Low rest voltage on GNB absolyte IIP cells

Dapdan

Re: Low rest voltage on GNB absolyte IIP cells

Gentlemen,

I think I have achieved what i set out to do. My 10yr used agm bank (gnb absolyte 100-A19) are now resting at a voltage of 25.91v. They have been off charge and not discharged for the pass 8hrs. When I started off the first resting voltage was 25.20 now 6 month later and 3 sets of water and catalytic caps I have improved their resting voltage and hence their capacity. Where as when I started off most of the cells were between 2.09 and 2.10 most of them are now between 2.15 and 2.17 with most of them over 2.16 (7 of them, 2 of them are at 2.17v). This has been an interest experiment for me and I have another bank that I have begun to do the same thing. This bank is in better shape since most cells are between 2.11 and 2.13 so I expect at least the same results from these.

Cheers...
Damani

Mark S.

Re: Low rest voltage on GNB absolyte IIP cells

How do these Absolyte batteries differ from a 'standard'? AGM battery?

I also read somewhere that AGMs were not to be equalized (I believe it was in the Trace SW4048 manual)?


I plan to check my batteries tomorrow, as one battery is reading in the high 8 volt range.

I have (4) Concorde PVX12255 (12v, 255aH) in a 48 volt configuration (installed May 2002). Combined Amp readings on (2) C40 controllers on a normal sunny day: (23 amps + 27 amps) for a total of 51 amps.

Is this too high? or is the excess sent to the grid? I was never really educated on what levels the charge controllers were to be set at.



My plan:

This evening:
Disconnect PV array from the charge controllers

In the morning:
Power down the inverter's loads
Power down the inverter
Disconnect inverter's AC input from grid
Disconnect main battery cables and jumpers
Clean the battery and cable terminals, although they do not show signs of corrosion
Read and note battery voltages

Q: Can I remove the caps to check water levels in the batteries? ...
... if so, add water as needed

Reconnect battery cables
Power up the inverter
Reconnect inverter's AC input to the grid

Tomorrow night:
Reconnect PV array to charge controllers

Anything else I should know ... or do?

Thanks ...

BB.

Re: Low rest voltage on GNB absolyte IIP cells

Mark S. wrote: »

I also read somewhere that AGMs were not to be equalized (I believe it was in the Trace SW4048 manual)?

True equalization (15-15.5 volts, 5% times 20 AH capacity) for several hours--That, from what I understand, it what will damage an AGM and/or Sealed battery.

My guess, 1/2 the energy goes into heating the battery. The other 1/2 goes into creating Hydrogen and Oxygen gas. All of that gas gets recombined at the catalyst cap...

So, you have the heat building up in the battery (from the inefficient electrolysis) and you have the heat building up in the catalyst caps themselves (recombining hydrogen and oxygen)--all that heat and gasses causes pressure vents to open--loss of gasses, water, and electrolyte. Plus aging the catalyst (sounds like the cat's eventually wear out from recombination).

So--the story was that AGMs should not be equalized...

But, the battery cells still did drift apart in charge--so people found that "light equalization" once or twice a year (essentially a few hours of "high side" of charging voltage range) brought the cells state of charge closer together (equalized specific gravity of electrolyte).

I plan to check my batteries tomorrow, as one battery is reading in the high 8 volt range.

You have a string of 4x 12 volt batteries? Then the one battery is either damaged (shorted cells if 8 volts on charge; or open cells if 8 volts during discharge ).

You could try taking that one battery out of the string and charging/discharging and see what it does. I would guess if it goes high voltage on charging--perhaps adding distilled water and "light equalization" and deep cycling might be worth a try...

But the problem is how to determine the correct amount of electrolyte to the cell--I don't know of any way for us mortals to do that... Add a little and test? Add a little more?

I have (4) Concorde PVX12255 (12v, 255aH) in a 48 volt configuration (installed May 2002). Combined Amp readings on (2) C40 controllers on a normal sunny day: (23 amps + 27 amps) for a total of 51 amps.

