external serial connection, but, still, I was willing to continue recommending them as entry level kits.

Cut to today and that is no longer the case after my everyday carry node decided to self destruct in a way that I am very fortunate wasn’t a fire.

I woke up and noticed the charge light was kicking on and off in a weird cadence. Clicked the button to see if it was even running (it was) but the battery was down to 30%. It was also hot. Very hot. It’s uptime was only about 5 minutes which was also odd.

So I unplug it and crack open the case. Everything on the board looks normal, so I pull the battery and hook it into USB. As I feared, it didn’t enumerate at all. Another one down, I sighed. But then things got worse. As I was holding the board in my hand (still connected over USB), I notice my finger started to get painfully hot. The hot component was the USB-UART chip.

On a hunch, I hooked my USB-C power meter inline with the cable, put it back on the USB charger it normally uses, and lo and behold, it was showing 9V. To rule out the USB charger, I tested it with another one of my Heltecs with a dead UART chip, and it was a steady 5V as expected.

So my best guess is the USB-UART failed in such a way that the data pins triggered the wall charger to go into quick charge mode and destroyed it with an over voltage. I’m genuinely surprised the battery didn’t catch on fire as hot as that chip was getting since it was right on top of the battery inside the case.

  • tofubl@discuss.tchncs.de
    4·
    6 天前

    I decided to play with my heltec v3 again a few days ago after it had been collecting dust for months, when I noticed the case not fully closing. Opened it up to find a very spicy boi. I immediately unplugged it, and I think the problem is the CPU sitting directly against the battery in the case I used. It’s a bad design.

    Handling lithium ion batteries gives me the same feeling of unease I get with strong springs under load or large neodymium magnets.

    • Iced Raktajino@startrek.websiteOP
      1·
      6 天前

      Out of curiosity, what case are you using?

      Most of my nodes are using the HT Pocket case. My EDC one was the one without the external antenna, but the bulk of my other nodes use the same case with the external antenna cutout.

      The fit is pretty tight in that model, but I love how compact it is. It also has a belt clip model I printed which is nice for strapping some of the antenna-clad units to trees when we go camping.

      • tofubl@discuss.tchncs.de
        2·
        6 天前

        That HT Pocket looks almost exactly like the one I have, only mine doesn’t have the cat on the front. A friend of mine printed it for me, so I don’t know which model it was exactly. Might be this one. But for these compact cases I’m betting they all have the battery right up to the CPU. Have you opened yours and checked for an inflated battery?

        • Iced Raktajino@startrek.websiteOP
          2·
          6 天前

          I did, and it doesn’t look puffy thankfully. I’ve got 4 more in the same case and will check on them soon. 3 of those 4 aren’t used often, though.