Time to Question the 3 day Rule ?

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Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    IF the 1yr old batteries are lightly used, properly maintained, the same SOC (using SG), and identical (brand/model) to the new ones, I'd use them in the new string.  Even a new string of identical batteries will have variances.

    That said, a year is plenty of time for batteries to get "old".  If there's anything to suggest the old batteries have had a tough year, I wouldn'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
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    My guess... In general, adding "new to old" batteries in series is the worst choice... Old batteries (especially flooded cell) tend to have higher self discharge--Vs new FLA batteries that have lower self discharge.

    When you charge/equalize a series string--The new batteries tend to get "well over charged" vs the older batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    To clarify, I agree with Bill's comment.  The "old" and "new" batteries need to be in much the same shape for it to work well.
    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
  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    Batteries are a year old but we're only in service for 3 months then floating for 9. Sg check is like new. What's the worst that could happen? Seems my choices are use  the 2 i have now for a 12 volt system for rv loads. and buy four new batteries for 24 volts for inverter loads.  running two  separate systems seem like a lot of trouble and money.  2 cc 2 arrays and 2 charger's. Or buy 2 and try paralleling old and new staying with 12 volts. Thoughts?
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I run two systems, and while it has its advantages, it is more money and work. 

    My guess is the "worst that can happen" is you end up boiling the newer batteries to death EQing the old ones.  If they're still in really good shape though, I'd be tempted to give it a go.  If it did turn out to be a problem, I'd figure out a way to EQ the old batteries on their own regularly, but that's just me.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    If you are adding AH capacity in parallel strings--Go for it. I don't think you will see any "obviously early deaths" by doing this. There is enough variability in battery life/death that it would be difficult to attribute any problems specific to this New/mostly New mix of parallel strings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    edited June 2019 #38
    Yes more capacity.     Using 1kwh per day on  200 ah GC batteries keeps me cranking the gen every morning.    Being on the north west side of a mountain doesn't help much either.     IF  $200 in batteries would give me 1/2 the gen run time. In 4 month's I'd Break even. Draining so much each day is sure to give these a early death.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • paulcheung
    paulcheung Registered Users Posts: 56 ✭✭
    Mountainman, 
    I think you need more PV power or a better charge controller. How much watts do you collect a day with that 400 watts panels and the charge controller. The 1kwh you use are just for the night load or is the all day? 
    XW6848+ Magnum 4448PAE (Backup) 7800 watts total mixed Panels, 370 AH @48volts battery bank. Grid assist and soon be Tied.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited June 2019 #40
    If I remember correctly for Mountainman, his home just does not have a lot of winter sun (trees, north side of valley, etc.).
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • paulcheung
    paulcheung Registered Users Posts: 56 ✭✭
    If Mountainman just get more battery and not the solar panels and charge controller, he sure run into more problem than he has now. actually he will make it worst. 
    XW6848+ Magnum 4448PAE (Backup) 7800 watts total mixed Panels, 370 AH @48volts battery bank. Grid assist and soon be Tied.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    If you have lousy sun, more pv and controller isn't a lot of help.  A given bank capacity only takes current so fast.
    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
  • paulcheung
    paulcheung Registered Users Posts: 56 ✭✭
    In that case. If were me, I would get another bank of battery and a smaller 1kw silent generator that can run 5 hours with 1 gallon fuel and a good 50 amps a/c charger to run the generator every other day or every two days if any sun do come out.
    XW6848+ Magnum 4448PAE (Backup) 7800 watts total mixed Panels, 370 AH @48volts battery bank. Grid assist and soon be Tied.
  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    edited June 2019 #44
    @paulcheung I have a iota charger and a 2000 gen  that runs 10 hour on 2 gal. At 50 foot away its quiet.     The way I see it location is everything.    On my side of the road mid summer  I get full sun by 11am. Gone by 3. 

