How to tweak absorb

jonr

Has anyone tried 100% glycerin (1.267@10C)  to accurately calibrate a hydrometer?

Estragon

Wouldn't 100% glycerin be pretty thick at 16°C? Seems to me it gets pretty goopy when it gets cool/cold.

jonr

Maybe better to use a higher temp or a known mix of glycerin and water.  Or perhaps there are other methods.

mike95490

A standard could be made from salt and distilled water. Or sugar,  Or baking soda. Or pizza sauce (no, couldn't read the float)

  But don't let salt into the flooded batteries, that will kill you dead !!!

mcgivor

Making a solution with sugar, salt or whatever, would mean weighing accurately the absolutely dry ingredient before disolving in pure water after weighing it too, which seems more complicated than its worth, IMO. The hydrometers I use, purchased 3, come with a calibration sticker attached, all read the same when tested together on the same cell. Obsession about the accuracy is for the most part just that, an obsession. Buying a quality hydrometer is probably the most important, knowing how to take a reading accurately is the other, bubbles, temperature correction  not taking one pull are equally important, as is understanding surface tension and the meniscus phenomenon. Keeping it clean by rinsing after use is good practice, in fact the ones I have recommend washing with dish soap and rinsing with distilled water, periodically. Just like any measuring  too,l the accuracy is dependent on quality and nothing is 100% accurate. Using it to record changes between cells is more important than obsession in accuracy. FWIW, YMMV, IMHO and all other disclaimers apply.

Freewilley

Thanks all.
To check on the hydrometer, I let the new string sit overnight resting. This morning the SGs read 1.250 across one battery and 1.255 to 1.26 in the other. I checked voltage and they show 12.7/8 so I guess they ARE fully charged? I guess a short EQ would not be bad in the next few days...

I do not see much heat in any of my batteries, unless I work at it. They are in a cool basement and I run a box fan on them when EQing.
120 is the hottest I have ever seen.

Freewilley

So today I have reoccuring the rotten charging situation that I have seen so many times over the years....
My good string of batterries was taken down to 50% or so (12.1 volts) over night. This morning I made up by running the generator for a couple of hours. Pretty good solar for over an hour now (about 900 watts) and this has driven my voltage up to absorb. 
But when I check the SG on the batteries, they are on.y 1.200. Charging at 35 amps.
My absorb setpoint is 15.1.
Why do they go into absorb when they are not even close to 80% charged, and more importantly, is this a problem??

Steve Higgins

Hey Guys...I hope you don't mind... I sometimes log into see what's going on, and saw this

When calibrating a glass hydrometer or box hydrometer for about 8 bucks you can buy premixed 1.280 Electrolyte from most automotive stores.   This is one of the reasons that buying refractometers makes more sense to me... Also decent quality ones are less than 50 bucks on amazon.   I purchased my first in 1998 for around 300 buck...now I only use glass hydrometers when showing people how to use them.
With Refractometers, you can calibrate to zero with distilled water.

 
On Absorb Times:

When you start the Absorb cycle you only have about 20% State of charge left... this is why absorb time has nothing to do with the DOD... If the batteries are healthy when you get to the Bulk/Absorb Voltage the batteries are at about 80% SOC with 20% to go...  The hard part is the current, because of Ohm's law... High Voltage... a multitude of things drops off. 

Also what makes absorb timers different is when you have multiple charging sources on a single bank, the voltage from each source can "confuse" the other source.  

Is our Absorb Timer formula perfect... generally it's about +/- 15%...  It's better than the guessing game that most installer/end users play regardless of what batteries they use. 

The bigger issue is with most of these systems everyone uses their systems a little bit different, so settings will/can be different form user to user, even using the same components in different houses you can get different systems. 

Estragon

Very roughly - assuming the generator is supplying ~10%C, and the bank was at 50%, running the generator for a couple of hours would get you to 70% or so. Assuming the solar in bulk suppied about the same, that gets you to 80% in another hour, so if the assumptions are right, the timing sounds about right.

