Getting the ending amps set correctly

[ClassicCrazy]

I am watching the system amps and specific gravity of the battery in order to make sure I have the ending amps set correctly.  How long a period should the amps settle in for before I say good ?  Or should I just call it when the specific gravity gets to about 1.265 ? 

The first time I watched today I had the ending amps set too high, and the absorb time too short. So I just set ending amps real low and 6 hour absorb time.  I am using refractometer and am wondering if I am getting some different readings as the battery is warming up during the day. The refractometer is supposed to be temperature compensated. I put distilled water at same outside cold battery temp on it and calibrated it to zero line. 

From what I have seen I had ending amps set too high all winter so I may have to equalize batteries first and check again tomorrow .

I am using Local Status app to graph the System Amps as my reference.  My batteries are East Penn Deka L-16 rated for about 330 amp hours capacity . It is looking like around 2.1  to 1.8  amps range  may be about right ending amps .

[vtmaps]

How long a period should the amps settle in for before I say good ?  Or should I just call it when the specific gravity gets to about 1.265 ? 

Hopefully both events will happen at the same time... that is, the absorb current will stabilize at the time that 100% SOC is achieved (where SOC is determined by SG). 

The refractometer is supposed to be temperature compensated. I put distilled water at same outside cold battery temp on it and calibrated it to zero line. 

Do not use distilled water to calibrate... it's SG is too far from the SG that your refractometer is designed to measure.  Use battery acid of known SG... a small bottle will last for many years.

btw, when you measure SG with a hydrometer you are NOT measuring the concentration of sulfuric acid... you are measuring SG.  If you make the ASSUMPTION that the electrolyte contains ONLY sulfuric acid and water, then the concentration of sulfuric acid can be inferred from the SG.

When you measure SG with a refractometer, you are NOT measuring SG... you are measuring index of refraction.  Once again you must make assumptions in order to infer the concentration of sulfuric acid from the index of refraction.

Finally, there are the many assumptions you must make to infer SOC from the measurements you make with either a refractometer or an hydrometer.   For example, many folks report that after charging a battery, the SG increases a bit as the battery rests.  This may be because of gas dissolved (or suspended) in the electrolyte being slowly released from the electrolyte.

--vtMaps

[ClassicCrazy]

Interesting points that I will need to consider.
I should have said that my refractometer has two scales on it - one is for glycol concentration and has 32 degree at the bottom of that scale . The instructions say that is that line to calibrate it with distilled water. It is an inexpensive instrument. But a lot easier to use than the confusing temperature calibration of the hydrometer that I have.  The floating bulb of the hydrometer takes a lot of battery juice to make it float and the glass bulb seems it it likes to stick on the side.

[Garret]

I prepared a calibration solution consisting of 27.25 % (weight percent) IN WATER sucrose (table sugar) that has the same refractive index as 1.265 g/ml H2SO4.  Works great, harmless and removes all doubt.  Confirmed the accuracy by comparing to the gold star method of weighing an accurately measured volume of electrolyte (SG=mass/volume).

Using end amps is kind of a trial and error game isn't it?   My 428 Ahr, 24 V battery bank seems to like 2.4 amps on the Whizbang when fully charged. This requires about 3:20 hours of Absorb time.  I also concur that the SG seems a little lower until the electrolyte degases.

[ClassicCrazy]

I prepared a calibration solution consisting of 27.25 % (weight percent) sucrose (table sugar) that has the same refractive index as 1.265 g/ml H2SO4.  Works great, harmless and removes all doubt.  Confirmed the accuracy by comparing to the gold star method of weighing an accurately measured volume of electrolyte (SG=mass/volume).

Using end amps is kind of a trial and error game isn't it?   My 428 Ahr, 24 V battery bank seems to like 2.4 amps on the Whizbang when fully charged. This requires about 3:20 hours of Absorb time.  I also concur that the SG seems a little lower until the electrolyte degases.

27.25 percent of weight of sulfuric acid  ? So 100 grams of sulfuric acid  I would add 27.25 grams of sugar  to get 1.265 specific gravity  calibration fluid ? I guess the sugar should be easy enough to find - sulfuric acid from a painting department at a store ?  seems like that is where I have seen it before.

Yes to the trial and error game - keeping a close eye on it for a day or two to make sure everything is correct. I did this a year or two ago but now it is a bit easier by using the Local Status App system amps monitoring graph. If someone could write an excel program to pinpoint the amps flat line from Local Status App exported data that would make it even easier ! 

thanks for the tips and info
Larry

[vtmaps]

27.25 percent of weight of sulfuric acid  ? So 100 grams of sulfuric acid  I would add 27.25 grams of sugar  to get 1.265 specific gravity  calibration fluid ?

Huh?  I'm not following this... DANGER  ... DO NOT MIX SUGAR and SULFURIC ACID.   

