Is my battery always undercharged?

[GeorgeF]

Many times i've read, also here, that charging with PV only your battery will always be undercharged cause there is not enough sun hours to charge it to 100% SoC.

Once I thought my non gel SLA deep cycle battery had been fully charged, resting voltage 12.8v.

I disconnected the battety from the chargecontroller and connected it to a AC 4 stage smartcharger and it charged for about 1 hour, no load. Connected again to the chargecontroller and it showed 13.0v and after a while 12.9v, no load.

The SoH of my few years old battery is I think still ok cause the slow deep discharge seems to be normal till now.

Questions:
Did the AC charger perform an eq-charge and/or was the battery not yet fully charged?

If the DAILY DoD is near 40% and the total discharge Wh is slightly lower than the capacity of the PV based on 3.5 sunhours and the weather is perfect will my battery always be slightly undercharged?

How long will the absorb stage usually take and for daily cyclic use is floatcharge necessary to reach 100% SoC?

[organic farmer]

I have access to grid-power [when the grid is up]. In the Summer of 2018, I made the attempt to perform regular equalize charges on my battery-bank. Knowing that I do not have enough sunlight to do a 30-hour charge. I went back on grid-power. But my batteries were so far gone. I had to remove a third of my batteries from the bank and over-charge them individually, to get each individual cell up to holding a full charge. This process has removed much of the vision for what we had thought we were doing by having solar panels. My wife is upset as our electric bill went through the roof during all of that over-charging.

I do not know what the right answer is.

[organic farmer]

... Questions:
Did the AC charger perform an eq-charge and/or was the battery not yet fully charged?

The only way to tell, is by taking the specific gravity readings from each cell.

Generally I would guess, 'no' it did not equalize them.

... If the DAILY DoD is near 40% and the total discharge Wh is slightly lower than the capacity of the PV based on 3.5 sunhours and the weather is perfect will my battery always be slightly undercharged?

'yes', and as each month goes by, each battery will gradually drift further away from being equal to it's brothers.

... How long will the absorb stage usually take and for daily cyclic use is floatcharge necessary to reach 100% SoC?

I do not know.

If I leave most everything in our house turned off, Our battery bank will usually reach 99% SOC before noon each day. So I had assumed that by 4pm they would have equalized.

But I discovered that my 'midnite classic 150' charge-controller does not work that way. Even when I manually tell it to 'equalize' it appears to have internal prerequisites that it must perform before it can begin its equalize cycle.

I have watched the midnite classic videos many times on how to perform an equalize charge. But I have never managed to get it to put out an equalizing voltage.

'advice' I have gotten to date on this forum, is the mods would rather spend their time, telling you how stupid you are, instead of giving any helpful wisdom.

You need very thick skin, and then ignore 90% of the insults that they will throw at you.

[GeorgeF]

Thanks for your replies above.

Gravity for me is difficult to measure cause mine is sealed lead acid.

You were talking about equalize. Do you mean controlled overcharged or float?

[organic farmer]

With the normal daily cycling of batteries, the individual batteries will take on different characteristics. Because each individual cell will do this. As time goes on, it gets worse.

Opinions vary over how frequently you need to perform an equalizing charge. I have neighbors who try to do one annually. Others [online] insist that equalize charges need to be done monthly.

By the time that I figured out something was wrong, my batteries were really bad.

Think of an equalize charge as a controlled over-charge, where you purposefully boil the water for 30 hours.

[GeorgeF]

So, although you have enough PV capacity your battery is frequently undercharged although you have stated that you reach 99% SoC at noon.

I am particularely interested why is it that when you daily discharge till +/- 40% DoD and charge with PV only and you have more than enough PV capacity the battery can not reach 100% SoC although the sun is shining bright till late in the afternoon (even with mppt and solar tracker) . When the weather is against you I understand.

Is it because absorb till or incl float needs a lot of time? If yes, how about if i only discharge 20%?

[organic farmer]

So, although you have enough PV capacity your battery is frequently undercharged although you have stated that you reach 99% SoC at noon.

I am particularely interested why is it that when you daily discharge till +/- 40% DoD and charge with PV only and you have more than enough PV capacity the battery can not reach 100% SoC although the sun is shining bright till late in the afternoon (even with mppt and solar tracker). When the weather is against you I understand.

Is it because absorb till or incl float needs a lot of time? If yes, how about if i only discharge 20%?

Starting with new batteries, our system seemed to be working great.
I set our Low Battery Cut-Off [LCBO] at 75% SoC to prevent cycling our batteries too deep.
After 3 years of usage, the battery problems seem to have cascaded.

Fixing the batteries, I have had to dive into the nuts & bolts of battery maintenance.

Many times I have gotten the Midnite Charge-controller to say the batteries were at 100%, but that does not mean all the cells are equal to each other. Getting the cells to all be equal requires an equalizing charge and lots of additional water.

I live in a region where off-grid solar-power seems to be pretty popular. [only about 25% of solar power system are net-metering in my town] Talking to others with off-grid systems, the consensus among them seems to be that within five years, you replace your batteries.

The best system I have seen among my neighbors is one farmer who built his system in the 1980s. His entire home is 12vdc. His batteries are all automotive batteries sourced from junkyards as 'cores'. At $10/each he does not care how many he must replace each quarter.

[GeorgeF]

Is is perhaps not better to set the cut-off voltage at max 50%. The deeper you discharge the faster you ruin your battery, or not?

[citabria]

I understand that Sealed Lead Acid batteries DO NOT get an equalizing charge for that may damage them. Make sure to read and understand the manufacturer charging recommendations.

Sealed batteries may only last half as long as Flooded Lead Acid batteries....Are your batteries at the end of their productive life?

[GeorgeF]

Yup i know that. Specs do not mention eq-voltage.

My sla seems to hold charge and the loads (slow discharge) till now seems to be ok. Disconnect the loads after several hours never reach 12.1v (resting voltage) , always above.

[Bala]

Short reply, my batteries are 12 years old, equalise as per sunking advice when sg is uneven, I don't need to equalise often. I live in tropics so use a lot of water. Sealed don't get equalised as you can not replace water. I don't have an under charge problem as my winters are better for solar than my summers.

[inetdog]

A much more accurate statement is that when using PV alone for recharging you do not typically have time for a classic Bulk/Absorb/Float charging scenario. Instead you need to run the Bulk stage to as high a current as the batteries can take and your PV can supply. Then push the Absorb portion of the charge cycle as hard as you can, because you will not have time in the day to use a small fraction of the PV potential for an extended time to finish the charging process with true Float.

[Mike90250]

A well designed and balanced system accounts for usage loads, weather, size of battery bank, size and orientation of PV array and use of a backup generator for the cloudy periods.

Neglect one factor, and you cause early damage to batteries. Since the OP did not share his system configuration, I can't help at this time. Supply us with the data, and we are happy to help solve the issue.

[GeorgeF]

Thanks again for all replies. Internetdog, if already reach aborb stage, no matter the DoD, is the duration of absorbtion till 100%SoC always the same?

The advises or algorithm of Sunking in serveral posts I did follow and I think to pass bulk is not much of a problem in a tropical country. Like he said somewhere, if I have to choose between undercharging or overcharging i will choose slightly overcharging.

[GeorgeF]

Well Mike for this and other purposes I am currently testing a 40Ah SLA with a 150Wp panel, discharge daily max 40% DoD.