Sounds like you have gotten good life from the battery bank so far (nearly 8 years).

51 amps into a 255 AH bank:

• 51/255 = C/5 charging rate (20%)

That would be too high of charge rate for a typical flooded cell battery bank... AGM--as long as the bank is not getting hot--is probably OK. Are you using Remote Battery Temperature Sensors?

If I recall correctly--this is the SW with the GTI interface? The batteries, once they are charged should be held at "float voltage" (relatively low voltage--just high enough to keep the battery charged) and the excess should be sent to the grid (what is your sell voltage which should be near the battery bank's float voltage?).

The batteries will have to accept the surge current (the tracking between output power and battery voltage/sell voltage may not be that fast--several seconds or longer to adjust to changes in sun/shade/charge current and GTI output power).

Is this too high? or is the excess sent to the grid? I was never really educated on what levels the charge controllers were to be set at.

What is the average bank voltage vs what is the float voltage recommended by the battery manufacturer. For long battery life, you want the GTI to pull just enough current from the charge controllers/battery bank to keep the batteries above (resting voltage at 100% state of charge)--You do not want the batteries to sit at 14.4 volts for hours on end (unless they have been discharged and need to be recharged).

My plan:

This evening:
Disconnect PV array from the charge controllers

In the morning:
Power down the inverter's loads
Power down the inverter
Disconnect inverter's AC input from grid
Disconnect main battery cables and jumpers
Clean the battery and cable terminals, although they do not show signs of corrosion
Read and note battery voltages

Check the positive battery posts--is the battery bulged near the positive posts? Does it look like any of the positive posts are being pushed up/out of the battery.

Check the side of the case of the battery--are the sides bulging?

If yes to either of the above questions--you may have "fatal" positive plate corrosion (oxygen from electrolysis collects at the positive plate during "equalization/charging/electrolysis" and the battery is not worth trying to recover.

Q: Can I remove the caps to check water levels in the batteries? ...
... if so, add water as needed

That is the $64 question--how to know how much, if any, water should be added. AGM mats are designed to have air space (acid starved) as part of the design. Too much water is not a good thing either.

Measuring cell impedance (from Dapdan's original posts; with gear none of us probably have) may give an indication of how much water is needed... And big telecom cells--they can measure these parameters on each 2 volt cell... Can anything be done with a small multi-cell AGM battery that does not have exposed inter-cell bus bars?

If you have to add water (cell vented)--one of the reasons may have been caused by catalyst failure--So if you add water and don't replace the catalyst/caps--then you still have not resolved the original problem (catalyst failure).

Can you even get replacement cat caps for your battery set?

My guesses--certainly not an expert here.

-Bill

westbranch

Re: Low rest voltage on GNB absolyte IIP cells

here is a (poor) cut from the Absolyte Manual re EQ
sorry for the run together words it is from a PDF file... tried to get them out , too much time...

12.2FloatCharge-Float Voltages
Following are the float voltage ranges recommended for the Absolyte Battery System. Select any “volts per cell” (VPC) value within the range listed that will result in the series string having an average volts per cell equal t ot hat value.
RECOMMENDED FLOAT RANGE(@77°F)
2.23 to 2.27VPC

NOTE: Recommended float voltages are for 77°F. For other temperatures a compensation factor of.003V/°F(.0055V/°C) per cell is recommended. The minimum voltage is 2.20 VPC, temperature correction does not apply below this voltage. The maximum voltage is 2.35VPC,temperature correction does not apply above this voltage.
TEMPERATURE CORRECTION
Vcorrected=V25°C-((Tactual-25°C)x(.0055V/°C))or
Vcorrected=V77°F-((Tactual-77°F)x(.003V/°F))