For that matter, don't even mix concentrated sulfuric acid with water unless you know what you're doing... it's very exothermic.   Buy some calibration fluid from a refractometer dealer or scientific supply house.  Or buy some electrolyte from a battery dealer.

--vtMaps

[Garret]

ClassicCrazy and vtmaps,

27.25 percent of weight of sulfuric acid  ? So 100 grams of sulfuric acid  I would add 27.25 grams of sugar  to get 1.265 specific gravity  calibration fluid ?

That's not what I said.  Read my post again.  The sugar solution is IN WATER and has the same refractive index as SG 1.265 electrolyte (sulfuric acid).  I am offering a safe alternative to using a bottle of known SG=1.265 battery electrolyte as a calibration standard for the refractometer.  I should have probably been more specific.  As a chemist, I sometimes assume others understand certain principles in much the same way as the Electronic Techs and Computer folks do on here.

Yes, for God's sake DO NOT mix concentrated sulfuric acid with sugar, it will char and catch fire.

[Garret]

If someone could write an excel program to pinpoint the amps flat line from Local Status App exported data that would make it even easier ! 

Yes, it would be easy enough to plot the amps curve and calculate the trend as a function of SOC in Excel to predict ending amps.  Thanks, I will do this.

[ClassicCrazy]

Thanks for the clarification on the sugar to WATER ratio - I had looked at that late at night and you must have edited WATER  or else I was half asleep ! I thought it would be with water .

I was trying to plot some of the exported data from Local Status app but I just don't know enough about Excel to put in the formulas even to get the dates and times right . I really need to take a class on Excel . If you do make up a sheet with formulas on it could you share the template or whatever you call it ?

Thanks,
Larry

[Resthome]

Couple things to remember when dumping the Live Data from the Local App into Excel. The first one is Cell B2 is the for UTC timezone Offset (GMT offset -- e.g. US PST time is GMT-7 so use -7. Brisbane Australia is GMT+10 so use 10).

Then you want to format all cells in column A as TIME this will give you the correct hours minutes and seconds for each reading.

There are a couple of errors in the way the time formulas are presented in column A by Andrew’s LA.

The first error is a bad formula in A4

=(B5/1000 +$B$2*60*60)/86400 + 25569

The correct formula is

=(B4/1000 + $B$2*60*60)/86400 + 25569

All formulas is column A are off by one row and you need to replicate the corrected A4 down through all cells in column A that have data. Doing this will get rid of a second error that occurs further down is column A. I’m not sure it occurs in the same place but the above formula will start over again with B5. In the case I’m looking at now this occurred in cell A12801. You will see it if you are looking at the time in column A and have change the cells to represent TIME because the time will most likely jump from PM back to AM if you were collecting data from the morning until the evening.

I'll post this in the LA thread and maybe Andrew can fix this.

[Garret]

Explains why the tips/comments in the spreadsheet were of little help.  I managed to solve the problem with the incorrect formulas and offset a couple of months ago.  I was afraid to post the corrections because I thought it was just me not being able to follow the instructions as usual.

[ClassicCrazy]

John,
Can you attach a copy of Excel sheet with the proper formulas in it ?
I was able to put one of the formulas in and reformat the cells in column A . What do you do with column B ?
Thanks,
Larry

[Resthome]

John,
Can you attach a copy of Excel sheet with the proper formulas in it ?
I was able to put one of the formulas in and reformat the cells in column A . What do you do with column B ?
Thanks,
Larry

Larry

I would but the forum limits don't allow that large of a file attachment.  For replicating column A all you have to do is grap the botom right corner of cell A4 with your mouse until you see a little + sign in that corner then hold down the mouse and drag it down through all your column A cells with data. It will correct all the formulas for you.

I just normally hide column B.  It's only need for the calculations in column A and has no viewing purpose. 

I'll try to put a file in Dropbox later today for you. But you will still have to change the formulas in coulm A for your own data.

Andrew also said in the LA thread he would look at this.

[ClassicCrazy]

I was able to fix the formula and drag down and fix the cells so they were all sequenced correctly. I have not figured out how to put in the time offset though. 

Can't you just upload an Excel with no data in it but the correct formula's ?  No big deal - the drop box method seems like good idea and no hurry on my part.

I will look in that other thread. 

Thanks,
Larry

[Resthome]

I was able to fix the formula and drag down and fix the cells so they were all sequenced correctly. I have not figured out how to put in the time offset though. 

Can't you just upload an Excel with no data in it but the correct formula's ?  No big deal - the drop box method seems like good idea and no hurry on my part.

I will look in that other thread. 

Thanks,
Larry

Larry,

The time offset is the same number you will see in the Timezone button when setting your PC clock. I'm in the PDT zone now and it is -8 for Daylight Saving time.

Here is what I think is a blank spreadsheet with the formulas and a WBjr tab for a second page that draws the graphs. It may vary by how much data you load.  The graph needs WBjr Amps, Battery Voltage and SOC data