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Inverter sizing (MM5000)

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  • Inverter sizing (MM5000)

    [FONT="Calibri"]I have 4 ET solar- 185w panels with a VMP of 36.9, VOC of 44.75, IMP of 5.014, and ISC of 5.54. I also have 2 Hanwhas 190w and 2 Makesen 180w with very close to the same ratings. It was suggested to me to do 4 sets of two panels into a combiner box, and onto one input breaker of the MPPT in the MM5000 I have. So this works out to around 74volts 5ish amps per string combined for 74volts 20ish amps total. I don't seem to find a temp coefficient % on the panel labels, but did find on Midnight Solar's web page a chart they use for temp considerations. I'm taking a pretty worse case scenario and saying in WI we could see a full sun day at -40F in winter. The chart shows using a multiplier of 1.25 on the VOC number. So in my case the VOC would be almost 90*1.25=112.5v[/FONT]

    [FONT="Calibri"]The MM5000 manual shows 120 input max. I see when Beacon made the M5 off the MM5000 when Advanced Energy went out, they lowered max to 110. Should I even be thinking about hooking it up, or go with a different MPPT and just use the inverter portion of the MM5000? Directions for either model don't go into that type of application. Was going to use the MM5000 as stand alone, no grid connection, 48volt 420amp hour battery bank (16 GC2 batteries with 210hr AH) , with the appr, 1480w going in. The batteries were going to be FVP batteries sold at a local big box store. Appears those batteries are made by Trojan. I'm sure I will trash my first set I will also be clamping a 48 volt 3 phase axial flux to the batteries via bridge rectifier. I have two Morning star TS 45 PWM I was told I could use in tandem in diversion mode using slightly different set points. Was going to dump into water heating elements. This was/is all going to be an experimental setup for me to learn and eventually expand on.
    Thoughts and constructive criticism please. I will try to take it well [/FONT]

    [FONT="Calibri"]David [/FONT]

  • #2
    Actually I could factor in the VD in my wires as the panels are going to be 250ft away. #6 copper @ 250 ft using the 112.5 number, and factoring the amps 1.25 higher also gives me almost a VD of 5v. So now I'm down to 107.5

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    • #3
      The maximum voltage will be panel open circuit, no current yet flowing, no wire voltage drop.
      Some induced voltage (change of current, lightning, etc) could add a short spike, I would not
      connect 120V peak rated equipment to a 110V source. Your choice. Bruce Roe

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      • #4
        Bruce, so are you saying there is no temp coefficient increase going to colder temps like there is a decrease going to higher temps? Thought I was understanding that it works one way or the other based off a certain temp.
        If the max panel voltage at any temp would indeed only be Voc of about 45v then in my scenario I only have to worry about 90v that's even better. I was thinking a safe number to be at would be 25% under max. So 120 less 25%= would be 90.

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        • #5
          PV panels increase their voltage in the cold, and on a hot sunny day, their voltage drops. Use a realistic 100 year record cold temp for your area, don't guess at -40

          you cannot rely on voltage drop in the wire, to prevent your controller from burning up.
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

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          • #6
            I was trying to find that realistic number just this morning in fact. I will have to do some more searching to see if I can find something archived. I did find a 100 year record low for our whole state, which was -50, but that recorded in far northern WI.
            The chart I found that 1.25 number on was when I was using Midnights string sizing tool, and they talk about Hyper VOC It was a blue like link, so I clicked on it, and that is where I found the different multipliers for different temps. 1.25 is the highest they have for -32 to -40 temps. Are there some different places to look for this info on voltage increase with temp decrease?
            I can't argue the fact that it wouldn't be a good practice to factor in the VD in the wire. Just trying to come up with a solution. I guess I may have to consider buying a different MPPT
            Last edited by pellets4fuel; 03-07-2019, 06:48 PM.

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            • #7
              So I was reading through the MM5000 manual again...and one of the things it states is out of the box it's configured to perform the following with no additional user adjustments. The second bullet point is "manage a 48-volt bank of sealed, maintenance -free lead-acid batteries" The similar inverter Beacons M5 says VRLA (so same thing)
              I was planning on using the GC2 batteries due to being a newbie and probably going to trash the first set as I learn. After reading some info in the battery section, and trying to wrap my brain again around the whole C/rate I am thinking I am reading that FLA batteries are not going to charge the same as the VRLA?
              David

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