2kw 48v off grid system with problems

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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #32
    Sorry for not being clear.....I thought to connect 3 panels in parallel keeping the 37.16vmpp then another 3 in parallel., joining the 2 x 3 together in series having 74.32vmpp which should be perfect for a PWM controller...
    Will that work?
    Thanks
    Craig
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #33
    Craig4321 wrote: »
    Sorry for not being clear.....I thought to connect 3 panels in parallel keeping the 37.16vmpp then another 3 in parallel., joining the 2 x 3 together in series having 74.32vmpp which should be perfect for a PWM controller...
    Will that work?

    It might work, but it means you would need 6 circuit breakers or fuses. Better to make strings of 2 in series, then put the 3 strings in parallel. That way you only need 3 breakers (one for each string). If you do what you have suggested and one panel has a shadow or a fault, you will be trying to push the current from 3 panels through 2 panels... it's not an optimal design.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #34
    Craig4321 wrote: »
    Sorry for not being clear.....I thought to connect 3 panels in parallel keeping the 37.16vmpp then another 3 in parallel., joining the 2 x 3 together in series having 74.32vmpp which should be perfect for a PWM controller...

    Perhaps it's a language barrier, but it sounds like you want to have 3 panels in each string? voltage adds so 37.16 + 37.16 + 37.16=...

    To have 74.3 volts VMP you will have to have 3 strings of 2 panels in series, 37.16+37.16=74.32.

    Either way never are 3 panels in parallel! 2 or 3 strings are in parallel. If three each will need it's own breaker. If put in parallel with current panels 2 added strings as well as existing strings will need breakers.

    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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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #35
    Got it....thank you so much
    Rgds
    Craig
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #36
    O.k, so far so good
    for a 40meter distance between the panels and the controller would a 4mm diameter cable be good or should I use 6mm diameter. 16.17amps isn't that much....
    the only issue with me is the cost really.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #37
    Craig4321 wrote: »
    O.k, so far so good
    for a 40meter distance between the panels and the controller would a 4mm diameter cable be good or should I use 6mm diameter. 16.17amps isn't that much....
    the only issue with me is the cost really.

    This is 6 luxor panels, 200 watts each, configured with a string length of 2. That would be Vmp = 74.32 and Imp = 16.14.

    6 gauge cable (4.12 mm) cable will give you a 2.3% voltage drop. At full current (seldom achieved) you will lose about 27.5 watts in the cable. The power loss goes as the square of the current, so at half power your cable loss would be about 7 watts.

    Bottom line: 4 mm cable will be OK. If you think you might ever expand the array with a PWM controller, put in 6 mm cable. On the other hand, if you expand the array and use an MPPT controller, you will be fine with 4 mm cable because you will use a higher transmission voltage.

    Now let's consider what happens if you use the same 6 panels with an MPPT controller: You will reconfigure the panels to a string length of 3 (Vmp = 111.48 and Imp= 10.76). You will not NEED circuit breakers or fuses in the combiner (but they are nice to have anyway). You will be able to use 3 mm cable and have about the same power loss.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #38
    Thanks that's great.
    don't know what I would do without you guys.
    kind regards
    Craig
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #39
    O.k. all up and running now. ...no hiccups so far.I have set the controller to
    pwm absorb voltage 57.6
    is that correct
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #40
    What is the brand/model of battery you are charging? 57.6 volts is a bit on the low side (14.4 volts @ 12 volts) for a flooded cell battery... For an AGM/Sealed battery, it is probably about correct.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #41
    The batteries are rolls s605 Fla 6v

    8×6v for 48v system
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #42
    O.k ..I have bumped it up a notch to 58.4v
    is that better for my batteries ?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #43
    Well, Rolls/Surrette certainly has different numbers depending on what you read:

    http://www.rolls-battery.com/content/technical-downloads?q=node/43&phpMyAdmin=2eda4dec0bd69647b9e3cf0f71e01d23&phpMy Admin=9dec4a269d70t7a63be7c
    http://support.rollsbattery.com/support/solutions/articles/428-state-of-charge-charging-flooded-lead-acid-batteries
    http://www.rolls-battery.com/content/technical-downloads?q=node/47&phpMyAdmin=2eda4dec0bd69647b9e3cf0f71e01d23&phpMy Admin=9dec4a269d70t7a63be7c

    So anywhere from 14.1 to 15.0 volts (12 volt bank) seems to be the recommendation... Not very useful.

    Many times, the charging voltage seems to be slanted towards Marine or other systems where there is usually a high percentage of time to charge (i.e., utility power means 24 hours per day of available charging current).

    For solar power systems (and especially those closer to the earth's poles) can have a relatively few number of hours per day of "useful" charging time (available sun). In general, it seems that for solar power systems, the absorb charging voltage should be set higher--You simply do not have much time to complete your daily charging.

    Do you have a remote battery temperature sensor for your system? Lead Acid Batteries are very sensitive to charging voltages, and "hot" batteries should have the absorb voltage reduced (typically -5mV per degree C per cell over ~20-25C). Keeping your batteries as cool as practicable is important... Charging/running them constantly at 115F to 125F (45C to 52C) is going to be a very short life. If you can keep them below 95F (35C) in a hot climate is a good thing.

