End amps vs Float current

[Barry Fields]

Amongst the myriad of things I do not know is the following:

Are all End Amps equal?

CASE 1  Consistent PV input. Absorb voltage (say 58v) constant until 2% of AH rating is reached.

Case 2  Inconsistent PV input. Absorb voltage reaches 58v then hangs at 57.5 for 1hr until finally again reaching 58v and 2% AH rating is achieved.

Are both ending SOCs the same?

[boB]

You would probably rather have it like case 1 where you have consistent Absorb BUT yes, the Absorb time is cumulative. 

In fact, if the battery voltage is just under the Absorb voltage when it goes back to Bulk MPPT, you may get a bit more Absorb time for lead acid batteries, although it is not exactly Absorb voltage.

Doesn't matter quite so much for lead acid.  And even lithium batteries in Absorb if that is being used so the BMS can do its balancing act for the lithium cells.

For the Classic and Kid controllers, the ending amps only works if the charging voltage is at the Absorb voltage or just above a few tenths of a volt below that absolute Absorb voltage setting.

I hope that makes some sense.
boB


 

[Barry Fields]

You would probably rather have it like case 1 where you have consistent Absorb BUT yes, the Absorb time is cumulative. 

In fact, if the battery voltage is just under the Absorb voltage when it goes back to Bulk MPPT, you may get a bit more Absorb time for lead acid batteries, although it is not exactly Absorb voltage.

Doesn't matter quite so much for lead acid.  And even lithium batteries in Absorb if that is being used so the BMS can do its balancing act for the lithium cells.

For the Classic and Kid controllers, the ending amps only works if the charging voltage is at the Absorb voltage or just above a few tenths of a volt below that absolute Absorb voltage setting.

I hope that makes some sense.
boB


 

What I think I hear you saying is that Case 2 would likely yield a slightly higher SOC depending on how much time was spent just under Absorb V.
I am ready to be corrected.  Barry

[boB]

I would say you are correct, Barry.

You got it.

boB

[ClassicCrazy]

Doesn't matter quite so much for lead acid.  And even lithium batteries in Absorb if that is being used so the BMS can do its balancing act for the lithium cells.

I hope that makes some sense.
boB

[/quote]

Bob -I am finally starting to figure out the lithium batteries and bms stuff. Most existing bms will balance at some point they are programmed for. But a lot of them are passive balancers shunting the high cells to resistors. The bms I have seen only shunt off 50 to 150 ma which isn't much when the cells are 100ah or more. My particular bms is on the lower range of like 50 ma but it only balances when charging - or if a cell goes to OVP overvolt protection , that shuts off charging but the balancing will stay on until the cell drops to whatever voltage it is programmed for.  And my bms won't balance anything unless the cell differential is higher than 20ma. But still not much is going to balance at that low ma rate.

But there are a newer generation of bms or stand alone balancers - active balancers that can move 2 to 5 amps from high to low cells , and some of these can be programmed to turn on and off at specific cell voltages. You only want them to balance at the very top of the charge curve. So they would work better with the longer absorb if the charging current is lower than full blast. Of course as the cells get full , they take in less current so that will decrease.

The youtuber OffGridGarage Australian - Andy - does some thorough testing of each new bms and best voltages to charge to. He has a very nice charge / discharger that will graph the results and helps explain what is really going on. Watching his videos along with messing around with my own batteries is helping me to finally  understand the lithium stuff.  I did buy an add on active balancer for my battery which has the weak passive balancer and it works wonders to balance in comparison.
Here is a recent video where he shows all the graphs on charging / discharging . https://youtu.be/aiiJ1IWSWos?si=xOu2vuOx3vx7oh_t

Anyway what we really need with lithium is accurate reading of the voltages to controller, or ideally have the controller able to read the battery voltage data that many bms provide via rs485 or CAN.

Larry

 

[Barry Fields]

Being elderly, I can only handle one battery chemistry at a time. For now I am concentrating on Lead Acid only.

I am asking these questions in consideration of a possible alternative to fixed Absorb Time or End Amps. If we can agree that our goal is 95% SOC at the end of the absorb cycle.

TO EAST PENN.
Barry: For the same replacement energy, 20 amp charging will yield anti-stratification bubbling at double the rate of a 10 amp charge rate. However that lower rate will occur for double the time. Therefore, stratification should not be a significant issue. (assuming a 95%-100% SOC is achieved at least every 3rd day).
EAST PENN: If the battery reaches 95%-100% SoC every 3rd day, it is reasonable to assume the sulphation can be avoided.

Consider the following also from EAST PENN:


Barry? If FLOAT is achieved, a FLOAT current significantly above 500ma (? 1amp ?) might indicate an incomplete ABSORB cycle.

EAST PENN  The float current of a fully charged battery is dependent on battery capacity and charge voltage.
    Fully charged float current of a GC10 would be around 450mA.
    If the float current is above 480mA, it is an indication that the battery is not fully charged.
    Additionally, if the current is above 800mA at the end of absorption charge, this is also an indication the battery is not fully charged.

