A clarification needed

hillsidehillside Registered Users Posts: 102 ✭✭
I began with:
"Need wiring advice--am upgrading our backup solar power...
24 volt system
SRNE 40A MPPT  controller
Cotek 3000W 24V. pure sine inverter
4- 208 AH 6V GC batteries...
Photowhit gave me this diagram....
Question: Is this for a 12 Volt system?

Image result for Solar panels in series and parallel
I've been told that this is the wiring needed for a 12 volt system and, that in this configuration, it will produce 48 Volts.


8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
Honda EU3000W generator for backup.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,022 admin
    With 2x 6 volt batteries in series, that is a 12 volt battery bus.

    4x 6 volt batteries in series, that is a 24 volt battery bus (24 volts @ 208 AH in your case).

    Without knowing more about your application/needs, I would suggest a 3,000 Watt inverter is way too big for your 4x 6 volt @ 208 AH battery bank.

    A 500-1,000 Watt inverter would probably be a better fit (larger AC inverter waste power and if loaded to 3kwatts would draw that battery back dead in 2 hours or less).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillsidehillside Registered Users Posts: 102 ✭✭
    Bill, the inverter is turned off most of the time. We use the system for washer/propane dryer, TV at night, but not always, and when the power is out we use a 3000W Honda generator and of course the solar power.
    The batteries are now 4 6volt 370 AH Dekas.
    The reason I ask if the above wiring diagram is correct is that recently I posted about a fried terminal at one of the junction boxes and what I think is the premature loss of the golf cart batteries.
    I now have 4 useless panels, 3 of which are new.
    A solar company I talked to today told me that wiring diagram is wrong because it is drawn for 12 volt panels. True?
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    With a 24v nominal system and an mppt controller, you want voltage (Vmp) from the controller of mid-30ish or higher.  The controller bucks this down to battery charging voltage.  There will also be a maximum string voltage for the controller.

    The numbers may vary depending on your panel and controller specs, but in general the diagram above would be a pretty normal way of wiring typical panels for a 24v system.  My 250w panels are wired like that for a 12v system, but with string voltage of ~60v, it would charge a 24v system just fine.  My charge controllers are rated for 150v.

    Using typical 12v panels could work on a mppt controller, provided Vmp at normal operating temp is over ~17v.  If using a pwm controller, there's no voltage buck (or current boost), so whoever said the diagram is for 12v panels may have assumed a pwm controller.  You say it's an mppt controller though.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Registered Users Posts: 102 ✭✭
    I was reading 52+ volts at the controller --from the panels.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Sounds about right.  Maybe a bit low depending on the panels and temperature.  The mppt controller should buck that down to ~25-30v charging voltage.  Most panels should be good for much higher string voltage.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 32,022 admin
    Here is something that may make understanding the battery series/parallel connections a bit better:

    https://www.newenergyco-op.co.uk/blog/how-to-connect-your-batteries-to-make-up-a-24v-or-48v-system.html

    Note, while the schematic is "correct", physically, how you connect the batteries does make a difference--Connecting the batteries correctly balances current flow through parallel strings of batteries (you only have one series string, so this does not apply to your system at this time):

    http://smartgauge.co.uk/batt_con.html

    As a rough rule of thumb for Flooded cell batteries, we use 500 Watts of AC inverter rating per 100 AH @ 24 volts. Your 370 AH batteries would suggest a maximum "practical" inverter of:
    • 500 Watt inverter (per 100AH @ 24 volts) * 370 AH / 100 AH = 1,850 Watt maximum
    • And 1/2 that size is good too (longer runtime at lower wattage) ~ 925 Watt inverter nominal
    Using a smaller 24 Volt AC inverter for your "evening household loads" might be something like this:

    https://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-600-24.html (600 Watt 24 volt TSW 120 volt @ 60 Hz inverter)
    http://smartgauge.co.uk/batt_con.html (remote)

    I don't know anything about Victron inverters (should be good quality)... This one has "ECO Mode" (aka "search mode")... The inverter will turn on when a 15 Watt AC load is connected/turned on (adjustable via bluetooth phone app?) instead of 7 Watts tare, less than 2 watts).

    Here is a search on our Host's website for 24 VDC TSW AC Inverters:

    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_frequency=434&nav_inv_input_voltage=437&sine_wave_type=549

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    Hi @hillside, You haven't given people enough information to make an informed correlation to if the wiring is correct. They need to know the specs of your charge controller and solar panels, which I posted on the original discussion.

    I think these are the specs of your controller, the link I provided no longer works and since I looked it up once I've got little interest in looking it up again. perhaps you downloaded the manual and can verify!

