Photowhit ✭✭✭✭


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  • Re: String size question

    Since you have repeated this, the math works out that voltages add but the amperage remains the same when solar panels are in series. If the panels are in parallel, the voltage remains the same and the amperage adds up...

    So if you want a 48 volt system(battery bank) you would need 2 panels in series to reach the proper charging voltage for an MPPT type charge controller and you might not be able to run 3 in series due to the VOC being to high in your climate, since the Flexmax is limited to 150 volts, I think it can handle a bit more without production, but please verify that if you want to try strings of 3. I think you can have 12 panels on 1 charge controller and 10 on the other if you want/have 22 panels. 12 panels will be slightly over there suggested 4000 watt max, but there will be very little loss and only in the coldest of days.

    For that many strings you will need a combiner box and breakers or fuses on each string. Midnite and Outback make one that will handle 2 arrays with up to 6 strings each.
  • Re: First electric bill

    Masterjoe said:
    Anyone know how I would set my system to invert from the batteries at night and not use grid power?
    You do understand that this will be less cost effective?

    Every watt you take out of the battery bank will require putting 1.15 watts to refill. You can add another 10-15 % for the inverter losses as well.

    If I understand you correctly, this will be counterproductive, as in more expensive.
  • Re: Form for off grid solar newbies?

    I think somewhere I had done a list of questions, it could be put into a form of sorts;

    peaks daily, weekly
    types 12v/120/240
    Seasonal peak

    Solar insolation for your array orientation;
    seasonal peak
    seasonal minimum

    Availability of alternate charging;
    desired days of autonomy w/o alternate charging.

    Type of battery bank /willingness to do monthly maintenance

    That would be a good start...

    Additionally would be distances,
    array to cc/battery bank
    battery bank to inverter

    Location of battery bank / Batter bank exposure to ambient temps

    Balance of loads day time vs night time.
    Willingness/availability to load shift.

    Queries about how they intend to handle;
    Water heating
    ...might save heartache and confusion.

    Might even ask about the NEC version that is required if any...

  • Re: Maximum mc4 cable run

    Photowhit said:

    Photowhit said:

    wow great info thank you, I will be using an mppt xantrex charge controller 60-150 i went trough tyour approach an factor in the whole picture 2 string of 2 panel 325 watts for a total of four panel, it seems the drop is faily hight 
    using the calculator i get


    Voltage drop: 5.28
    Voltage drop percentage: 7.88%
    Voltage at the end: 61.72

    Please note that the result is an estimation based on normal condition. The actual voltage drop can vary depend on the condition of the wire, the conduit being used, the temperature, the connector, the frequency etc. But, in most cases, it will be very close.

    i will be charging a 24 volts battery bank would that work?
    It sounds like you did something wrong, If you have a string of solar panels or batteries, the voltage adds, but the amperage remains the same. If you have 2 panels or strings of panels in parallel, the amperage doubles but the voltage remains the same.
    I did my calculations working backwards from the 650 watt string of 2 panels;

    "With a VOC of about 94 with 2 panels in series, I would assume a VMP of about 74. So the amps of a string of 2 would be wattage 650/74=8.8 amps 2 strings would be 17.6 amps at 74 volts, with a run of 120 feet on 8 gauge wire."

    So my number represented all 4 panels.
  • Re: New member questions.

    You generally want to stay in the top 20% of capacity, since you would be recharging after each discharge, you could push that a bit.

    But with without more info on load, will you run a fridge? I'll give a bit generous addition of 800 watt hours for personal lighting, radio, pump (this could be a large load!) I'll use 4000 watts of AC. A fridge would add about 1000 watt hours. 

    For 4000 watt hours of AC load, you would first need to figure out what the DC load would be... Inverters are roughly 85% efficient.
    So 4000 x (100/85)= 4706 watt hours of DC

    watts = amps x volts

    4706/12= 392 amps

    392 amps should be 20% of your capacity, so x5 for 100% of capacity
    392x5=1960 amps at 12 volts for a battery bank size. T105's have about 230 amps each at 6 volts. If we divide by 230

    1960/230= 8.5  --  x2 for 12 volts we get 19, call it 18, natural voltage will start at 12.7 volts and fall to around 12 volts under load over 24 hours. Several things here, your loads will be handled by the generator when the generator is running so your actual time discharging will be less, and the load on the battery bank for less time.

    As I stated above the battery bank will accept the current at 15% or less of it's capacity, So While you need to push 392 amps back into the battery bank, it will take some time. With  8 strings at 12 v x 230 amp= 1840 amp bank maximum charging capacity would be 1840x1.5= 276 amps per hour, but you will also run up against another characteristic of Flooded Lead acid batteries as they approach full charge they will accept less current. 2 hours of charging should get you close to full capacity.

    Please note Trojan uses 13% as the max charge rate, you can run the numbers using that as well. Also understand that the input voltage will be 15-20% higher than the resting battery voltage. Think of it as the generator being  cup of water/current and the voltage as being the height, you have to have the height higher than the battery to facilitate the water/current to flow to the battery. So 276 amps at 14.4 volts = about 4000 watt generator. I don't know how efficient inverter/chargers are at making DC current, but suspect you would need around a 5000 watt generator.

    I hope others will check over this, I don't use generators, just having tried to help people here.

    As I said earlier, a Lithium battery bank might be = in cost. and take the energy at a faster rate saving you generator run time if you have a larger generator. Lithium would be able to use 80% of it's capable. So you would need about a 500 amp 12 volt battery bank... 

    In general I would suggest higher system voltage for a few reasons, 8 strings of flooded batteries are hard to keep in balance. 2 strings of 8 at 48 volts would be less likely to get out of balance.