midnight solar battery monitor

wastwast Posts: 41Registered Users ✭✭
edited May 21 in Solar Beginners Corner #1
I have installed a midnight solar battery monitor which tells your battery percentage of charge which shows batteries to be at 100 %charged.. monitor also tells when last time that batteries received full charge... the monitor tells me the batteries have not been fully charged for 2 wks or more.. how is this possible if they are 100 percent charged?? system has been turned off for over a month with charging with panels the only thing taking place.. (remote cabin)
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  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    How is the charge controller terminating absorb? With no loads, and using a MN Classic end amps termination, for example, it could hit end amps before the 2 hr timer (for flooded) expires to reset the fully charged timer in the meter.

    Another possibility is temp compensated absorb voltage is < the meter absorb threshold, or voltage drop between controller and bank is high enough to make the controller think it's hitting absorb voltage when it really isn't.
    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
  • wastwast Posts: 41Registered Users ✭✭
    thks for the reply.. I am learning as I go with this so please bear with me.. my battery bank consists of 6 -6 volt batteries which I have wired up parallel to give 3 12 volt batteries.. batteries are surrette 550S .. my charge controller is a 30 amp midnight solar which is not mttp .. I have 3 130 watt panels for charging.. am about to add 2 190 watt panels and 2 40 amp mttp charge controllers.. the charge controller that I am now using  shows batteries are full and not taking any more charge..  because of remote location I am only now able to get back to cabin...
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    edited May 19 #4
    You might want to double check the dip switch setting in the controller for battery type (if set to "gel" type, absorb voltage may be too low). If so, set for "flooded" then reboot by turning off pv breakers first, then battery, wait 30secs, then turn on battery breaker first, then only after it boots fully, turn on the pv breaker.

    If the controller is properly set, you may want to check the voltage at both the controller battery output terminals, and at the battery end of the wire while charging in full sun. The battery side shouldn't be any more than 0.1v or so less than the controller side.

    It's good that you're adding panels etc. That bank really should get ~50a minimum available charge if you're just there weekend to ~100a if full time, unless you're ok running a generator lots. Also, with three strings in parallel, you should have a fuse on each string. It may be wise to get a DC clamp meter (note some are AC current only, you need one that measures DC current). Parallel strings can see different resistances, leading to some potentially over/undercharged.
    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. Posts: 27,933Super Moderators, Administrators admin
    Ok... First, do you have a DMM? I highly suggest an AC/DC Current Clamp DMM (make sure is DC Current Clamp, there are many AC only clamp meters too):

    https://www.amazon.com/gp/product/B07546L9RT (inexpensive--aka cheap)
    https://www.amazon.com/gp/product/B019CY4FB4 (mid range)

    And a hydrometer (make sure to rinse well before putting away--Glass hydrometers are very easy to break--make sure put away safely):

    https://www.solar-electric.com/brin1bahy.html
    https://www.solar-electric.com/midnite-solar-battery-hydrometer.html

    Next--You have a huge battery bank (for a 12 volt system)... Each battery is ~428 AH battery... 3x parallel strings is a 1,284 AH battery bank @ 12 volts. Normally, I suggest going to a 24 volt (or higher) voltage battery bank when you get >~800 AH...

    Anyway, your bank. Normally we suggest 5% to 13% rate of charge for lead acid batteries. 5% for a weekend cabin, 10%+ for full time off grid (more than just summer weekends). 1-2% rate of charge for "float" charging (charged battery bank in storage).
    • 1,284 AH * 1% rate of charge = 13 amps float/storage
    • 1,284 AH * 2% rate of charge = 26 amps float/storage
    • 1,284 AH * 5% rate of charge = 64 amps minimum cycling
    • 1,284 AH * 10% rate of charge = 128 amps daily cycling full time
    • 1,284 AH * 13% rate of charge = 168 amps full time off grid "typical" cost effective maximum array
    Mapping that to a solar array:
    • 1,284 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.01 rate of charge = 242 Watt array float
    • 1,284 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.02 rate of charge = 484 Watt array float
    • 1,284 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 1,209 Watt array minimum
    • 1,284 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 2,418 Watt array nominal
    • 1,284 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 3,143 Watt array "cost effective" maximum
    390 Watt of solar panels--You are just "floating" the battery bank. Not really a large enough array to support any loads. So the battery monitor is never "seeing" a "real" charging cycle.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wastwast Posts: 41Registered Users ✭✭
    recently purchased a hydrovolt for testing the SG.. new to this,well not so much new as not that good at it.. I get good sun from march until oct but then it starts to diminish quite a bit.. only get 8 hrs of daylight for 4-5 months. during winter months I run generator for 4-5 hours every day that I am there.. I have an iota 55 amp 3 stage charger and a 15 amp 3 stage that I use when generator is running. all hooked to auto transfer so as soon as generator fires up it takes over the charging.. I plan on using the 40 amp MTTP charge controller with the new 190 panels hooked up in series.. also have another 40 amp mttp charge controller that I was going to use with 3 130s hooked in series..  any thoughts on this?? I am sort of a "jack of all trades" master of none as we say here in newfoundland..  electrical is about hardest of all for me to comprehend.. really appreciate the advice.. this may seem like a dumb question but as I stated I am not the that good at anything to do with electricity so I will ask anyhow.. Is possible that my battery monitor is showing that my batteries have not received a full charge in the past couple of weeks because they are only being maintained by the panels?.. both charge controller and monitor are saying they are fully charged.. tester shows the bank at 13.7 volts...I have not turned on inverter for over a month and we have had really good sun in that period of time.. last time I checked SG with the hydrovolt was towards end of march when it was really cold and they showed mostly 1.26  on all cells...
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    In order to flip the bit for last fully charged, the monitor needs to see a voltage of 14.x for "Y" hours. I don't recall the exact numbers, but basically either the numbers aren't being hit (see previous post for possible causes), or there's a problem with the meter.

