Increase the capacity on Lead Acid batteries

kjetilkjetil Solar Expert Posts: 31
Hi, I have a few Lead Acid 55Ah 12V batteries holding it's voltage at 12.7V, but I've measured the capacity to about 20Ah. Is there a way to increase the capacity on these batteries?

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    What is the SG of the cells? If it is out of balance you might need to do an EQ charge.
     
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  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    kjetil wrote: »
    Hi, I have a few Lead Acid 55Ah 12V batteries holding it's voltage at 12.7V, but I've measured the capacity to about 20Ah. Is there a way to increase the capacity on these batteries?

    Not likely, If they are flooded batteries an equalizing charge might increase the capacity, but I suspect that the 55 ah 12v it's an AGM battery?

    I might ask how you tested the capacity? The rated capacity is for a discharge over 20 hours, if you put a higher load than 1/20th of the rated capacity or 5.5 amps, and it failed in 10 hours, your rating of 20 ahs might be low...

    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.
  • muliamulia Solar Expert Posts: 62 ✭✭✭✭
    How old are they?

    According to battery manufacture, new battery won't perform at their full capacity until few (~50 cycles) and old battery also will decrease in capacity.
  • kjetilkjetil Solar Expert Posts: 31
    westbranch wrote: »
    What is the SG of the cells? If it is out of balance you might need to do an EQ charge.

    What is SG? How do I do an EQ charge? They are flooded batteries.

    Resting voltage is 12.7
    The discharge rate I used was 1A with my Imax B6 Multifunction Charger. The display showed mostly 0.5A during discharge.
    I stopped discharging at about 10.8V. After sitting a few hours the rest voltage was 12.0V exactly.

    The discharge test took about two days. I don't know the battery age.
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    SG is specific gravity and is the best way to check a batteries state of charge(SOC). You can find most common SG values in the battery FAQ's - NEVER MIND THE BATTERY FAQ"S APPEAR TO HAVE BEEN STRIPPED OF BATTERY SPECIFIC GRAVITY INFORMATION!!!!!!!!!!

    Specific gravity of the Electrolyte is the best way to check a batteries State of Charge. The use of a hydrometer which draws a sample of the electrolyte and gives a visual reading of the SG of the battery, You can find Hydrometers at auto parts stores for as little as $5. Most batteries will have a SG at full charge of 1.265 - 1.29. Here is a link that gives rough SOC % for SG readings. When fully charged you are looking for reading that are very close across all the cells of the battery.

    Equalizing is a controller over charging of the battery, if the battery is fully charged it won't accept much current. by presenting a voltage that is about 10% above the normal charging voltage, the battery will out gas/boil the electrolyte this helps mix the electrolyte from top to bottom and will aid in recombining or actually by action removing sulfation on the plate surface. Here is a link to the same site about equalizing, this is a European site and states equalizing every 6 months. This might be due to the different alloys used in the European community, most battery manufacturers recommend an equalizing charge every 30 days for flooded deep cycle lead acid batteries in the US.
    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.
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Just for fun, here is a youtube video from Trojan about "Equalization is Key to Extending Battery Life and Performance"

    This is 'fun' since Trojan specifically states only to equalize if the cells are out of balance in their product information sheets!
    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.
  • kjetilkjetil Solar Expert Posts: 31
    Photowhit wrote: »
    Specific gravity of the Electrolyte is the best way to check a batteries State of Charge. The use of a hydrometer which draws a sample of the electrolyte and gives a visual reading of the SG of the battery, You can find Hydrometers at auto parts stores for as little as $5. Most batteries will have a SG at full charge of 1.265 - 1.29. Here is a link that gives rough SOC % for SG readings. When fully charged you are looking for reading that are very close across all the cells of the battery.


    Thank you Photowhit. I bought a hydrometer as you said. One of the batteries have filler caps and I measured SG between 1.25 and 1.26 in all the cells with my hydrometer. I also did some equalizing, 4 hours with 15.2V from a power supply. After equalizing I did a capacity test with about 2.75A load down to 10.8V. I measured 43Ah on that battery. After sitting a few hours the resting voltage was 11.9V. :)

    Two other batteries is maintenance free and doesn't have filler caps. I did some equalizing, 4 hours with 15.2V here as well. One of them got worse and couldn't holdt the 12.7 resting voltage any more. It suddenly was 10.7V at rest without any load. The other batteri I did a capacity test and I only got 11Ah with about 2.75A load down to 10.5V. After sitting a few hours the resting voltage was 12.43V. Is it possible to increase the capacity on this?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    kjetil wrote: »
    Two other batteries is maintenance free and doesn't have filler caps. I did some equalizing, 4 hours with 15.2V here as well. One of them got worse and couldn't hold the 12.7 resting voltage any more. It suddenly was 10.7V at rest without any load. The other battery I did a capacity test and I only got 11Ah with about 2.75A load down to 10.5V. After sitting a few hours the resting voltage was 12.43V. Is it possible to increase the capacity on this?

