What is the optimal SOC range for cycling lead acid batteries?

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  • PhotowhitPhotowhit Solar Expert Posts: 4,913 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    zoneblue wrote: »
    I do have a water heater ready, but dont have the inverter capacity, nor dc elements yet. Its on a list. But what about this for an idea.

    Zoneblue, you might check through the threads about water heating. Your current water heating elements may well work for what you want to do. 240v elements will work at about 1/4 of the wattage with 120. This is what I did with my 3600 watt elements and 30 gallon water heater. it's working fine if a considerable longer heating at @900 watts on 120watts A/C. Being a pure resistance load they will also work on DC with similar reduction of wattage based on voltage.
    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
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    Photowhit wrote: »
    240v elements will work at about 1/4 of the wattage with 120.

    Yep - 240V heater elements work fine on 120V at 1/4 the wattage rating of the element. The only thing is, try to build your system so when the element comes on, it stays on for a long time and does not continuously cycle on and off. If the element don't get hot enough and you have "hard" well water the element will build up with scale over time and reduce its efficiency and possibly burn it out when you do get it hot.
    --
    Chris
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    ChrisOlson wrote: »
    If the element don't get hot enough and you have "hard" well water the element will build up with scale over time and reduce its efficiency and possibly burn it out when you do get it hot.

    I don't understand that. (I'm not saying you're wrong, just that I don't understand why). In my tea kettle the scale builds up more on the bottom than the sides. I thought that was because the bottom was hotter.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    vtmaps wrote: »
    I don't understand that. (I'm not saying you're wrong, just that I don't understand why). In my tea kettle the scale builds up more on the bottom than the sides. I thought that was because the bottom was hotter.

    I don't know - that's just been my experience with it. They make low wattage density elements for "hard" water that have a lot more surface area. So when they build up with scale they have more surface area to dissipate the heat and don't burn out. From what I've seen in our heaters, the hotter I run them the cleaner they seem to stay. I had a lot of problems early on with 2,000 watt elements running at 500 watts. I'd pull the element out and it was a ball of white scale on it. Since I've been using higher wattage elements they don't seem to build up that bad. But still bad enough so that if I put the full 4,500 watts to them, they'd burn out.

    Maybe it doesn't make any difference and with high lime content in the water they're going to build up anyway.
    --
    Chris
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    Scale settles to the bottom of the kettle when it cools, then adheres. Hot heating element = more water circulation to keep scale off. It's some weird chemistry goes on. :p
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    Hot heating element = more water circulation to keep scale off.
    ChrisOlson wrote: »
    From what I've seen in our heaters, the hotter I run them the cleaner they seem to stay.
    The above two quotations are consistent. The next one is not:
    ChrisOlson wrote: »
    They make low wattage density elements for "hard" water that have a lot more surface area. So when they build up with scale they have more surface area to dissipate the heat and don't burn out.
    I'm not less confused:confused: Low wattage density means they run cooler and should build up more scale.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,246 admin
    Re: What is the optimal SOC range for cycling lead acid batteries?

    In our area, we have pretty soft water... And I can see that "hot elements" may last longer.

    From the electric water heaters I replace (I help take care of a small apartment with 4x 40 gallon water heaters)... The elements seem to build a soft scale around them, but the slight "boiling action" (hotspots below "scale"?) appears to cause the elements to shed the buildup before it hardens.

    When I drain a heater after it fails, I sometimes see this "soft scale" drain out looking all the world like draining water ice slush from the heater (very soft/gelatin feeling "scale").

    In our case, the water chemistry could be causing a different "scaling" effect.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    vtmaps wrote: »
    The above two quotations are consistent. The next one is not:

    I'm not less confused:confused: Low wattage density means they run cooler and should build up more scale.

    I think the theory behind those low wattage density elements is that if you have hard water that tends to build scale on the element, the low wattage density element with its greater surface area, can handle it without burning out. The scale deposits act like insulation so the element can't get rid of its heat. With greater surface area the heating per square inch isn't as great so the element survives it.

