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kau
kau Registered Users Posts: 8 ✭✭
in Off Grid Solar & Battery Systems #1
So we have had a small 12 volt  solar setup for about 7 years, it consists of one 265 watt panel , 2- 6 volt golf cart batts, one 35 amp KID charge controller, and a 600 watt inverter, we usually get lots of sun, we run a generator early in the morning to power a blender, we have a 12 amp battery charger connected to the battery’s, so every time we run the generator the batts are receiving a charge,  I notice in the morning when the batts are on the charge they read 16+ volts, the other morning the overcharge light was on.
  I sometimes run the generator during the day for power tools, we have fiber optic for our internet and we have been having problems with not having internet in the morning, which is attributed to our power system, I have tried plugging the modem(?) up to the generator, it is a Honda 2300 EU, that does not work, but it will work when sun starts to hit the panel , seems the modem does not like the power from the gen, also our inverter is sine wave.
 Anyway I will stop there
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  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    #2
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    My thoughts? After 7 years your batteries are toast. Sure sign of a worn out battery is instant charging and dismal capacity.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    Welcome to the forum Kau,

    I am guessing you are somewhere around Hawaii?

    More or less, generic Golf Cart Batteries last around 3-5 years. Flooded Cell Lead Acid (FLA) Batteries in warm/hot climates, tend to age faster. Your batteries at 7 years are doing real well.

    It is possible that the "overcharge" light is turning on because the batteries are just plain warn out (FLA batteries "sulfate" over time... basically the soft/fluffy grey lead sulfate turns into hard black crystals--Which do not participate in the charge/discharge electro-chemical process (batteries lose AH capacity and have increased internal resistance).

    If they have given you good service for 5+ years--You seem to be taking pretty good care of them (filling with distilled water, don't let plates get exposed, don't let batteries sit below ~75% state of charge without recharging... Cycle to 75% SoC daily--And usually avoid going below 50% SoC (and recharging quickly).

    Are you trying to pull modem power from the 120 VAC or 12 VDC genset output (if present)?

    Monitoring Battery Voltage and Specific Gravity (with a hydrometer) is helpful to catch problems early.

    More or less, Flooded Cell Lead Acid Batteries should be charged at 5% to 13% rate of charge--And if full time off grid, 10%-13% or so is better. For a pair of 6 volt @ 200 AH batteries connected in series for 12 volts @ 200 AH bank:
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 188 Watt array minimum (weekend/sunny weather usage)
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 377 Watt array nominal (minimum recommended for full time off grid usage)
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 490 Watt array "typical cost effective maximum" array
    Say you are somewhere near Honolulu Hawaii... With a 265 Watt array... The average sun for that area is:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Honolulu
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 69° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.98
         		5.84
         		6.24
         		6.50
         		6.43
         		7.37
     
    JulAugSepOctNovDec
    6.52
         		6.63
         		6.60
         		6.10
         		5.24
         		4.83
     

    This average harvest for an off grid system in June would be:
    • 265 Watt array * 0.52 off grid AC system eff * 7.37 Hours of sun per day (June) = 1,016 WH per average June day
    If you cycle the FLA battery to 75% SoC (optimal cycling for longer battery life--And gives you 2 days of storage to 50% capacity):
    • 12 volts * 200 AH * 0.25 Capacity * 0.85 AC inverter eff = 510 WH "overnight" or drain in cloudy weather.
    Does any of this help answer questions for you?

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