battery voltage Help.

Shawn-H
Shawn-H Solar Expert Posts: 107 ✭✭
okay I'm trying to figure out the best combination of batteries on my 24V system. I'm looking to stop huge voltage swings when using my large appliances like microwave, table saw, skill saw, things like that. I'm thinking about 16 X 220 AH 6v batteries. but I'm afraid if I pull more then 36 amps from them I will get an unhealthy voltage drop any ideas? I need to pull 76 amps for as long as 25 minutes at a time.
100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
Vag woodstove for heat.
Follow our journey at
https://www.facebook.com/ShawnpHarvey

Comments

  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    Re: battery voltage Help.

    16 GC's will give you a healthy power reserve, but as has been pointed out many times, you will be managing no less than four paralleled strings of batteries.

    If you really need that many amps for 25 minutes, you might consider some sort of larger cells to make up a battery bank with fewer cells/parallel strings.

    16 GC's also make for a lot of connections to buy, clean and maintain.
    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.
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    706jim wrote: »
    16 GC's will give you a healthy power reserve, but as has been pointed out many times, you will be managing no less than four paralleled strings of batteries.

    If you really need that many amps for 25 minutes, you might consider some sort of larger cells to make up a battery bank with fewer cells/parallel strings.

    16 GC's also make for a lot of connections to buy, clean and maintain.

    So what would be your suggestion? http://www.solar-electric.com/batteries-meters-accessories/batteries/suprdecyba/6voltbatteries1/suba6vo350am.html
    This is what I'm looking at or its smaller brother at 225Ah.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.

    Maybe 2 parallel strings of this:

    Crown Renewable Power Battery - 6 Volts, 395 Amp-hours


    76 Amps from such a bank would be around a C/10 discharge rate... Not too bad.

    Do you have a choice to go 48 volt battery bank? Same number of batteries all in series. Makes the DC wiring much easier (one series string) and a single 60+/- amp or so Solar Charge controller will do fine. A 24 volt battery bank would be pushing 80 amps for a 10% charge rate. Any more charging current would probably need a second (not cheap) solar charge controller.

    I hope that others with more battery experience than I can give you some better numbers/experience and/or other options.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    BB. wrote: »
    Maybe 2 parallel strings of this:

    Crown Renewable Power Battery - 6 Volts, 395 Amp-hours


    76 Amps from such a bank would be around a C/10 discharge rate... Not too bad.

    Do you have a choice to go 48 volt battery bank? Same number of batteries all in series. Makes the DC wiring much easier (one series string) and a single 60+/- amp or so Solar Charge controller will do fine. A 24 volt battery bank would be pushing 80 amps for a 10% charge rate. Any more charging current would probably need a second (not cheap) solar charge controller.

    I hope that others with more battery experience than I can give you some better numbers/experience and/or other options.

    -Bill

    I have 6k in panels and 2 vfx3524's. I'm able to run 181amps to the batteries. So I'm not stressing charging I'm worried about voltage drop due to high amp drawers. truth be told it's only the water pump and microwave that hit the batteries the rest is daylight power and I don't even see the voltage drop.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.

    Sounds like a reasonable system... Not worth changing to 48 volts at this time.

    What size/type battery bank do you have right now?

    What size of voltage swing are you seeing with your peak loads?

    Are the batteries you have right now in "good shape"? Questionable?

    With ~160 amps of charging current, your wiring does not sound like it should be having any voltage drop questions (unless you have poor connections some where).

