Float and % of charge

[frankz66]

Hi everyone, if during the day I consume energy regularly and I find myself the next day around 12.00 PM in float, have I performed a complete charge cycle or not? In the morning I have a residual voltage of 12.30 volts (very charged battery). Is a battery cycle determined by the float regardless of the percentage ?

 

[OzSolar]

I'm not sure what you mean by residual voltage but 12.30 is not a "very charged battery" assuming you're talking about standard 12v LFP or lead acid battery.

FWIW: voltage is a poor indicator of state charge. Most people use something like a Victron Smart Shunt which once set up properly does a very good job keeping track of battery. Money well spent.

 

[frankz66]

I'm not sure what you mean by residual voltage but 12.30 is not a "very charged battery" assuming you're talking about standard 12v LFP or lead acid battery.

FWIW: voltage is a poor indicator of state charge. Most people use something like a Victron Smart Shunt which once set up properly does a very good job keeping track of battery. Money well spent.

Hello and thank you . Sorry I'm AGM, the measurement I do at the moment is without the shunt. Soon I will buy this too, but with a load of 40 watts on 330 amps the voltage is that. I am sure in very approximate time that the % is that, as after consuming during the day and night it is 700 watts, the daily residue towards the batteries is 1.9 kwh. Anyway, I wanted to know about the cycle.

 

[OzSolar]

Hello. Ok I get your question now and your assumption is correct!

Generally speaking a cycle is defined as bringing a battery back to full after discharging it. The deeper the discharge the fewer cycles you get out it. However, after 30 years of being in this business one form or another I can say that I've never seen a battery die from cycles regardless of depth. Not properly charging them soon after a cycle is what get's them so don't get too tied up in the below example chart I found.

Charge controllers will bring your battery to it's "absorption" voltage and hold it there for a predetermined time (or until the amps drop to certain number) and then enter float. What is the highest voltage you are seeing?

 

[RCinFLA]

Lead acid battery chemistry is more complex than LFP battery chemistry. This means more chemical conversions, meaning there is more overhead power consumed to drive the chemical conversions causing terminal voltage slump during discharge and voltage bump up during charging.

AGM are a bit better than flooded lead acid, primarily because they have a shorter electrolyte path between plates and slightly higher sulfuric acid electrolyte concentration (about 35% acid at full charge) compared to most flooded lead-acid batteries.

You can only get a determination of state of charge by allowing a battery to reach unloaded rested equilibrium. For lead-acid this takes about 20-30 minutes of rested no load idle period. For LFP cells the time to equilibrium unloaded is less than 3-5 minutes. LFP cells also have a fairly flat electrode voltage, so you need a fairly accurate, good resolution voltmeter with accuracy and resolution to better than a few mVdc. (<0.05% accuracy/resolution)

Both can develop a surface charge that will artificially bump up open circuit terminal voltage and is primarily like a super capacitor after full absorb level charging. This surface charge has very little actual capacity compared to actual battery capacity and burns off very quickly upon some actual load on battery.

Left on float charging for a long period, lead acid batteries will build up a thicker layer of lead-oxide on positive plates that will add some increase in series resistance until discharging burns off some of the thickened lead oxide. You may see an initially greater battery voltage slump when starting discharge that will rise up again before continuing normal discharge voltage drop on lead-acid battery.

 

[frankz66]

Hello. Ok I get your question now and your assumption is correct!

Generally speaking a cycle is defined as bringing a battery back to full after discharging it. The deeper the discharge to fewer cycles you get.
However after 30 years of being in this business one form or another I can say that I've never seen a battery die from cycles regardless of depth, it is not properly charging them soon after a cycle, so don't get too tied up in the below example chart I found.

Charge controllers will bring your battery to it's "absorption" voltage and hold it there for a predetermined time (or until the amps drop to certain number) and then enter float. What is the highest voltage you are seeing?

Hello and thank you . I understand now from what you write that the number of cycles does not matter but the DOD related to the cycles. As for the voltage I see as you say, I notice that the batteries go in float as the voltage from the regulator to the batteries is maintained at the values I set or 13.70 volts with -2 of c / m / v. I also see that the absorption in amperes at the moment with three batteries varies from 4 total amps to a maximum of 9 amps. So when I read from the software, I usually see 13.75 volts float and ampere 6 or 9 . In fact, despite me in those moments I have a load of 100 watts, as long as there is light this situation does not change. I just wanted to lower the boost reconnect to 13.00 to avoid that maybe a darkening of the sky leads me to the boost.

 

[RCinFLA]

You must fully recharge lead acid batteries at least every month or two or they will sulfate to hard crystals that will not recharge.

Float level of 13.25-13.7 vdc is normal but will not keep the negative lead plates fully charged. You need to do a full absorb charge to about 14.3v periodically to keep lead acid battery from creating hardened lead sulfate crystals that will not recharge.

Above float voltage there will be some electrolyte electrolysis that create hydrogen and oxygen gas, reducing the amount of water in electrolyte. With sealed AGM's, which also have less electrolyte, you have to be careful of too much overchargng that eats up water you cannot replace.