13.0EqualizingCharge
Under normal operating conditions an equalizing charge is not required. An equalizing charge is a special charge given a battery when non-uniformity in voltage has developed between cells. It is given to restore all cells to a fully charged condition. Use a charging voltage higher than the normal float voltage and for a specified number of hours, as determined by the voltage used.
Non-uniformity of cells may result from low float voltage due To improper adjustment of the charger or a panel voltmeter Which reads an incorrect(higher) output voltage. Also, variation since ll temperatures greater than 5°F(2.78°C) in the Series string a t a given time, due to environmental conditions Or module arrangement, can cause low cells.
13.1EqualizingFrequency
An equalizing charge should be given when the following conditions exist:
A. The float voltage of any cell (asperSection14.0) is less than2.18VPC.
B. A recharge o f the battery is required in a minimum time period following an emergency discharge.
C. Individual cell(s )float is more than+/-0.05voltsfromaverage.
D. Accurate periodic records(SeeSection15) o f individual cell voltages show an increase in spread since the previous semi-annual readings.
An annual equalize charge is recommended to help ensure uniform cell performance.

13.2EqualizingChargeMethod
Constant voltage charging is the method for giving an equalizing charge. Determine the maximum voltage that maybe applied to the system equipment. This voltage, divided by the Number of cells connected in series, will establish the maximum volts per cell that may be used to perform the equalizing Charge in the shortest period of time(nottoexceed2.35VPC applicableat77°F,25°C).Refer to Table C for voltages and recommended time periods.
NOTE: ChargevoltslistedinTableCarefor77°F.For other temperatures a compensation factor of.003V/°F(.0055V/°C) per cell is recommended. The minimum voltage is 2.20 VPC.
Themaximumvoltageis2.35VPC.Temperature correction does not apply outside of this range.
Vcorrected=V25°C-((Tactual-25°C)x(.0055V/°C))or
Vcorrected=V77°F-((Tactual-77°F)x(.003V/°F))
SeeAppendixAforstandardvalues.
STEP1
A.Set constant voltage charger to maximum setting without exceeding 2.35 VPC.
Example:For a target charge of 2.35 VPC on a 24-cell system,you would set the charger voltage to 56.4 volts.
B.Record time and current at regular intervals–every hour as a minimum.
C.Continue charging the battery until there is no further drop
in charge current over 3 consecutive hours.
D.When the current has stabilized, proceed to step 2.
STEP2
A.Continue the charge for the time listed in TableC depending on the charger voltage setting. The time is IN ADDITION to the time spent charging in Step 1.
Example, charge for 12 hours if the charger voltage is set to 2.35VPC.
TABLEC
EQUALIZE CHARGE (77°F)
CELL VOLTS TIME(HOURS)
2.30 24
2.35 12
B.Recordcellvoltageshourlyduringthelast3hoursofthe
charge time. If,after the charge time has completed, but the lowest cell voltage ha s continued to rise, you may extend the charge,monitoring cell voltages hourly, until the lowest cell voltage ceases to rise.
C.ProceedtoStep3.
STEP3
The Equalize charge i s now complete. Charger voltage can now be reduced to floatvoltagesettingperSection12.2.For A target float charge of 2.25VPCona24-cell system,you wouldsetthechargervoltageto54volts.


HTH Eric

MarkC

DapDan - Still looking at posts? I've got a local supplier of a rack mounted (all connectors, massive steel structure) GNB Absolyte IIP 24-cell 432AH AGM battery that appears to be ~ 9 years old. Resting voltages on each of the 4 "packs" is 12.6+ volts. I've asked them to do another charge and rest cycle and take each cell voltage (24 count). The cost with me picking them up (it's a one-ton tomato!) seems reasonable. Don't really need them as I use a golf cart with Trojan 12 volts for my batteries - however, this seems possible to do (lots of heavy work!), I have a place for them and it appears with some concentrated effort, I might get them to a point of reliable years of service with minimal maintenance requirements for my off-grid backup system.

BB.

Dapdan's last visit was around October 2014...

-Bill