    Do you have parallel battery strings? Have you used a DC Current Clamp Meter to make sure the strings are sharing current loads/charging properly?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.

    thank you Bill. I have just assembled my system and I've been running off of some very cheap Marine / RV batteries 4 X 12v and 100Ah. and the voltage drops that I see from them are absolutely horrific. I'm trying to find out whether or not I'm going to suffer the same thing if my battery bank is not large enough. I would hate to spend $3000 on batteries and still have the unsafe drops. I don't want to hurt my batteries or stress my inverters.

    as for a clamp meter I do believe that my Klein tools CL2000 true RMS meter should be good enough lol
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: battery voltage Help.
    Shawn-H wrote: »
    thank you Bill. I have just assembled my system and I've been running off of some very cheap Marine / RV batteries 4 X 12v and 100Ah. and the voltage drops that I see from them are absolutely horrific. I'm trying to find out whether or not I'm going to suffer the same thing if my battery bank is not large enough. I would hate to spend $3000 on batteries and still have the unsafe drops. I don't want to hurt my batteries or stress my inverters.

    as for a clamp meter I do believe that my Klein tools CL2000 true RMS meter should be good enough lol

    Not mentioned yet, I think, is what the voltage drop in your wiring is. Even if you have a high voltage drop at the battery terminals, voltage drop in the wires to the inverter will still hurt you by causing the inverter to draw more DC amps to get the same AC output power.
    And are you using diagonal wiring ( http://smartgauge.co.uk/batt_con.html ) for your two strings and using large enough interconnecting cables?

    The combination of voltage measurements at all points, with amp measurements on the two strings individually should tell you a lot about where the problems are.

    BTW, a voltage drop from the float voltage of ~28V to an under load voltage of ~24V is not a significant voltage drop, since the batteries resting voltage will be lower than the float voltage.
    Any numbers you can give us will help a lot.

    Both the water pump and the microwave will draw more current at lower AC voltages to try to keep the power the same. That means that voltage drop in the AC wiring can hurt your power consumption too. Not to mention that the start up surge to the pump will be a really high short term load on the inverter.
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.

    How much voltage drop are you seeing?

    76 amps / 200 AH = 0.38 = C/2.6

    For a deep cycle battery bank a C/2.5 discharge rate is really only "supportable" for a few 10's of seconds or minutes. If the batteries are somewhat discharged, the voltage collapse is going to be even worse (especially beyond those first few 10's of seconds).

    For a ~800 AH battery bank, you are at a C/10 rate... In general, a good deep cycle battery should be able to support a C/8 discharge rate just fine.

    Again, I am not in the business, so I hope somebody else here can address your questions directly from experience. But I don't see this as being a big issue.

    There is the other question of how much storage do you need (the old 2 days of storage to 50% maximum discharge "nominal" battery bank sizing we use here a lot).

    If your surge currents are high, but your general loads are not (i.e., not a lot of AH over hours over several days), you could look at other battery types (AGM, possibly even LiFePO4, etc.) batteries. They can have much higher surge/short term surge/high discharge current support. And you can have a smaller battery bank overall.

    In general, for fixed applications (i.e., off grid home/business), the weight/size of standard lead acid storage batteries are not a big issue, and much lower purchase costs are hard to ignore vs the (typically) much higher costs of AGM and Li-Ion type cells.

    Your present array could support upwards of a 1,600 AH @ 24 volt battery bank (~10% rate of charge) very nicely--Not that I would suggest you "over size" the battery bank if the loads do not justify the larger bank. Over paneling a battery bank/off grid system has never been cheaper (given the low costs of solar arrays these days).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    inetdog wrote: »
    Not mentioned yet, I think, is what the voltage drop in your wiring is. Even if you have a high voltage drop at the battery terminals, voltage drop in the wires to the inverter will still hurt you by causing the inverter to draw more DC amps to get the same AC output power.
    And are you using diagonal wiring ( http://smartgauge.co.uk/batt_con.html ) for your two strings and using large enough interconnecting cables?

    The combination of voltage measurements at all points, with amp measurements on the two strings individually should tell you a lot about where the problems are.

    BTW, a voltage drop from the float voltage of ~28V to an under load voltage of ~24V is not a significant voltage drop, since the batteries resting voltage will be lower than the float voltage.
    Any numbers you can give us will help a lot.

