Rapid Voltage Drop Under Heavy Load... Normal?

TramblinTramblin Registered Users Posts: 5 ✭✭
First, I have to say that I wish I had found this forum sooner.  I recently purchased and installed a full off-grid kit from AIMS Power and wish I had asked a few questions of this forum first!

I have 16 200Ah 12v AGM AIMS Power batteries connected in a 48v bank of 4s4p.  These are connected to a 8,000 watt inverter operating at 50Hz and 230v.  We also have 18 AIMS panels at 265w each connected to a 100a SCC.  I set the system up and all seemed to be working.  At any time we are only ever using about 6% of the inverter (around 500 watts of power) so go through about 12kWh per day.  Every day I make sure the batteries get fully charged to 54.2v (shows as 100% on the SCC) and every morning our batteries run down to around 50v (shows 75%).

Just this past week we set up a pool with a 12amp pool pump.  The pump uses around 850 watts while running.  Every day I have waited for the batteries to show 100% charge (54.2v) before turning on the pool pump.  I then turn the pump off around 3pm so that it doesn't draw down the batteries.

Yesterday, I wanted to run the pump a little bit more around 3:30pm so turned the pump on.  The sun was still shining and the SCC showed 82v and 1500w coming in the from the panels.  I watched as the batteries dropped from 54.2v to 53v within 5 minutes.  I then turned the pump off and within 2 minutes the batteries showed 54.2v again.  I wondered if this was an error with my SCC so I connected a multimeter directly to the battery bank and observed the exact same voltage reading.

Is this normal behavior for AGM batteries under a heavy(ish) load?

I have noticed over the past 3 months of using the system that it seems to drop very quickly from 54.2v (100%) down to around 50v (75%) from 4pm - 9pm and then stops dropping.  When I check again in the morning it is never below 50v (75%).

Thanks in advance for any help!


Comments

  • mike95490mike95490 Solar Expert Posts: 9,187 ✭✭✭✭✭
    AGM batteries require a long, gentle Absorb cycle to charge the last 20% of capacity.  I would add 30 minutes to your absorb time and see if that helps. However, you may have been deficit charging for months and as resistant as AGM are to sulfation, that may have happened.  See if your AGM mfg has any recommended Equalize procedure.
    What is your current Absorb time now ?  2 hrs ?  3 hrs ?

    Finally, AGM batteries are tricky to use wired in parallel.  Their low internal resistance leads to one bank hogging the load till it's damaged and then the other bank takes over till it's damaged too, then it ping pongs till final death.
    Look into 6V batteries of the Ah capacity needed, wired in series, no parallel.
    Powerfab top of pole PV mount | 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 ,

  • VicVic Solar Expert Posts: 3,064 ✭✭✭✭
    And,  in addition to Mike's comments,   seems to me,   that 54.2 V is not high enough to fully charge an AGM,  that is in cyclic use  --  recharged from Solar each day (usually an off-grid system).

    For a system that is constantly Floated from grid power,  and is a back up system,   54.2 V might be OK.

    Would expect that you would want an Absorb voltage of 58 V,  +/--  a bit,  as needed.

    FWIW,   Good luck,   Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 31,326 admin
    I agree with Vic--Typical AGM charging voltage for ~75F, is (14.4 volts * 2 batteries = ) 57.6 volts.

    When the battery charging current falls (below ~1% to 0.1% rate of charge -- i.e., 800 AH battery bank * 0.01 = 8 amps) or lower--Then they are usually fully charged.

    54.2 volts / 4 = 13.55 volts--That is a typical range for float charging (after bulk/absorb charging has been completed).

    Question about your pool pump... Uses 12 amps at What Voltage (230 VAC, or ~54 VDC)? 

