Battery considerations FLA vs Recombinant

Niki · August 2019

Seems to me that battery CYCLE EFFECIENCY is not mentioned much but is of paramount importance especially in off grid applications as every watt hour of energy used to replace self discharge, overcharge and equilizing is a watt hour paid for but not available for use. A flooded deep cycle battery can be in the range of 90% efficient when new but goes South pretty quick. If you’ve ever walked into a FLA battery room when under high charge mode you can hear ( and see) churning and bubbling as well as the smell of Sulphur in the air. All this is due to the conversion of water into Hydrogen and Oxygen floating about the battery room which is powered by your system at the expense of efficiency. Add to that self discharge which is measured in days with FLA batteries and months with recombinants and things become more apparent. Gel and AGM technology offer improved efficiency due to a recombinant design that recombines the 2 gases into water vapor within a sealed battery jar thereby avoiding the loss of water, waisted energy overcharging, and equalizing charge as well as the production of combustible gas, required maintenance, terminal corrosion, high power loss through self discharge etc.

Recombinant batteries offer very low self discharge over the life of the battery. Now days industrial sealed AGM and Gel cells are available that last 10 to 15 or more years when charged properly, with depth of discharge ratings as high as 1500+ cycles to 50 % DOD. They’re not cheap but when one considers all the time, effort, $ and waisted energy both electrical and human fussing with FLAs alternatives are worth considering.
However recombinant batteries require a quality programmable charge controller and temperature compensation for longest life. See OPzV technology. Niki

mike95490 · August 2019

I agree, they are wonderful batteries. As long as you are a perfect caretaker. One overcharge incident that pops the seals, and it's downhill from there.

And generally, overall lifetime is shorter then premium flooded batteries, so to come up with a fair comparison:

Higher initial cost

Unforgiving

Shorter life

vs

maintenance needed

forgiving of overcharge mistakes

Both will need vented enclosures, because sealed, at end of life, can go into thermal runaway and vent some fumes.

mvas · August 2019

Niki said:

Gel and AGM technology offer improved efficiency due to a recombinant design that recombines the 2 gases into water vapor within a sealed battery jar thereby avoiding the loss of water, wasted energy overcharging, and equalizing charge as well as the production of combustible gas, required maintenance, terminal corrosion, high power loss through self discharge etc.

... with depth of discharge ratings as high as 1500+ cycles to 50 % DOD.

. Niki

AGM batteries waste energy creating hydrogen & oxygen gas, just like flooded batteries.
You get the water back, but you do not get that energy back.

ALL lead acid batteries should be equalized,
the fact that some cannot be equalized is actually a bad thing = shorter life & fewer cycles.
Some AGM batteries can be, and must be, equalized to obtain maximum lifetime & cycles.

Having access to the Specific Gravity of the electrolyte helps determine over-charge vs under-charge.
In a sealed battery you have to use charging voltage & charging amps to guess-timate when 100% SOC has occurred.
As the AGM Battery ages, the charging voltage and charging amps at 100% SOC is different.

There are pro's and con's for both ... flooded vs sealed.

There are Flooded Lead Acid batteries that are rated 3,600 cycles at 50% DOD
So, your "1,500 cycles rating" is not a big deal.
OPzV is old news ...

Estragon · August 2019

I suspect the reason charging efficiency isn't mentioned a lot is because in many/most cases off-grid it doesn't really matter that much. Charging efficiency of flooded is pretty good until the last 10% or so in absorb, (when charge current is dropping off anyway), leaving unused pv capacity.

Opportunity loads can be run to use some of the extra pv potential, but unused potential is a fact of life off-grid.

mcgivor · August 2019

mvas said:

Niki said:

Gel and AGM technology offer improved efficiency due to a recombinant design that recombines the 2 gases into water vapor within a sealed battery jar thereby avoiding the loss of water, wasted energy overcharging, and equalizing charge as well as the production of combustible gas, required maintenance, terminal corrosion, high power loss through self discharge etc.

... with depth of discharge ratings as high as 1500+ cycles to 50 % DOD.

. Niki

AGM batteries waste energy creating hydrogen & oxygen gas, just like flooded batteries.
You get the water back, but you do not get that energy back.

ALL lead acid batteries should be equalized,
the fact that some cannot be equalized is actually a bad thing = shorter life & fewer cycles.
Some AGM batteries can be, and must be, equalized to obtain maximum lifetime & cycles.

Having access to the Specific Gravity of the electrolyte helps determine over-charge vs under-charge.
In a sealed battery you have to use charging voltage & charging amps to guess-timate when 100% SOC has occurred.
As the AGM Battery ages, the charging voltage and charging amps at 100% SOC is different.

There are pro's and con's for both ... flooded vs sealed.

There are Flooded Lead Acid batteries that are rated 3,600 cycles at 50% DOD
So, your "1,500 cycles rating" is not a big deal.
OPzV is old news ...

So true, having the access to the fundementals, the electrolyte, is extremely important, sure it takes some time, however if it's important, it's worth doing. The choice for using AGM should be based on the availability of someone, or the lack thereof, to do regular maintenance. Regular maintenance can uncover potential problems before they occur, flooded batteries are way more forgiving, allowing more latitude with regards to charging, or overcharging, AGM are not as forgiving

One really needs to understand what's going on, AGM batteries can lead to a false sense of security, especially to those without previous experience, the experience gained from using flooded in the first place.