    Both the water pump and the microwave will draw more current at lower AC voltages to try to keep the power the same. That means that voltage drop in the AC wiring can hurt your power consumption too. Not to mention that the start up surge to the pump will be a really high short term load on the inverter.



    here are a few numbers. when the batteries are full at 26.6 and my water pumpkicks on at night it's not uncommon to see it drop down to 23.8 in less than a minute. Same with the microwave both pull about 1100 watts not including their surge.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    BB. wrote: »
    How much voltage drop are you seeing?

    76 amps / 200 AH = 0.38 = C/2.6

    For a deep cycle battery bank a C/2.5 discharge rate is really only "supportable" for a few 10's of seconds or minutes. If the batteries are somewhat discharged, the voltage collapse is going to be even worse (especially beyond those first few 10's of seconds).

    For a ~800 AH battery bank, you are at a C/10 rate... In general, a good deep cycle battery should be able to support a C/8 discharge rate just fine.

    Again, I am not in the business, so I hope somebody else here can address your questions directly from experience. But I don't see this as being a big issue.

    There is the other question of how much storage do you need (the old 2 days of storage to 50% maximum discharge "nominal" battery bank sizing we use here a lot).

    If your surge currents are high, but your general loads are not (i.e., not a lot of AH over hours over several days), you could look at other battery types (AGM, possibly even LiFePO4, etc.) batteries. They can have much higher surge/short term surge/high discharge current support. And you can have a smaller battery bank overall.

    In general, for fixed applications (i.e., off grid home/business), the weight/size of standard lead acid storage batteries are not a big issue, and much lower purchase costs are hard to ignore vs the (typically) much higher costs of AGM and Li-Ion type cells.

    Your present array could support upwards of a 1,600 AH @ 24 volt battery bank (~10% rate of charge) very nicely--Not that I would suggest you "over size" the battery bank if the loads do not justify the larger bank. Over paneling a battery bank/off grid system has never been cheaper (given the low costs of solar arrays these days).

    -Bill

    Thank you again. You answered my question so 600 to 800 Ah, would do me just fine is what I'm hearing? That's great. We have a crazy power hungry Off gid home and this has been costly but we are just now making it work.

    As for sizing I will have 2 day of power at 1567Ah to 50% DOD, bit can't afford that much led. So ill do 8 of these.
    http://www.solar-electric.com/suba6vo350am.html
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.

    If your nighttime loads (and poor weather days) are not that great, yes you can run with the smaller battery bank.

    If you still need to power 400 AH @ 24 volt loads (~9.6 kWH) per day even when the sun is not shining, you may find you needing to use the genset a lot more with a 600 to 800 AH battery bank.

    With lead acid batteries, it takes a fair number of hours of sun per day to fully recharge a deep cycled battery bank (i.e., 50% discharged)--It can be difficult to get enough hours per day to recharge a deeply cycled battery bank in one day.

    For your system, if I understand correctly, you would need 3+ hours of bulk plus another 4+ hours of absorb to fully recharge the bank--Or a good 7+ hours of good sun.

    You may end up running the genset in the early morning for a few hours to give the solar a head start on recharging the batteries after a bad day of solar.

    To a degree, you may need to run your Bulk charging voltage a bit higher to get the batteries charged quickly while the sun is up.

    Do you have a generator setup yet?

    Can you work on more conservation of electrical power?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    BB. wrote: »
    If your nighttime loads (and poor weather days) are not that great, yes you can run with the smaller battery bank.

    If you still need to power 400 AH @ 24 volt loads (~9.6 kWH) per day even when the sun is not shining, you may find you needing to use the genset a lot more with a 600 to 800 AH battery bank.

    With lead acid batteries, it takes a fair number of hours of sun per day to fully recharge a deep cycled battery bank (i.e., 50% discharged)--It can be difficult to get enough hours per day to recharge a deeply cycled battery bank in one day.