    The low wattage density elements are not installed in water heaters, that I know of, as OEM. They are usually only put in where known "hard" water is a real problem. So that's what I meant about if you have high lime content in the water (usually meaning very good pH) that the scale is probably going to build regardless of how hot you run the element. Our water here does not test real high on lime. But it's enough so that a cool running element seems to collect the white slushy stuff that Bill mentioned quite rapidly, where a hotter running element does not seem to collect it as fast. I think 'coot had a good explanation - the water circulates quite rapidly around a really hot element so it tends to keep it cleaner.
    --
    Chris
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    A difference of "what will prevent the scale from building up" and "what will prevent the element from burning out when it does". :D
  • Ralph DayRalph Day Solar Expert Posts: 886 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    I removed the sacrificial anode from my sdhw tank (to change the thermosiphoning characteristics...it got better). Are these anodes not present in most water heaters anymore? My understanding is the anode sacrifices (gives off ions or corrodes away to nothing eventually) to save the heating elements.

    Ralph
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    Sacrificial anodes are present in glass enamel mild steel tanks. If the tank overheats the enamal cracks, and the exposed steel starts to rust. Youre supposed to change them out every 5 years or so. Better quality tanks are now mostly stainless
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    vtmaps wrote: »
    That's not good. From the wind-sun battery FAQ: Over at batteryfaq.org they say much the same, except they recommend cycles be at least 10%.

    Welll my point was "shouldnt my charge controller know best". Apparently not.
    I'm not sure how applicable this advice is to AGM batteries... my understanding (which is limited) is that they tolerate floating better than flooded cells.

    Quite, they are a mystery to me as well.
    but I am starting to notice more voltage sag with even moderate loads. I take this to mean that I am developing increased internal resistance because of positive plate corrosion.

    Around here they say (for FLA anyway) to increase the voltages by 0.1V each year of the batterys age. At year 10 that would make absorb and float 1.0V higher. Its a way to overcome the growing internal resistance.
    Stephendv has written about how the sunny island will not do a daily absorb unless the batteries are discharged far enough. I don't think I can easily mimic that with my controller,

    This and your other comments below make your average charge controller look postively dumb. In a web connected world tomorows forecast is a simple http api request away.
    but I am hopeful that lower absorb voltage with longer absorb time will have much the same beneficial effect.

    What do you think of using EQ?

    BoB: "I still believe it is better to overcharge and watch the electrolyte level than to undercharge.... That is, to err on the side of overcharging... If you have only those 2 choices."

    Isnt that at odds with the premise of this thread? Because of positive plate grid erosion, that lead acid is better operated primarily in the mid zone, with regular but less frequent absorbs?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    zoneblue wrote: »
    Around here they say (for FLA anyway) to increase the voltages by 0.1V each year of the batterys age. At year 10 that would make absorb and float 1.0V higher. Its a way to overcome the growing internal resistance.
    The problem with internal resistance is that during discharge there is too much voltage sag. Changing the charge parameters will not affect that.
    zoneblue wrote: »
    BoB: "I still believe it is better to overcharge and watch the electrolyte level than to undercharge.... That is, to err on the side of overcharging... If you have only those 2 choices."
    Isnt that at odds with the premise of this thread? Because of positive plate grid erosion, that lead acid is better operated primarily in the mid zone, with regular but less frequent absorbs?
    boB qualified his comment with: "If you have only those 2 choices". We have more than those two choices... we can undercharge for a while, as long as we periodically do a full charge. That is what some of the european chargers do.
    zoneblue wrote: »
    What do you think of using EQ?
    Do you mean using EQ as a method of doing the periodic full charge? I suppose that might work. I've never used automatic EQ, and I seem to remember some discussion here about how some controllers, when they do automatic EQ, do not do a complete absorb first. Some controllers do not go into float after EQ. I plan to stick with manual EQ.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PhotowhitPhotowhit Solar Expert Posts: 4,913 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    vtmaps wrote: »
    Do you mean using EQ as a method of doing the periodic full charge? I suppose that might work. I've never used automatic EQ, and I seem to remember some discussion here about how some controllers, when they do automatic EQ, do not do a complete absorb first. Some controllers do not go into float after EQ. I plan to stick with manual EQ.

    Some/most batteries need an equalizing charge, of flooded lead acid batteries, only Trojan batteries do not recommend a regular Equalizing charge(that I am aware of). Large forklift batteries should be equalized at least monthly as maintenance. There is also corrective equalizing which done to correct battery imbalances, and should be monitored. I've been quite happy to let my charge controller do maintenance equalizing every 30 days.
    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
  • RybrenRybren Solar Expert Posts: 348
    Re: What is the optimal SOC range for cycling lead acid batteries?