    You can have multiple different charge controllers on a single bank, but it can get complicated to manage if you end up with lots of differerent brands and models. You may want to check the max voltage on the controllers and strings you're considering. A string of 3 190w panels on a cold morning (use record low temp for your location) may overvoltage some 40a controllers, for example.

    I don't know if 1.26 is fully charged for your bank or not. If you don't have a history of SG readings, you might want to run an equalization cycle to establish a baseline number for your bank.
    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
  • wastwast Posts: 41Registered Users ✭✭
    Estragon said:
    In order to flip the bit for last fully charged, the monitor needs to see a voltage of 14.x for "Y" hours. I don't recall the exact numbers, but basically either the numbers aren't being hit (see previous post for possible causes), or there's a problem with the meter.

    You can have multiple different charge controllers on a single bank, but it can get complicated to manage if you end up with lots of differerent brands and models. You may want to check the max voltage on the controllers and strings you're considering. A string of 3 190w panels on a cold morning (use record low temp for your location) may overvoltage some 40a controllers, for example.

    I don't know if 1.26 is fully charged for your bank or not. If you don't have a history of SG readings, you might want to run an equalization cycle to establish a baseline number for your bank.

    like I stated I am in the learning process.. the meter was added when I visited camp for an hour or so.. only had installed for a short time so maybe need to leave it connected for awhile.. the 2 mppt charge controllers are both 40 amp of the same brand and model.. reason for my using the two is that I thought that one would not be able to handle all 5 panels and also did not want to mix and match ( 190s and 130s) when I get in again I will check the SG.. when checking SG should everything be turned off? also can solar equalize or do u need to use generator and charger... I have a 55 amp iota charger but am not sure if it can handle equalization...
  • mcgivormcgivor Posts: 2,226Solar Expert ✭✭✭✭✭
    Equalization is a higher voltage controlled overcharge with low current, so using solar is preferable, with a generator it would be wasting fuel.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • boBboB Posts: 952Solar Expert ✭✭✭✭
    Sounds like you have a MidNite Solar BRAT (controller) and the MNBCM (meter)....    The way that the BCM monitor works is that is looks at the time the battery voltage spends above a certain value...  If that voltage has been over that value for at least 2 hours, then the MNBCM assumes that the controller with the solar has given the battery a good absorb charge and then it can start another 1 and 2 week cycle.

    So, the DIP switches and battery type selections can be adjusted so that the charge voltage from the BRAT overlaps the minimum battery voltage type adjustment on the MNBCM so they jive.

    As was mentioned, temperature compensation can make a difference too because then the BRAT will raise or lower its absorb voltage adjustment a little bit.  Higher the battery temperature, the lower the voltage the BRAT will charge the battery.

    Hopefully you have enough sun and panels that the battery voltage can get up high enough for that all to happen.

    boB

  • westbranchwestbranch Posts: 5,090Solar Expert ✭✭✭✭
    edited May 20 #11
    WAST:  as you have mentioned earlier 'electricity' is not your strong suit.  So I have to ask, did you do an initial start-up charge regime, also called a 'commissioning charge'  which is a full (normal) charge to a Specific Gravity (manufacture specified) followed by a EQ for X hrs.??
    I suspect not and now would be a good time to go through the entire procedure and bring all cells up to the same SG, hopefully what the maker wants....

    ps boB is one of the principals of MidNite Solar... :) Information right from the top...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    I check SG just after absorb (soon after transition to float). The last bit of absorb can make the batteries spit a bit, so I wait until that's done to read. Absorb mixes the acid up some, so the SG read should be pretty representative of the electrolyte overall. Reading after a long period of float can be misleading because the acid tends to stratify, especially with L16s.