    My neighbor across the road SE side  half way up the mountain gets sun at a little after 8 am.  It is what it is .    With  4 100 watt panels I pull 22 amps with  per hour with good sun for 180 minutes provided my bank is low which it pretty much always is.    3 hrs is as much as I can set bulk.   Then the last hour  in absorb  2-3pm. 11 ah. So 77 ah a day is my best. Mppt or pwm pretty much the same output.    At 3 pm the sun  goes behind a tree  on my property If it were cut I could get sun till 5 or so.            But 3-5 sun how much is it gonna benefit   I'd have 3 hours bulk and 3 hours of absorb.   The tree is very tall and 55 foot from a power line on one side.  and a highway on the other.   Definitely need a man in a bucket to cut it.     On the east side to get  930 sun  in middle summer I'd have cut  trees 200ft wide   and 1300 hundred foot up to the top of my mountain.   For 1.5 of sun that ain't gonna happen.   Now on on the other hand if i put an array on the top of my mountain and ran a  1300 foot cable Id have great sun year round  with unobstructed south facing .(except rain snow ect.)   In winter sun is none existent here.   Snow and clouds and the low angle of 28 degrees.  it makes it over the mountains for for an hour in December. The way im thinking If there is a need to charge then there would still be a need to charge albeit less often but for longer periods with a bigger bank. Even with a adequate amount of panels.    4 hours of direct sunlight is not enough for flooded.  And lithium just cost to much.  For a summer mountains vacation spot.   I have 2 cc. pwm for my closest  400 watt 12 volt panel array.   mppt for 380 watts of gt panels 100 ft away.  780 watts on 416 ah @12 volts.  batteries are $180 for 2 and   $100 for  2 190 watt used panels.   (local pickup) .Im gonna get that tree cut and give it a try.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • paulcheung
    paulcheung Registered Users Posts: 56 ✭✭
    @mountainman, If is a summer vacation home, I won't bother cut the tree, like you said. 3 to 5 pm won't give you lot of power unless you use tracker. more panels and more battery will cut the genny run time. 
    XW6848+ Magnum 4448PAE (Backup) 7800 watts total mixed Panels, 370 AH @48volts battery bank. Grid assist and soon be Tied.
  • stmoloud
    stmoloud Registered Users Posts: 111 ✭✭
    edited July 2019 #46
    I live within 7 mile of a supermarket but off-grid. If I get three days of cloudy weather and a red-only LED from my Morningstar, I'm going to pull the refrigerator plug. Next sunny day I'm going to consider plugging in the refrigerator. But only if the forecast is good for the next three days. Keep it simple, exploit your advantages.
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    edited July 2019 #47
    @stmoloud I understand what you saying. it's about being conservative. But my fridge is propane.    My power use is bare minimum.    36watt TV 4 hours.    charge phones in the truck     4 hours of led lights. Water pump for short showering.      My biggest consumer is a 20" box fan on med.   for 10-12 hours per day.    Keeps me from running the generator for ac.   1 tree would not be missed. Might take a while to get over the cost of cutting it though.   Im parked in the shade Of a 12 acre hard wood mountain forest. My array is pole mounted and adjustable. Right in the middle of a 100 foot wide poco  right of way.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited July 2019 #48
    @stmoloud I understand what you saying. it's about being conservative. But my fridge is propane.    My power use is bare minimum.    36watt TV 4 hours.    charge phones in the truck     4 hours of led lights. Water pump for short showering.      My biggest consumer is a 20" box fan on med.   for 10-12 hours per day.    Keeps me from running the generator for ac.   1 tree would not be missed. Might take a while to get over the cost of cutting it though.   Im parked in the shade Of a 12 acre hard wood mountain forest. My array is pole mounted and adjustable. Right in the middle of a 100 foot wide poco  right of way.
    Sell the tree, wood has a value, I got $400 for a single offending tree in Thailand, contact local firewood vendors, they may cut and dispose and give you $$. Mine was hardwood, had to get permission to allow the felling from the government for the particular type of tree, Teak to be precise.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.