    I recently received the following from US Batteries. They recommend monthly EQs...

    'Corona, CA -

    Recharging deep-cycle batteries with a charger using a constant voltage or a fixed charge algorithm can, over time, lead to a condition called stratification. Stratification occurs when the acid in the electrolyte separates from the water and settles to the bottom of the battery causing damage to the bottom area of the battery plates.
    To prevent stratification, it's important to regularly perform an equalizing procedure to your batteries. Equalizing adds an extended charge at the end of the normal charging process necessary to promote gassing of the electrolyte in order to "re-mix" the acid and water.
    The Equalizing Process
    The method used to properly equalize batteries is as easy as using a high-quality battery charger that features an automatic equalizing mode, or has the capability to extend or restart the charging process as needed. Follow these procedures to properly equalize charge your batteries.
    1. Make sure the battery is a flooded Lead-Acid type.
    2. All electrical loads to the battery must be removed.
    3. Connect your charger and charge the batteries until the charger terminates a normal charge cycle.

    a.) If the charger is equipped with an automatic equalizing mode, make sure the charger is connected and powered up long enough to complete equalization.

    b.) If the charger is not equipped with an automatic equalization mode, assure the charger completes a full, automatic charge, and then restart the charger by disconnecting AC power and reconnecting. The charger should restart and extend the charge time by 1-3 hours.

    4. Correct equalizing will cause gassing and bubbling of the electrolyte.
    5. Take specific gravity readings every hour.
    6. You will know that the equalization process is complete when the specific gravity values no longer increase during the gassing stage. If the charger terminates the charge automatically, before the hourly specific gravity readings are constant, restart the charger and continue the process until specific gravity readings are constant.

    7. Make sure to replace any water lost during the process.

    Equalizing your deep-cycle batteries is a great way to extend battery life and lower operational costs over time. It will also help to remove a buildup of lead sulfate crystals on the battery's plates, a condition called sulfation. This condition lowers the battery's ability to take a full-charge and diminishes its full power. Equalizing is just one of several procedures you should be adding to your maintenance schedule every time you service the batteries. This regular service, including watering, should be performed at least once a month, or more frequently during periods of heavy use. For more information, contact U.S. Battery Manufacturing, 1675 Sampson Ave. Corona, CA 92879. (800) 695-0945. Visit http://www.usbattery.com.'
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    What i was suggesting, as a way to prevent the bank reaching 100% each day, is to reduce the absorb voltage to the float voltage, then set the eq voltage to the absoorb voltage, and set it to run every 7 days. As a way to prevent daily absorbs on banks with high SOC. The long pm floats will probably still bring the SOC up to 100% in many cases, but lowering the float voltage would combat that.

    This is of interest:
    "Disadvantages of the traditional 3-step charge curve:
    • During the bulk phase the current is kept at a constant and often high level, even after the gassing voltage (14,34 V
    for a 12 V battery) has been exceeded. This can lead to excessive gas pressure in the battery. Some gas will escape
    trough the safety valves, reducing service life.

    • Thereafter the absorption voltage is applied during a fixed period of time, irrespective of how deep the battery has
    been discharged previously. A full absorption period after a shallow discharge will overcharge the battery, again
    reducing service life. (a. o. due to accelerated corrosion of the positive plates)

    • Research has shown that battery life can be increased by decreasing float voltage to an even lower level when the
    battery is not in use.

    http://www.victronenergy.com/upload/documents/Datasheet%20-%20GEL%20and%20AGM%20Batteries%20-%20rev%2007%20-%20EN.pdf
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    zoneblue wrote: »
    • Thereafter the absorption voltage is applied during a fixed period of time, irrespective of how deep the battery has
    been discharged previously.