    It doesn't matter if everything is turned off when reading SG. Done right, SG is a pretty straightforward check on battery state of charge. Unlike voltage, which can be influenced as a SOC measure by loads or charging sources, SG is a real measure of a physical property of the electrolyte. An ideal EQ charging regime will have all individual cells near the same (+/- 0.01 pt) SG, and not rising after ~ 1/2hr at EQ voltage. I normally record all cells at the start of an EQ, and just measure the weakest couple of cells during the EQ, and stop the EQ when they stop rising.

    Definitely do EQ with solar. Get through bulk with generator if need be, then absorb/float with solar and check SG. EQ takes very little current, which even late afternoon sun can often handle.

    boB has likely forgotten way more than I'll ever know about Brats or battery status monitors.
    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
  • boBboB Posts: 952Solar Expert ✭✭✭✭
    Estragon said:

    boB has likely forgotten way more than I'll ever know about Brats or battery status monitors.
    Right.  And before I forget too much, I figure that if I drop little snippets of my brain around the internet, maybe I can eventually find and use them again later.

    boB
  • PhotowhitPhotowhit Posts: 4,709Solar Expert ✭✭✭✭
    To give you an idea about the balance of your system, go back and reread BB's statement. 

    I have only a slightly larger battery bank than you do and have a 4000+ watt array...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • wastwast Posts: 41Registered Users ✭✭
    WAST:  as you have mentioned earlier 'electricity' is not your strong suit.  So I have to ask, did you do an initial start-up charge regime, also called a 'commissioning charge'  which is a full (normal) charge to a Specific Gravity (manufacture specified) followed by a EQ for X hrs.??
    I suspect not and now would be a good time to go through the entire procedure and bring all cells up to the same SG, hopefully what the maker wants....

    ps boB is one of the principals of MidNite Solar... :) Information right from the top...

    Photowhit said:
    To give you an idea about the balance of your system, go back and reread BB's statement. 

    I have only a slightly larger battery bank than you do and have a 4000+ watt array...

    Thks guys.. WB when I purchased batteries directly from Rolls Surrette factory was told "fully charged and ready to go"  so to answer your question no did not go through charge regime.. Photowhit looks like you are off the grid for home.. this is a remote cottage... recently purchased kilometer to try and get a handle on exactly what I am using... mostly lights and tv and am planning on adding refrigerator (10 cu ft danby).. also when I leave camp I most always shut inverter off.. forgot to mention I also have 4  170 ah dekka unigy batteries that I have not in use but I do charge(generator) every so often.. going to add a couple more 550s to the system and go 24 volt as estragon suggested... was going to add a new inverter so will look for a 24 volt inverter.. wish I had come here when I started. will be looking to add more panels as I go.. Panels in this neck of the woods are costly so will be adding on gradually...The rolls surrette factory is in next province to us and every now and again they have what they call blems for half the cost.. factory cosmetic defects.. which is better for your panels parallel or series? so confusing for and old brain.. watts and amps thrown in with all the other stuff that is up there could be quite the jumble LOL
  • BB.BB. Posts: 27,933Super Moderators, Administrators admin
    Actually, figuring out series/parallel panel connections for solar charge controllers is not obvious or trivial. It is fairly complex.

    Need to know:
    • battery bank AH and voltage
    • exactly what brand and model of charge controller
    • what brand and model of solar panels (there are Vmp-std panels that are ~18, 30, 36, and >36 volt panels
    • what is the number of panels you want to install
    • where you will be installing them (minimum/maximum temperature for location--In cold weather, panel Vmp goes up and in hot weather, panel Vmp falls).
    PWM charge controllers, for a 24 volt battery bank, need a Vmp-array in the range of ~35 to 40 volts.

    MPPT charge controllers need Vmp-array with a minimum of ~40 volts and typically around 60 volts works well. Higher end MPPT controllers can use upwards of Vmp-array~100 VDC maximum for cold weather (freezing mountain locations--where Vmp-cold does not exceed ~140-150 VDC). There are MPPT charge controllers that have Vmp-array nominal of ~400 VDC or so (not cheap controllers).

    It is so complex, that many of the US companies have a website where you can input your array and temperature information, and they will tell you the acceptable configurations for your specific application.

    It is not too hard to do all of this when we follow the steps above based on your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    I have a remote (water or ice access only) cabin in NW Ontario. A bit colder in winter, warmer in summer, and likely less snow, but otherwise similar situation. With the AC fridge on, we use ~3kwh/day. Using tools, pumping water to a gravity storage tank etc after batteries are charged can run it up to maybe twice that.

    My main bank is about the same watt-hours of storage as yours ([email protected] ~= [email protected]). At 48v, I need 4x less charge controller capacity, can run higher voltage pv strings a bit more efficiently, can support larger inverter loads, uses smaller DC wiring to get the same voltage drop, and the bank is a single series string. If you're upgrading for higher voltage anyway, it might be worth thinking about 48v if you think your loads may grow over time (they tend to).