    We can double check a bit of math... Typically, 5% to 13% rate of charge from solar panels recommended. 10% or more for "full time off grid" system usage (5% can work for emergency backup/summer/sunny weather usage).
    • 800 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 6,025 Watt nominal array suggested
    • 18 panels * 265 Watts = 4,770 Watt rated array
    • 4,770 Watt array * 0.77 panel+controller deratings * 1/58 volts charging = 63 Amps typical "best harvest" from array into battery bank
    Guess that you are around Praia, Cape Verde:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Praia
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 75° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    6.33
     
    6.58
     
    6.88
     
    6.43
     
    6.77
     
    6.54
     
    JulAugSepOctNovDec
    6.20
     
    5.57
     
    5.86
     
    6.24
     
    6.18
     
    6.04
     
    For your system, the typical (long term average) harvest for July would be:
    • 4,770 Watt array * 0.61 end to end off grid system eff (AGM battery based) * 6.2 hours of sun per day = 18,040 Watt*hours per day (July, average)
    If you are using ~12,000 WH per day--That is using just a little less than your system can produce in July (long term average)... Some days will be better harvest, some days will be less.

    Normally, would suggest your "base loads" (loads that you need to run every day, vs those loads that can be put off until sunny weather) would be somewhere about 55% to 65% of predicted output:
    • 18,040 WH per day (July) * 0.65 "derating" for base loads = 11,004 WH per day for "base loads" in July max suggested
    Anyway--lots of guesses... Your thoughts and corrections to my estimates?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    I will guess you are new to living on a solar electric system?

    I'd like to help you understand somethings, some of which you likely are figuring out reading some of the other replies.
    Tramblin said:
    First, I have to say that I wish I had found this forum sooner.  I recently purchased and installed a full off-grid kit from AIMS Power and wish I had asked a few questions of this forum first! (I agree, though Aims has cleaned up their act, in recent years, they tend to have lower end equipment. There have been considerable improvements in recent years!)

    I have 16 200Ah 12v AGM AIMS Power batteries connected in a 48v bank of 4s4p.  
    This is normally a bad idea, typically you would want a single string or at most 2 strings, this has to do with uneven power distribution. I certainly understand being in a remote location, this might have been your only option for the size battery bank you need. It is a shame Aims sells a 4 string package! but perhaps it's just for shipping to remote areas.

    I do not know what you have been given in your package deal to wire these up, but I recommend going here, and being sure your battery bank is setup for as even a resistance across each string as possible.

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

    Tramblin said:
    I have 16 200Ah 12v AGM AIMS Power batteries connected in a 48v bank of 4s4p.  These are connected to a 8,000 watt inverter operating at 50Hz and 230v.  We also have 18 AIMS panels at 265w each connected to a 100a SCC.  I set the system up and all seemed to be working.  
    Note that the inverter is rated in watts, watts is a unit of power. 
    You have provided all the information we need to calculate the power available in your battery bank and array, which is great! I wish more people would do that. You can also say you have a 800Ah 48 volt battery bank, or a (8000 x 48=) 38,400 watt hours of storage (or 38.4 kWhs)  and a (18x265=) 4770 watt array. Also of interest would be the type of Charge Controller (Which I guess is the SCC?)

    Likely you will also want to know the characteristics of your battery bank and how comfortable you are in drawing down the battery bank to a low State of Charge (SOC) Some AGM's are pretty good and others not so good at deep cycling. These characteristics will help you determine if you want to start the generator at 50% SOC or 30% SOC.

    Tramblin said:
    I set the system up and all seemed to be working.  At any time we are only ever using about 6% of the inverter (around 500 watts of power) so go through about 12kWh per day.  Every day I make sure the batteries get fully charged to 54.2v (shows as 100% on the SCC) and every morning our batteries run down to around 50v (shows 75%).
    Voltage is a very poor way to determine the battery bank's SOC.

    Here is how 3 stage charging works;

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    BULK;
    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    ABSORB;
    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    FLOAT;
    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage.

