Dialling in the SOC reading...

[alyaz]

I read a few threads here and am wondering if you guys have any suggestions or if it is possible to get the SOC % reading a bit closer than what it is currently showing.

From reading the threads, I suspect this is going at it back asswards, but wondering if this way around is also possible...

Today my three Classics went into float (set for end amps) at the same time that the SOC% reading was toggling between 92-93%.

So would you adjust the battery efficiency parameter (currently set at 85%) or the capacity parameter which is currently set at 1075 a/hrs (1105 a/hr bank) or both?  Steve at Rolls suggests that the FLA’s are about 80% efficient, so in your opinions should I just lower that parameter?   

Thanks.

[ClassicCrazy]

If you are using follow me they will all go to float at the same time - that is what it does.
Yeah - I would lower the efficiency .
Then I would monitor the specific gravity sometime when they are charging and if it hits full by SG when it is says at SOC ( and by ending amps)  you are okay.
Main thing is you want the batteries to be charged. 
Do you have the Absorb Voltage at the lower end of the range - if not I would lower that.
You may want to adjust your ending amps too if needed.

Larry

[alyaz]

Thanks Larry.

Yes I have the absorb amps set at the low end of the range.

Will try the 80% then...

Should have mentioned I did check a few of the cells and SG was between 1.260 and 1.275.

[ClassicCrazy]

Sometimes I see my batteries go to end amps and float at around 92% .  Seems like it depends on how cold my batteries are, how deeply discharged they were the night before, and how many amps are flowing in . 
Do you have your Absorb time set long enough ? I ask because if your absorb time runs out before it gets to your end amps it will go to Float no matter  what the SOC is at.

Larry

[alyaz]

Yes.  I have my absorb time set at five hours and today I got to float after 3:15 hours in absorb. 

[ClassicCrazy]

Actually now that I think about it - if your batteries filled up at 92% then you want to raise the efficiency not lower it.
Did you notice if all the amps taken out the night before had been filled back in and then some extra before it went to to Float ?
Mymidnite makes it easy to look back at the history because you can drag the line across the graph and see the negative amps  go up as it charges , and you can see the SOC at the same time . So if it fills 100% of what is taken out , and then keeps charging some more above that to make up for the efficiency - that is the point where you want to see the ending amps terminate the Absorb. On the graph you should able to see the system amps - battery charging amps start to level off for a bit - that should be your ending amps setting.

Larry

[boB]

Amp-Hour efficiency should be in the around mid-90% area typically.

Maybe old  batteries might be less.  But shouldn't be 80 or 85% for pretty sure.

And for ending-amps, you might want to let them charge for many hours and watch to see where the current goes to a flat low spot and stops decreasing.   It can't be any lower than that and shouldn't be too much higher of course.

[Vic]

Speaking as someone who is NO battery expert,   will make a few IMO-comments:

Yes,   there are many variables when trying to set battery parameters.

It seems that one important variable in choosing an Ah Charge Efficiency factor for a Flooded Lead Acid battery is  the rate at which it was discharged  --  the Peukert factor.   When  we count Ah into and out of the battery,   and cannot account for the Peukert factor,  that some significant variable is accounted for,  because the actual SOC at the end of the discharge really does depend on the Rate of the discharge.

Also,   most FLA battery manufacturers do note that the Charge efficiency of their batteries is 85%,   but this is almost certainly based on a discharge to 0% SOC (as this would make the efficiency appear to be its highest).

Battery Charge Efficiency is highest during the part of the charge that is at low SOC  --  very efficient  to about 80%  SOC,   much less so for batteries that cycle from 70,  or 80% SOC to a full-charge.

Again the following Link to some tests done at Sandia Labs on FLA Lead Antimony batteries:
https://xtronics.com/uploads/batpapsteve.pdf

The above tests were performed with C/30 discharge and charge Rates,   so will not necessarily be comparable to most of our off-grid,  Solar charged FLAs.