    My XW-MPPT60's don't do that. If our batteries go thru a normal absorb and get to float - then my wife turns on something big and makes the voltage drop to the Recharge Volts, the MPPT60's will take the battery back up to absorb after the load is off. But they will absorb for only a very short time before returning to float.
    --
    Chris
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    ChrisOlson wrote: »
    My XW-MPPT60's don't do that. If our batteries go thru a normal absorb and get to float - then my wife turns on something big and makes the voltage drop to the Recharge Volts, the MPPT60's will take the battery back up to absorb after the load is off. But they will absorb for only a very short time before returning to float.
    --
    Chris

    Since (temperature compensation aside) the Absorb stage will always use the same voltage, the timing of that Absorb stage will either be calculated by the CC in advance based on a fixed time, a time dependent on the length of the Bulk stage, or some combination of the two.
    For the Absorb to be cut short based on the SOC of the battery, it is necessary to have a CC which terminates Absorb when the battery current drops below a set value. In some CCs with this feature, the End Amps setting is derived from the battery bank size (in AH) that you entered, in others it is a separate setting. In either case, if the CC supports it, it usually needs to be specifically enabled before it will be used.
    SMA SB 3000, old BP panels.
  • PhotowhitPhotowhit Solar Expert Posts: 4,913 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    I think you could do what you want with the MidNite classic, setting end amps to be much higher than the 2%(?) and reducing the Absorb voltage.
    ... but I would worry about day time loads leaving the CC in absorb all day.

    So I'd wait until MidNite has their battery module up and running. I suspect MidNite will get to the point of control you want but it may be a few years yet.
    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
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    inetdog wrote: »
    In some CCs with this feature, the End Amps setting is derived from the battery bank size (in AH) that you entered, in others it is a separate setting. In either case, if the CC supports it, it usually needs to be specifically enabled before it will be used.

    In the XW Power System it's set by entering the amp-hours of the battery. The XW System knows what the net amps is to or from the battery, regardless of loads or if the generator is running, and/or input from multiple MPPT's. The whole works communicates and coordinates charge stage over Xanbus, with the controllers telling the XW inverter how much they're putting out, the inverter telling the system how much it's using for loads and how much it's getting in from the generator and sending to the battery (if the generator is running).

    Someplace in the system (I think in the XW's main operating system) it adds and subtracts all this up and comes up with DC power IN, DC Power OUT to loads, and DC power to or from the battery. And it's pretty darn accurate - I see +/-7% at lower amps below 20 and about +/-3% at 100 amps (measured with my Sun tester and comparing to the Net Battery Amps reading on the SCP or ComBox).

    So it exits absorb when the net current to the battery drops below 2% of C for more than one minute.
    --
    Chris
  • westbranchwestbranch Solar Expert Posts: 5,141 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    ZB, give this on VRLA publication a read http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

    As Fox Mulder said 'the truth is out there....somewhere...'

    My read/thoughts are that AGM venting is to be avoided at all times if possible, otherwise you need to replace the H2O gasses in a liquid form.. see posts by Dapdan on AGM recovery.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 29,246 admin
    Re: What is the optimal SOC range for cycling lead acid batteries?

    Here is the DapDan thread that WestBranch referenced (GNB batteries):

    Low rest voltage on GNB absolyte IIP cells

    Sulfated Lifeline Concorde AGM Batteries

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inthejungleinthejungle Solar Expert Posts: 91 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    I have been reading and listening to the discussion and wanted to ask a question.

    I am living in a pretty remote location on the equator in W. Africa, 6 months of sun and 6 months of heavy rain, 300 inches total. Good news is that I have always been able to get power to the batteries.

    My system is simple, 2 s-430's from Surrette 350AH CAP, all of my power usage is 12vdc, I have created a shelf with cigarette adapters and USB ports. I have two items that are heavy hitters, my 12v sundanzer freezer and my shur flo 2088 pump that runs 15 minutes -30 minutes a day.


    Currently I am charging my system with a Outback FM80, three panels on the roof, 245 watts in series.


    I have the FM80 set to absorbe at 14.7 for 4 hours and float at 13.1

    The deepest discharge of the system was about 100AH,

    I have a couple of questions:

    1- How does one put voltage into a level of discharge, i.e. 50% equal 11.6??

    2- If the theory holds that batteries like to run at about 70-80% discharged cycle I am currently hitting about 20% used up every day and getting filled back every day.

    What should I do? Should I not allow the system to charge but every other day? I would like to get this figured out as the dry season is coming and we will have lots of sun and lots of power, that means each day we will be hitting 100% with maybe not be that great for the longevity of the battery.

