• May 30, 2018 at 3:17 pm #12366
    ainut
    Participant

    On this BEC, can we use the “backup power” cable, with it’s 2 separate ground and power (black and red) lines to power other things besides being a backup power for the Cube 2.1? I’d like to power a Raspberry Pi (RPi) with one pair, and use the other pair for the Cube’s Aux ports. Is this advisable? Are both pairs limited to a combined 3 amps at 5vdc?

    May 31, 2018 at 2:01 pm #12372
    Thomas Lauzon
    Keymaster

    Hi Ainut,

    Thank you for you question.

    It depends in part on how many peripherals you have on your Cube. Check page 10 of this doc:
    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiZ963vybDbAhWIt1kKHQZ6BXAQFggpMAA&url=http%3A%2F%2Fwww.hex.aero%2Fwp-content%2Fuploads%2F2016%2F07%2FDRS_Pixhawk-2-17th-march-2016.pdf&usg=AOvVaw0GpxAW30xjwgwk0BbCbH_x

    The Cube draws 250mA and can provide 2.5A to peripherals.
    The Raspberry Pi will consume up to 1A typically.

    This means that you may need 3.5A, which is more than the 3A provided by the PL BEC. You would have to be sure that your peripherals and Cube combined do not draw more than 2A.

    You could separate the pairs of cables as you suggest, but you need to be aware that this will increase your failure rate as you will be reducing the redundancy of the power supply to the Cube. There are two pairs on each supply in case one of the wire is cut or the connector fails. This will depend on the safety requirements of your project.
    A good configuration could be a dual PL BEC connected to POWER 1 an POWER 2 on the Cube. You could power the RPi through the Cube, being careful about peripheral current limits described in the document above.

    Best,
    Thomas
    Craft and Theory

    June 13, 2018 at 9:06 pm #12513
    ainut
    Participant

    I’m not proficient in your area, so the document you referenced simply confuses me even more, but thanks for the effort. My ignorance is not your responsibility. So, you’re saying we are limited to 2.75A TOTAL on all the 5vdc lines combined? Do the 12vdc lines have their own power “bank” or does that 2.75A limit include the 12V output? If separate, what is their limit, please?

    To refresh your memory, just in case, I have the 200A “sensor,” with the ‘OUT’ leads bridged, and the PL 4-6S BEC, which has the “sensor” feed to the Cube, 2 separate ‘5’vdc outputs, and a 12vdc output.

    Thank you.
    David

    June 14, 2018 at 12:01 pm #12520
    Thomas Lauzon
    Keymaster

    Hi David, no worries, our support is here for that. I’m happy to help you understand the product and help you make it work in your project.
    I’m sorry that my explanation hasn’t been clear enough.

    Each BEC (i.e the 2x 5V BECs and 1x 12V Bec) on the PL 4-6S 3x is independent and can provide up to 3A each. So the total combined would be 9A. However, you wouldn’t combine the 12V BEC with a 5V BEC because of the difference in voltage, and the backup 5V BEC is a backup so it’s not intended to be combined with the main 5V BEC.

    The problem I was trying to explain to you is that if your main BEC, connected to Power 1, fails you will be powering the Pixhawk, peripherals and RPi with the backup BEC. You may not have enough current because each BEC can only provide 3A but the Pixhawk requires .25A, peripherals up to 2.5A (if powered through the Pixhawk) and Rpi up to 1A. The total may add up to 3.75A, which none of the PL BECs can provide independently.
    If you want to power the RPi in the configuration you suggest, (i.e. using 2 wires from the backup 5V BEC), make sure your peripherals use less than 1.75A.
    Alternatively, you could use a completely separate BEC to power the RPi if you want to be on the safe side.

    What I’m trying to say is that you may find that everything works fine, until the main BEC fails or the line is cut, and then you don’t have enough power on the backup line to power everything because you have more things connected on your backup BEC.

    I hope this is clearer. Please don’t hesitate is you have more questions.

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