MNGP Volts vs Battery Charge

[ddxv]

I am not entirely clear, what is the relationship between the Batt Volts reported by Midnite Solar and the % charge of the batteries?

Is this a reliable way to estimate charge?

[boB]

Not a lot of relationship between volts and SOC% when just measuring AH in and AH out except that when the Classic has done an absorb cycle for at least the proper amount of time, (Anti-Sulfation Stage I am calling it nowadays), when it drops voltage and goes to float, it's DEFINITELY fully charged !  So at that time, we stop the SOC% from flashing and KNOW that it is 100% charged and can then start counting amp-hours being pulled from it.

But you don't really know the actual capacity of the battery unless you measure it.  There are automatic methods of
doing that too, and some of those methods do involve measuring voltage and noting the current in or out of the batter
at those times.  That's not in the Classic quite yet.

So, to answer your question, at least for short term SOC% over a week or two, amp hours out of the battery and amp hours into the battery, taking into account amp-hour charge efficiency does a pretty good job at telling your State Of Charge.

boB

[vtmaps]

But you don't really know the actual capacity of the battery unless you measure it.  There are automatic methods of doing that too, and some of those methods do involve measuring voltage and noting the current in or out of the batter at those times.  That's not in the Classic quite yet.

All the progress on the whizbang jr and the battery monitor has got me more and more interested in trading in my outback FM60 for a Classic.  A battery capacity tester (is that some sort of impedance tester?) would definitely push me over the limits of my ability to contain my feature envy.   

--vtMaps

[mahendra]

So Bob ,Are you implying that the classic with a whizbang in the near future ,can accurately/closely  determine the Ah of a battery bank regardless of age.

[mahendra]

If so i am elated

[dgd]

So Bob ,Are you implying that the classic with a whizbang in the near future ,can accurately/closely  determine the Ah of a battery bank regardless of age.

Eh?  There must be a lot more to the Classic/Whizzbang combo than I can imagine. Perhaps we will will soon get a Wetwizz gizmo interfaced to the Classic that measures the wet cells SG and then an AUX control to drip feed water into each cell and with automated Ah measuring a close estimate date, based on current usage, of when the cell will need replaced.
And maybe an automated new cell ordering routine in the firmware to ensure replacement cells just at the right time. Of course the Classic would need your credit card info etc....

[Resthome]

So Bob ,Are you implying that the classic with a whizbang in the near future ,can accurately/closely  determine the Ah of a battery bank regardless of age.

Good luck with that one. 

[TomW]

So Bob ,Are you implying that the classic with a whizbang in the near future ,can accurately/closely  determine the Ah of a battery bank regardless of age.

This may be possible to do empirically but I seriously doubt the Classic will ever be that well endowed with features and circuits to do it.

It would seem to require charge / discharge cycling at known rates and then massaging any data to obtain the value you seek.

Or not.

I still think SOC is more black art than pure science with way too many variables that are hard to track to give extreme accuracy. I ain't the sharpest tack in the box, however.

Just my early morning opinion likely not shared by many.

Tom

[vtmaps]

This may be possible to do empirically but I seriously doubt the Classic will ever be that well endowed with features and circuits to do it.

It would seem to require charge / discharge cycling at known rates and then massaging any data to obtain the value you seek.

There are a variety of impedance testing techniques that can be done very quickly (in seconds).  Some industrial battery chargers do this every time they are connected to a battery.

--vtMaps

[ChrisOlson]

when the Classic has done an absorb cycle for at least the proper amount of time, (Anti-Sulfation Stage I am calling it nowadays), when it drops voltage and goes to float, it's DEFINITELY fully charged !  So at that time, we stop the SOC% from flashing and KNOW that it is 100% charged and can then start counting amp-hours being pulled from it.

Kind of an old thread now, but I'd like to point out that this is not always the case boB.  If the battery is sulfated its internal resistance is high enough to "fool" a charger using end amps into ending the absorb stage before the battery is fully charged.

The hydrometer is the only accurate method to determine if your battery is actually fully charged.

So what I'm saying is, get out your hydrometer when you calibrate your Battery Monitor and charge controllers and make sure the battery is actually at 100% SOC when everything else says it is.  Then, if your battery monitor is working right, it SHOULD show you eventual loss in capacity from that initial baseline calibration.

