Added another Solar Panel and Controller Says Watts Dropped

CorttttCortttt Registered Users Posts: 19 ✭✭
I had 165 and 175 watt solar panels on the van. After adding a large freezer I noticed the battery running low in the morning (It's a carbon foam Firefly http://fireflyenergy.com/products/12v-e31-battery/ - which I got because I heard they were basically pretty indestructible and 3 or 4 years later it has been. I've really punished it.)

Anyway it was getting low in the AM (as low as 10.9 volts) so I added another 175 watt panel to the mix - only to find the controller reporting that the watts were going down not up (???). I have a Morningstar TS-45 PWM controller. 

I tried altering the plug sequence of the three in one plug socket for the solar cables and it made no difference. The Newpowa Panel doesn't seem to be the problem. 

Virtually every time I bring the third panel online - whether its the Newpowa or the Grape Solar or the Renogy the controller shows the watts going down. Not what I expected :)

I wondered if I was maxing out the controller but even later in the day when I added the third panel the watts dropped from 88 to 80 and then went back up to 88 when I removed the panel?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    What is the Vmp/Imp of the three panels?

    All connected in parallel? 12 volt battery bank?

    It sounds like that one panel could be installed with reversed polarity... But given which panel order you connect, you see the same behaviour (loss of wattage with 3rd panel connection?).

    Can you tell us the Current (amps), Array Voltage, and the battery bank voltage when this stuff is happening?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,173 ✭✭✭✭
    Cortttt said:
    I had 165 and 175 watt solar panels on the van. 

    Anyway it was getting low in the AM (as low as 10.9 volts) so I added another 175 watt panel to the mix - only to find the controller reporting that the watts were going down not up (???). 
    So are these 36, 60 or 72 cell panels?

    What is the VMP of the solar panels?
    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
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks for the questions. I will get you the figures when the sun climbs higher. They are all connected in parallel. 12-volt battery. It appears that it doesn't matter which order I connect them in but I will check that further to make sure. I wonder if 3-panel branch connector could be the problem?

    VMP

    Both Newpowas (175 Watt) - 17.0
    Grape Solar (165 Watt) - 18.5

    Cell #

    The new Newpowa - 72 
    The older Newpowa and Grape Solar - 36 

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Ok... Just to be clear in how we use "72" cell panels... In solar panels, cells are put in series because--each cell is ~0.5 volts Vmp, and you need 36 of them in series to get Vmp~18 volts (a "12 volt" panel).

    Your 72 cell panel is actually two 36 cell strings in parallel to get Vmp~18 volts (and ~10 amps Imp).

    From what you have posted, connecting all three of those panels in parallel to a PWM solar charge controller is a well designed system.

    Technically, with most solar panels, when you connect 3 or more panels (or series strings of panels) in parallel, you generally install a combiner box that has a fuse/circuit breaker per string to prevent two parallel strings from feeding one shorted string and possibly starting a fire--While technically accurate that most panels "need" a combiner box for 3+ parallel panels/strings, it is a close call. You need to check the series fuse/breaker rating for the panels (l.e., are the series fuses 15 or 20 amps?).

    At this point, not sure I see what the problem is. Checking the Voltage and current of each panel, one at a time, on the charge controller (hopefully, you can read Vpanel and Ipanel on the controller) will tell us that each panel is working correctly.

    The only other thing I could see--If your battery bak is near full, it naturally reduces charging current (>~80-90% full, no major DC loads). That sometimes confuses debugging... For example, adding more solar panels and getting the same or even reduced charging current--Battery bank is already near full, and charging current would be reduced with or without the "3rd panel".

    If you are into doing your own debugging/better understanding of solar power... Getting a DC current clamp DMM (really an AC+DC current clamp DMM, vs an "AC only current clamp meter). They make debugging and understanding your system much easier (and current clamp meters are very safe and easy to use--Unlike the normal DMM that you have to cut a wire and put the meter leads in series with the wire to measure current):

    https://www.amazon.com/gp/product/B019CY4FB4 (mid priced meter)

    There are less expensive AC+DC Current Clamp DMMs (round $50 +/-) out there--But this whole COVID/China trade stuff is making them less available and driving up prices. Do you research.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks Bill. 

    I hope I haven't wasted everybody's time and brainpower. At the very least I'm learning alot. 

    First I disconnected each old panel and added the 72 cell new 175 watt Newpowa in. Each time all the readings increased with the Newpowa panel connected to the old panels

    Original older panels

    122 watts
    9.5 amps
    12.8 V

    One old panel plus the new Newpowa panel

    143 watts/151 watts 
    11.1 amps/11.8 amps
    12.9 V/ 12.9 V

    Then I added them all together again and this time it worked:

    210 Watts
    16.7 a
    13.2 V

    The only thing I did differently was disconnecting the first panel and replacing it with the old panel during the first test. 