    For flooded lead acid, The transfer of current is pretty much 1:1, but  there must be a higher voltage, usually 10-15% to get current to flow to the battery bank. So if your battery is at rest at 50% SOC around 48 volts,  you  charge controller would limit voltage to around 48+4.8(10%) for a voltage of around 52.8 volts or even higher! 

    For more efficient AGM the voltage difference will be slightly lower, but set absorb point should likely be around 57.6-58 volts as others have mentioned.

    So reaching 54.2 volts doesn't indicate fully charged, at least the first time through. Likely the voltage will continue to rise to 57.6-58 volts and at that point the charge controller will not allow the voltage to rise any further, and batteries will accept a bit less current over time, as they slowly become fully charged. Once fully charged the charge controller (SCC?) will reduce the voltage to Float, which is likely the 54.2 volts. 

    So when you say this, does the voltage ever run above 54.2?
    Tramblin said:
    Every day I make sure the batteries get fully charged to 54.2v (shows as 100% on the SCC) and every morning our batteries run down to around 50v (shows 75%).
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    Tramblin said:
    Just this past week we set up a pool with a 12amp pool pump.  The pump uses around 850 watts while running.  Every day I have waited for the batteries to show 100% charge (54.2v) before turning on the pool pump.  I then turn the pump off around 3pm so that it doesn't draw down the batteries.
    We usually ask people to 'get a handle on their loads', So a 12 amp pool pump is likely at 230 volts or a possible load of  (12x230=) 2760 watts. Perhaps it only needs 850 when you turn it on, because you have cleaned the skimmers and the pump so this is the minimum load. Even then it seems low to me. Even a 850 watt load is considerable. Wonder how you are measuring this?

    I do run a lot of 'opportunity loads' once my charge controllers reach absorb voltage set point, I know the battery bank is taking in less current as it tops off the batteries, I tend to want to keep this load at about 50% of the available power from the array. If indeed the pump is drawing 850 watts, you should be good. I'll often wait until it's at the float level of charging to run higher wattage loads. Most of this is just be feel. I rarely look at the system readouts.

    Tramblin said:
    Yesterday, I wanted to run the pump a little bit more around 3:30pm so turned the pump on.  The sun was still shining and the SCC showed 82v and 1500w coming in the from the panels.  I watched as the batteries dropped from 54.2v to 53v within 5 minutes.  I then turned the pump off and within 2 minutes the batteries showed 54.2v again.  I wondered if this was an error with my SCC so I connected a multimeter directly to the battery bank and observed the exact same voltage reading.

    Is this normal behavior for AGM batteries under a heavy(ish) load?

    I have noticed over the past 3 months of using the system that it seems to drop very quickly from 54.2v (100%) down to around 50v (75%) from 4pm - 9pm and then stops dropping.  When I check again in the morning it is never below 50v (75%).
    Any time the battery bank is connected to the system, consider it 'system voltage'. The actual battery voltage would be some thing less while charging and something more while discharging.

    People who are new to solar electric systems often benefit from a 'SHUNT BASED' batter monitoring system. These are connected between the battery bank and the main breaker, so that all the current passes through them. In this manner they can give you a good estimate of the true State Of Charge of the battery bank.

    The 2 main ones available are the Trimetric (and Pentametric?) by Bogart Engineering;
    https://www.solar-electric.com/bogart-engineering-tm-2030-rv-battery-monitor.html

    And the Victron Energy BMV-712

    https://www.solar-electric.com/victron-energy-bmv-712-smart-battery-monitor.html
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • TramblinTramblin Registered Users Posts: 5 ✭✭
    Wow!  I want to start off by saying thank you for the amazing responses!  It is now quite clear to me that my first mistake was trusting the vendor.  You are all correct that this was our first off-grid system.  We sent pages and pages of questions to multiple vendors, but in the end trusted their advice.  I will attempt to answer questions and respond as best I can.  I also have a bunch of further questions.  

    mike95490 said:
    AGM batteries require a long, gentle Absorb cycle to charge the last 20% of capacity.  I would add 30 minutes to your absorb time and see if that helps. However, you may have been deficit charging for months and as resistant as AGM are to sulfation, that may have happened.  See if your AGM mfg has any recommended Equalize procedure.
    What is your current Absorb time now ?  2 hrs ?  3 hrs ?

