determine aH capacity

elesaver

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.

vtmaps

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

elesaver

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.

Blackcherry04

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

vtmaps

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

Photowhit

Blackcherry04 said:

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.

mike95490

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