    For your system, if I understand correctly, you would need 3+ hours of bulk plus another 4+ hours of absorb to fully recharge the bank--Or a good 7+ hours of good sun.

    You may end up running the genset in the early morning for a few hours to give the solar a head start on recharging the batteries after a bad day of solar.

    To a degree, you may need to run your Bulk charging voltage a bit higher to get the batteries charged quickly while the sun is up.

    Do you have a generator setup yet?

    Can you work on more conservation of electrical power?

    -Bill

    Thank you BB. This is what I have. 20 XAstronergy 305 Watt Solar Panels, 6 X Fm80 (only using 3), 3 midnite solarcombiners, 1 X FW-500, with 2 vfx3524's, 2 X 100Ah of interstate marine/RV batteries, 1 X predator 8000w genset, 1 X 2200w predator inverter generator.
    my nighttime loads are not long running but there's not much I can do about them my water is unfortunately not the most efficient and someday I will replace it but at the moment it's a one horsepower booster pump that runs anytime I get more than half a gallon of water and then there's the blower motor which is 400w and unfortunately the microwave is going to run inevitably once or twice a night at 1100 watts. what's unfortunate is the microwave seems to turn on at the same time the blower motor for the heat does.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.
    Shawn-H wrote: »
    Thank you BB. This is what I have. 20 XAstronergy 305 Watt Solar Panels, 6 X Fm80 (only using 3), 3 midnite solarcombiners, 1 X FW-500, with 2 vfx3524's, 2 X 100Ah of interstate marine/RV batteries, 1 X predator 8000w genset, 1 X 2200w predator inverter generator.

    Hmm. Lots of solar panels. What size battery bank would they support (5-13% rate of charge, 10%+ for full time off grid home recommended):
    • 20*305 Watt panels * 0.77 panel+controller derating * 1/29 volt charging * 1/0.13 rate of charge = 1,246 AH @ 24 volt battery bank minimum
    • 20*305 Watt panels * 0.77 panel+controller derating * 1/29 volt charging * 1/0.10 rate of charge = 1,620 AH @ 24 volts nominal
    So, you could certainly justify a larger battery bank with your present array/hardware.
    my nighttime loads are not long running but there's not much I can do about them my water is unfortunately not the most efficient and someday I will replace it but at the moment it's a one horsepower booster pump that runs anytime I get more than half a gallon of water and then there's the blower motor which is 400w and unfortunately the microwave is going to run inevitably once or twice a night at 1100 watts. what's unfortunate is the microwave seems to turn on at the same time the blower motor for the heat does.
    The 1 HP water pump--That is a killer... Can you justify a pressure tank (40 gallons with 20 gallon draw down)?

    Running a 1 HP pump every time you turn on a faucet sounds like terrible overkill (and hard on the pump/pump cycling). Isn't that something like 10-20 gpm of water at pressure (vs 2-5 gpm for most household fixtures)?

    http://www.solar-electric.com/wind-and-water-products/sodcwapu/shacdcwapu/shurflo-5050-series-water-pumps.html
    http://www.solar-electric.com/lib/wind-sun/5050-2301-G011.pdf (~3 gpm at 30 psi and <100 Watts @ 24 VDC for $277)

    Some less expensive 24 volt pumps:

    http://www.solar-electric.com/wind-and-water-products/sodcwapu/shacdcwapu/sh20sepuanda.html

    Use them with even a smaller pressure tank--More or less like an R/V.

    I would avoid sizing your off grid power system just for running the pressure pump (unless you need it for fire fighting/etc.).

    You can always wire something up to stop the furnace from turning on when the microwave is running (intercept the 24 volt controller wire or such). But if you get rid of the 1 HP load, your microwave and furnace should be OK together on a ~2 kWatt AC inverter or larger (note, some high efficiency electronic furnaces seem to be a bit picky about their AC power--Just something to think about if you do have problems at some point).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.