They (should) go into absorb when they hit Vabs. In a healthy bank, that will be ~75-80% full. If the SG is reliably measured low, I would set absorb to a long time (eg 12hrs), disable end amps, and watch current and SG over the next 4-5 hours if possible.

Freewilley

I do not think the batterries are near 80% charged. I have been complaining about that for years on this board and to Steve (who has helped lots, but not solved the problem identified here...his advice was to turn float up to the absorb setpoint, in effect continuing an unending absorb cycle)....it was always thought that it was a battery issue. But these are new batteries that have been babied. They should not be sulphated.

I am now one hour into absorb and the SG has not come up (1.200) and the current has dropped to less than 10 amps. Mild, slow bubbling at cells which are 80F. Lots of solar available At this rate I would reach 100% in a week? Is this current at 50% charged normal?

Vic

Hi Steve,  Nice to see you here.

The systems here,  and those that I look-in on,  do seem to have different Absorb times,  that appear to be primarily based upon the DOD the bank experienced on the previous discharge.

Speaking of the Formula in the Surrette (Rolls) Battery Manual,  yes,  there is no variable for the DOD.  BUT,  IMO,   the value of current seems to assume that the current will be a CONSTANT (assume that this is due to one using a Constant Current charger).   For most of us with RE power sources,  the battery charge current during Absorb  is not constant,  as we  are using Constant Voltage charging during Absorb.

If one would say,  CV charging is OK with the formula,   then it would seem that if one would just need to use the average of the current during Absorb,   then one would really need to WAIT until the end of the Absorb,  to be able to calculate just what was the average charge current during Absorb.

Also,  have guessed that there must really be Peukert effect regarding charge rates,  not just discharges  --  where the effectiveness of charge current varies,  at least somewhat depending upon just what is the battery charge current,   and perhaps therefore,   CV charging could cause a variable in charge time based upon the amount of battery discharge,  the Rate of the discharge,  and the Rate of the charge ...   and so on.

As an aside,   have noticed that there is also a change in the necessary EA current,  depending upon the DOD of the battery.   Discharge the battery fairly deeply,  and the EA that customarily works for a nominal full recharge will NEVER be attained,  at least in one Solar day.   The Finishing current plateaus above the EA setting for the customary discharge value,  causing the battery to hang in Absorb,  until the Absorb timer times-out.

Anyway,  just my read on things.    Thanks again Steve for weighing-in on this.    Vic

Estragon

With the current dropping off, some gentle fizzing/bubbling, and SG not rising much, it sounds to me like the bank is at higher than 80% SOC.

Steve Higgins

Freewilley sent me a PM noting that I hadn't answered or commented on one of the issues. So here goes... 

The issue with a charger or battery voltage progressing thru Bulk to Absorb too fast,  in my experience, this can be a few things.   

1. Sulfated Batteries.-- When batteries are sulfated, the plate are covered in sulfation, this sulfation increases the resistance of the battery, and this causes a voltage drop across the battery... This voltage drop causes the voltage to rise as noted by the charger. 

2. Voltage Controlled Chargers. --If using a voltage controlled charger (Like Everything is) this can confuse the charger into thinking that the batteries are charged so the charger changes modes. 

3. Multiple Charging Sources. -- Multiple charging sources can also do this... this can cause the voltage to rise too fast and the "smarts" built into the chargers often confuse what charge stage the batteries are in.. 

4. Connections Cables... 

I personally like some of the newer controllers that allow you to control how many stages they will operate... 2 Stage or 3 Stage. 

Absorbing a flooded battery does nothing but cause gassing... gassing isn't a problem.  So one of the things I often say it distilled water is a
lot less expensive than replacing batteries.   Having a longer Absorb isn't going to cause a problem with your batteries. 

Freewilley said:

So today I have reoccuring the rotten charging situation that I have seen so many times over the years....
My good string of batterries was taken down to 50% or so (12.1 volts) over night. This morning I made up by running the generator for a couple of hours. Pretty good solar for over an hour now (about 900 watts) and this has driven my voltage up to absorb. 
But when I check the SG on the batteries, they are on.y 1.200. Charging at 35 amps.
My absorb setpoint is 15.1.
Why do they go into absorb when they are not even close to 80% charged, and more importantly, is this a problem??