    Personally, I would probably start at 14.7 volts (58.8 volts) (temperature compensated) and monitor the specific gravity (using a hydrometer) to see how things are going. If the battery is cycling daily (normal use), you don't have to reach 100% state of charge every day--That can be pretty hard on the battery cells (high charging voltage, high battery temperature, lots of "gassing" or equalization, etc. are all very hard on lead acid batteries).

    If you get >90% state of charge several times a week--You should be doing fine.

    Depending on the type of lead plates (Rolls has at least two types), some folks here have found that they need ~15.0 to 16.0 volts (60-64 volts for a 48 volt bank). Especially if their specific gravity measurements have been low for several months (apparent long term under charging).

    Here are some other threads about charging Rolls/Surrette Batteries:

    http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/advanced-solar-electric-technical-forum/8753-charging-large-surrette-rolls-batteries
    http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/off-grid-solar-battery-systems/17016-rolls-surrette-s-1590-cell-death

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #44
    Do you have a good glass hydrometer? If not, you might look for a Hydrovolt (I think they are out of Germany):

    http://www.solar-electric.com/midnite-solar-battery-hydrometer.html

    A few members here have used this unit--Very happy.

    With any hydrometer, make sure you rinse it very well with distilled water when you are done--Otherwise the floats tend to stick and give inaccurate readings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #45
    O.k ...I will start with 14.7 (58.8 ) it is quite hot here at the moment.38 to 42 deg c...
    today was very humid so the the day was not to great for charging but I did see 57.7v on the controller So on a better day I should get to see an absorb charge.....if there is wind then I have more than enough charging amps to see full absorb and an equalization cycle.
    something I haven't seen in a few years...hopefully with the new panels and new batteries. My problem will be solved.
    Thanks
    Craig
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #46
    Craig, watch the temperature of your battery bank... For example, if your bank is at 40C:
    • -0.005 volts per C per cell * 24 cells * (40C-25C) = -1.8 volts vs standard temperature
    So, My 58.8 volts -1.8 volts for 40C bank becomes ~57.0 volts charging at battery bank. And you want to hold that voltage for around 2-4+ hours (shorter if less State of Charge is >80%, longer if State of Charge gets down to 50% or so).

    You should have an accurate volt meter to measure the battery bank charging voltage. Some charge controllers have been known to put a 'temperature corrected" reading on the display (i.e., actually charging at 57.0 volts but because room or battery bank temperature is 40C, it displays 58.8 volts).

    In the end, temperature corrected specific gravity measurements are your "gold standard" with flooded cell batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #47
    O.k thanks, I have a good volt meter so I will use that and I will get a hydrometer. I broke mine.
    my two Tristar ts-45s showed 51.6v in night mode earlier whereas the wind controller showed 51.8v .
    so I see how different units show different readings.

    -Craig
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #48
    All seems to be well...I am getting about 3 hours absorb charge .

    My wind turbine controller seems to be one of the charge problems I had...the dump voltage is set to 56v with no option to change it...does that influence the solar controllers?.
    to be sure,I have put the turbine brakes on and turned the controller off ....there is no wind this time of year anyway...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #49
    The wind turbine should not be hurting as long as you do not have too much total charging current for the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #50
    Does the wind turbine controller that is set to dump load at 56v not influence the solar charge controllers which are set to 58.8v absorb .?
    even if the turbine is not turning or producing
    would it not dump any charging amps from the panels after the batteries have reached 56v Thanks
    Craig
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #51
    Oops... Your are correct. I was not thinking. The wind controller set as a dump load on the battery bank is going to be a big problem.

    There are ways of placing a dump load or shorting relays on the turbine up stream of the rectifier block that would allow you to "dump energy" directly from the turbine, but not affect the battery bank.

    Perhaps, if the turbine is worth it to you--You can look at changing over to a more adjustable dump load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #52
    Thanks for that....I only noticed it because after setting up my new controller and new panels I was achieving an absorb charge.. So after close inspection of the system I saw that the wind controller started to dump load at 56v even though there was no wind.....I turned the brakes on and controller of and within 15 to20 minutes the voltage went from 56v to 57.4v.....
    there doesn't seem to be a way to change its settings.
    no worries with the wind turbine,I can leave it off until winter ...when there's wind but no Sun.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #53
    A few folks here really like pwm version of the MorningStar T'S controller family for turbine dump loads. Long term, might be worth a look.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Craig4321
    Craig4321 Solar Expert Posts: 29 ✭
    #54
    I have been using this wind controller for 4 years it's a Chinese one..exmork. and never noticed the voltage dump problem....I used a southwest wind power one with a whisper 500 turbine but sadly the turbine. And controller were demolished in a very bad storm...I still have the dump load for it though....perhaps I will buy another morning star controller and use that.as suggested.
    they cost 117 Euro so quite cheap.
    craig
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