    The system is designed so we can run (frugally) on battery for two cloudy days, the generator charges on day 3 if still no sun. Most of the year this works out well, but from Oct to Feb the sun is too low, weak, and short. For us, it's a reasonable trade-off between cost of solar vs noise and PITA hauling fuel etc for the generators.

    For battery banks, it's best to avoid parallel connections. Each added parallel connection increases the odds of unbalanced loads. For pv, it's more situation dependent. Higher voltage series strings are good when there are long distances between pv and battery bank because they allow the use of smaller wire for an acceptable voltage drop. The downside is charge controllers need to be more expensive mppt type, and if any part of the string gets shade, the output of the whole string drops a lot.

    For the fridge, you may want to check the energy rating. An inefficient 10 cu.ft. model might use as much power as a more efficient model twice the size.
    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
  • westbranchwestbranch Posts: 5,090Solar Expert ✭✭✭✭
    Here in off grid  mid BC we have a GE 18CFt top freezer running full time from March to Nov when we have good sun a little fewer days if the sun does not show.  No Gen needed in summer unless w have visitors from the city... my sig line shows my set up, 12 x 140W in 48V configuration into a ageing 900Ah AGM battery. when we are here we can 'use ' ~ 2.5 - 3kWH of oir panels production, when we are away the system pulls in 1.5  to 1.9 kWH... the 1.9 is the days usually right after we leave, and then it settles in @ ~ 1.5 till we return.
    So be sure to check out the good all Sears like stores and see what  an off-the-store-loor  has to offer,  we just looked at the EPA estimated usage and there are a lot of units less than 1 kWH a day...
    hope this helps...
    btw I believe that most of the regulars here might be labeled old  farts or similar term... I am 69 so don't give up on the  numbers yet
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    Also worth noting WRT pricing of panels is shipping can be a big part of the price. Larger panels are really costly to ship in small quantities and can be pretty spendy buying onesy - twosey. Smaller 12v panels are cheaper to ship, but tend to be a high cost per watt to purchase.

    If you're likely to end up with an array in the 4-5kw range anyway, it would likely make sense to get a pallet quantity, which tends gets you a bit better pricing on the panels, and more importantly makes shipping cost per panel more reasonable. I got a pallet of panels and other gear from our hosts delivered to a parcel service in a US border town, then picked it up and cleared customs myself, which saved a lot vs buying locally at the time (~4 yrs ago).
    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
  • wastwast Posts: 41Registered Users ✭✭
    BB. said:
    Actually, figuring out series/parallel panel connections for solar charge controllers is not obvious or trivial. It is fairly complex.

    Need to know:
    • battery bank AH and voltage
    • exactly what brand and model of charge controller
    • what brand and model of solar panels (there are Vmp-std panels that are ~18, 30, 36, and >36 volt panels
    • what is the number of panels you want to install
    • where you will be installing them (minimum/maximum temperature for location--In cold weather, panel Vmp goes up and in hot weather, panel Vmp falls).
    PWM charge controllers, for a 24 volt battery bank, need a Vmp-array in the range of ~35 to 40 volts.

    MPPT charge controllers need Vmp-array with a minimum of ~40 volts and typically around 60 volts works well. Higher end MPPT controllers can use upwards of Vmp-array~100 VDC maximum for cold weather (freezing mountain locations--where Vmp-cold does not exceed ~140-150 VDC). There are MPPT charge controllers that have Vmp-array nominal of ~400 VDC or so (not cheap controllers).

    It is so complex, that many of the US companies have a website where you can input your array and temperature information, and they will tell you the acceptable configurations for your specific application.

    It is not too hard to do all of this when we follow the steps above based on your needs.

    -Bill
    I have 3 banks 12 volt rolls surrette 550S ( 1284 ah)  
    4 dekka unigy 12 volt 170 ah
    charge controller is epever 40 amp mppt tracer series  (max 100 v) (have 2 of those)
    solar panels are 190 x2 Canadian solar 36 v.. 
    temperature is not really cold with a few days a winter below -20c and about the same above 30c

    other panels are 130 watt x 3  (not sure what brand) as they are at camp installed

    I am shooting for 2 systems one with the rolls batteries for daytime and dekka unigy for night time. 