    I'm confused but happy and a little worried if it might happen again... I should noted that a couple of times yesterday it did seem to work briefly but then dropped. 

    All is well for now. I will keep a close eye on it. 

    I am replacing the connector just in case. 

    Thanks for everyone's help so far. 


  • CorttttCortttt Registered Users Posts: 19 ✭✭
    I will check the fuses and see if the same thing happens in the day as the battery charges up. 
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Do you recommend a brand of combiner box? 

    Thanks for the recommendation on the clamp meter. It was recommended the last time I was here - with another problem :) and I got one - just haven't used it yet.
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    edited May 13 #9
    At 2:30 pm I added the new solar panel again - and this time  watts and amps dropped. It appears that adding the solar panel in the afternoon results in a drop in watts, amps and PWM 

    Two solar panels

    14.5 V
    121 W
    8.4 amps

    PWM - 78%

    Three solar panels

    14.5 V
    107 W
    7.4 A

    PWM- 49%

    If I understand PWM correctly - and I may not - the two panels were feeding energy to the battery 78% of the time while the three panels were feeding energy to the battery 49% of time - despite the fact that they were feeding less energy (107 W to 121 W) to the battery? Is that right? 
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    It does sound like your charge controller is limiting the current to the battery bank.

    PWM is Pulse Width Modulation... When the pulse is "on" (transistor/switch) 100% of the time, that is the maximum current allowed. When the PWM is 1%, then the cycle (whatever that is, 10x per second or whatever), it is on for 1/100 of that cycle, and off for 99/100 of the cycle.

    Now, in the earlier results, the battery was something like 12.8 to 13.2 volts under charge--That is indicating that the battery is in need of charging...

    The controller should be at 100% (always on, or almost always on) during these low battery voltage times. Basically, passing 100% of the available current from the solar array to the battery bank.

    This last set of tests--The battery bank is at 14.5 volts in both cases, with less than 100% duty cycle. Depending on the battery type of your bank, and what the controller is set for--Typically, the charge controller is set for around 14.4 volts (AGM type) to 14.8 volts (flooded cell type) battery bank.

    Assuming that the battery charge set point is 14.5 volts, then your controller (and the solar panels) appears to be working correctly. The controller with fewer solar panels was at a higher PWM rate 78% and when you added another panel it dropped down to 49% (of a higher available current from the array). The 8.4/7.4 amps is the "average" current from the solar array to the battery bank (i.e., if PWM is 50% at 8 amps, then, in theory, the array is outputting 16 amps for 1/2 a PWM cycle, and 0 amps for the other 1/2 of PWM cycle--For an average of 8 amps).

    The fact that there was less current (somewhat less), with the larger array--I would chalk that up to natural variation (battery bank state of charge, variation of voltage measurements, etc.)--Overall, looks to be working correctly.

    Depending on the controller brand/model/battery condition, it should hold 14.5 volts for ~2-6 hours (absorb stage, the deeper the discharge, the longer the absorb stage). Then when the controller decides the battery bank is full, it should drop back to 13.6 volts or so (float)--Again, depending on the controller/model/etc.

    Things you can still check--With the controller outputting higher current, check the voltage at both the Charge Controller's Vbatt and at the battery bank itself... For a 12 volt battery bank, you want (roughly) 0.05 to 0.10 volt drop (you want the charge controller to accurately measure the battery bank voltage).

    Another check... What is the type of battery bank you have (FLA, AGM, GEL, etc.)... If AGM, typically 14.4 volts. If Flooded Cell, typically 14.75 or 14.8 volts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks Bill, So a lower PWM means that the battery is being "fed more" than a higher PWM. The PWM kicks in as the battery is filling up. 
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    I am guessing, but your 100% PWM is "high current" (100% of available array current. 50% would be 1/2 the available current, etc.)...

    In this case, the battery voltage is (probably) at the 14.5 volt set point... You can add panels and make more current available, but if there was "more current", the battery voltage would rise beyond 14.5 volts.

    Guess at the math:
    • 8.4 amps / 0.78 PWM cycle = 10.77 Amps available from array (100% of 2x panels)
    • 7.4 amps / 0.49 PWM cycle = 15.10 Amps available from array (100% of 3x panels)
    Pure guessing--But it would appear that things are roughly working correctly--Approximately each panel is responsible for 1/3 of the total available current.

    Both Newpowas (175 Watt) - 17.0
    Grape Solar (165 Watt) - 18.5
    • 175 Watt Pmp / 17.0 volts Vmp = 10.29 amps Imp
    • 165 Watt Pmp / 18.5 volts Vmp = 8.92 Amps Imp
    • (2x10.29) + 8.94 = 29.5 Amps Imp-array (under full sun)
    • you are getting (3 panels) 15.1 amps or 15.1/29.5 = 0.51 = 51% of array rating (based on 0.49 PWM cycle)
    Guessing (again) that your array is capable (at that point in time) of outputting ~51% of its rated Imp... Depending on time of day, angle of sun to array, how clear the day was, etc... If there was any haze, or the sun was "off angle" of the panel, etc. -- 51% of the array Imp rating is not "bad"... Just not perfect (when everything is aligned, noontime sun, very clear day).