    Vic
     said:
    And,  in addition to Mike's comments,   seems to me,   that 54.2 V is not high enough to fully charge an AGM,  that is in cyclic use  --  recharged from Solar each day (usually an off-grid system).

    For a system that is constantly Floated from grid power,  and is a back up system,   54.2 V might be OK.

    Would expect that you would want an Absorb voltage of 58 V,  +/--  a bit,  as needed.

    FWIW,   Good luck,   Vic

    Here are the settings from the Charge Controller (I thought it was abbreviated down to SCC for solar charge controller.  Is that not the case?)



    These seem to fit what everyone said they should be.  I have never noticed the voltage go above 54.8v.  That being said, does it make sense that it might hit 58v and then quickly drop down to 54.8v to stay in float?

    mike95490 said:
    Finally, AGM batteries are tricky to use wired in parallel.  Their low internal resistance leads to one bank hogging the load till it's damaged and then the other bank takes over till it's damaged too, then it ping pongs till final death.
    Look into 6V batteries of the Ah capacity needed, wired in series, no parallel.
    Photowhit said:
    Tramblin said:
    First, I have to say that I wish I had found this forum sooner.  I recently purchased and installed a full off-grid kit from AIMS Power and wish I had asked a few questions of this forum first! (I agree, though Aims has cleaned up their act, in recent years, they tend to have lower end equipment. There have been considerable improvements in recent years!)

    I have 16 200Ah 12v AGM AIMS Power batteries connected in a 48v bank of 4s4p.  
    This is normally a bad idea, typically you would want a single string or at most 2 strings, this has to do with uneven power distribution. I certainly understand being in a remote location, this might have been your only option for the size battery bank you need. It is a shame Aims sells a 4 string package! but perhaps it's just for shipping to remote areas.

    I do not know what you have been given in your package deal to wire these up, but I recommend going here, and being sure your battery bank is setup for as even a resistance across each string as possible.

    http://www.smartgauge.co.uk/batt_con.html
    My jaw dropped when I read these two comments.  We bought a kit from AIMS that included everything (cabling, panels, batteries, charge controller, and inverter).  We sent them our power needs and they put together the system and then sent the following diagram on how to connect the batteries.


    These are the cables that connect the batteries to each other and the batteries to the inverter.

    https://theinverterstore.com/product/battery-jumper-cable-10-awg-6%e2%80%b3-ul-listed/
    https://theinverterstore.com/product/inverter-cable-set-10-awg-lugged-ul-listed/

    I don't understand why AIMS would sell us a substandard battery setup.  After reading through the info on batteries it does appear that we have a slightly better than worse case setup for our batteries.  Is it worth us recabling our system?

    BB. said:

    Question about your pool pump... Uses 12 amps at What Voltage (230 VAC, or ~54 VDC)? 

    We can double check a bit of math... Typically, 5% to 13% rate of charge from solar panels recommended. 10% or more for "full time off grid" system usage (5% can work for emergency backup/summer/sunny weather usage).
    • 800 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 6,025 Watt nominal array suggested
    • 18 panels * 265 Watts = 4,770 Watt rated array
    • 4,770 Watt array * 0.77 panel+controller deratings * 1/58 volts charging = 63 Amps typical "best harvest" from array into battery bank


    We usually ask people to 'get a handle on their loads', So a 12 amp pool pump is likely at 230 volts or a possible load of  (12x230=) 2760 watts. Perhaps it only needs 850 when you turn it on, because you have cleaned the skimmers and the pump so this is the minimum load. Even then it seems low to me. Even a 850 watt load is considerable. Wonder how you are measuring this?