    I am hoping to have 24 volt system before long (as soon as I get another 2 of those 550s 

    Hope I am not being too much of a pest with the questions

    trying to gather as much info as possible

    wayne
  • wastwast Posts: 41Registered Users ✭✭
    Here in off grid  mid BC we have a GE 18CFt top freezer running full time from March to Nov when we have good sun a little fewer days if the sun does not show.  No Gen needed in summer unless w have visitors from the city... my sig line shows my set up, 12 x 140W in 48V configuration into a ageing 900Ah AGM battery. when we are here we can 'use ' ~ 2.5 - 3kWH of oir panels production, when we are away the system pulls in 1.5  to 1.9 kWH... the 1.9 is the days usually right after we leave, and then it settles in @ ~ 1.5 till we return.
    So be sure to check out the good all Sears like stores and see what  an off-the-store-loor  has to offer,  we just looked at the EPA estimated usage and there are a lot of units less than 1 kWH a day...
    hope this helps...
    btw I believe that most of the regulars here might be labeled old  farts or similar term... I am 69 so don't give up on the  numbers yet


    danby 10 cu refrigerator has a rating of 280 kwh per year and is energy star.. by my calculations this should be approx. .75 kwh a day, which would seem to be very good for what I need.. (if my calculations are correct)
  • BB.BB. Posts: 27,933Super Moderators, Administrators admin
    No problem Wayne. We all started in the same place, and others helped us too.

    You have to double check the voltages... The panels are generally marked with Voc (voltage open circuit) and Vmp (voltage maximum power). Something like this (Canadian Solar 190 Watt panels):

    https://www.ecodirect.com/Canadian-Solar-CS5A-190M-190W-36V-Solar-Panel-p/canadian-solar-cs5a-190m.htm

    Watts (STC)     190 W
    Watts (PTC)     137 W
    Max Power Voltage (VMPP)     37.0 V
    Max Power Current (IMPP)     5.27 A
    Open Circuit Voltage (VOC)     45.0 V
    Short Circuit Current (ISC)     5.62 A
    Max System Voltage     DC 600 V

    Notice that solar panel models come and go... 190 Watt panels are becoming scarce (as an example).

    Your controller is something like this (I did not find a manual):

    https://www.amazon.com/EPEVER-Controller-Display-Battery-Charging/dp/B01GMUPGZA
    Rated charge current: 40A
    Max.PV input power: 12V/520W,24V/1024W
    Battery voltage range: 9V~32V
    Max.PV open circuit voltage: 100VDC

    Some quick generic notes first. Always connect the battery bank to the charge controller first, then connect the solar panels. And always disconnect the solar panels first, then the charge controller from the battery bank. Most charge controllers get their power from the battery connection (to run their internal electronics). If you connect PV Panels first, it can confuse the charge controller (and possibly even damage it).

    Next, if you have a remote battery temperature sensor, use it. With your wide temperature swings, the charge controller needs to know the battery temperature for proper charging (and charging voltages). If you don't have a remote temperature sensor, put the charge controller in the same room/same temperature as the batter bank (not too close or in the battery box--electrolyte mist from charging will ruin the electronics).

    As a guess, Vmp-array should be a maximum of ~2/3rds (~66.7%) of the Vmax input to the controller (to allow for cold temperatures causing high solar panel voltage) or ~66.7 volts Vmp-std. And with the 12 volt bank, the Vmp-array minimum should be about (1.3x15.0 volts) = 19.5 volts Vmp minimum (Vmp~18 volts would work, but would be much better if >=24 volts Vmp-std for MPPT controller).

    So, Vmp-array should be in the range of ~24 volts to ~66.7 volts.

    For your Canadian 190 Panels (if I got the right ones), they will be a good fit if you put them all in parallel (Vmp-array~36 volts).

    However, if you ever go to 24 volt battery bus--The EPEVER is not a great fit... Two panels in series gives you Vmp-array~72 volts--Getting on the high side of Voc (voltage open circuit)

    As an example, here is Midnite Solar's solar array calculator for their products. Also handy for doing the math for other setups:

    http://www.midnitesolar.com/sizingTool/index.php

    I put in the basics (2 series x 2 parallel) and the Voc/Vmp/Ioc/Imp/Pmax with -20C to +30C:


    PV Array
    Rated PV Array Power: 760 Watts
    Anticipated Array Power @ 30C: 743 Watts
    Rated PV Array Current: 10.6 Amps
    Battery Charging Current @ 28.8 V: 26.4 Amps
    VMP (Maximum Power Point Voltage) : 74 Volts
    VOC (Open Circuit Voltage): 90 Volts
    VMP @ -20 C°: 89 Volts
    VOC @ -20 C°: 103.4 Volts

    And you can see that Voc at -20C is just over the 100 VDC Vmax for the EPEVER controller. And using ~82% for hot panel derating would give (0.82 * 37 volts Vmp=) 30 volts Vmp-hot... that is really close to the ~29-32 volts you need to charge Lead Acid 24 volt battery bank.

    Is this helping?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wastwast Posts: 41Registered Users ✭✭
    edited May 20 #23
    BB. said:
    No problem Wayne. We all started in the same place, and others helped us too.

