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AA and relay question — Parallax Forums

AA and relay question

Ok hello. So I am needing a good power supply for an rc car. I don't care about weight and I want to use AA 1500mah 1.5 boots with 4 separate 4 battery containers run through relay switches to power a propeller activity board. Now the output for a single container would be 6v but all 4 together would be 24 v and that would ruin the board I think. I want to know if using a 4 channel relay switch and only running a single container of batteries until it reaches 15% of power left and then it switches Another container on and the depleted one off and continue to do this until they are all dead would work? I don't want the ab to temporarily loose power eigther or get ruined. I didn't know if I could run a setup like this or not. The relays would also be activated and deactivated by the board itself and if I can do this it should almost quadrupole the battery life I think. Sorry for the mass and run on sentences I'm on my phone and can't structure it very well. Also keep in mind I'm still in concept with this and am open to suggestions of cheap reliable sources of energy and the power doesn't just need to be AA batteries. Thanks.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2015-08-07 18:28
    Assuming the RC motors run on 6V, a simpler approach would be to connect the batteries in parallel on the negative side and use 4 schottky diodes (on the positive side) to supply the motor from whichever battery pack has the highest output voltage. You will have a small voltage loss (~0.3V) across the diode, but using a relay would draw extra current for the coil so the losses probably even out.
  • Ok and would that still have a good battery life too? And also would this still overload the ab?
  • Also do u mean that I would be using a separate battery pack for all motors and board? I think I'm miss reading or understanding it.
  • PublisonPublison Posts: 12,366
    edited 2015-08-07 19:32
    plau45 wrote: »
    Also do u mean that I would be using a separate battery pack for all motors and board? I think I'm miss reading or understanding it.

    When you speak of "ab" do you mean Activity Board or another Parallax product?
  • activity board my apologies.
  • ok another problem I'm wanting to run this motor (750-90002) with this esc ( 750-90000 ) and with a 9v dc 450 mA and I et it turned on but the motor or esc just makes a beep every second in intervals and wont stop unless its unplugged. How do I get it working? I meet the volts required but don't know after that.
  • That Motor ESC combination will pull at least 6 Amps. You will need a battery of this sort:
    https://www.parallax.com/product/752-00010

    Can you draw out exactly what you want to do? You will get better answers.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2015-08-07 23:00
    plau45 wrote: »
    ok another problem I'm wanting to run this motor (750-90002) with this esc ( 750-90000 ) and with a 9v dc 450 mA

    It's not surprising you're having trouble powering a 30A ESC with 0.45A of current if that's what you meant.

    What kind of 9V battery are you using? If it's the kind made for smoke detectors it is way underpowered.

    How are you controlling the ESC? I think the ESC needs to be sent a low throttle pulse when it's first turned on.

  • sorry I'm using a wall outlet that has a 9v rating not a battery. I used it cus I cant find its rating.
  • kwinnkwinn Posts: 8,697
    @plau45

    You cannot power that esc and motor from one of the low current 9VDC wall warts. You need a battery pack like you described in your first post. You may also want to provide a separate battery pack for the activity board to avoid problems caused by noise and voltage sags when the motor draws high currents.

    I can post a block diagram tomorrow.
  • kwinnkwinn Posts: 8,697
    edited 2015-08-08 13:23
    Here is the block diagram.

    The diodes could be replaced with relays or transistors but you would need control signals for them. The battery packs could also be wired in parallel directly, but that may result in self discharging. The diode between the batteries and the AB needs to be there to prevent resetting it when the motors are drawing heavy current surges. A large capacitor to supply current during the voltage dips is also needed. It may be better to have a separate battery pack for the AB.
  • kwinnkwinn Posts: 8,697
    Oops, here is the diagram.
    852 x 233 - 6K
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