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Is Multiple batteries for efficiency the answer?

  1. Jan 8, 2015 #1
    Hello, concerning power supplies.

    I am at the stage where all the components are ready except for the batteries.

    The thing is, not all the components have the same voltage. My first thought was using a high voltage battery connected to a custom made Power Distribution Board which splits and steps the voltage down into each component.

    Problem with that is the inevitable power that constantly being lost into the Voltage regulators. Since the battery needs to supply all the components it needs to be high voltage, and
    high voltage+voltage regulators=inefficiency

    Now my second thought was.. multiple batteries with different voltages to suit bundles of components, say 1 for the servos, 1 for the camera and microcontrollers, and so fourth. All having the desired Voltage. The only thing that Irks me off is the fact that some batteries may last longer the others with no way to move the energy between them So I'd be getting a drained microprocessor while everything else was still running, this just seems kind of stupid to me.

    I'm a total newbie in power systems, first time I design a machine so I came here,

    What is the general, most efficient/lightest way to create a power supply for multiple components in a robot? how is this generally achieved?

    Thanks in advance,

    -Gabriel
     
  2. jcsd
  3. Jan 8, 2015 #2

    mfb

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    You can also start with a lower voltage and make a higher voltage out of that.

    Or use some mixture of everything - different batteries at different voltages, but voltage regulators to cover some other voltages. Batteries in parallel, in series, ...
    There are tons of options, and the best solutions will depend on your specific system.
     
  4. Jan 8, 2015 #3

    berkeman

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    Can you say more about your system? What are the different voltage rails you need, and what is the max current consumed for each rail?
     
  5. Jan 8, 2015 #4
    The system is a hobby robot project I am doing for school,
    we're talking about:

    2x big brushless motors for moving it around 14V, 14Amp each
    2x 6V robotic actuator, 700mA each
    2x 6V robotic servos, not sure about consumption
    2x micro processors at 8V, <0.5Amp each
    1x Possible camera add on

    I already own a 5000mah battery with 14.8 Volts,
    then I own 2 smaller 2000mah 13Volt batteries and lastly some AA rechargeables.
    Adding all of those into the system will probably be too heavy

    Does converting from a lower to higher voltage waste less energy than changing from higher to lower voltage? What is such a device called?
     
  6. Jan 9, 2015 #5

    Averagesupernova

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    Can you go with two 6 volt batteries in series for motion? One robotic actuator and servo per battery then. You would be 2 volts short of your 14 but that may not be a problem. Microprocessors at 8 volts? Really?
     
  7. Jan 9, 2015 #6

    berkeman

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    Yeah, I was confused by that as well. But I remember a recent thread where I called out the OP for posting something similar, and it turned out they were using a pre-packaged uC development board, which was powered by a wall wart transformer around 9V or so. The board used non-LDO linear regulators to make the 5V and 3.3V rails, so that's why the input voltage specification was so much above what the uC actually used. Not very efficient, but convenient I guess.

    I wonder if some of these uC development boards have an option for you to supply the 5V and 3.3V rails directly, so you don't have to lose all that power in the linear regulators on-board...
     
  8. Jan 9, 2015 #7

    Averagesupernova

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    I was thinking something similar berkeman but thought I'd let the OP reply. I recall working on products when employed by a test equipment manufacturer that had a lead acid battery. They used a switcher to generate a half a dozen different voltages. It used only one transformer and the switcher was regulated using one of the outputs. So that one output was ALWAYS right and the others moved around depending on battery voltage and whether the charger was plugged in. It seems like there were some low power linear regulators involved downstream. It worked ok, but I always thought it was an example of what not to do.
     
  9. Jan 9, 2015 #8
    Yup, like berkeman said, development boards. But 7.4Volts will work too.

    Actually this is a simple Idea, I like it.
    I think you mean using the 2x6V batteries for everything other than the big motors, while combining them for using the wheel motors.
    Something like this might work: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=21379 [Broken]

    This battery is 7.4 volts, 58000mah, great specs. Actually I think the weight of two of these is LOWER than the weight of my 5000mah 14.8V battery.
    two of them will be enough for low speeds of the wheels giving 14.8 volts. And the 7.4V would be enough for the development boards, etc.
    So we have:

    2x 7.4V batteries:

    I: connected in series, giving 14.8V for the brushless motors.

    II: connected in parallel giving 7.4 for Actuators, servos and development boards.
    With only a slight voltage drop needed(about 1 Volt), I assume the energy lost isn't too bad

    This system would be somewhat annoying though if someone is using an odd number of 6-8V components, since one of the batteries would be getting drained BEFORE the other, unless there is some sort of method to move power between them in a series connection?

    Now I just have to toss away the 15V battery and create a circuit that achieves a series and parallel connection at the same time
     
    Last edited by a moderator: May 7, 2017
  10. Jan 9, 2015 #9

    Averagesupernova

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    Series and parallel connection at the same time? Ummmm, not really possible. If you are driving stuff with relays there is no reason you cannot isolate things enough to drive various actuators off of different batteries. This would keep battery discharge more even.
     
    Last edited by a moderator: May 7, 2017
  11. Jan 9, 2015 #10
    How is that not possible?

    Keep in mind, the two batteries are not sharing the parallel connections, there are two isolated circuits for each battery. Those circuits provide power to several devices in a parallel manner.

    Meanwhile, the two separated batteries form a series connection, I don't see why it wouldn't work?
     
  12. Jan 9, 2015 #11

    Averagesupernova

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    Your wording indicates that you want the batteries to be wired in series and at the same time be wired in parallel. Is this not what you meant?
     
  13. Jan 10, 2015 #12
    Not sure we are on the same page here,
    There are 3 cirquits, 2 are normal battery cirquits from + to -, they supply power to several devices each in a parallel connection.
    then the last cirquit is the two batteries connected together, in series, at the same time. This circuit is connected to two motors in a parallel manner.

    I'm not sure if this picture is too grainy, but maybe it'll help you get what I mean.

    Again I'm not 100% sure if this is possible, but it'd simplify everything without the need for batteries of different voltages.
     

    Attached Files:

  14. Jan 10, 2015 #13

    Averagesupernova

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    Your choice of wording is dodgy. You have two batteries in series. That's it. The 14.8 volt load that you call series is connected across this pair of batteries. This is basically how I described it in my first post. Wording all comes down to this: If you have a single battery that is connected to a single load (light bulb), are the battery and bulb connected in series or parallel? Generally I believe they are considered to be in parallel. If you have a pair of batteries as you have shown they are in fact in series. But this is where it ends. The load is in parallel with the source until you insert something in series with the load.
     
  15. Jan 10, 2015 #14
    My native language is not english, my reading skills are limited.

    Don't listen to my words as much as the picture, the picture is what I am trying to describe,
    Yes the batteries are in Series, BUT they are also creating a cirquit that is not in series each on their own,

    I'm not 100% clear in electric engineering, but this will work, right?
     
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