    You have to double check the voltages... The panels are generally marked with Voc (voltage open circuit) and Vmp (voltage maximum power). Something like this (Canadian Solar 190 Watt panels):

    https://www.ecodirect.com/Canadian-Solar-CS5A-190M-190W-36V-Solar-Panel-p/canadian-solar-cs5a-190m.htm

    Watts (STC)     190 W
    Watts (PTC)     137 W
    Max Power Voltage (VMPP)     37.0 V
    Max Power Current (IMPP)     5.27 A
    Open Circuit Voltage (VOC)     45.0 V
    Short Circuit Current (ISC)     5.62 A
    Max System Voltage     DC 600 V

    Notice that solar panel models come and go... 190 Watt panels are becoming scarce (as an example).

    Your controller is something like this (I did not find a manual):

    https://www.amazon.com/EPEVER-Controller-Display-Battery-Charging/dp/B01GMUPGZA
    Rated charge current: 40A
    Max.PV input power: 12V/520W,24V/1024W
    Battery voltage range: 9V~32V
    Max.PV open circuit voltage: 100VDC

    Some quick generic notes first. Always connect the battery bank to the charge controller first, then connect the solar panels. And always disconnect the solar panels first, then the charge controller from the battery bank. Most charge controllers get their power from the battery connection (to run their internal electronics). If you connect PV Panels first, it can confuse the charge controller (and possibly even damage it).

    Next, if you have a remote battery temperature sensor, use it. With your wide temperature swings, the charge controller needs to know the battery temperature for proper charging (and charging voltages). If you don't have a remote temperature sensor, put the charge controller in the same room/same temperature as the batter bank (not too close or in the battery box--electrolyte mist from charging will ruin the electronics).

    As a guess, Vmp-array should be a maximum of ~2/3rds (~66.7%) of the Vmax input to the controller (to allow for cold temperatures causing high solar panel voltage) or ~66.7 volts Vmp-std. And with the 12 volt bank, the Vmp-array minimum should be about (1.3x15.0 volts) = 19.5 volts Vmp minimum (Vmp~18 volts would work, but would be much better if >=24 volts Vmp-std for MPPT controller).

    So, Vmp-array should be in the range of ~24 volts to ~66.7 volts.

    For your Canadian 190 Panels (if I got the right ones), they will be a good fit if you put them all in parallel (Vmp-array~36 volts).

    However, if you ever go to 24 volt battery bus--The EPEVER is not a great fit... Two panels in series gives you Vmp-array~72 volts--Getting on the high side of Voc (voltage open circuit)

    As an example, here is Midnite Solar's solar array calculator for their products. Also handy for doing the math for other setups:

    http://www.midnitesolar.com/sizingTool/index.php

    I put in the basics (2 series x 2 parallel) and the Voc/Vmp/Ioc/Imp/Pmax with -20C to +30C:


    PV Array
    Rated PV Array Power: 760 Watts
    Anticipated Array Power @ 30C: 743 Watts
    Rated PV Array Current: 10.6 Amps
    Battery Charging Current @ 28.8 V: 26.4 Amps
    VMP (Maximum Power Point Voltage) : 74 Volts
    VOC (Open Circuit Voltage): 90 Volts
    VMP @ -20 C°: 89 Volts
    VOC @ -20 C°: 103.4 Volts

    And you can see that Voc at -20C is just over the 100 VDC Vmax for the EPEVER controller. And using ~82% for hot panel derating would give (0.82 * 37 volts Vmp=) 30 volts Vmp-hot... that is really close to the ~29-32 volts you need to charge Lead Acid 24 volt battery bank.

    Is this helping?

    -Bill
    helping for sure.. that is the exact same panels (190s) rated pv array of 760 would be with both panel arrays correct??

    My plan is to use a separate charge controller on each array...having  the 2 190s in series would that be okay and the 3 130s in series also each with their own charge controller..

    if I can access the other 2 550s I will change system to 24 volt... but will keep the 2 charge controllers and add enough panels on each controller so as not to max it out..

    how important is it not to mix and match panels?? from what I have learned u should not do it with batteries but am not sure with the panels.. I have a meter that came with controller that is supposed to help with assessing batteries.
  • BB.BB. Posts: 27,933Super Moderators, Administrators admin
    edited May 21 #24
    Yes... Assuming the same EPEVER solar charge controllers for each array and a 12 volt battery bank.

    Don't jump to 12 volts without thinking of the issues... The EPEVER controller plus the Canadian 190 Watt panels... You would (ideally) put them in 3x series string for a 24 volt battery bank. A bit too high of voltage for the EPEVER (right on the edge in cold weather). And you would now have 3x panel array and 1 panel left over (need to get 2x more panels in make a second 3x series string).

    Also--You need to get a 24 VDC input AC inverter, 24 VDC battery charger(s) for the battery bank, and such.

