how to decipher data on GNB 3-90A25?

westbranch · September 2007

I have been looking for data on the 50% discharge for my GNB battery.

found the basic info so far... a discharge table ... but can not decipher it.
Here is the link

http://www.staticpower.com/pdf/26.10.pdf

the rating of 'final volts' puzzles me 1.75 v / 2v cell = 10.5 v total and 1.94v = 11.64 v total for a 12 v battery. Would these values not 'kill' a wet cell battery? and are they ok for a gelcell battery?

Eric

crewzer · September 2007

Re: how to decipher data on GNB 3-90A25?

Here's a link to a document containg a Voc vs SOC chart for GNB Absolyte IIP batteries. Note that these VRLA batteries are AGM and no gel.

http://industrialenergy.exide.com/exidepdfs/Absolyte_62_61.pdf

The rated AH capacity of a 12 V battery is based upon it's voltage dropping to 10.5 V under load. That spec is equivalent to 1.75 V per cell (Vpc).

HTH,
Jim / crewzer

niel · September 2007

Re: how to decipher data on GNB 3-90A25?

westbranch,
even among their own batteries the voltages varies slightly for 100% dod and i understand you want the voltage specs for various dod percentages points esprecially the 50% point. you should contact them for any specifics on any particular battery. you should also suggest that if they have that info that they should publish these percentages at their respective voltages and place them online for access to their customers citing that many rely on these voltages as direct indicators of the soc and inversely the dod. make sure you remember that it is the at rest voltage you seek and that this is conveyed to them.

rplarry · September 2007

Re: how to decipher data on GNB 3-90A25?

Eric
I used to have the GNB batteries, they are great batteries. I have since acquired new different batteries, but when I sold my GNBs they were 9 years old and showed no signs of slowing down.
The chart you are referring to is just a discharge rate table and means that if you start with a fully charged battery you can draw X amount of amps for X hours before the cell voltage will drop to 1.75 vpc. My bank was 12v and I set my charge controller to 14.4v absorb for 2 hours and then let them float 13.4v and never had any problems. Also my charge contorller is temp compensated. Hope this helps.
Good luck with yours,
Larry

crewzer · September 2007

Re: how to decipher data on GNB 3-90A25?

Eric,

Did you get the info you needed from the link I posted, or are you looking for something else?

Regards,
Jim/crewzer

westbranch · September 2007

Re: how to decipher data on GNB 3-90A25?

Jim, I have been away for the weekend and am about to go into "absorb mode".. Will get back to you. I think I will attempt a contact with Exide re Niels suggestion re data.

Eric

westbranch · October 2007

Re: how to decipher data on GNB 3-90A25?

Well gents, I finally have some information to share, just dont know if it moves us down the road much... here we go..

""The 50% DOD is 2.01 volts per cell at the 24 hour rate of discharge measured under load.""

""A load of 51 amps at 12 volts(nominal) will bring your battery down to 10.50 volts after 24 hours""

The local rep does not have the 10 to 40% DoD values nor the approx time in which a 'new' battery would achive the 50% mark. Have written to Exide in the US to see if they can deliver...

Quote from my emails

"" Next, using section 26.10 of the Absolyte manual, I find that there are a variety of ' end voltages ' / cell, (1.75 v to 1.94 v.) all of which are well below the 50 % DoD value (2.01 v) you indicated , Would not achievement of ANY of these end voltages produce a 'dead battery' ie not rechargeable???

Answer
No. These are typical end voltages for applications that do not discharge the battery on a regular basis (the battery may only be discharged 2 or 3 times a year) and when the battery is discharged the charger is large enough to bring the battery back to 100%
state of charge in a short period of time. If you did this you could not recharge the battery properly.""

New Question: As this is a 1055 amphr battery what type / size / brand of charger is recommended for this size unit if taken to 50% DoD ? I estimate my 15 amp charger would take about 35 hrs to recharge ( [1055 / 2] / 15 )... does this seem a bit long?

Alternatively, using PV to charge, it would need ??? amps to adequately recharge?? I guess what I am looking for is a recommended target recharge rate and time that takes into account the present 'light ' use the battery gets now and the extended non-use periods. (2 panels at 7 amps, Mppt CC)

PS just digging into the graphs at the bottom of the link I posted at the start of this thread pages 16 and 18 for the 90A series especially the last one seems to be quite useful and may allow extrapolation to the 10 , 20 , 30 and 40 % values, will see.