One thing to keep in mind that what's happening with the Sg's is a delayed reaction...  Ideally when you measure your Sg's you measure them 2-3 hours after the charge cycle with absolutely zero load.. In your average system doing this is very difficult to do... Be-careful when taking measurements and be mindful that there may be a +/- .10 change after the mixing full occurs.  

As for FreeWilly's issue, it's hard to sit miles away to troubleshoot these systems sometimes you get it... sometimes you are just trying to walk the end user/installer into the solution....

My Best guess... There is a little bit of sulfation, this is causing a rise of voltage tricking the controllers to floating early.  It's a good think you disabled the end amps.  This is why I suggested to set the float a bit higher, as this can trick the controllers to stay at a higher voltage longer helping break up some of this sulfation...

Freewilley

Thanks Steve. I really appreciate the hours you have spent working on my system.

Some GOOD news, and Vic proves right....just got a new hydrometer (although the cheapie that Canadian Tire handles, better one on the way from the U.S.) and it is showing .10 to .15 higher than my old one.
So after the absorb, the SG readings are 1.240. As Steve points out, that is ACTIVE SG readings. I have put the new batteries on a short 1-2 hour EQ as there may be some sulphation and I WANT these puppies to see 100% charging today.

 Steve Higgins said:

Freewilley 
My Best guess... There is a little bit of sulfation, this is causing a rise of voltage tricking the controllers to floating early.  It's a good think you disabled the end amps.  This is why I suggested to set the float a bit higher, as this can trick the controllers to stay at a higher voltage longer helping break up some of this sulfation...

But the problem I think is that the absorb cycle starts when the bank is only 50-60% charged. Now this may be sulphation (that is what I have always blamed it on) but is there any other possible causes?

Thanks to all...and the struggle continues....

Estragon

> @Freewilley said:

>
> But the problem I think is that the absorb cycle starts when the bank is only 50-60% charged. Now this may be sulphation (that is what I have always blamed it on) but is there any other possible causes?
>

One would be improper temperature compensation.

jonr

It would be an interesting diagnostic to see if bubbling is starting at the bulk to absorb transition point.

Steve Higgins

Just so that you know, gassing on Rolls batteries starts generally about 2.25 to 2.3vpc Ambient temps also can effect this... So even in float you'll see a bit of bubbling. 

mike95490

What has the water usage been like - needs lots, or hardly any ?

Very little bubbling in BULK, as Absorb starts, so does bubbling, and in EQ, they should be fizzing pretty well

Multiple charging sources does not  "confuse"  the battery or chargers.   What happens is the max charge rate for the battery can be exceeded and because of internal resistance and too much charge current, the voltage rises and the battery appears to be be entering Absorb,

Freewilley

mike95490 said:

What has the water usage been like - needs lots, or hardly any ?

 What happens is the max charge rate for the battery can be exceeded and because of internal resistance and too much charge current, the voltage rises and the battery appears to be be entering Absorb,

Eureka??????????? 
Mike! You may have hit on it. With these 2 batterries I AM overcharging as my solar will put out 1300 watts (would that be approx 12 amps?) If so, that is about 50% more than the rated charging...
I will turn down the solar, by turning of one string of PV panels or try the alternative....please give me your thoughts on this....switching to the whole bank. The concern here is that one of the cells on one old battery is lagging...the SGs right now are 1.250 with laggart 1.190

I think the first one is the way to go today....

Very little water use. Although these new batteries have not been cycled much...maybe 10 times max (I am using an old string to switch to when weather limits taking the new ones back to 100%).

BB.

• 1,300 Watts * 0.77 panel+controller deratings *  1/15.0 volts charging = 67 amps typical max charging rate on a good day around noon with batteries at absorb voltage
  

10 amps * 15 volts = 150 Watts of power

During "bulk" charging (below absorb set point voltage), the combination of available sunlight and limits of charging controller set the amount of charging current (power).