    As far as I can tell--All looks to be operating as designed and programmed at that moment in time.

    Note that "just looking outside", it is not easy to see even a 50% loss of solar energy with the Mark 1 Eyeball (haze, smoke, off angle sun on panel, etc.)... But everything seems to be consistent with how the panels+charge controller+battery bank work together.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks again Bill for walking me through this. I haven't' checked but I think the set point is 14.5. 

    Fascinating stuff. The amps/PWM data seems to me explain everything. 

     I added the 3rd panel and then played with the load - eliminating one refrigerator. The results fit your hypothesis, I believe. 

    With Both Fridges Hooked Up - more drain on the battery equals more energy flows (amps/watts) from the solar panels allowed - and higher PWM

    • 14.6 V
    • 107 W
    • 7.3 Amp
    • PWM - 49%
    With One Fridge Hooked Up - less drain on the battery - less energy flows (amps/watts) from the solar panels allowed - and lower PWM

    • 14.6 V
    • 76 W
    • 5.1 amp
    • PWM - 36%
    I'm satisfied that the controller is working properly. 

    One last question, do you have any suggestions on how to determine how healthy a battery is? 


  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    What kind of battery do you have (flooded cell lead acid, AGM, etc.)?

    What voltage, AmpHour? How many batteries? 12 volt battery bus...

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks Bill. 

    I have a kind of a funky battery -  a 12V carbon foam 116 AH Firefly http://fireflyenergy.com/products/12v-e31-battery/ / http://fireflyenergy.com/wp-content/uploads/2017/08/12VE31-brochure-SPI-LV.pdf which I got because I heard they were basically pretty indestructible. 

    Just one battery.....

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    • OK, looking around, 14.4 volt AGM type battery (basic chemistry)... So, if you do a 50% discharge that would be:
    • 116 AH * 0.50 = 58 AH
    • 58 AH * 12 volts = 696 WH
    • (2*165W panels) + 175 Watt = 505 Watt Array
    • 695 WH load * 1/0.77 panel+controller derating * 1/505 Watt array = 1.8 hours of "sun" per day
    So--If you take the battery down by 50% (just a stab in the dark), and your current array, flat to roof, and 1.8 hours of sun equivalent per day--It is not a badly designed system.

    You can use this solar calculator (your location, angle of array, Monthly average) and you can double check the expectations.

    You should technically drop the charging voltage (75F) to 14.4 volts (AGM do not like to be 'overcharged').

    Your discharging voltage (under load) should be around 11.5 volts (roughly 50% state of charge, with battery under load)...

    Can you tell us what your daily loads are (AH @ 12 volts or Watt*Hours)? Location of your system?

    At some point, it would probably be nice to get a Battery Monitor or AH/WH monitor for your system... Or at least watch the battery bus voltage... You really do not want to go much below 11.5 Volts... And when you recharge you want to hold 14.4 volts for several hours to get the battery recharged...

    Going down to 10.9 volts is usually not good.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Thanks again Bill, 

    I found out that controller is set at 14.35. 

    The battery went down to 9.5V a couple of times. (It's actually been down to around 5 V a couple of times but that was earlier.). Now with the extra panel it's going down to around 12.2 V. - so I am much relieved - thanks. 

    I think I can find out amp hours from the log. 

    Thanks again for your time and help. 

    :)
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    You are very welcome Cortttt,

    Longer term, you probably don't want the battery much under 11.5 volts (under load) or 12.4 volts or so (resting)...  That is something like 50% state of charge. You can go lower on occasion, but it is very important to get the battery bank  >~80% state of charge as soon as you can (next day, or sooner with genset--If no/little sun is predicted).

    Pretty much everyone has "murdered" there first sets of batteries (been there, done that). All part of the education.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • garynappigarynappi Registered Users Posts: 80 ✭✭
    If I may ask the OP, what kind of refrigerators are you running all night long on a single 115Ah battery? 
  • fratermusfratermus Registered Users Posts: 42 ✭✭
    BB. said:
    it is very important to get the battery bank  >~80% state of charge as soon as you can (next day, or sooner with genset--If no/little sun is predicted).
    OP's carbon-foam battery was designed to operate at partial state of charge.  The firefly requires full charging only 1-2x/month to retain capacityu. 
    2017 Promaster 159" DIY camper
    570W mono / 220AH GC
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Sounds good. The recharge quickly applies to deep cycle lead acid storage batteries...

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CorttttCortttt Registered Users Posts: 19 ✭✭
    Two Engels - a bit 80 quart on freeze, no less - and a 45 quart on refrigerate. 
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