Barry? If I were to take a GC10 that is verifibly at 95% SOC and put it into FLOAT, what might I expect for an initial Float current. ?
EAST PENN  We temperature compensate the charge voltage to in order keep the polarization of the positive and negative plates the same as they would be at 25°C (higher temperature we lower the voltage, lower temperatures we raise the voltage).
Additionally, we say temperature compensation of the charge voltage should be only done in the range of 10°C to 35°C.
Abiding by these rules, the stabilization current will remain relatively the same, could fluctuate a couple of milliamps.


As the FLOAT voltage is temperature compensated (-3mv/cell/degree C), would the FLOAT current be reasonably consistent over a battery temperature range of 5 degrees C to 35 degrees C ?

My suggestion is to use a somewhat short ABSORB TIME, let it go to FLOAT, and measure the FLOAT CURRENT.
If the current is above what is expected for a 95% SOC, re-initiate ABSORB for another 1/2 hr and repeat.

My thought is that this is a way to effectively evaluate the preceding ABSORB CYCLE for completeness.

[Barry Fields]

My take on this proposal is as follows:

It will assure a 95% SOC based on daily PV conditions with NO user intervention.

It will minimize battery over charging due to extended ABSORB times.

Both of these extend battery life and ensure that sufficient time is spent in the SOC range of desulphation and self equalization.

ISSUES TO RESOLVE
Low current discrimination - The 500A Wbjr most likely is insufficient.
I would suggest a 10A or 20A halleffect toroid in series with the Wbjr.
My understanding is that over-amping a halleffect device will not damage it.

Settling time between ABSORB and FLOAT - ?

Baseline FLOAT current - There are many combinations of battery chemistries. (flooded, agm, gel, alloys, electrolytes, etc)  I suggest the following procedure:

Slightly overcharge the battery bank to assure 100% SOC
go to Float and record 100% FLOAT current
Discharge the Battery Bank by 10% of the rated AH capacity
go to FLOAT and record 90% FLOAT current
Select a current level between those data points and use that as the trigger for the "lather rinse repeat" process described in my previous post.

Note that some long term changes will occur with these FLOAT currents due to battery age and health. The BASELINE procedure may be required on a periodic basis.(?6mths/12mths?) Changes in the BASELINE might be helpful in predicting battery replacement.

One last thing
Is it too soon to ask for a promotion?  I do realize that a raise is out of the question.

[ClassicCrazy]

I think someone once mentioned that if people had kept as close track of each lead acid cell and balanced them like is now done with lithium , they probably would last a lot longer. I know that the place I used to get batteries from would load test each cell in older forklift batteries and then match the cells to make up a new renovated pack. The battery guy  told me that heat was probably the cause of most of the cell degeneration since the cells in the center of the pack were the ones that most often failed.
If someone has a large lead acid battery pack with separate cells, an active balancer like is used with lithium would help them also since it can monitor each cell individually and adjust charge to them as needed. This may go a long way also to eliminate the equalization charges that try to do the same thing , though at the expense of overcharging the higher cells to try and bring up the lower ones.
I think the Neey active balancer may have lead acid setting or capabilities.
Of course there are so many variables with different systems and the loads on them that play into lead acid care and lifespan - like stratification if large capacity cells don't get a high enough charge to bubble up the electrolyte. That may not be an issue though with gel or lead crystal types of lead acid batteries.

Larry

[Barry Fields]

Larry,
I appreciate your input. My take on battery balancers:

If as you say you are using 2volt LEAD ACID cells, there is a benefit to keeping the CELLS balanced. However, without an appropriate charge regimen that routinely puts the batteries in the 95-100% SOC range, I fear that all we have done is guarantee that all cells will sulphate evenly.

If the 2volt Lead acid cells are 2 to 3 times the height of a monobloc battery, then it seems to me that stratification of the electrolyte would be more of an issue. That can only be resolved by a more vigorous charge rate (independent of the SOC). Shaking the battery won't do it.

For a majority of us that are using 6v, 8v & 12v monobloc LEAD ACID batteries, a balancer would only balance the batteries, NOT the individual cells. I know of no other way of balancing the individual cells of a monobloc battery but through an appropriate charge regimen. Therefore, for monobloc batteries, balancers are an expense of little to no value.

I started this post in the LEAD ACID category in an attempt to find the best possible LEAD ACID CHARGING REGIMEN. I had kinda hoped to keep this chain centered on that specific subject.

Regards
Barry

[ClassicCrazy]

Vic has made a lot of posts in the past about lead acid batteries.
His advice always suggested taking electrolyte sampling to determine the proper charging values are achieved. And then to keep taking the samples as regular maintenance to ensure that no cells are low and to be able to do equalizing and see if corrections have been achieved.
Of course this won't work for sealed lead acid batteries - only flooded where you can get samples .
I used that method to dial in the proper charging and ending amps - along with getting the SOC values on the Classic calibrated to be close .
Larry

[boB]

Robin and I wanted to make an active lead acid battery balancer 20+ years ago.

boB

[Barry Fields]

The company Multitel has an extensive explanation of FLOAT CURRENT MONITORING.

https://www.multitel.com/float-current-monitoring-a-complete-overview/

Below are two quotes I feel are worth highlighting:

Battery chemistry, battery design, quality of material, manufacturing process and battery capacity (AH) will ultimately influence the rate of self discharge of any lead acid batteries. Thus, the typical float current value will differ from one model to another.