During "absorb", the controller is holding a set voltage, and the battery is limiting charging current (based on State of Charge, Charging Voltage, Temperature of Battery, Battery Condition, etc.). When controller flips from Bulk to Absorb, charging current will be high (typically around 80-90% State of Charge, depending on rate of charge to battery bank--Higher rates of charge, the "closer" to 80% SoC that "flip" from bulk to absorb will occur). As battery aproaches 90-100% state of charge, absorb current will tail down to 1% steady state current (old flooded cell battery with high self discharge) to ~0.10 to 0.01 rate of charge (newer flooded cell or AGM/Sealed batteries).

If your charging current remains at 2% or higher rate of charge in absorb/float when the battery is "full", you either have a battery that is about to fail (and should be replaced), are charging at too high of voltage, or are "Equalizing" charging (for flooded cell only--AGM and other Sealed Lead Acid Batteries should not be floated at high charging voltages in normal situations).

-Bill

Freewilley

BB...so is it possible that charging at the 67 amp level will cause the CC to see a higher state of charge in the batteries and flip to absorb when the actual SofC is 70%?
And would that carry through the absorb cycle causing the current to reduce earlier than desired?

I have reduced the max charger total on one CC to 14 amps and that limits the solar wattage on that string to 200 watts. I am in absorb, the SGs are 1.230 and there is a very light bubbling going on. Current draw is 4-6 amps.

BB.

I would not say it the way you are.... The lead acid voltage during charging is highly variable, based on SoC, rate of charge, etc... Take a look at this (generic) lead acid charging chart:

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

Everything that is done with charge controllers is somebody's guess at how to get a lead acid battery properly charged in a highly variable. That is why some controllers have "absorb" times(timers). With variable depth of discharge and the whole solar variable stuff--Holding absorb voltage for 2-6 hours (2=shallow cycling, 6=deep cycling) hides a whole bunch of issues.

-Bill

Freewilley

I took Steve's advice and ordered a refractometer on amazon for $22. Rated 5 stars.
I think that will be way better than hydrometers....

Estragon

I'm really tempted to do the same. The only thing keeping me from doing it is the fact I'm a total klutz, and putting acid a few inches from my eyes might be tempting fate

mvas

What if you are dealing with ... stratification of the electrolyte?
If the electrolyte is not bubbling thoroughly for some time, to mix the electrolyte,
then the top layer will be a higher % of water vs the bottom layer and will be a lower SG reading.
Which is exactly what you are intermittently experiencing.
This is not a good thing.
Your tall S-550 batteries must bubble to reach 100% SOC and to mix the electrolyte.

mvas

There is no guarantee that Bulk Charging until Battery = 15 Volts equates to 80% SOC.

Consider this "example" ...
Bulk Charge at 60 amps until 15 Volts = 70% SOC
Bulk Charge at 50 amps until 15 Volts = 75% SOC
Bulk Charge at 40 amps until 15 Volts = 80% SOC
Bulk Charge at 30 amps until 15 Volts = 85% SOC

This is due to the internal resistance of the battery.

In the above example, the battery will never get to 80% SOC at the end of a 60 Amp Bulk Charge if terminated at 15 volts.
The SOC, State Of Charge, at the end of Bulk varies tremendously per the Bulk Amps, with a fixed End Volts.
Since the SOC at the end of Bulk varies, so too the time for Absorb Mode must vary as well.
Absorb Mode cannot be a "timed" event.
"Ending Amps" is a good way to terminate Absorb Mode, and always with bubbles.
No bubbles = PSOC = very bad news
After the electrolyte is re-mixed by the bubbles, then you can accurately measure the SG, not before.

With PV Panels and limited sunlight hours,
we do not have an infinite amount of time to Bulk Charge at low amps and then Absorb Charge forever.

I seriously doubt that you a over-charging.
Most likely you under-charging.

mcgivor

Agree with @mvas with the under charging, rationale behind my previous statement , isolate all loads charge fully, then EQ until the SG's are at the manufacturer recomendations, this process can take several days with solar. Continuous discharge and partial recharge is deteremental to the heath of the battery, sulfation sets in, then over time the crystals harden, making restoration more difficult.