    And why do you have/need two separate solar power systems? Generally, it is better to have one combined battery bank with one solar array (or several solar arrays+charge controllers is OK too). That way you harvest the maximum amount of energy (i.e., the first bank was full and the second bank needed more charging current to get full too).

    Ideally, you don't want to mix old/new batteries or different brands/models of batteries. There are a lot of variations in construction, additives to the plates, etc. And it is possible that you will get less than ideal life (i.e., one string is over charged and the other string is under charged).

    Lastly, you can mix solar panels into one array... You want to match Vmp rated voltage for adding in parallel and Imp current for series strings--Within 10%. (i.e., a 35 volt string + a 36 volt Vmp set of strings in parallel is fine. And a Imp~5 volt panel and a Imp~5.3 volt panel in series is fine).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wastwast Posts: 41Registered Users ✭✭
    BB. said:
    Yes... Assuming the same EPEVER solar charge controllers for each array and a 12 volt battery bank.

    Don't jump to 12 volts without thinking of the issues... The EPEVER controller plus the Canadian 190 Watt panels... You would (ideally) put them in 3x series string for a 24 volt battery bank. A bit too high of voltage for teh EPEVER (right on the edge in cold weather). And you would now have 3x panel array and 1 panel left over (need to get 2x more panels in make a second 3x series string).

    Also--You need to get a 24 VDC input AC inverter, 24 VDC battery charger(s) for the battery bank, and such.

    And why do you have/need two separate solar power systems? Generally, it is better to have one combined battery bank with one solar array (or several solar arrays+charge controllers is OK too). That way you harvest the maximum amount of energy (i.e., the first bank was full and the second bank needed more charging current to get full too).

    Ideally, you don't want to mix old/new batteries or different brands/models of batteries. There are a lot of variations in construction, additives to the plates, etc. And it is possible that you will get less than ideal life (i.e., one string is over charged and the other string is under charged).

    Lastly, you can mix solar panels into one array... You want to match Vmp rated voltage for adding in parallel and Imp current for series strings--Within 10%. (i.e., a 35 volt string + a 36 volt Vmp set of strings in parallel is fine. And a Imp~5 volt panel and a Imp~5.3 volt panel in series is fine).

    -Bill


    forgive me but am a little confused.. did u mean don't jump to 24 volts without thinking of issues as I am already at 12 volt... I already have 5 panels so if I put 3 x series string I would have 2 panels left over or am I missing something?? before I get to carried away here was my original thought .. I was going to use the 4 170 ah batteries to run nothing only the refrigerator as I have a separate cable run to cabin for refrigerator plug in.. my main system would be the surrettes which is hooked into my main ac panel by way of a 1500 watt inverter... the only thing that I need to power up is the tv which doesn't get much use especially during summer season... light bulbs which are all led.. for charging I was going to use the new 190s hooked in series for the 170 ah batteries and the mttp controller . for my surrettes I have the 3 130s and supplemented with the gen set and charger as needed.. I was going to purchase another inverter for the refrigerator set up... It seem like a waste to have the 4 170s just setting there being charged occasionally when I could put them to use.. I was thinking a 1000 watt inverter would run the refrigerator with nothing else added....my electrical needs are small as my water is gravity fed and to heat the water I plan on using propane hot water on demand... From what I am reading here lots of charging seems to be more important then a whole lot of storage without the ability to keep system charged 
  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    Yes, too much storage without the ability to charge properly = likely early demise for batteries.

    Just to throw it out there, another option for the 550s would be to rewire 4 of them in series for 24v and keep the 2 remaining as spares (top-up charged every month or two). From your description of loads, 2 strings is more than you need, and it's not really unusual for a first go around with solar to be hard on a first bank. Having spares to put into service if/when needed may be better than adding even more capacity.
    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
  • wastwast Posts: 41Registered Users ✭✭
    Estragon said:
    Yes, too much storage without the ability to charge properly = likely early demise for batteries.

    Just to throw it out there, another option for the 550s would be to rewire 4 of them in series for 24v and keep the 2 remaining as spares (top-up charged every month or two). From your description of loads, 2 strings is more than you need, and it's not really unusual for a first go around with solar to be hard on a first bank. Having spares to put into service if/when needed may be better than adding even more capacity.
    so would the 4 170 12 volt gel with the 2 190 panels in series be able to run a refrigerator which will use less the 1 kwh per day keeping in mind that this is not a permanent residence and is only used for 2 or 3 months a year with the rest of the time batteries will just be in charge mode with panels... also have gen set and charger .. when I go to cabin first I will start gen set to let refrigerator cool down so then all it has to do is normal cool down cycles.. 

  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    All IMHO...