    Thank you again BB. right now I just don't have the money to replace the pump or pressure tank I'm tapped out for the next 13 to 14 months but after that things will get much better. I have decided on 8 Surrette Battery - 6 Volts, 375 Amp-Hours.

    My 1hp pump (570w) draws less then my microwave(1124w)
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: battery voltage Help.
    Shawn-H wrote: »
    here are a few numbers. when the batteries are full at 26.6 and my water pumpkicks on at night it's not uncommon to see it drop down to 23.8 in less than a minute. Same with the microwave both pull about 1100 watts not including their surge.

    How do the kids say it?...

    Yes, No... Lets not talk about your current battery bank, it's unrealistic to draw at such a rate from such a small battery bank.

    I have a 24v forklift battery 800 Ah, and I will see significant voltage drop at a discharge of 1/10th of capacity, though it truth I can only get close to that unless I have both inverters running. I do often draw 45 amps sustained for a couple hours from time to time, That's some normal night time loads and a 900watt water heater. I can run this for several hours, and I do get voltage drop but it's load related, I do see recovery when removed.

    I would actually shoot for the largest battery bank your array could support at a 13% charge rate, which would be around 12-1400 Ah if you plan on having this pattern of use for a long period of time. I have the panels to expand my array, but I'm slightly over paneled right now.

    I seriously doubt you're running a microwave for 25 minutes, suspect it's mostly your table saw and shop area.

    I'd cook a pizza for you tonight in my toaster oven and give you some real world voltage drops, but I have plans and it will be cloudy tomorrow.

    About that battery bank we aren't discussing, when do you see a voltage of 26.6? I would expect to see voltages around 25.4 fully charged after sunset... I'd actually expect to see a greater voltage drop after a minute while the microwave was running with such a small bank. I had a 24v 220Ah for 4 years, I would see the voltage drop to 24-23.5 while running and it would quickly recover after. I had a smaller microwave 8-900watt.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    Photowhit wrote: »
    How do the kids say it?...

    Yes, No... Lets not talk about your current battery bank, it's unrealistic to draw at such a rate from such a small battery bank.

    I have a 24v forklift battery 800 Ah, and I will see significant voltage drop at a discharge of 1/10th of capacity, though it truth I can only get close to that unless I have both inverters running. I do often draw 45 amps sustained for a couple hours from time to time, That's some normal night time loads and a 900watt water heater. I can run this for several hours, and I do get voltage drop but it's load related, I do see recovery when removed.

    I would actually shoot for the largest battery bank your array could support at a 13% charge rate, which would be around 12-1400 Ah if you plan on having this pattern of use for a long period of time. I have the panels to expand my array, but I'm slightly over paneled right now.

    I seriously doubt you're running a microwave for 25 minutes, suspect it's mostly your table saw and shop area.

    I'd cook a pizza for you tonight in my toaster oven and give you some real world voltage drops, but I have plans and it will be cloudy tomorrow.

    About that battery bank we aren't discussing, when do you see a voltage of 26.6? I would expect to see voltages around 25.4 fully charged after sunset... I'd actually expect to see a greater voltage drop after a minute while the microwave was running with such a small bank. I had a 24v 220Ah for 4 years, I would see the voltage drop to 24-23.5 while running and it would quickly recover after. I had a smaller microwave 8-900watt.

    as always sir you have hammered the nail right on the head truth having it I could probablynot hurt my battery so bad if I ran the microwave less and yes my shop area does do a number to the batteries. here's the problem I'm suffering I cannot push my battery bank up that high right now I don't have the money. I do believe that I'm going to get 750 to 850 and towers of batteries. I do wish that I could get forklift batteries but I cannot figure out a practical way to get them into the room where my batteries need to go. I would have to take down to walls and part of my porch. and as far as the 26.6 it was just a voltage drop that I had just seen that afternoon The Sun was not completely down yet. but I was really only getting 60 or 70 Watts from the panels.