    The pool pump is a Hayward pump from the US so is actually 110v.  I have it connected to a 5kva voltage converter so that it works with our 230v system.  I have the converter plugged into a smart plug that tells me how many watts it is currently using.  When the pump is running the plug reports around 850 watts.  My main 8000 watt inverter shows the load going from 6% to 16-18%.  That tracks with the 850w being used by the pump and the converter.  Am I missing anything there?

    Question about the nominal array suggested...  Are you saying here that we actually need more panels?  Would our system charge better if we had the 6,025 watts available?

    BB. said:

    Guess that you are around Praia, Cape Verde:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Praia
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 75° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    6.33
     
    6.58
     
    6.88
     
    6.43
     
    6.77
     
    6.54
     
    JulAugSepOctNovDec
    6.20
     
    5.57
     
    5.86
     
    6.24
     
    6.18
     
    6.04
     
    For your system, the typical (long term average) harvest for July would be:
    • 4,770 Watt array * 0.61 end to end off grid system eff (AGM battery based) * 6.2 hours of sun per day = 18,040 Watt*hours per day (July, average)
    If you are using ~12,000 WH per day--That is using just a little less than your system can produce in July (long term average)... Some days will be better harvest, some days will be less.

    Normally, would suggest your "base loads" (loads that you need to run every day, vs those loads that can be put off until sunny weather) would be somewhere about 55% to 65% of predicted output:
    • 18,040 WH per day (July) * 0.65 "derating" for base loads = 11,004 WH per day for "base loads" in July max suggested
    Anyway--lots of guesses... Your thoughts and corrections to my estimates?

    -Bill
    We are actually on the island of Fogo, about 100 km from Santiago where Praia is located.  My wife and I moved here about a year ago to set up an off-grid ecolodge.  We were planning on opening on April 1 and then coronavirus happened.  All flights have been canceled since March and we aren't sure when tourists will be able to start coming back to Fogo.  Great timing to open a hotel!  That being said, this is giving us a bit more time to work out some of our kinks!

    Those sun hour estimates seem correct based on our observations here.  A question for you...

    This is a diagram showing our complete solar setup:



    We are not connected to the grid so disregard that.  Does this setup all look correct?  After learning about the substandard battery setup, I am concerned that we have other issues.  When our panels are in full sun the charge controller normally registers around 85-90v and 1500-2500 watts coming in from the solar panels.  That seems low to me.  Our panels are about 30 meters from the inverter at an angle of 25 degrees facing directly south. 

    Here is a picture of our solar panel mounting system (and our German Shepard, Nymeria).



    Is there anything with that setup that we could improve to increase the amount of power we are getting from our panels?

    Is 25 degrees correct for our latitude?  Did we put the panels too far from the batteries?

    The voltage seems low to me with 3 panels in series.  Here is the rating for the panels:



    Shouldn't we be getting more like 38.3 * 3 = 114.9v? 

    Photowhit said:
    I will guess you are new to living on a solar electric system?
    We are indeed new to this and very much appreciate all of the help!  One of our long term goals here is to help other people on our island get set up with solar.  Sun is one of the only resources we are not lacking in Cabo Verde!

    Photowhit said:
    Also of interest would be the type of Charge Controller (Which I guess is the SCC?)

    Likely you will also want to know the characteristics of your battery bank and how comfortable you are in drawing down the battery bank to a low State of Charge (SOC) Some AGM's are pretty good and others not so good at deep cycling. These characteristics will help you determine if you want to start the generator at 50% SOC or 30% SOC.
    Our charge controller is a 100amp AIMS controller.

    https://theinverterstore.com/product/aims-100-amp-solar-charge-controller/

    How would we determine how low of a SOC our battery bank could handle?  All of the research I did before purchasing said never draw it below 50%.  My goal was to not draw below 66% so as to increase the life-span of the batteries.  Thus far we have never gotten down to under 70%.  I have attached a PDF of the full specifications for the batteries.  
  • TramblinTramblin Registered Users Posts: 5 ✭✭
    Voltage is a very poor way to determine the battery bank's SOC.