I spent some time on the phone with Ralph Hiesey (founder of Bogart Engineering) a few weeks back and he explained to me how to use the average amp loss in the H4.x function of the TriMetric to track cycle efficiency.  The TriMetric uses "weighted" values for its calculations, such as charge efficiency being almost 100% efficient up to where the battery starts to gas.  That man has been living and breathing batteries and battery monitors for over 20 years.  I don't think it's as much "black art" as TomW says, as our TriMetric tracks it very well here (we have the TM-2025 which has different algorithms and menus in it than the old TM-2020 had).  The really hard cycles to track are ones that run 100-150 hours between full charges because you're cycling your battery in the most efficient part of its charge curve for many days.  The TriMetric 2025 tracks that with perfection.

I been gonna get one of them WhizBangs for our Classics so I could try that to see how it compares to our TriMetric.  But haven't gotten around to it yet.

[mahendra]

I think Tom was implying that it is black art for newer technologies of batteries i.e sla,nicad,lithium ,since one cannot use a hydrometer to test on these technologies.

[ChrisOlson]

I think Tom was implying that it is black art for newer technologies of batteries i.e sla,nicad,lithium ,since one cannot use a hydrometer to test on these technologies.

I would tend to agree.  However, those technologies have not really gained big inroads into the RE business.  FLA hasn't really changed much in technology in over 150 years.  The venerable FLA battery is a pretty simple device, still the most economical per kWh, the batteries today are made of almost 100% recycled lead so they have a very low environmental impact, and the methodology used to track them for capacity is also pretty simple.  I don't see them being displaced by more exotic technology any time soon.

[boB]

when the Classic has done an absorb cycle for at least the proper amount of time, (Anti-Sulfation Stage I am calling it nowadays), when it drops voltage and goes to float, it's DEFINITELY fully charged !  So at that time, we stop the SOC% from flashing and KNOW that it is 100% charged and can then start counting amp-hours being pulled from it.

Kind of an old thread now, but I'd like to point out that this is not always the case boB. If the battery is sulfated its internal resistance is high enough to "fool" a charger using end amps into ending the absorb stage before the battery is fully charged.

The hydrometer is the only accurate method to determine if your battery is actually fully charged.
........

I agree totally about the resistance fooling the ending amps...  That is one reason why I said "timed" rather than using ending amps.   One could also just disconnect the battery and the controller voltage would immediately be in absorb and zero current and end the Absorb cycle.

When doing an intermittent (e.g. weekly) Absorb (Anti Sulfation Stage  A.S.S.), Ending Amps is NOT useful except to possibly start the Absorb timer.   Then there is the boost charge that can be done in addition to all this but that is additional goodness.

[ChrisOlson]

When doing an intermittent (e.g. weekly) Absorb (Anti Sulfation Stage  A.S.S.), Ending Amps is NOT useful except to possibly start the Absorb timer.

Not totally sure I follow you on that one, boB.  We have our system set up to cycle our batteries 60-70 times per year.  So our absorb cycles normally happen once every 5-7 days or so, on average.  But we have run a couple cycles that went over 2 weeks.  I have max absorb time set at 5 hours and on a long cycle like that the timer will time out before the battery ever reaches end amps.  And when I check SG, sure enough, the battery is still not at 100% SOC with SG's in the 1.245-1.250 range.  It takes a second day of absorbing to finally get them to end amps, and when they hit end amps and the system exits absorb the SG's are 1.265-1.270, right on the money.

If a battery gets sulfated, however, you can either time out the absorb timer, or reach end amps, during absorb stage and the battery will still not be at 100% SOC, even after two days of absorbing.  We were gone this winter for 6 weeks and our batteries got sulfated.  It took two days and 21 hours of equalizing, plus and additional week of nice sunny weather with Absorb V set to EQ voltage to finally get them back to 1.265-1.270 (ornery frickin' Surrettes).  The warning I had that they weren't "right" when we got back home and fired our system up was the fact that the TriMetric said they were only at 88% SOC after all the other system settings said they were fully absorbed.

[vtmaps]

The warning I had that they weren't "right" when we got back home and fired our system up was the fact that the TriMetric said they were only at 88% SOC after all the other system settings said they were fully absorbed.

Hi Chris,
Your experience is mine also... after a few days of SG down, it takes a few days of 'parameters met' to get the SG back up.

Two questions...
1) I have an older trimetric 2020... how does yours work?  On mine, I set 'end amps' parameters that, when met, cause the trimetric to reset to 100%.   If my charger and my trimetric both use the same parameters, then both should be fooled when the parameters are met at less than 100% SOC.  Why does your trimetric get it right when your charger gets it wrong?

2) How did you maintain your batteries while you were gone?  Were they cycled, or were they on some 'float' type maintenance?

--vtMaps