    2 x 190w panels x .75 likely output with well aimed but sun warmed panels x 4 hours full sun equivalent = ~1.1kw/day. Assuming summer only use might increase full sun equivalent hours to 5 or so, say 1.3kw. You can check for something close to your location at pvwatts.nrel.gov

    That about covers one day of power, but if you have a couple of cloudy days, there are also battery charging losses and "catch-up" to consider. 4 x [email protected] batteries = ~8000watt-hours. Say the 2 cloudy days draw the bank down by 2000 watt-hours (2kwh). That's not bad, they're still at ~75% full (going under 50% is a bad idea with a lead acid battery). The issue is when you get a sunny day 3, the 1.3kw produced has to cover the 1ish kwh load for the fridge, plus the 2kwh deficit (plus charging losses) in the bank. After many sunny days, it might catch up, or not.

    With inverter and charging losses, it looks pretty marginal to me to depend on solar. If you're okay with charging the bank with a generator after cloudy days, it could work.
    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
  • wastwast Posts: 41Registered Users ✭✭
    Estragon said:
    All IMHO...

    2 x 190w panels x .75 likely output with well aimed but sun warmed panels x 4 hours full sun equivalent = ~1.1kw/day. Assuming summer only use might increase full sun equivalent hours to 5 or so, say 1.3kw. You can check for something close to your location at pvwatts.nrel.gov

    That about covers one day of power, but if you have a couple of cloudy days, there are also battery charging losses and "catch-up" to consider. 4 x [email protected] batteries = ~8000watt-hours. Say the 2 cloudy days draw the bank down by 2000 watt-hours (2kwh). That's not bad, they're still at ~75% full (going under 50% is a bad idea with a lead acid battery). The issue is when you get a sunny day 3, the 1.3kw produced has to cover the 1ish kwh load for the fridge, plus the 2kwh deficit (plus charging losses) in the bank. After many sunny days, it might catch up, or not.

    With inverter and charging losses, it looks pretty marginal to me to depend on solar. If you're okay with charging the bank with a generator after cloudy days, it could work.


    thk you .. I have no problem with charging with generator when needed...would 2x24 be a better idea instead of 4x12?? I realize  I would need 24 volt inverter and charger...

  • EstragonEstragon Posts: 2,856Registered Users ✭✭✭✭✭
    I assume you're talking about batteries to run the fridge (2x24 vs 4x12)? If so, yes, for a couple of reasons. Four batteries in parallel could charge/discharge differently, leading to unequal states of charge. Second, at 24v the DC currents are 1/2 those at 12v. For example, say the fridge draws 600w to start. Ignoring inverter losses, that's 600/[email protected], vs 600/[email protected]

    If you already have a good (pure sine wave) 1000w 12v inverter, I'd use it. If you're planning on buying one, 24v may be a better choice. A cheap hardware store square wave inverter may cause heating of the fridge motor and potentially reduce lifespan or possibly not run at all.
    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. Posts: 27,933Super Moderators, Administrators admin
    Or are you talking about 2x series "24 volt panels" vs 4x series "12 volt panels"?

    In general, they are identical solutions. In practice there are usually tradeoffs--But it depends on your specific needs, hardware you have or can obtain, etc.

    Roughly, "12 volt" panels are about 140 watts maximum. They are smaller and easier to ship (and usually cheaper to ship). And easier for one person to move around and install on a roof. However, they are also more expensive ($$$/Watt). "12 volt panels" are generally Vmp~18 volts per panel and are a good match for PWM controllers (less expensive type of solar charge controller) and 12/24/48 volt battery banks (1, 2, or 4 panels in series). Smaller format panels, more panels to mount and wire for XXX Watt array.

    "24 volt panels" are in the range of 200-300 Watts (or larger). They are physically large and usually require "truck" or pallet based shipping. Shipping a single panel can cost as much as shipping a whole pallet of 10-20 panels. Panels over >~175 Watts typically need two people to safely handle and install. And the panels themselves are usually much less expensive ($$$/Watt). "24 volt panels" can be Vmp~30 volt, Vmp~36 Volt, or even higher. For PWM controllers Vmp~36 volt  panels are a good match for 24 or 48 volt battery banks (1 or 2 in series). Other panels with Vmp~30 volts, are not a good "native match" to 24 or 48 volt battery banks and an MPPT type solar charge controller is needed (more expensive charge controller, more options/sophisticated). Larger format panels, fewer panels to connect and wire for XXX Watt array.

    Regarding solar charge controllers... Generally, for smaller systems (400 Watt and under arrays), PWM controllers and "12 volt" panels end up being less expensive.

    For larger systems (>~800 Watts), MPPT controller systems with cheaper "24 volt" panels end up being cheaper and easier to wire (higher voltage solar array, smaller AWG cables from array to charge controller--much better for arrays that are a longer distance from "battery shed" to array... >~20 feet or so).

    I suggest that people "do the math" (size the battery bank to the loads, then size the array to charge the battery bank and the loads). Then do 2 or more paper solar designs and see what variation(s) best meet your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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