determine aH capacity

elesaverelesaver Solar Expert Posts: 185 ✭✭
Is there such a thing as an easy way to check the aH capacity of a battery?  I've looked online and it doesn't seem practical to time the battery discharge.  Plus, I wouldn't want to discharge too far anyway.

Here's the deal:  I bought 2 new 12V forklift batteries and have them in series for 24V.  I bought these with the understanding they were 938aH each.  When the batteries arrived, the label said 1365 aH each.  I called the company and at first they tried to say I wasn't reading the label right.  Can you imagine?!  I had to send a picture of the label to them.  Anyway, after they saw the picture of the label, they agreed to send corrected labels which I received today.  These labels say 535 aH each!  Totally incorrect...or else they need to issue a refund.  But, I digress.

I will be calling them tomorrow and through all of this, I still trust the guy I've been working with there.  He's very knowledgeable.  BUT, being the skeptic I am, I'd like to check this myself if it is at all possible.  Is there a way to do this without a long discharge and/or expensive equipment that I don't have?  Thanks for the help.
1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    elesaver said:
    Is there such a thing as an easy way to check the aH capacity of a battery?  I've looked online and it doesn't seem practical to time the battery discharge.  Plus, I wouldn't want to discharge too far anyway.
    <snip>
     Is there a way to do this without a long discharge and/or expensive equipment that I don't have?  Thanks for the help.
    A capacity test will require a deep discharge.  It can kill a battery.  In the forklift industry, a battery that is at 80% capacity is replaced.  If the capacity test kills the battery, then it was time to replace the battery anyway. 

    A used forklift battery with 80% capacity still has life and may serve an off-grid system for a few more years.   The capacity test that matters is your loads.  Are your batteries serving your needs?  If not, then it's time to replace them.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • elesaverelesaver Solar Expert Posts: 185 ✭✭
    I understand what you've said vtMaps, but these are NEW batteries.  I just got them in September 2015.  If I don't have the correct aH programmed into the CC, then I could be drawing out more than is good for the batteries so I will be killing them.  If I'm not drawing out enough, then that's not good either.  But, it sounds as though there is no practical way to know.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    edited February 2016 #4
    Some of your / their confusion is that forklift batteries are capacity rated at a 6 hr rate and in RE we use the 20 hr rate. So some of the stuff you read here does not apply the same as far as AH. At 80%  your going to have a huge voltage sag, because 80% is 21-22 volts.

    http://gbindustrialbattery.com/Battery_Options/AH_Ratings.html

  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    elesaver said:
    I understand what you've said vtMaps, but these are NEW batteries.  I just got them in September 2015.  If I don't have the correct aH programmed into the CC, then I could be drawing out more than is good for the batteries so I will be killing them.  If I'm not drawing out enough, then that's not good either.  But, it sounds as though there is no practical way to know.
    A load test is definitive, but you can still use resting voltage and SG measurements to get a good estimate.  Start with a fully charged battery and draw off 200 amphours.  What was the resting voltage and SG before and after the discharge? 

    There are lots of generic charts that relate SG and resting voltage to SOC, but it would be best to get that info for your batteries from the manufacturer.

    Example:  you draw off 200 ah and the SG and resting voltage indicate that SOC is 60%.  Therefore your battery's capacity is 500 ah.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PhotowhitPhotowhit Solar Expert Posts: 5,657 ✭✭✭✭✭
    edited February 2016 #6
    Some of your / their confusion is that forklift batteries are capacity rated at a 6 hr rate and in RE we use the 20 hr rate. So some of the stuff you read here does not apply the same as far as AH. At 80%  your going to have a huge voltage sag, because 80% is 21-22 volts.

    http://gbindustrialbattery.com/Battery_Options/AH_Ratings.html


    Please note that the published 20 hour/Ah rating from GB Industrial is not correct! We have had a discussion about that here somewhere (I have one!) The multiplier should be  closer to 1.35 x the 6 hour rate. Their published rates. I will try to hunt down the thread for you when I get a chance.

    http://gbindustrialbattery.com/Forklift_Battery_Sizes_and_Specifications_Zone15.html

    Ask them for or look at your sheet for a break down of the battery. You should get something like 6-100-13 which is 6 cells, 100 amps per positive plate(6hr rate), and 13 plates (of which 6 are positive) for 600 Ah at 6hr rate or @810 20hr rate.

    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.
  • mike95490mike95490 Solar Expert Posts: 9,362 ✭✭✭✭✭
    the frequency/amount of water you have to add, can be used as an indicator if you are charging fully.  If you only have to add water every 3 months, you are undercharging.  If you have to add weekly, you are overcharging
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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