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Understanding BEC/UBEC/PMU/VU

Discussion in 'General Discussion' started by discv, Oct 11, 2013.

  1. discv

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    My original idea was to rob the Phantom to build up a TBS Discovery. But after crunching the numbers, it is a nonsense.
    New plan is to build up a TSB from scratch using a Naza Lite

    My short career in RC has been with the Phantom guided by you guys- so forgive me posting this question here.

    Please correct my understanding of the electronic 'drive train' in the Phantom.

    The VU [Versatile Unit] is in fact a UBEC, combined with an LED and a USB interface. This unit has nothing to do with voltage regulation to the motors. Fitting a PMU v2 would not help-that only increases the options for gimbals etc.

    To, for example, fit a 4s battery, I would need to install ESCs with their own BECs rated to suit the larger motors. The feed from these ESCs back to the Naza is disconnected- leaving the VU to do that task.

    How near am I ? :roll:
     
  2. martcerv

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    My understanding is that that PMUv2 is needed as the BEC, the phantom board has its own crappy BEC which then powers the NAZA but this only support 3s batteries. The PMUv2 can take 2s-6s input and you simply need to have ESC's and motors that can handle the battery type you want to use powered directly off the battery. The stock motors should handle 4s as they are used in 450 and 550 kits but the 18A esc likely is not for anything higher then 3s. You then can simply power your ESC's directly from the main battery via a built in PCB or use any other method of splitting the power to all your ESC's

    [​IMG]

    You can see on the PMU the power input is 2s to 6s, then it outputs 3A @ 5v to the NAZA via the X3 input.

    If you have other no DJI devices you need to power that cant take direct input at 4s then you will also need another BEC. The PMU supplies power to the other DJI devices via the canbus port but you will need to find a way to power your vtx, camera, gimbal etc
     
  3. discv

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    Thanks Martcerv. I think we agree on our understanding except- I believe that the Phantom BEC is contained in the VU module, and not on the board.
    And so far as I can work out, the PMUv2 would serve no purpose for me. I would be feeding the ESCs [uprated] directly from the 4s and leaving it to the integrated BECs to sort it out.