Measure present Full Battery Capacity (as it declines)

[john61ct]

SoH can only be measured accurately by

1. a proper load test, or

2. super expensive lab-grade equipment

In theory a SmartGauge, calibrated against an accurate AH counting meter like BMV-712, may give a sort-of acceptable guesstimate.

And sorry what does SP stand for?

[rgleason]

Sorry, meant SG specific gravity.

[Maine Sail]

Originally Posted by rgleason

If the only way to measure the battery capacity is by 20hr test down to 10.5v, then how could Smartgauge possibly be accurate at this task?

What is it's methodology such that it is accurate?

The Smartgauge is measuring SOC not Ah capacity.



A partial discharge test can be very misleading.

[Pete7]

Originally Posted by john61ct

When the capacity has dropped to 203AH, that is now the new 100%.

On an AH counting SoC meter, that is the number that needs regular updating to keep the SoC guesstimates as accurate as possible.

Just to update this "some AH counting SoC meters need that number" but not all. I use one of these and it doesn't matter what capacity the bank is, nor is there anyway to enter this information.

https://sterling-power.com/products/...nagement-panel

[john61ct]

Originally Posted by Pete7

Just to update this "some AH counting SoC meters need that number" but not all. I use one of these and it doesn't matter what capacity the bank is, nor is there anyway to enter this information.

https://sterling-power.com/products/...nagement-panel

That is a much more general product that happens to includes an AH counter.

Not disparaging it, but does not count as a proper SoC monitor IMO.

[a64pilot]

Originally Posted by Maine Sail

The Smartgauge is measuring SOC not Ah capacity.



A partial discharge test can be very misleading.

Question, if you spend 10 hours discharging to a smart gauge reading of 50% SOC, Read the amps used from an AH counter, and double that to get bank capacity, is that decently accurate?

[john61ct]

That's the idea that's been floated here.

The key word is "decently".

For most people's needs, to adjust the AH-counting SoC meter, IMO yes, **if** the SG has been shown to be accurate in **that** given setup with that bank.

Historically showing a slow consistent decline in capacity.

But an occasional load test is needed to confirm just **how** accurate.

Most people just scoff at this level of OCD effort wrt a bank's care.

[rgleason]

Thank you John and a64 that is helpful.

Should we be defining OCD in some definitions thread? ...Just kidding, just as long as it is not ADHD

[Maine Sail]

Originally Posted by Pete7

Just to update this "some AH counting SoC meters need that number" but not all. I use one of these and it doesn't matter what capacity the bank is, nor is there anyway to enter this information.

https://sterling-power.com/products/...nagement-panel

This is because it only measures Ah's taken out and put back in, it is simply an Ah counter with no SOC functions. In other words it is not an Ah counter + SOC meter.

If you don't know your banks actual Ah capacity then this data does you no good. This meter does not even compensate for Peukert or Coulombic efficiency but, for the price, is a good value for current and voltage data.

"USING THE AMP HOUR COUNTER
The Power Management Panel will tell you exactly how much power you have used from your batteries. From your overall battery capacity you can then calculate how many amp hours you have got left to use, and you will know when it is time to recharge your batteries."


If you don't know how many Ah's your batteries can deliver, or your "overall battery capacity" at their current SOH, then the data you get is not going to be accurate. For example if your batteries say, on the sticker, they are 200Ah and you remove 100Ah, based on the meter, you might assume you're at 50% SOC. However if the batteries have aged, and lost capacity, and are now a 130Ah bank and you remove 100Ah...... Oops....

[Mike OReilly]

This is the thing that confounds me as a cruiser Mainsail. My batteries are ALWAYS in use; either discharging or recharging. And therefore they are always changing.

I understand the 20 hr test procedure to ascertain current capacity, but it's both difficult to do, and completely impractical. So what am I to do?

I have a victron battery monitor. It is programmed with the official specs for my batteries. But I'm sure my 120 amp-hr batts are no longer at that level. So I mostly ignore the SOC measure, and monitor amps in and amps out. Mostly I monitor unloaded voltage (not resting, just unloaded). And I rely on my mppt 3-stage solar charger to keep things healthy.

[a64pilot]

For whatever it’s worth using my Smart Gauge as a way to determine AH capacity of my bank I come up with that my almost four yr old Lifeline 660 AH bank has 600 AH capacity, now I’m conservative but I think that is close.
When I program my Magnum BMK kit for the bank to be a 600 AH bank, it tracks very, very close to the Smart Gauge in the early morning before Solar starts working.
Once Solar begins putting current into the bank, the Smart Gauge seems to lag behind in charge, it appears to be most accurate after an all night discharge before any charging begins.

I would think my bank hasn’t lost much if any capacity as it’s voltage as compared to the voltage under load chart that Lifeline has published is about .15 V higher than chart voltage, but it is what it is.

I know that an honest to goodness 20 discharge with the current being held constant is the only true measure, but I’m not spending the money or time, nor dedicating the storage space for the equipment.
For me close is just going to have to be good enough, that and to be sure to err to the side of caution and assume my bank is lower in capacity than it really is, so that I don’t inadvertently pull it lower than I want to.

I try to keep discharge to 25%, but occasionally will go lower.

[Zil]

Lead acid batteries don't lose capacity (AH) because the acid weakens (SG). Rather they lose capacity because the plates deteriorate. They still can charge to full voltage and high SG. They just will not last as long.

[motion30]

Living on the hook with solar power I am unable to do the 20-hour test. I guess when I start waking up in the morning and my voltage is below 12 volts I will know it is time to buy new batteries

[Zil]

20 hour test is not practical for any but Maine Sail. But, Yes, that is what we have. What does it look like in the morning. Hopefully after coffee.

[wsmurdoch]

Originally Posted by Zil

Lead acid batteries don't lose capacity (AH) because the acid weakens (SG). Rather they lose capacity because the plates deteriorate. They still can charge to full voltage and high SG. They just will not last as long.

Wouldn't a "sulfated" battery have much of its sulfuric acid permanently and irreversibly converted into lead sulfate reducing the amount of sulfuric acid in the electrolyte and lowering the specific gravity of the fully charged "sulfated" battery?