    Anyone got any suggestions?

    Do I lower the absorb to 13.9 or 14 and only actually absorb through an equalization setting once a week or what would be the recommendation?

    Thanks
    In Niger, trying to keep a LG FMA 102NAMA fridge(This has the inverter compressor) backed up with solar using a Victron Multi-Plus Inverter/Charger Compact 12v 1600w with a 70a charger built in.I want to back it up for 4-8 hours. I am also running a few O2 cool fans and a few Thin Lite LED's of my batteries for when the grid is down so my kids can sleep.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    I have a couple of questions:

    1- How does one put voltage into a level of discharge, i.e. 50% equal 11.6??

    Voltage is not a reliable gauge of battery SOC while the battery is in use (charging or discharging). If you leave the battery to rest for a few hours, 50% SOC is about 12.0 volts.
    2- If the theory holds that batteries like to run at about 70-80% discharged cycle I am currently hitting about 20% used up every day and getting filled back every day.

    What should I do? Should I not allow the system to charge but every other day? I would like to get this figured out as the dry season is coming and we will have lots of sun and lots of power, that means each day we will be hitting 100% with maybe not be that great for the longevity of the battery.

    Its just a theory. The battery is much more efficient when being bulk charged than during absorb charge. That matters a lot if you are using a generator. Doesn't matter so much if you have adequate solar resources to do the absorb.

    I don't know of much good data to prove or disprove the theory. My opinion is that it doesn't hurt to not reach 100% every day, and it may or may not contribute to longer battery life.

    One thing going for the "100% every day" approach is prevention of stratification buildup. Stratification causes the upper part of the plates to do more work than the lower parts, and the uneven wear may cause decreased capacity and or shortened life of the battery.

    I think that if you have a battery electrolyte recirculation system, the "not 100% every day" approach is probably better. In the absence of electrolyte recirculation, I'm not so sure.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    What should I do? Should I not allow the system to charge but every other day?

    Assuming you have enough charging capacity to fully recharge if the battery does get down to 50%, about all you can do is add some opportunity load to use up the excess.

    It seems like absorbing for 4 hours every day is a little excessive for batteries that only get discharged to 80% SOC every day. I hate timer-based chargers because they tend to do that. Is there any way that you can calculate your load amps, add in 2% of the amp-hour capacity, and use that for the ending amps so the charger exits absorb when the net current to the battery drops to 14 amps?

    You should have 30-40 charging amps available on the average day (roughly). If you exit absorb at 14 amps to the battery, the hydrometer shows that the SG is normal for full charge, and it cuts down from that 4 hour absorb time, that alone will save your batteries from a lot of excessive wear and tear being held at absorb voltage for longer than they need.

    Surrettes don't mind higher voltages either. Once you get the end amps set properly, you could try bumping your absorb to 15.0 volts and let it exit absorb based on end amps. Might be able to cut your absorb time and peak battery temperature even further. I use 2.58 VPC for absorb with our MPPT60's and they exit absorb at 2% C. When our battery has not received full charge for a week or more, they will absorb for 3+ hours. If the battery gets fully charged two days in a row, the absorb only lasts for about an hour on the second day. The MPPT60's are taking much better care of our batteries than our previous timer-based chargers were.
    --
    Chris
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    I have a couple of questions:

    1- How does one put voltage into a level of discharge, i.e. 50% equal 11.6??

    In an operating system Voltage is a poor indicator of SOC. For it to be reasonably accurate the batteries have to be at rest: no current in or out for several hours. At that point 12 Volts is approximately 50% SOC. If you try to judge this under load it is going to depend on how heavy the load is. One thing you can do is drain the batteries to a 50% at rest Voltage (12V), then remove the load and see how much the Voltage comes up. The difference is roughly the most you want to go below 12V with your system under load. It is not perfect.
    2- If the theory holds that batteries like to run at about 70-80% discharged cycle I am currently hitting about 20% used up every day and getting filled back every day.

    The really important thing is to not be below 75% SOC for more than a couple of days. As such you can 'allocate' 25% off the top as usage for however many days you go without sun. If it's more than 3 days and still no sun you need some charging from some source.

