iconocastic question.

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Thomas
Thomas Solar Expert Posts: 291 ✭
in Solar Beginners Corner #1
My bubble has been shattered about my safety threshhold of 12v paralel.
If I expand to higher volts/lowaer amps what can be expected?
this is only a sounding question, planning purposes for I do not really have the capacity[money] to do this or a realistically strong 12v base to start from only 240w. currently. thanks
Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
2.3kW [10] Enecsys SMI-240-60 micro inverters

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: iconocastic question.

    are you talking pvs, batteries, or both being increased in voltage? small systems (about 1000w and under) are usually ok with 12v for both pvs and batteries. higher voltages allow for lowered losses in wires because when doubling the voltage occurs for a given wattage the current gets cut in half going through the wire. this can also allow more power to be handled by a controller, even pwm types if the nominal input voltage is equal to the battery voltage.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
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    Re: iconocastic question.

    Niel, I believe Thomas had an earlier post explaining he had $1200 to spend, and wanted to purchase a kit that would run a bunch of stuff all at once, a couple of computers, a couple of fairly large TV's and I think a fridge. Definitely not possible on $1200 sorry to say.
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  • Thomas
    Thomas Solar Expert Posts: 291 ✭
    #4
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    Re: iconocastic question.

    I am honestly in new territory about this beacause of the law, I only know it from Geometry/Trigonometry all angles of a triangle = 180' PERIOD. Watts/volts/amps change-vary directly... Isocoles/Right etc.
    So unless a charger or another photovoltaic convention I would be unaware of, there should really be no difference.
    Unless non-scientific reasons like budget/location, extraneous irrelevancies like that, economics etc...have influenced the pragmatic derivations/applications of this fire triangle.
    I imagine staying true to the sciences the amps would get lopsided and outa hand. You say 1000w good threshhold. I would agree.
    However I think I would like to begin experimentation at about 500/13/38 instead of 1000/13/76
    I read here on this forum that the kind of inverter I have should only be used at 1/2 the advertized specification. It is a 12-24 volt inverter[no higher] so at 500w I may change it and my battery bank over, if all goes well...
    what happens with pwm controllers with higher input volts than battery volts w/in the amp rating? What could be an adjustment for op amps/charging amps across 24v sourse to 12 v batteries?
    Am I scaring any one yet,? The balancing factor is I do not like to hurt/damage Capital Equipment, nevermind buy new stuff, so I don,t just do it.!!!haha
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #5
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    Re: iconocastic question.
    Thomas wrote: »
    what happens with pwm controllers with higher input volts than battery volts w/in the amp rating? What could be an adjustment for op amps/charging amps across 24v sourse to 12 v batteries?

    Solar panels are, basically, current sources. From Vmp to zero volts, the solar panel output (roughly) Imp (based on the amount of sunlight on the panel--lots of full sun, nearly full Imp current output).

    A battery, which is a voltage source, outputs more current the lower the voltage falls (the "opposite" of solar panels which output a "fixed" amount of current as the voltage falls).

    A couple examples. A 175 watt panel, one with Vmp=17.5 volts @ 10 amps, the second is Vmp=35 volts @ 10 amps.

    Say you have a PWM controller with a 12 volt battery bank charging at 14.5 volts, then the wattage into the battery would be:
    • 17.5 volt Vmp panel: 10 amps Imp * 14.5 volts charging = 145 watts into battery bank (10 amps into battery bank)
    • 35.0 volt Vmp panel: 5 volts Imp * 14.5 volts charging = 72.5 volts into battery bank (5 amps into battery bank)
    If you have a MPPT type charge controller:
    • 17.5 volts Vmp * 10 amps Imp / 14.5 volt battery charging = 12.1 amps into battery bank (175 watts)
    • 35.0 volts Vmp * 5 amps Imp / 14.5 volt battery charging = 12.1 amps into battery bank (175 watts)
    The above ignores efficiency/losses of the system (overall charging efficiency averages around 77%).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Thomas
    Thomas Solar Expert Posts: 291 ✭
    #6
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    Re: iconocastic question.

    My MPPT Inverter sure seems to gobble everything my panels make up, and then it turns on the battery and if... It would kill it.,, How does this voracious constant effect charge[ing], and my soon to be xantrex c35 w/temp sensor. Does the mppt in the charger effect the battery charge, like some wiring arrangements I have seen? potentially real and surreal both. IE xantrex dump load/charger arrangement.
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #7
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    Re: iconocastic question.

    The only way an MPPT controller affects the battery charging is in the formula:
    • Vmp*Imp=Pmp-batt-charging
    Vs for PWM:
    • Imp*Vbatt-charging=Pbatt-charging
    The farther Vbatt-charging is below Vmp of the panel/array, the more power is lost with MPPT.

    The efficiency is roughly:
    • Vbatt-charging/Vmp-array
    Notice that the farther Vbatt is from Vmp-array, the less efficient the system is (ignoring losses and the fact that Vmp falls as the panels get hot, and there is wiring drop).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Thomas
    Thomas Solar Expert Posts: 291 ✭
    #8
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    Re: iconocastic question.

    I dont really rem. claiming that I was attempting to do allof that, It may have been in a context of what my load is/ grid tie inverter is up against, but say I could find, 12v 900watts for that money, what then? Realistically the connections at Home Depot are 1200 dollars alone!:cry:
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

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