TTFN
Eric

crewzer · October 2007

Re: how to decipher data on GNB 3-90A25?

Eric,

I believe I can decipher all of of this data and translate it into something useful. I just need a bit more info about your battery configuration.

I read the 3-90A25 to be a 6 V battery consisting of three 2 V cells connected in series. I suspect you're not running a 6 V system. Do you have two, four, or eight of these batteries connected in series to make 12 V, 24 V, or 48 V, and do you have any series strings connected in parallel?

More later,
Jim / crewzer

westbranch · October 2007

Re: how to decipher data on GNB 3-90A25?

Jim, I have a 12 v arrangement, 2 of the 6 v units in series to make one 12 v 'battery'.

Eric

crewzer · October 2007

Re: how to decipher data on GNB 3-90A25?

Eric,

I’d consider your 2 x (3-90A25) battery bank to be rated at 12 V x 1,224 Ah. The 1,224 Ah spec is derived from the ability of the bank to sustain a 51 A discharge current for 24 hours until the battery voltage reaches 10.5 V, or 1.75 V per cell. 51 A x 24 hours = 1,224 Ah.

I suspect that some of numbers now make sense to you. A battery’s capacity is typically rated against a 20 hour discharge period. 24 hours is close enough.

A chart in the link I provided earlier indicates that the Voc (no load) for each cell at 50% SOC is 2.075 V. For your 12 V battery, that would be 2.075 V x 6 = 12.45 V. GNB’s message to you says that a battery that measures 2.01 Vpc (12.06 V for your 12 V battery) while supplying 51 A (the 24 hour rate) is 50% discharged. A battery under load will register a lower voltage than one at rest (Voc).

Charge current into a healthy AGM battery can be anywhere from 3% to 30% of 20 hr capacity. In your battery’s case, that would be anywhere from 37 A to 370 A. As a practical matter, something in the 5% to 10% range (~60 A to 120 A) should work well.

AGM battery coulombic efficiency (Ah out/Ah in) is ~98% or so. If you need to replace ~612 Ah (50% DOD), then you’ll need to supply ~625 Ah. Allowing for the fact that absorption stage charging is current limited, I estimate it would take a 60 A charger ~12 hours or so to recharge the 1,224 Ah battery bank from 50% SOC.

Is this the type of info you were looking for?

HTH,
Jim / crewzer

westbranch · October 2007

Re: how to decipher data on GNB 3-90A25?

Thanks Jim, more than I needed (wanted) to know. This may require a total rethink on my part as to additional equipment needed and configuration... I am going into 'absorb mode' to let this info digest fully. I now see where the PV input = 3%, 5% and 10% values come from and, now, what they are for my battery. I knew I would have to increase the PV input but ~40 amps (min.) is a lot more than I expected. I hve been waiting for boB to announce the release of the 'Classic' (time ticks on)

As I have not reached 50% DoD and do not expect to with the loads I apply at this time, plus the PV recharge capability I presently have, I am trying to determine the state (health) of my setup, ie is the load I apply reflected by the battery voltage while discharging or after rest? I have the observed values but unable to compare them to anything.

I have been mulling over the shape of the line between 100 and 50% SOC and the graphs in the document... I am thinking that it would be a curve rather than linear (straight)? comments?

Eric

westbranch · October 2007

Re: how to decipher data on GNB 3-90A25?

Jim, more FYI re alignment of the cells as to how it can affect optimal SoC.

"" Because the batteries are the absorbed glass mat type (AGM) which is one of
the two types of sealed lead acid batteries (the other is gel) it requires
that the liquid acid be spread evenly over the plates by almost saturating
the spun glass material (feels like cotton) which is wrapped around the
plates. If the plate is more than 14 inches high the spun glass will not
wick the acid optimally because of gravity so we recommend the horizontal
position. ""

from the data tables/Unit (6 V) Height = 23.5 ", width = 8.6 " length = 33.5 "

so... the top 1/3 of the cells are not performing to max as I have the units in a vertical position. will have to realign

how to decipher data on GNB 3-90A25?

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