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Thread: Portable external power source for Teensy LC

  1. #1
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    Portable external power source for Teensy LC

    Hello,
    I have tried to use an external power source to power my Teensy LC. I soldered together a cable with a USB male on one side and a DC jack on the other. I cut the VIN VUSB lead as instructed on the main site, and connected the 5V pin to 5V coming from a 5V 1A powerbank and the GND pin to ground.
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    Unfortunately I ended up cooking 2 Teensy LCs in the process, and I can't figure out why. The powerbank provides 5V on my voltmeter initially and then drops to 2.3V after a about 15 seconds (this behavior was described here https://forum.pjrc.com/threads/24476...126&viewfull=1)

    But what I don't understand is why this would kill a Tennsy LC. Do power banks have unpredictable voltage swings that could kill a Teensy? SHould I use a Teensy 3.2 that has voltage regulator in it?

    I'm fairly new to all this, perhaps a power bank is not a smart solution for an external power source and I should look towards a different power source? What do people us for a 5V input to a Teensy that is portable?

    Thanks to anyone with any insight into these issues!

    Best,

    Leo

  2. #2
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    I typically use 4xAA NiMh; expecially because most power banks will auto-turn off after a minute if the power draw is too low.
    But if the power bank works correctly and the Teensy has no shorts (headers?) you should not have any problem nonetheless!

  3. #3
    Senior Member+ MichaelMeissner's Avatar
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    I've powered LCs with various things.

    I do have some USB battery chargers that do not drop the power on low loads.

    A lot of times, I'm powering WS2812B (neopixel) LEDs, so that is usually enough power to not have the battery shut down.

    A lot of times I use a li-po (lithium ion polymer) battery that powers things at 3.7 - 4.2v. Sometimes I just connect the battery directly, but I usually prefer to incorporate a battery charger.

    One way to do this is to cut the pad between VIN and VUSB. The advantage of cutting the pad is you can then turn off power to the Teensy via a switch. One you cut the pad, you can use one of these lipo chargers:


    An alternative is to use the Adafruit Teensy -> Feather adapter. You can use the adapter without using any feather boards. The lipo plug is a lot sturdier than the above chargers. You do not need to cut the VIN/VUSB pad. The downside, is the board is a little wider (for the feather pins) and longer (for the lipo battery plug). You also can't turn off the Teensy using the lip connector:


    In terms of on/off switch, I normally use the LC to power a neopixel ring on a wooden bowtie (taking advantage of the level shift for pin 17/A3). Mine broke before a convention and I wrecked it further trying to unsolder things and re-attach wires. I moved up to using a Teensy 4.0, instead of an LC, because the Teensy 4.0 has an on/off pin, that if you connect it to ground for 15 seconds, it turns off the Teensy, and turns it back on the next time you connect the pin to ground. I used a feather adapter for this. The one downside is I needed to run the neopixel LED ring at 3.3v instead of VIN, but the newer LED ring can handle 3.3v (with the 16 LEDs in the ring, I make sure the power is well within the Teensy's power rating for 3.3v).

    I tend to like the 1200 maH batteries. They are a little wider than a Teensy, but about the same length. Generally, for me, they will last doing a neopixel ring all day. Depending on your needs, there are various other sizes of li-po batteries.


    You could use a 16850 battery instead of the lipo flat battery. There are various chargers for the 16850 batteries (these batteries are sometimes used in vaping).

    Note, lithium batteries can present a problem with fire, so you generally need to select a shipper in your country and ship via ground transportation. And when the battery needs to be properly disposed of at the end of its life.

    I should mention, I have a love/hate relationship with the JST-PH plug that is used on many li-po batteries. It holds the battery plug in, but it can be problematical in removing the battery. In addition, I find my li-po batteries sometimes hanging by the two wires, and eventually those wires will pull out of the solder connections. I've occasionally re-soldered the wires back in, but you do have to be careful, and usually I just take the battery to the town battery bin.

    You could use 4 rechargeable NiMH AA batteries (which gives 4.8 volts nominal). I rechargeable batteries for things like Teensys, and save non-rechargeable batteries for low current things like computer mice or TV remote controls. If you wanted, you could use 3 non-rechargeable alkaline batteries for a bit. Note, alkaline batteries will drop the current over time, so if you have some thing that needs a fixed amount of current, it will eventually fail.

    Adafruit has some learning tutorials about batteries:
    Last edited by MichaelMeissner; 05-20-2020 at 01:07 AM.

  4. #4
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    Quote Originally Posted by XFer View Post
    I typically use 4xAA NiMh; expecially because most power banks will auto-turn off after a minute if the power draw is too low.
    But if the power bank works correctly and the Teensy has no shorts (headers?) you should not have any problem nonetheless!
    Thanks for that response, but wouldn't 4 x 1.5 V give you 6V and overload the 5V max of the Teensy? I feel like I'm missing something obvious...

    EDIT - i see that 4 AA NIMH gives 4.8V, which makes sense. Sorry, I'm still learnign!!

  5. #5
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    [QUOTE=MichaelMeissner;240368]
    Wow, that was an awesome response!! Thank you so much

    Since you seem to be quite knowledgeable, here is a followup question about power supplies. I have some circuits where my Teensy LC connects to a low voltage stepper motor driver (https://www.pololu.com/product/2134 to be exact). It all works great, and I follow the advice of every tutorial that I see that the power supply to the Teensy has to be separate from the power supply to the stepper motor driver.

    But I have a fundamental misunderstanidng I think about why this has to be done. If I have a 5V power source, why can't I feed that to the Vin of the Teensy and also feed it to the Vin of the stepper motor driver? If the total Amps being pulled in total between the Teensy and the stepper driver does not exceed the max current of the power source, then what is the harm? If the worry is voltage spikes reflecting back onto the Teensy then wouldn't a diode to the Vin of the Teensy solve that problem?

    It just seems inconvenient to have to have 2 independent power supplies to power projects that are intended to be portable, but I can't seem to find any tutorials that use the same power supply for logic and for stepper motors, so I feel like I'm missing something essential!

    Thanks in advance!

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