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Thread: I keep burning Teensys. Tips?

  1. #1
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    I keep burning Teensys. Tips?

    Hi,

    I've burned two teensy boards while working on an LED wall, and I would welcome advice on how to avoid this in the future!

    The first one, I believe I connected the Data In pin to GND or V+ on the WS2811 strips; shortly thereafter, the power cables grew very hot and my teensy transformed in a space heater. Does that sound about right? That's my own fault of course, so I'm being a lot more careful when wiring up the strips now.

    The second teensy's death was a bit more mysterious. The power supply (5V, 40A from aliexpress) started making strange noises as I was putting it under moderate load (3-4A). Of course I kept going, and soon after, the teensy board stopped responding, freezing the LEDs in their pattern. These LEDs are still working however.

    Click image for larger version. 

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    I'm guessing this was due to a voltage surge? Unlike the first teensy, when I connect it to power, the microcontroller doesn't heat up. If yes, what can I do to avoid this in the future, taking into account my hobbyist wallet?

    • Separate the teensy's power supply from the strips
    • Buy a new PSU, doh
    • Use a component (which one?) to prevent teensy's input voltage from going over 5V?


    Maybe the PSU making ominous noises is a sign that I should stop straight away and put it into the garbage bin. But it still seems to deliver current as I need. Any advice on that is appreciated, too!

  2. #2
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    Have you actually measured the voltage of the power supply under load ?


    Also, please post a schematic, or perhaps how the teensy and the rest of the project are connected.

    Edit: went to your blog and saw how things are connected. For a project with LEDs that have forward voltages in the 2.5 -3 V range a 5V power supply seems a little under dimensioned. When the LEDs get warm the forward voltage usually increases. This may be the reason that your PSU started making funny noises(?)
    Last edited by Headroom; 10-14-2013 at 11:20 AM.

  3. #3
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    Note the "+V adj(ust) - need to check +V under a resistor dummy load, with a voltmeter. Also, if you can, check with a 'scope to make sure it doesn't overshoot at startup.

  4. #4
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    Thanks stevech and Headroom for your tips. I've checked the voltage during operation, and it stays very close to 5V (think it drops to 4.98, but that's all). I'll see if it overshoots at startup, as that can definitely be a problem. Not sure if it explains the teensy burning halfway through normal operation, but worth making sure of. I'm really spooked by the noises and I hope the PSU won't start catching fire

    I'm not sure if the forward voltage changes much during operation - these are regular WS2811 LED strips, which (officially, at least) need to be supplied with 5V to work, and include all the resistors, ICs, etc. Do you think that would affect the PSU? It's rated until 40A and I'm barely using 2A. But without a way of logging the voltage during operation (and perhaps burning another teensy) I'm stuck

    Thanks both!

  5. #5
    Senior Member PaulStoffregen's Avatar
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    You could use a 5 to 3.3V regulator, like a LM317 with 169 and 100 ohm 1% resistors (that's what I have here in my parts bin) or any number of other 5 to 3.3V regulators on the market. If you use a LDO type, be careful to use the correct output capacitor it requires, because LDOs are unstable without the right capacitor.

    If you power the Teensy3 from regulated 3.3V, it can't be damaged by noise or spikes on the 5V power, as long as the regulator blocks them. But do be careful making the connection, since the Teensy3 has no reverse polarity protection on the 3.3V pin. It just connects directly to the chip.

    Also, be sure to use at least 100 ohm resistors in series with the output pins. If you get clean enough signals without the resistors, adding 100 ohms or more really helps prevent damage to a Teensy3 pin if something "bad" happens on the other end of the wire.

  6. #6
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    Thanks Paul, that's exactly what I was looking for. In the meantime, I'll go and boost your teensy orders by a few more units!

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