    You told Bill that the VMP was;
    hillside said:
    Thanks, Bill, 30.1 and 30 for the older Trina, 30.5 for the one that is 255watt.
    You have told us that you have a 24 volt system with 4 golf cart batteries. Please hook up the batteries in series. + to -. In series the voltage adds, 4 in series is a 24 volt battery bank.
    hillside said:
    A solar company I talked to today told me that wiring diagram is wrong because it is drawn for 12 volt panels. True?
    The diagram has no voltage listed for the panels and is correct, Any solar company thaat told you that should be ignored and not used. It's just a simple diagram that shows the results of hooking up 4 identicle panels in series and parrallel.
    hillside said:
    The reason I ask if the above wiring diagram is correct is that recently I posted about a fried terminal at one of the junction boxes and what I think is the premature loss of the golf cart batteries.
    I now have 4 useless panels, 3 of which are new.
    Pretty hard to make a panel useless, if you have problems post a photo of the output of the panels and try adding a load. Not sure what a 'fried terminal' at a junction box. Might check your wiring to be sure it matches the diagram.  As I said before you don't need to have a juction box for just 4 panels, you can use branch connectors to combine them.

    Image result for mc4 brach connector types



    It sounds like you are concerned about the 48 volts running into the charge controller. 
    hillside said:
    I've been told that this is the wiring needed for a 12 volt system and, that in this configuration, it will produce 48 Volts.
    Perhaps youshould read the manual or an article on how MPPT type charge controllers work. Here is one posted by our sponsor;

    https://www.solar-electric.com/learning-center/mppt-solar-charge-controllers.html/

    Not sure what the problem was with fixing this last year. The specs say you can handle an input voltage of 75 volts. If you run a single string you will be above that and burn up your charge controller. It also says the maximum input voltage (this would be VOC) must be under 100 volts.

    To hook up your 4 panels (if the same as last year) you need 2 in series and 2 in parallel.

    In series the voltage will add, so 2 - 30 volt VMP panels will be roughly 60 volts. 

    In parrallel the panels or strings of panels the amperage adds but the voltage will remain the same. so 2 strings in parallel will produce twice the amperage at the same 60 volts.

    The charge controller will take care of delivering the proper voltge to the battery bank. Follow the instructions and hook up the battery bank first (if that is whaat it tells you)



    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.
  • hillsidehillside Registered Users Posts: 102 ✭✭
    I've read about the mppt c/c's. I will read all that's been linked.  I've tried to add the specs on my little system to the bottom of each post but haven't figured out how. They are in my profile if you click on my screen name.
    24v. system, SRNE 40A C/C (ML2440)

    Here is the wiring diagram I was given yesterday for wiring the panels--bought 4 used, 250Watt, good condition. Is this right or wrong?


    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    That puts the 4 panels in parallel, which raises a couple of issues.

    1.  250w panels likely have NOCT Vmp of ~30v.  Flooded GC2 batteries will likely want a target absorb voltage of ~29.x volts at 25°C (higher if cool/cold).  There's a good chance the controller will have trouble providing this voltage at least some of the time, which means the bank may not get proper absorb cycles regularly.  You will want to keep wire length short, and sized heavy to minimize wire loss (I'd check with an online voltage drop calculator using your actual numbers).  You may want to consider using a pwm controller instead of mppt with this setup.

    2. With 4 in parallel, each should have a fuse or breaker (vs a 2 string series/parallel setup which could be wired with a 'Y' connector) to prevent a short in 1 panel being fed current from the other 3.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Registered Users Posts: 102 ✭✭
    No longer using the flooded GC batteries. Now Deka 370AH 6 volt.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • hillsidehillside Registered Users Posts: 102 ✭✭
    Batteries are wired in series. In this diagram, like I just recently had, one of the terminals (not at a junction box, there was none) on the + side of one panel melted but was still powering the system.
    If one of the mc4 connectors (or a branch connector) was not making proper contact, could that have been the problem? A couple of panels were showing reduced voltage, as in 20-25% less.
    Image result for Solar panels in series and parallel
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Those would be a flooded L16?  These taller batteries really need high enough absorb voltage regularly to bubble a bit.  Mine are set to 58.8v (=29.4v for 24v nominal).
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Registered Users Posts: 102 ✭✭
    Yes, they are. Do you think one missed contact could have been the  problem? I sure hope so because I'm reluctant to do it again with new panels and have the same problem (fried terminal and low voltage)
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Mc4 connectors can be prone to damage, particularly if connected/disconnected while current is flowing.  The resulting DC arc can burn/melt the contacts.  Once damaged in this way, they can be prone to more heating in operation. 

    In addition to turning off the charge controller and opening breakers, I generally cover the panel(s) with a blanket or something when making/breaking mc4 connections to be really certain no current is flowing.

    They can also be prone to damage from mishandling (eg lifting using the leads loosening crimps), and sometimes even from mating with a connector from a different manufacturer.


    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Registered Users Posts: 102 ✭✭
    I do cover the panels with tarps when setting up and connecting, as well as turning off the C/C and the breakers.
    I'll go with the series/parallel connection and report back.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    4 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    Honda EU3000W generator for backup.
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