 

[frankz66]

Lead acid battery chemistry is more complex than LFP battery chemistry. This means more chemical conversions, meaning there is more overhead power consumed to drive the chemical conversions causing terminal voltage slump during discharge and voltage bump up during charging.

AGM are a bit better than flooded lead acid, primarily because they have a shorter electrolyte path between plates and slightly higher sulfuric acid electrolyte concentration (about 35% acid at full charge) compared to most flooded lead-acid batteries.

You can only get a determination of state of charge by allowing a battery to reach unloaded rested equilibrium. For lead-acid this takes about 20-30 minutes of rested no load idle period. For LFP cells the time to equilibrium unloaded is less than 3-5 minutes. LFP cells also have a fairly flat electrode voltage, so you need a fairly accurate, good resolution voltmeter with accuracy and resolution to better than a few mVdc. (<0.05% accuracy/resolution)

Both can develop a surface charge that will artificially bump up open circuit terminal voltage and is primarily like a super capacitor after full absorb level charging. This surface charge has very little actual capacity compared to actual battery capacity and burns off very quickly upon some actual load on battery.

Left on float charging for a long period, lead acid batteries will build up a thicker layer of lead-oxide on positive plates that will add some increase in series resistance until discharging burns off some of the thickened lead oxide. You may see an initially greater battery voltage slump when starting discharge that will rise up again before continuing normal discharge voltage drop on lead-acid battery.

View attachment 148265

View attachment 148266

Hi Ric, I should study the graph .... But from what you have always written to me, the measurement must be done with unloaded batteries and after at least 30 minutes .. These days what I can see is that at the cut off of the panels and after 1 hour with very little load I read a value of 12.70 volts sometimes 12.67 etc.

 

[frankz66]

You must fully recharge lead acid batteries at least every month or two or they will sulfate to hard crystals that will not recharge.

Float level of 13.25-13.4 vdc is normal but will not keep the negative lead plates fully charged. You need to do a full absorb charge to about 14.3v periodically to keep lead acid battery from creating hardened lead sulfate crystals that will not recharge.

Sorry, I'm sending you the current parameters and you tell me what I can vary or if they are good for you.

 

[frankz66]

You must fully recharge lead acid batteries at least every month or two or they will sulfate to hard crystals that will not recharge.

Float level of 13.25-13.4 vdc is normal but will not keep the negative lead plates fully charged. You need to do a full absorb charge to about 14.3v periodically to keep lead acid battery from creating hardened lead sulfate crystals that will not recharge.

I wanted to add that if you induce equalization, it absolutely should not be done on the AGMs.

 

[RCinFLA]

With AGM, I would set equalize voltage same as float voltage just to avoid having it do damage if initiated.

Absorb reconnect likely means the battery voltage discharge point voltage where a new full absorb cycle is initiated. 13.2v is too high. With load current the battery will drop to 12.4v on a regular basis. You do not want to repeatedly trigger a new full absorb cycle as that will eat up electrolyte.

Usually there is a timer that also times the amount of time below a discharge voltage before it starts a new absorb cycle. This allows an inverter load to temporarily drag the battery voltage down without immediately tripping a new full absorb cycle.

Another way to terminate absorb voltage hold cycle is by current taper off, but that is unreliable when there is an inverter/charger that can randomly jump to discharge due to an AC load.

Anyway, if Absorb reconnect is voltage that triggers a new full absorb voltage charging cycle I would lower it down to about 12.4-12.5vdc to avoid too many full absorb voltage charging cycles.

You also have absorb cycle timer set to 3 hours. That is too long for AGM. Should lower that to 2 hours or less. About above 13.6v is where water electrolysis of water in electrolyte increases so without ability to add water you want to limit the time spent above this voltage to only what is necessary to fully recharge battery. Electrolysis rate increases the greater the absorb voltage. Also why you should avoid equalize which typically goes to 15v charging to bust lose harden lead sulfate, but eats up a lot of electrolyte water.

AGM's have an internal pressure relief vent. Venting should be avoided. A little bit of electrolyte gas will be confined within battery and recombine but if too much of an internal pressure due to overcharging, the relief vent will release gas relieving internal pressure to avoid case from bursting. If it does vent due to overpressure from overcharging you lose the gas so there will be no recombining back to water in electrolyte.

If you hear a low squealing whistle sound, it is venting, and you are overcharging battery.

 

[frankz66]

With AGM, I would set equalize voltage same as float voltage just to avoid having it do damage if initiated.

Absorb reconnect likely means the battery voltage discharge point voltage where a new full absorb cycle is initiated. 13.2v is too high. With load current the battery will drop to 12.4v on a regular bases. You do not want to repeatedly trigger a new full absorb cycle as that will eat up electrolyte.

Usually there is a timer that also times the amount of time below a discharge voltage before it starts a new absorb cycle. This allows an inverter load to temporarily drag the battery voltage down without immediately tripping a new full absorb cycle.