AGM  batteries have much higher Ah Charge Efficiencies,  due to their relatively high SG electrolyte,   which raises Gassing Voltage.  Resulting in considerably less time spent in the least efficient part of a LA battery charge stage  --  Gassing.

IMO,  for off grid FLA,  Solar-charged batteries,   the Charge Efficiency factor could vary considerably  from day-to-day based upon DOD,  discharge/charge Rates,   and a number of other variables.

Bottom line to me,   is that the WBjr  is a valuable,   inexpensive tool to help us monitor the charge and discharge of our batteries.   Am very pleased with the  performance of the WBs in use here.   But any Battery Monitoring device  will have limitations in its ability to show actual SOC,   and similar data.    A  great arrow to have in the battery-management quiver.

Just some personal opinions.   FWIW,   etc,   Vic

[boB]

I'm definitely not opposed to changing % efficiency to 80 or 85%

One can do a lot of charging and measuring specific gravity and voltages after waiting a while as well to tell what the proper efficiency is.

I was going on the recommendations of Ralph from Bogart Engineering's SOC calculations in his manuals.

He had a lot of years of experience doing this.

But then again, it will not really hurt anything to lower the efficiency a lot lower.  It will just take longer to say 100% and possibly use water faster.

[alyaz]

Thanks gang.  I will play around a bit with it and report back.  I couldn’t make sense if I should be upping or lowering the efficiency %. 

[ClassicCrazy]

Thanks gang.  I will play around a bit with it and report back.  I couldn’t make sense if I should be upping or lowering the efficiency %. 

Like Vic said above - it may be a bit different every day and SOC is just an estimate to make the invisible visable . 
There are probably more accurate ways to guess what is going on in a battery cell like monitoring individual cell voltages and temperatures and comparing them in relation to the charge they are getting at the time and in relation to each other.
But most people just seem to settle in for the good enough rough estimate.  Flooded lead acid cells can take a lot of abuse and still give pretty good performance so giving them better care than that is probably good enough .

Larry

[Westbranch]

Uh, er....AL aren't these the new batteries ?

If so have they been through the 50 or so cycles that most battery makers recommend before worrying about the SoC etc?

I agree with a raise in the efficiency value especially if you are through the break in period.
have fun...

[Vic]

Uh, er....AL aren't these the new batteries ?

If so have they been through the 50 or so cycles that most battery makers recommend before worrying about the SoC etc?

I agree with a raise in the efficiency value especially if you are through the break in period.
have fun...

Wb,   am NOT Al,   but,   ...

These batteries have been in off-grid use for about four months.  See Reply #39:

http://midniteftp.com/forum/index.php?topic=4158.30

SO,   they should be sufficiently broken-in,   IMO.

FWIW,   Vic

[alyaz]

Yes, they are in full-time use so well over 50 cycles.

I didn’t get a chance to watch when it went into float today so will wait for another sunny day.  If nothing else, it’s all good information and experience for me to get to know the workings of the ‘system’ better.

Here’s another question (yes, yet another question).

While using end amps...

So, the absorb voltage used is the voltage that we set into the controllers.  The absorb time is the default time should the end amp setting not be reached.

What is the correlation between the absorb voltage and reaching the end amp setting.  For example, is there any difference using an upper parameter absorb voltage setting versus a lower parameter absorb voltage setting when using end amps?  Or as long as I am in the ballpark (in my case between 29.4 - 30v) will the batteries accept and react to the end amps the same?  Hope that makes sense.

[ClassicCrazy]

With new batteries I would use the lower end of the absorb voltage range . You can raise it as your batteries age and may need it. They don't need it now so all you do with a higher voltage is theoretically heat them up more which shortens their life.

Ideally you would want SOC to be at 100% at the exact that ending amps is reached.  You want the end amps to be when the batteries are 100% charged according to SG test. The end amps at that point should be leveling out and not changing too fast - if you looked at it on the graph  you would see it start to plateau and smooth out.

Hard to get it all perfect because of real world variables and the batteries are not precision devices but they last a long time if a minimal effort is taken to get them set up right and check them seasonally to ensure they are happy.

Larry