    Thank you Photowhit you are primarily responsible for my entire system and have given me invaluable information save me time money and labor thank you for everything you've done for me and I'm sure I will have 2 million more questions for you.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: battery voltage Help.

    As Photowhit said... Look at the 25.4 volts the "fully charge" resting voltage of the battery bank. Any voltage about that is due to charging and "surface charge" on the battery bank.

    For the battery to deliver any energy (i.e., current in excess of the that available from the solar array/previous battery charging/float state), you will see a drop to 25.4 volts, then another volt or so drop as the battery starts to deliver current... A loaded battery with upwards of 50% discharge will output around 23.0 volts (very rough numbers at 70F/25C).

    So, 23.8 volts is "not bad" for a fairly heavy load (on your smallish battery bank). If it stays at 23.8 volts for awhile (it can even increase a small amount)--Things are working OK... If the battery discharges below ~23.0 volts (at C/8 load or so), then it is either getting significantly discharged and/or getting old and sulfated/weak.

    Per these graphs, estimating State of Charge for a lead acid battery bank is not very straight forward:
    leaf wrote: »
    Am trying to upload the charts I am using...

    Attachment not found.Attachment not found.

    attachment.php?attachmentid=3655

    attachment.php?attachmentid=3654

    [note charts are from: I believe those charts are from Home Power #36, August- September 1993. Lead-Acid Battery State of Charge vs. Voltage ©1993 Richard Perez.
    Here is a link: http://www.scubaengineer.com/documen...ing_graphs.pdf

    vtMaps
    ]

    I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

    Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: battery voltage Help.
    Shawn-H wrote: »
    Thank you Photowhit you are primarily responsible for my entire system and have given me invaluable information save me time money and labor thank you for everything you've done for me and I'm sure I will have 2 million more questions for you.

    Well, gosh... You're welcome.

    I guess I really didn't state what I was thinking, and that was to try to keep sustained loads at 1/20th of your battery bank, we all use more in short cycles, but I worry even with my healthy large battery about the increased speed of discharge when pushed past this level, the voltage sag also requires more current to maintain the same wattage and there is that nasty multiplier effect of using more current and the battery having a reduced capacity due to the higher drain.

    It's incredible what you've done with such a small battery bank! Might consider a small cheap step up to a 2 string of cheap golf cart batteries, if you have a desire for an even larger bank in a couple years. Could be had for about $700 (Sam's Club or Costco) and should ease your mind about microwave and pump and bit yet not a huge investment. Just thinking out loud.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    Re: battery voltage Help.
    Photowhit wrote: »
    Well, gosh... You're welcome.

    I guess I really didn't state what I was thinking, and that was to try to keep sustained loads at 1/20th of your battery bank, we all use more in short cycles, but I worry even with my healthy large battery about the increased speed of discharge when pushed past this level, the voltage sag also requires more current to maintain the same wattage and there is that nasty multiplier effect of using more current and the battery having a reduced capacity due to the higher drain.

    It's incredible what you've done with such a small battery bank! Might consider a small cheap step up to a 2 string of cheap golf cart batteries, if you have a desire for an even larger bank in a couple years. Could be had for about $700 (Sam's Club or Costco) and should ease your mind about microwave and pump and bit yet not a huge investment. Just thinking out loud.


    I believe I'm ready to move up. I'm thinking of two strings of 6 volt either
    http://www.solar-electric.com/batteries-meters-accessories/batteries/suprdecyba/6voltbatteries1/suba6vo350am.html
    or
    http://www.solar-electric.com/batteries-meters-accessories/batteries/suprdecyba/6voltbatteries1/rolls-surrette-s-550-deep-cycle-battery.html
    I'm going to be honest I do not want to exceed what's capable of being charged off of my inverter generator situation if my inverter cannot handle giving 100 percent of what the battery needs then I could get stuck with undercharged batteries. so I'm attempting to stay around the 850 Ah, rang. this may be an unfounded fear but I'm still not willing to throw away so much money because of the month of bad weather.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey