mppt and amperage

ws9876
ws9876 Solar Expert Posts: 453 ✭✭✭
in Advanced Solar Electric Technical Forum #1
Regarding the KID 30 amp controller...Midnite Solar says to only use 2 panels in a 12v set up. But if you put 3 in series and have about 105v
and 9 amps
to start...the KID isn't going to boost that to 30 amps..? or even to 25 amps..? Maybe 20-22...
so 3 in series wouldn't hurt a 12v set up...no?
What do you think?
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  • Photowhit
    Photowhit Solar Expert Posts: 6,017 ✭✭✭✭✭
    #2
    You appear confused.

    What says to only use 2 panels?

    Did you run your panels through Midnites string sizing tool?

    MidNite Solar - KID Sizing Tool.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,122 ✭✭✭✭✭
    #3
    What is the Voc? voc x 3 in cold weather is likely to be too high.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • ws9876
    ws9876 Solar Expert Posts: 453 ✭✭✭
    #4
    if VOC is too high then why does their manual show multiple 3 panel in series options? 

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,122 ✭✭✭✭✭
    #5
    Don't know what options you are looking at. It's all based on max open circuit voltage. Your panels are particularly high voltage. Also the colder the panels get the higher the voltage they produce.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,122 ✭✭✭✭✭
    edited October 2022 #6
    Another factor may be the allowable wattage in 12 volt vs. 24 or 48 volt systems. You can double the allowable wattage in a 24 volt system and quadruple wattage in a 48 volt system.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,976 ✭✭✭✭✭✭
    edited October 2022 #7
    ws9876 said:
    if VOC is too high then why does their manual show multiple 3 panel in series options? 

    maybe this will help, I thought the previous responses hit the mark. You do not want to damage the electronics with high VOC !!!!

    Some people live in places that do not get as cold, typically just before sunrise. It can be simpler for 3 in series also.

    A 12v battery is going to get more solar power to it when you use 2 panels in series compared to 3 if the panel numbers were equal.

    Maybe 3 in parallel will work if the panel model was listed. It would be best.

    There is higher conversion loss as the voltage increases with 3 panels in series for a 12vdc battery bank.

    There is more to this also, as always....


    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    edited October 2022 #8
    It depends also on how many cells the panels in series have.  Is that 60 cells ?  72 cells ?   Less ?

    Typically, these days, the PV module voltages are higher than they were say, 20 years ago.  Also, it is usually easier to buy the higher voltage modules used for grid tie now.  I find that 12V nominal PV costs more than these newer modules.  Been  while since I looked though.

    That being said, 105 Voc at 25 degrees C ambient will only go up to 150 Voc at really cold temperatures.

    For silicon, that is ~around~ 10 or 11% higher Voc at every drop of 25 degrees C or so as I remember.  It would have to get pretty cold, like, -50 degrees C ?   I may be a bit off on this but something like that.

    Also, the higher the Vmp, (and Voc) the hotter the unit will get in general.  If you are charging a 12V battery, I would try more panels (even number)  in series-parallel if that works out which would take care of both problems.

    I think the sizing chart/program may give a good idea what is going to happen ?

      I think I would just move somewhere sunny.   Solar works better where there is sun anyway.

    boB

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,122 ✭✭✭✭✭
    #9
    boB said:
    .That being said, 105 Voc at 25 degrees C ambient will only go up to 150 Voc at really cold temperatures.


    boB

    It's not clear whether were talking Voc or Vmp here. I was figuring the OP gave us Vmp. divided by 3 were talking 35 volts per panel. IF thats the case then Voc will be higher. I probably shouldn't be assuming anything here.

    ws9876, can we get the specs from the back of the panel?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,122 ✭✭✭✭✭
    #10
    105 volts x 9 amps is 945 watts, divided by 12 volts =78.75 amps. Clearly higher current than a 30 amp controller is capable of handling.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • ws9876
    ws9876 Solar Expert Posts: 453 ✭✭✭
    edited October 2022 #11
    your right....I will stick to 2 in parallel for now.I thought that was beating 2 in series but maybe not..its close..
    Canadian Solar 315 watt/KID controller/SOK LiFePo 12v
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,976 ✭✭✭✭✭✭
    #12
    I would say that Canadian solar has made over 1,000 models of panels. 
    You need a model number!  It would have saved alot of the time on this thread.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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