Another way to terminate absorb voltage hold cycle is by current taper off, but that is unreliable when there is an inverter/charger that can randomly jump to discharge due to an AC load.

Anyway, if Absorb reconnect is voltage that triggers a new full absorb voltage charging cycle I would lower it down to about 12.4-12.5vdc to avoid too many full absorb voltage charging cycles.

You also have absorb cycle timer set to 3 hours. That is too long for AGM. Should lower that to 2 hours or less. About above 13.6v is where water electrolysis of water in electrolyte increases so without ability to add water you want to limit the time spent above this voltage to only what is necessary to fully recharge battery. Electrolysis rate increases the greater the absorb voltage. Also why you should avoid equalize which typically goes to 15v charging to bust lose harden lead sulfate, but eats up a lot of electrolyte water.

AGM's have an internal pressure relief vent. Venting should be avoided. A little bit of electrolyte gas will be confined within battery and recombine but if too much of an internal pressure due to overcharging, the relief vent will release gas relieving internal pressure to avoid case from bursting. If it does vent due to overpressure from overcharging you lose the gas so there will be no recombining back to water in electrolyte.

If you hear a low squealing whistle sound, it is venting, and you are overcharging battery.

Ok, as for the equalization as you can see it is at 0 of time and equal to the charging voltage of 14.50. I thought I'd lower the reconnect tension as you say but I wasn't sure. I will try to change the value at 12.50 boost reconnect voltage, decrease the duration of the boost from three hours to 1 hour. In addition the float voltage at 13.62 as recommended by the battery manufacturer , value at 25 degrees . What do you think about how much I would like to do?

 

[RCinFLA]

Sounds good.

Charging profiles and low battery shutdown on inverter depends on your use case.

Off grid you usually want to keep battery as fully charged as possible so will take a rougher treatment of battery. On grid with top off recharging you can manually manage how often you do an absorb charge to keep battery from sulfating but avoid the stress of absorb cycling too often.

If you have enough PV to achieve a full absorb charge anytime you want, you can shorten the absorb hold time and allow a full absorb charge more often.

 

[frankz66]

Sounds good.

Charging profiles and low battery shutdown on inverter depends on your use case.

Off grid you usually want to keep battery as fully charged as possible so will take a rougher treatment of battery. On grid with top off recharging you can manually manage how often you do an absorb charge to keep battery from sulfating but avoid the stress of absorb cycling too often.

If you have enough PV to achieve a full absorb charge anytime you want, you can shorten the absorb hold time and allow a full absorb charge more often.

At the moment I thank you and I will update you!

 

[frankz66]

Sounds good.

Charging profiles and low battery shutdown on inverter depends on your use case.

Off grid you usually want to keep battery as fully charged as possible so will take a rougher treatment of battery. On grid with top off recharging you can manually manage how often you do an absorb charge to keep battery from sulfating but avoid the stress of absorb cycling too often.

If you have enough PV to achieve a full absorb charge anytime you want, you can shorten the absorb hold time and allow a full absorb charge more often.

Hello I update you after the parameters you suggested. Despite today cloudy weather with light rain at 13.30 here is the situation as seen from the image. This morning at 7:00 with 35 watt load the voltage was about 12.27 volts.

 

[RCinFLA]

Hello I update you after the parameters you suggested. Despite today cloudy weather with light rain at 13.30 here is the situation as seen from the image. This morning at 7:00 with 35 watt load the voltage was about 12.27 volts.

Only thing I don't like in attached pict is there was a max battery voltage of 15.01 vdc. Unless that is a left over max battery voltage from before you reset parameters. Do you know how far back in time the record is kept? You may want to reset history record and start with keeping new history.

If your early morning battery voltage is low, it just means you do not have enough battery capacity to survive the night comfortably. Don't forget your inverter idle power overhead consumption in your consumption planning.

 

[frankz66]

Only thing I don't like in attached pict is there was a max battery voltage of 15.01 vdc. Unless that is a left over max battery voltage from before you reset parameters. Do you know how far back in time the record is kept? You may want to reset history record and start with keeping new history.

If your early morning battery voltage is low, it just means you do not have enough battery capacity to survive the night comfortably. Don't forget your inverter idle power overhead consumption in your consumption planning.

No the rercord is expressed in 24 hours, probably yesterday even under cloudy sky it loaded 1 kwh but with very little load therefore I believe that the epever based on the pametri goes with those declared which if you see from the settings they are 15.00 vols and even 16 volts the disconnect . In my opinion, these parameters are exaggerated I think .. but I don't know how to modify them exactly, if you know and you will surely know it, you can, if you wish, modify the parameters that must be set according to you. I know the batteries are 6 cell 12v c100 110 amps. Today I got the fourth and I'll stop here. Thanks for the voltage suggestions.

 

[pollenface]

You have 90 minutes Boost Duration, for 12.3v I would extend this to the maximum 180 minutes

Ignore the overvoltage settings unless you require a load to disconnect from your SCC at a given high voltage point.