Niki · August 2019

Eqilization charges are needed many times because of electrolyte stratification in FLA cells. When they used to use them in Submarines they used an air pump air up from the bottom of the jar to mix the dense electrolyte from the bottom with the weak mix on top. FLA technology has become obsolete in such applications in favor of OPzV technology.
In consumer use FLA just need to be overcharged until the acid is fully mixed which is not needed in immobilized electrolyte designs. Equalizing charges are generally not recommended although a freshening charge of up to 2.4 VPC can be employed if the cell has been standing for up to a year without charging. Of course FLAs will suffer from sulfation due to excessive self discharge due to antimonial poisoning of the positive plates. Excessive self discharge is a real issue with older FLAs.

BB. · August 2019

Niki,

OPzV batteries are tubular plate sealed GEL lead acid batteries (as I understand)...

What makes them different/better?

At least with US (probably flat plate) GEL batteries, too high of charging voltage will cause them to gas and leave "permanent" bubbles in the GEL--Reducing battery capacity (again, as I understand). Also, US GEL tend to be limited to C/20 or 5% maximum charging current.

I have seen European GEL batteries (probably OPzV) that seem to have higher charging current and voltage support--And I always wondered what their "secret sauce) was.

-Bill

Niki · August 2019

Gel technology requires “fractures” in the gel for proper capacity and performance . Manufacturers generally suggest the Gel battery be deep cycled 5 to 10 times before it will meet its new battery capacity spec as it takes this to create the cracks in the gel for oxygen recombination
process to work properly along with sodium silicate to take effect. They call this conditioning and usually mention this in their manual for
industrial gel cells. East Penn sometimes will precondition them for certain customers so they will meet specs out of the box.
the OPzV Design is totally different as it utilizes a Lead, Calcium, Tin collector rod (grid) suspended in a pourous tubular gauntlet filled with pure lead grains kind of like a straw one next to the other across the jar for the positive plates, resulting in almost no shedding of active material. Then the free spaces around the tubes are filled with gel electrolyte. White paper lab studies and excellerated (hot water bath) life tests have been published on this technology world wide with predicted life up to 27 years. It compares FLA antimoney, tubular flooded and OPzV side by side in various sizes. The flooded tubular with lead Selenium rods do slightly better but the OPzV type are much more user friendly and unlike the others the current to offset self discharge actuall goes down instead of up like conventional batteries over time. I don’t think they have a full understanding of why this happens. They also benefit from very tall jars as the tubular design is ideal in that regard providing a small footprint for a high capacity cell.
All batteries considered in these white paper publications are 20 year rated industrial batteries made up of individual 2 volt cells as as monobloc batteries have built in liabilities due to mid cell temperature issues.
Re AGM over charge the self resealing pressure relief valves are designed to accommodate this and an occasional high voltage spike is
o k but not abusive overcharge.
Golf cart and L-16 type batteries also are subject to increased wear and tear from overcharge, grid erosion, excessive water consumption and the inevitable dry cell which usually happens after a few tears of operation when water consumption gets out of hand with many consumers, it usually happens eventually.just offering this for non intransigent readers. Not trying to sell anything just sharing information.

Niki · August 2019

Bill,
as far as rate is concerned these are industrial batteries. In the US ratings are usually 8 hr but in Europe where Tubular plate batteries are made they rate them nominally at 10 hours. Of course distributors always give you 20 hr and even 100 hr ratings to make the battery look more like a better deal. Not very honest. I like to talk watt hours any way not amp hours.
Niki

48 Kilowatt hour (at 10 hr rate) OPzV battery.

BB. · August 2019

Thank you Nikki.

Bill

Marc Kurth · August 2019

Overcharging of AGM's to the point of damage is a constant theme on the web. In my experience, it is actually very unusual nowadays. (Some Gel's are in a whole different category.)

I strongly agree with the previous poster that occasional over voltage spikes are not particularly harmful to quality AGM designs. In fact, it can be beneficial in many cases. EQ is 2.58v/cell for Concorde and they specify 3v/cell at a controlled current, under certain circumstances to recover from neglect or damage. (Others, no way)

At the risk of being overly repetitive, UNDER charging is the enemy and it accounts for MOST early failures that we see - by far and away.

There are many people here, who are far, far more learned on the chemistry and theory of operation of batteries than I. When I offer my opinion, it is only based on what I have learned from my own applications. Does this make me an AGM expert? Oh HECK NO, but I do have more than a little accumulation of field based anecdotal data spanning 20,000+ AGM batteries.

Marc

mvas · August 2019

Niki said:

Bill,
as far as rate is concerned these are industrial batteries. In the US ratings are usually 8 hr but in Europe where Tubular plate batteries are made they rate them nominally at 10 hours. Of course distributors always give you 20 hr and even 100 hr ratings to make the battery look more like a better deal. Not very honest. I like to talk watt hours any way not amp hours.
Niki

48 Kilowatt hour (at 10 hr rate) OPzV battery.

Do you deep discharge these batteries every night ?
What is the final state of charge = 50% SOC ?
How many months have they been in service?

Niki · August 2019

These particular batteries are rated at 1000ah at 10 hr rate, weigh about 175 lbs per cell, 1500 cycles to 80% DOD and have been in service for about 8 years so far. They have a 20 yr Design life and are doing well so far running a large deep well pump, a house with all the typical appliances, a guest house etc. since they don’t outgas they can be located in close proximity with electronics. They came with all intercell cables and no exposed terminals with a provision for test lead access to each cell for yearly record keeping. The DOD varies greatly due to ocean fog in spring, times of extended partial state of charge etc and have a system design of 3 days of autonomy with no sun, a
15 kw propane Onan genset for backup if necessary. Rarely used as 6 kw of LG modules take care of business.
SOC is 2.18 VPC at 100% and 1.80 VPC at 20% (77 degrees)

Niki · September 2019

Make that 1.85 VPC at 20% SOC AT REST.

Battery considerations FLA vs Recombinant

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