Attached is some very useful and interesting information 

mike95490

This is what the generator is for, start it at dawn, and get the batteries charged.  Bulk with genset, Abs & Eq with solar if you can.

mvas

If I used my genny to Bulk Charge the battery bank to 85% SOC every day then that would cost me nearly $300 per month.
That ain't going to happen.
$300 is the price of one new Solar Panel every month.

If your PV Array is way too small, on a daily basis, then:
a) Increase the wattage obtained from Solar - immediately
b) decrease your daily usage - immediately
c) get higher efficiency appliances - immediately
d) all of the above - immediately

Burning $'s of fuel daily is not a reasonable substitute for installing an under-sized PV array, on purpose.

A properly sized PV array + a sunny day should Bulk, Absorb, Float daily and run the house loads.
And if the OP is doing 50% DOD then he must Bulk at >= 15% of C/20, otherwise PSOC at sunset !
PSOC must be avoided, it is like cancer.
You should only require the genny when you have too many consecutive cloudy days.
Cloudy days ( ie rainy season / winter ) - that is what the genny is for ...

mvas

Vic said:

Freewilley,

Ok on the Trimetric from years past.

It is a very good idea to gently clean the battery terminals and lugs as necessary.   Tin plated lugs  often fare well without very much burnishing at all,   just do what is necessary to make them generally shiny.  The Tin plating is thin so gentleness is usually good,  and all that is needed.

IMO,  once the battery terminals and lugs are clean and fairly shiny,   coat all of the mating surfaces and all of the battery terminals and cable lugs with petroleum jelly.   This is inexpensive and tenacious.   There seems to be no compromise in conductivity between the batt terminals and the cable lugs ...   this,   too,   may be a bit controversial.

There is the following formula for calculating the time for Absorption of a LA battery,   then,  one would see,  that there is NO variable for SOC,  or DOD of the battery:

t = 0.42 x (C/I)
 Where:

t = Absorption Charge Time (Hours)

C = 20 hr Rated Capacity (AH)                [ex: 2 strings x S-550 models (428 AH)  = 856 AH rated capacity]

I = Charging Current (Amps)                  [charger output min 5% up to max 10% of 20 hr rate] 
(above formula stolen from Surrette Battery Ltd possible Copyright applies)

BUT,  to me,   the above is for Constant Current charging (IUI).

For most of us that are using RE charge sources,   we really cannot use Constant Current chargers.

SO,  we  use Constant Voltage for Absorb.

All of the battery banks here  have Absorb times that require a wide variation in Abosrb times,  that does depend upon the DOD of the battery in the previous discharge.

Otherwise,  using the EA functions in the good solar CCs  would be of no use,   and also,  why would there need to be a Max Absorb time setting in many CCs,  if the Tabs was NOT a variable in battery charging?

The above,  just mo read on things,   not to argue too much,  FWIW,   Vic

The above formula incorrectly assumes ...
a) That Bulk Amps were exactly 10% of the C/20 rating
b) That Bulk Charging stopped at exactly 15.0 Volts (temperature compensated)
c) At the end of Bulk Charging, the battery is now exactly 80% SOC.

The chance for all of that happening with a PV Array, that varies the power due to sun position and clouds, is like 0%.
The above formula only applies to an AC Powered Charger that performs Bulk & Absorb at precise / constant Volts & Amps.
There is nothing precise or constant about Solar PV charging & Daily Loads.
Every day is an adventure, even in Arizona.
I do not get constant sunlight / constant watts for all 12 hours, nor constant House Loads.
Do you? 

And we can not charge at a slow 10% of C/20 when 50% DOD,
because we do not have enough hours of daylight to get back to 100% SOC before sunset !!!

The "Max Absorb Time" charger setting is for those who do not understand battery charging from PV Panels.

The battery bank is 100% SOC when the Absorb Amps drops below a specific value at a specific Absorb Voltage.
The "Ending Absorb Amps" value is not a timed value.
This 100% SOC state should occur as the electrolyte is bubbling and two SG readings taken 1 hour apart are the same.