    Maintenance Free batteries (as opposed to AGM/GEL or other sealed batteries) generally have caps you can remove... You may have to pop off a cover "plate" to get to the real caps (or the flat cover plate also have integrated caps under it).

    You can then get to the cells, check electrolyte levels, and specific gravity. If the electrolyte levels are low (exposed plates for a period of time), then the batteries are no good.

    Try cycling them (don't take them dead, but down to 50% to 20% state of charge maximum level of discharge. Taking them "dead" (10.5 volts resting), and the Lead Acid batteries generally will not survive.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kjetilkjetil Solar Expert Posts: 31
    BB. wrote: »

    Maintenance Free batteries (as opposed to AGM/GEL or other sealed batteries) generally have caps you can remove... You may have to pop off a cover "plate" to get to the real caps (or the flat cover plate also have integrated caps under it).

    -Bill

    How can I get to the caps on this battery?

    Attachment not found.
  • kjetilkjetil Solar Expert Posts: 31
    I did a capacity test on one of the sealed 55Ah battery as shown in the graph. I got 14Ah (168Wh) from the battery with a 3.1A load down to 10.9V. After sitting a few hours the resting voltage was 12.4V. The test was taking four and a half hour.

    Attachment not found.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    I don't know... If you have a few batteries and one is "near dead"--Just try prying the top off. Some are snap on, others are thermally fused (heat used to melt plastic plate on).

    Does not hurt to try on an old battery (standard warnings: wear something over your eyes, old clothing, have water near by to flush off skin/face, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kjetilkjetil Solar Expert Posts: 31
    I cycled the other sealed lead acid battery as you said, and measured the capacity. After discharging it raises quickly in voltage, what does that say about the battery? The resting voltage was 12.45V

    The first test with this battery I got 11Ah, but this time I only got 9.5Ah...

    Attachment not found.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    In general, try not to go much below 11.5 volts in normal operation (under load)--That is a good place to stop (very roughly, ~50% level of discharge).

    In your case, it looks like you may be discharging at C6 hour rate (~3 hours to 50% discharge)--That is a pretty heavy load for most lead acid batteries--Although there are AGM/GEL type batteries design for very low internal resistance for use in computer UPS systems and such (run at high power for 15 minutes until computer is shut down/backup generator is started).

    In the end--A battery/system needs to perform to your needs. If you need X and the system is only capable of Y--Then either the batteries are going bad, the wrong batteries were chosen, etc.

    Try to be conservative with your system design. One that meets your needs in the first year and does not 3-6 years down the road is frustrating... You either need to replace the batteries too often, or you have a crippled system for years to come that does not do what you need.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kjetilkjetil Solar Expert Posts: 31
    Thank you. I do this only for testing/learning and perhaps getting some use out of my old SLA batteries.
    After discharging it raises quickly in voltage, what does that say about the battery? High internal resistanse?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    In general, we recommend a conservative design at C10 to C20 discharge rates (10 to 20 hour discharge rate)... Running a flooded cell lead acid battery at below C8 discharge rate is pretty much the limit for a "typical" storage battery. You might be able to get C5 to C2.5 discharge rates--If the batteries are fully charged and run for less than an hour to less than a minute at those rates.

    AGMs and GELs can discharge at C1 and one vendor AGM's will discharge at C0.25 rate (yes, take battery dead in 15 minutes). Be aware that many UPS battery systems may only will run a hand full of these high/deep discharge cycles before the batteries need to be replaced.

    What is the load/use of these batteries... If you are using 10 or 20 hour discharge rates--Then test at those rates and see how they perform. Otherwise, they are being over stressed for an application you are not using them in.

    Small AH batteries--I never really had much luck with long life with them. After a few years, most were dead (over discharged, poor recharging practices, cheap charge controller that boil them dry if not unplugged after 24 hours, etc.). It is hard to lay short life at the battery or the surrounding hardware/application.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kjetilkjetil Solar Expert Posts: 31
    Would cycling the battery a few times increase the capacity?
    BB. wrote: »
    In your case, it looks like you may be discharging at C6 hour rate (~3 hours to 50% discharge)--That is a pretty heavy load for most lead acid batteries

    -Bill

    Is that calculated by the original capacity or the capacity I actually get?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Just looking at your chart (~3 hours until the output starts to collapse--Plus the voltage recovery after the load is removed seems to be ~50% state of charge).

    If the current draw was ~3 amps * ~3 hours or so--That would seem to indicate around 2x your "measured" capacity of ~20-28 AH present capacity... If you discharge at a slower rate, I would guess the capacity (AH) will appear to be higher.

    Nothing accurate here--Batteries are not doing too good here and who knows what exactly is going on internally.

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