Since the early 2000, float current measurements have been accepted for determining SoC (State of Charge) of VLA and VRLA batteries (see IEEE-450). As hygrometers are not easy to use and testing is time consuming, SG measurements can be replaced by float current measurements. Float current has an advantage in that it provides an indicator of the entire battery string, while specific gravity is measured on a cell-by-cell basis.

Should MidNite decide to pursue the CHARGING REGIMEN I have proposed, Multitel may be a valuable engineering resource.

I am surprised that I have not yet received ANY negative feedback on my proposal. I cannot possibly be that correct.

PS - Thanks for the promotion to Jr Member. At 74 it has been a while since I have been called Jr. Maybe ROJM (Really Old Jr Member)

[Barry Fields]

Robin and I wanted to make an active lead acid battery balancer 20+ years ago.

boB

The following is a question I posed to East Penn about a year ago and their response.

If I were able to compare all the battery voltages in a bank string, and one battery (6v 3cell) was more than 30 millivolts +/- from the average, would that be (while not perfect) an indicator that the string should be equalized?

Yes, that is a good trigger, but cell to cell equality is not our only goal.  You must also regularly ensure the electrolyte in each cell gets mixed bottom to top by enough gassing time and get the plates fully charged all the way to the bottom.

Hope this might help.

PS I sent you a private message about 3 weeks ago. I know, nag, nag, nag.
Barry

[boB]

Robin and I wanted to make an active lead acid battery balancer 20+ years ago.

boB

The following is a question I posed to East Penn about a year ago and their response.

If I were able to compare all the battery voltages in a bank string, and one battery (6v 3cell) was more than 30 millivolts +/- from the average, would that be (while not perfect) an indicator that the string should be equalized?

Yes, that is a good trigger, but cell to cell equality is not our only goal.  You must also regularly ensure the electrolyte in each cell gets mixed bottom to top by enough gassing time and get the plates fully charged all the way to the bottom.

Hope this might help.

PS I sent you a private message about 3 weeks ago. I know, nag, nag, nag.
Barry

Yes, this is true !  Depending on the battery type, 30 mV may or may not be a problem.  For lead acid, no problem IMO.

boB

[Vic]

The company Multitel has an extensive explanation of FLOAT CURRENT MONITORING.

https://www.multitel.com/float-current-monitoring-a-complete-overview/

Below are two quotes I feel are worth highlighting:

Battery chemistry, battery design, quality of material, manufacturing process and battery capacity (AH) will ultimately influence the rate of self discharge of any lead acid batteries. Thus, the typical float current value will differ from one model to another.

Since the early 2000, float current measurements have been accepted for determining SoC (State of Charge) of VLA and VRLA batteries (see IEEE-450). As hygrometers are not easy to use and testing is time consuming, SG measurements can be replaced by float current measurements. Float current has an advantage in that it provides an indicator of the entire battery string, while specific gravity is measured on a cell-by-cell basis.

Should MidNite decide to pursue the CHARGING REGIMEN I have proposed, Multitel may be a valuable engineering resource.

I am surprised that I have not yet received ANY negative feedback on my proposal. I cannot possibly be that correct.

PS - Thanks for the promotion to Jr Member. At 74 it has been a while since I have been called Jr. Maybe ROJM (Really Old Jr Member)

Hi Barry,

It is just me,  but, any "Authority", regarding FLA batteries,  that calls an Electrolyte Density-measuring device, a "Hygrometer" (which generally measures the proportion of water, present in, gas/es,    like those in air, instantly loses 98.998% of any credibility, about all the other "info", provided.

IMO,  there are many, many ...   many variables when charging/discharging,  and measuring/inferring SOC, and SOH of batteries.  None of the methods used need to be perfect,  just, perfectly adequate.

It is often proposed, that, when possible,  a person needing a battery system,  buy a set of batteries, ideally,  FLAs, true deep-cycle, like GCs,  and learn how to use them,  and use accepted measurements  --  a Hydrometer,  and Pilot Cells, for quick readings on the average, nominal SOC.

Monitor, carefully,  the amount of replenishment Distilled Water, for each battery  ...
Create a Log Book,  for that batt bank,  record charge settings, EQ duration, and voltage,  battery current, etc,  then sit back, and enjoy the fruits of the labor,  and wisdom that you have gained.
Over time,  the battery current reduction, during EQ can imply battery SOH,  and when further EQing will probably have diminishing effect.
IMO, again,  USE A BTS, with FLA batts,  AND, Temp Comp the EQ voltage   ...

AND, as always,  I am NO battery expert,  am still practicing, though.

IMO, FWIW ...  YMMV, and so on Vic