    That's very interesting!  It seems to me that our charge controller and inverter are using voltage to determine the SOC.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage.
    Some morning I will disconnect our battery bank from the inverter and charge controller for a period of time and see what the actual voltage is.  Question... How accurate is the voltage that is being reported on the charge controller, inverter and my multi-meter when it is all connected?

    So reaching 54.2 volts doesn't indicate fully charged, at least the first time through. Likely the voltage will continue to rise to 57.6-58 volts and at that point the charge controller will not allow the voltage to rise any further, and batteries will accept a bit less current over time, as they slowly become fully charged. Once fully charged the charge controller (SCC?) will reduce the voltage to Float, which is likely the 54.2 volts.

    So when you say this, does the voltage ever run above 54.2?

    I honestly do not know if the system goes above this voltage as I have never seen it.  I will watch the system today as it charges and see if it goes above and then quickly drops back down.

    I do run a lot of 'opportunity loads' once my charge controllers reach absorb voltage set point, I know the battery bank is taking in less current as it tops off the batteries, I tend to want to keep this load at about 50% of the available power from the array. If indeed the pump is drawing 850 watts, you should be good. I'll often wait until it's at the float level of charging to run higher wattage loads. Most of this is just be feel. I rarely look at the system readouts.
    I try to do the same with running washing machines and other optional electrical uses.  Question about "available power from the array."  How would I calculate this?  Say my array is bringing in 1500watts at 85v, what is the available power in 230vac that I could use?

    Sorry for the very long response!  

    One other question that might have been answered indirectly but I missed... Does it sound like there is an issue with our batteries that when I apply a load of 1500 - 2000 watts the voltage reported on the battery bank would quickly drop?  I am trying to figure out if our batteries have a problem, it is just normal behavior, or there is something we can tweak to make the system better.

    Again, thank you all very much for your time and amazing responses!  I have learned more from this than I did in weeks of going back and forth with vendors!  It's almost as if they just wanted my money.  
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    Looks like you are at 14.9500°N 24.3425°W with a Latitude of 14.9N, I would likely have my array angled about 25 degrees facing south. Typically your best harvest is within 10-15 degrees of your latitude. The steeper angle helps rain naturally clean your panels, and a steeper angle typically increases your harvest in the winter. That looks good to me.

    Most batteries can 'handle' a certain amount of deep discharges. So this is basically a tradeoff on battery life VS alternative fuel use.

    If your AGMs can only handle perhaps 50-100 cycles down to 20% SOC, then you might want to use your generator more often to be sure it never gets that low. On the other hand if it can handle 1000 cycles that low. well you might just allow it to get lower and save the fuel. If you can find the characteristics of your battery this gives you more information to use. Also understand that it is both how low and how long the battery stays at the level of charge. If your battery info contains this 'cycles to SOC' information, it's based on being fully charge after getting that low. With solar we don't have that option, unless we are using alternative sources of power.

    You have the right idea, to never let the battery get very low.
    Tramblin said:
    How would we determine how low of a SOC our battery bank could handle?  All of the research I did before purchasing said never draw it below 50%.  My goal was to not draw below 66% so as to increase the life-span of the batteries.  Thus far we have never gotten down to under 70%.  I have attached a PDF of the full specifications for the batteries.  
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    Solar panels are interesting creatures, they are tested to give you figures for power output, but there are only a few of their numbers displayed on the back of the panels;

    Tramblin said:
    The voltage seems low to me with 3 panels in series.  Here is the rating for the panels:



    Shouldn't we be getting more like 38.3 * 3 = 114.9v? 
    So the 38.3 volts is just a Voltage Open Circuit number, it is helpful in determining if your equipment is sensitive to high voltage, but the number for panels in use is VMP so the max you should see under load is 30.9 volts. So 30.9 volts x 3 = 90.27 volts.

