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jrnymn7's avatar
jrnymn7
Explorer
Jun 21, 2015

Running 24v and 12v Solar in parallel???

Just curious what would happen if one was to run two systems, side by side (i.e; in parallel)... 12v/pwm and 24v/mppt?

In particular, how would the two charge controllers handle things?

Would the pwm just go along with whatever the mppt decided was best, for example? Or would the pwm perhaps confuse the mppt controller? Or???
  • the only reason to compare
    you already have both on hand, and want to see which one provides the most yeild

    starting new, just buy ONE system

    if you already have a system, .. buy more of the same
    i bought three new panels, i did not switch up to 24v panels
  • 2oldman wrote:
    westend wrote:
    For the OP's situation, it may be more economically efficient to sell the 12 V system and add a third 24V module.
    Or series the 12vs and parallel to the two 24s.


    Either way, it would be taxing the 30a mppt controller. Its specs say 780w/24v, 390w/12v, but that's assuming less than full power, and not leaving that 20% margin. But I've already seen my two 140w/12v panels put out over 300w on several occasions, so even the addition of a 100w/12v panel would be pushing it. And even three 250w/24v panels would be, as well.

    So, short of replacing pretty much everything, I think I'd be better to just add two 24v panels, and run two systems... and yes, I would like to have the option of running the 12v pwm system as a portable, at some point in the future.

    ------------

    But back to my original concern... would I be able to do a real time comparison in a paralled configuration, i.e;, two systems on one bank?
  • Revisit my 60 cell 24v results. 60 cell 24 is not the same as two 12s in series which is a 72 so at some point the 60 will lose "overhead" Then it is a question whether by that point you care, ie can the rest finish the job before dark or not.

    Comparison of what? You can see what each controller is doing for its output amps. Both will be at the same battery voltage at output.

    If you want to swap arrays/controllers it gets complicated for quick-connects etc.
  • If I simply added an additional 12v/100w panel, in parallel, the solar30 would be pushed to it's 80% limit, at 380w/12v... as that could potentially yield 24a (2x 9a/140w + 6a/100w).. and that would only add about 36% more power, (100w/280w). The tracer 30a mppt would see less than 8a in, but over 27a out, potentially, so again, pushing the controller's limit, all for only a 36% increase.

    Two systems, paralleled would net me a 178% increase in power, (500w/280w), for the cost of two 24v panels and some 10awg cabling.

    All said and done, less than $1100 u.s. for 780w... so say $1.40/watt u.s., for the two systems... (one system would be less, of course). As it is, I'm into about $1.80/watt u.s. for the 12v/pwm system, alone. ($500/280w)

    So I'm actually saving money, not spending it! (I wish... :))
  • BFL said,

    "Comparison of what? You can see what each controller is doing for its output amps. Both will be at the same battery voltage at output."

    That's essentially my concern... would either controller operate at a different voltage, if on it's own? Indeed, they would combine amps, and match volts, but would it take the same voltage to maintain the pwm's amps to bank, as it would to maintain the mppt's amps to bank, if operating individually? I'm thinking, no, it would not. So I suspect that would skew the data, especially with two such mismatched systems, (either 500w or 250w mppt vs 280w pwm). And yes, I could pro-rate the numbers to compare, but it's the original numbers I'm concerned about.
  • I don't understand the question. Each controller with its own array does its own thing and they add their amps until the lower voltage charger loses its overhead. This will be after they do whatever is next once they both reach set Vabs of 14.8v at the same time.

    You might have to arrange settings to keep the voltages similar after that so they keep adding their amps depending on charging profiles.
  • Yes, I'm wondering if either controller will effect the others performance... not so much during the huge "bulk" of the charge, while in bulk, but especially in abs. Obviously one would take over, if the voltages were even slightly different, so this could skew overall results of how many Ah's got to the bank.

    I've watched the pm4b and vec do a little dance, deciding who will lead. Eventually the vec wins out, as it has the higher Vabs setting, ultimately. So even if I set each solar controller to the same Vabs, I can see them not agreeing, as each controller has its own idea of what 14.4v is. I know the tracer goes to 14.44v at a 14.4v setting, for instance. But what does the solar30 go to at the same 14.4v setting? So I guess I've answered my own question. For daily charging it would make no difference, but for running a side by side test it could very well make quite a difference, if one controller was to drop out early.
  • So, this raises another question I'm still confused about... splitting the bank using a "1, 2, or both" switch.

    As far as drawing power off two separate strings (1 & 2), I still don't understand what would happen if the switch was turned back to 'both' while each string was at a different % soc, and then a load was applied. How would each string react? Would they quickly balance out, or would one string do all the heavy lifting, and draw down faster than it would in a normal series/parallel configuration.

    And would a simple 1, 2, or both switch actually isolate the two strings for separate charging???
  • When two chargers are on the job and one has a little more overhead than the other, they both still add their amps while they both have some overhead at all, but one does more amps than the other in proportion with how much more overhead it has.

    So during absorption (even if that is called "float" by that controller)they will still each do something and the total can be as much as the batts will accept or something less if there aren't that many amps (small arrays, some cloud, late in the day, whatever.

    By the time one controller drops out completely, the battery acceptance rate is likely to be low enough that the one controller can do it all anyway.
    --------
    The VEC1093 is temp comp so its voltage varies and it could be the higher voltage in winter or the lower voltage charger in summer.
    ---------
    Once you get going on solar, likely you won't need to equalize very often (shallow cycles to near or true full) so split banking not needed for that. You can do the Es on an opportunity basis with the VEC on shore power, assuming that is every two or three months.
  • Hi,

    My Blue Sky 3024di plays well with the alternator, and progressive dynamics converter. It does not play well with the Magnum inverter/charger.

    jrnymn7 wrote:
    Yes, I'm wondering if either controller will effect the others performance... not so much during the huge "bulk" of the charge, while in bulk, but especially in abs.

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