    There is nothing wrong with hitting 100% SOC daily as far as the batteries are concerned. Absorb Voltage should be left at the recommended level for the batteries. You can turn the Float level down a bit. And do not use a charge controller with a fixed Absorb time. Fortunately the FM80 uses a clock, so Absorb will be no longer than Bulk. If it takes little time to Bulk it will hold Absorb for a that same short time; no stress on the battery.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?
    The really important thing is to not be below 75% SOC for more than a couple of days.

    Surrette says you can go up to 30 days and 50-80% is optimal for daily cycling. Steve Higgins from Surrette weighed in on this from another thread

    The optimum for most lead acid batteries is 50-80% cycling. As long as the flooded cells see a full 100% state at least once per month.
    http://forum.solar-electric.com/showthread.php?19947-I-don-t-really-like-my-Surrettes/page5&highlight=steve+higgins

    And if you read the rest of Steve's comments, he also says most people are using too low of voltages for their Surrette batteries.
    --
    Chris
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    Fortunately not everyone uses Surrette batteries.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    Batteries , ain't it fun ?? I just had a customer tell me he ordered a set of Roll's S-1725's for $3,200. He was upset that he only got 6 years out of a set of $1,100 GC-2's. I can't wait to see how this one works out, he doesn't know what end of a battery you put the water in.
  • inthejungleinthejungle Solar Expert Posts: 91 ✭✭
    Re: What is the optimal SOC range for cycling lead acid batteries?

    THANK YOU THANK YOU



    to everyone for your thoughts. Let me give you a bit of background and then ask another question.


    The reason that I set the absorb for about 4 hours, and 14.7 was for several reasons.

    We have had many friends of ours using Surrette's here and after a few years they are not holding a charge very we'll. After speaking to steve at Rolls his thoughts and mine where that the batteries were not receiving an adequate charge and in turn getting heavy sulfating on the plates.

    After several weeks of adjust settings and such on our system, at the end of the day the SG's were only 1.260. I thought well maybe I have stumbled on the problem; the charge controller that we use here OB are not properly charging the batteries and the Rolls want more charge.

    Steve at rolls had suggested that I should really try to get this number up to 1.275. I had a very difficult time getting the Outback to get the proper charge to get the SG's up. Yet when I called back to Rolls and spoke to someone else they suggested that as our ambient temp is 80F then 1.260 is a full charge. Does anyone know how to calculate the proper SG's based on ambient temps?

    I was able to reach this 1.260 by adjusting the absorb time. I really don't want to have these batteries around for some time.

    After reading much of what everyone suggested, I was left with a couple of questions:

    "It seems like absorbing for 4 hours every day is a little excessive for batteries that only get discharged to 80% SOC every day. I hate timer-based chargers because they tend to do that. Is there any way that you can calculate your load amps, add in 2% of the amp-hour capacity, and use that for the ending amps so the charger exits absorb when the net current to the battery drops to 14 amps?


    if 4 hours is excessive, then by your math I would calculate the end amps like so

    Load amps are that which I am using,

    freezer run 5a with about 7-8 hours a day of run time
    If the water pumps comes on, maybe every two days it does that that changes this number to 11, what to do with that?

    percentage of battery AH capacity would be .02*350=7

    This would mean that 12 would be the number

    Because there are a few items that get added each day maybe 14 would be correct. So your suggestion is to keep the 14.7 absorb, add an end amps time of 14 amps. Let it run for a few weeks and check SG's see how things are looking. If things look good then bump up the voltage to 15? Float voltage would be set to 13.1 and that would be correct?

    This would reduce the overcharging and extend the life of the batteries. I can use more current, but at this point we have more than we need and have at times just turned on all the lights in the house, but at 2 amps for the whole house it is not a large load!


    The other thought I had was what if I kept everything set as it, 14.7 for 4 hours for absorb and 13.1, every other day I just shut of the PV array and just charge batteries every other day?


    Thanks and Thoughts

    Ben
    In Niger, trying to keep a LG FMA 102NAMA fridge(This has the inverter compressor) backed up with solar using a Victron Multi-Plus Inverter/Charger Compact 12v 1600w with a 70a charger built in.I want to back it up for 4-8 hours. I am also running a few O2 cool fans and a few Thin Lite LED's of my batteries for when the grid is down so my kids can sleep.
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