    The more interesting number is Their Normal Operating Cell Temperature value, or NOCT. Solar panels are 'flash tested' to give you the above numbers these are called Standard Test Condition or STC values. It allows you to compare solar panels as all are tested in this manner. BUT the more important numbers are the NOCT values. Many manufactures are putting these numbers in their literature. I looked to see if AIMS provided this information, but it appears they don't. Instead giving values to allow you to figure what you will actually received based on the panels temperature. They look like this found for AIMS 275 watt panels;

    Of course they could do the math for you, but don't, I'll likely get this wrong, but the power and voltage are reduced by the Coefficients by the factors in the chart, from the STC which is done at 25c, for each degree above the STC to the NOCT of 45c. It will very likely end up close to 75% of STC for Mono and Poly crystalline solar panels.

    Here's an example of a panels manufacturer who does publish the NOCT numbers;

    So you can expect about 75% of your STC rating from your solar panels, much of that reduction in power is from the loss of voltage when the panels are hot. 

    So your 4770 watt array, will normally be able to produce around (4770x.75=) 3577 watts, and that is before reduction due to loss in any wiring and the charge controller...

    The pool pump info now brings everything into proper perspective for me. 12 amps at 120 volts for a max of 1440 watts so a minimal stressed pump could be expected to need 850 watts +/-.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    So AIMS does provide some battery information, here's their chart for their current 200amp, AGM, 12 volt battery.

    They also say they have a max charge rate of 30 amps or 15%,  Of course the AIMS displayed amperage differs from the 60 amps in their manual, but 15% is a good place to start.  I didn't ask if you have a battery temperature sensor for your charge controller and inverter/charger? You will want to have one connected.

    Manual;
    https://www.aimscorp.net/documents/AGM12V200A.pdf
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • TramblinTramblin Registered Users Posts: 5 ✭✭
    Photowhit said:
    I didn't ask if you have a battery temperature sensor for your charge controller and inverter/charger? You will want to have one connected.


    Yes, we have a temp sensor on both sides of the negative bank going to the charge controller and the other going to the inverter.  Our batteries are always between 27C and 28C.
  • TramblinTramblin Registered Users Posts: 5 ✭✭
    Photowhit said:
    So your 4770 watt array, will normally be able to produce around (4770x.75=) 3577 watts, and that is before reduction due to loss in any wiring and the charge controller...
    We never show more than 2500 watts at the charge controller.  Does that sound like an appropriate amount of loss?  Seems a bit high to me...
  • PhotowhitPhotowhit Solar Expert Posts: 5,495 ✭✭✭✭✭
    Tramblin said:
    Photowhit said:
    So your 4770 watt array, will normally be able to produce around (4770x.75=) 3577 watts, and that is before reduction due to loss in any wiring and the charge controller...
    We never show more than 2500 watts at the charge controller.  Does that sound like an appropriate amount of loss?  Seems a bit high to me...
    It may be that the normal process of charging never requires the full available wattage. While the sun rises into the sky your system starts charging, by the time the sun is high enough to give maximum charging, you may have reached the absorb setting (I think your charge controller calls it Bulk setting(57.2 volts) this normally equates to reaching 80% charged. At this point the batteries will reduce the amount of current they will accept, hence less wattage from the array is needed.

    Unlike wind or hydroelectric, Solar doesn't HAVE to produce maximum wattage.

    If you would like to see what your array is capable of, try to run a lot of heavy loads during 'solar noon' the hour or so either side of the sun being directly over head. You can look up the sun rise and sun set and split the difference. The charge controller is pretty much a voltage regulator, when the voltage drops because the inverter is using most or all of the current coming in the current from the array will pass through the charge controller and give you some better idea of the available wattage.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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