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Combine different power sources?

Discussion in 'General Electronics Discussion' started by NuLED, Jan 14, 2012.

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  1. NuLED

    NuLED

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    Jan 7, 2012
    Hi. I would like to know how I might combine different power sources.

    For example, 9v battery, 1.5 AA battery, 3v "watch" battery. Without putting them into series, how do I consolidate their current so that I get a single voltage/current source? Can I use a bunch of diodes "force" the current to go one way and just combine them in some kind of parallel circuit?

    I am asking this because primarily I want to consolidate all the various solar PV panels I have around the house, from various pieces of equipment, and try to get a single source with higher current.

    I tried to model this using circuit simulators but they all give errors because I have more than one voltage source.

    Help appreciated!
     
  2. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi there NuLED.
    I think your imposing different voltages on each other, apart from the use of a diode i dont know of another way of the voltages not being imposed on each other.

    Perhaps a more experienced member might have some ideas, i would be interested if they could be combined in some way with out a diode volt drop, interesting, i know you can with the use of a diode, polarity observed of course, mmmm, looking forward to some ideas should anyone else pop in. :)
     
  3. NuLED

    NuLED

    294
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    Jan 7, 2012
    i don't really mind either way. if diodes are to be used, then would there be a "best practices" arrangement, or just follow common sense and route the current like water and valves (a crude analogy I know but works for this). I didn't want to try it out yet until I got word here, as I didn't want to damage my DMM or anything.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    I have a solar system with two sets of panels facing in different directions. This is essentially the same problem as yours as the two strings of panels can't be assured of giving the same voltage (to allow them to be placed in parallel) or current (to allow them to be placed in series).

    My system allows 2 input strings. Essentially it means there are 2 independently controlled channels feeding into (in my case) the inverter.

    Practically, unless your panels are either the same voltage or the same current *and* have the same orientation, you can't connect them together to get a combined source of power.

    The only real option is to have each connected to a MPPT regulator that is capable of its output being summed.

    I'm not sure that such devices exist.

    It would probably be useful to know what sort of panels you have to connect together. If you have some that are similar, you can connect them in series or parallel, remembering that the worst performing panel will tend to dictate the overall performance.
     
  5. NuLED

    NuLED

    294
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    Jan 7, 2012
    Ok so I guess what I can do is measure voltage produced and just take the ones with similar voltage in parallel? These are all sorts of panels from toys I took apart to some of those solar power rechargers for phones, and some for AA batteries, etc.

    What would happen if I just linked them all up in series? (Assuming the high current/voltage from the big ones don't destroy the small ones?)
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    If you link them all in series, you will be able to sum the voltages, but your current will be limited to that of the panel which can supply the least current.

    You should measure the open circuit voltage and the short circuit current of all the panels whilst the illumination is identical for all of them.

    To do this you need either a very bright and powerful light source, or doing it at midday (ish) with *no* clouds in the sky, and being careful not to shade the panels.
     
  7. NuLED

    NuLED

    294
    0
    Jan 7, 2012
    Ok thanks; will check that out.
     
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