Depth of Discharge Myth?

[wsmurdoch]

Originally Posted by Dockhead

It seems to be a fact that our batteries fail a lot from "sulfation" and hardly at all from positive plate corrosion. Did you ever hear about anyone's batteries failing from being equalized too much?

How can I tell without cutting a FLA battery open at the end of its life whether the battery died from "sulfation" or from positive plate corrosion due to overcharging while equalizing them. Similarly, how about other failure modes; active material shedding, soft cell shorts, plate warping... ? Do people just say "sulfation" and go on?

If I could tell how this set of batteries failed, I could change my treatment of the next set and do better.

(When I was a kid and delivered newspapers, I picked up and folded my papers at a battery rebuilding business. They cut open the old 6V black rubber car batteries with tar in the tops of the cells, pulled out the guts, and repaired the batteries. I've seen the guts of lots of bad batteries.)

The only tools I seem to have are battery (not cell) voltages, cell specific gravity, a view in thru the cell caps, and a miserable shadow view of the bottom of the cells with a strong flashlight.

Bill

[a64pilot]

Again hopefully not mis-quoting Maine Sail, but unless I’m mistaken he has posted that he has only seen one battery killed by overcharging, it was apparently a Boat on a mooring with the Solar panel connected directly to the battery.
I believe unless mistaken again that he cut open the battery and it was pretty much dry, an AGM I think.

While possible, it appears that battery death due to overcharging on a cruising boat that is being used, is very unlikely, more likely in a boat in a marina that has a malfunctioning charger or similar.

Me personally, I’m no Marine Professional that is installing and replacing batteries regularly, I really only have my own bank to draw experience from.

[sailorboy1]

I’ve killed a battery by overcharging. It was my start battery and was a sealed battery. When I increased my charge voltage to 14.8v to. match Trojan recommendations for my house bank I didn’t think about the start battery. After a year I prayed off the start battery covers it was pretty dry. This of course was my fault. I now keep the start battery isolated.

[a64pilot]

I assume it was killed by its proper Absorption voltage being exceeded?
Yes, of course too high a voltage will kill one, I guess I should have said that as long as proper absorption voltage isn’t exceed, killing a battery from overcharging is a rare event.

[john61ct]

Originally Posted by kmacdonald

A lot of 3 stage chargers have fixed absorption times that aren't adjustable. A simple internal regulator set at about 14.4 volts is often the best solution. They usually aren't adjustable but a few are. I know the gourmet systems are in vogue now but only because you have been lead to believe you have extraordinary electrical needs. Add to that a little fear mongering and you have a great little niche market. A realistic analysis of your electrical needs and a cost vs rewards analysis needs to be undertaken. The best solution won't be the same for everyone. Be careful, these are shark infested waters.

Since quality infrastructure can last for decades, and I want to be free to choose FLA, GEL or LFP at any point down the road,

Batteries are consumables, usually only last 5-8 years, silly to design infrastructure around a short-term variable

Therefore I would only purchase charge sources with fully user-adjustable setpoints.

In solar this is standard.

Shore chargers it is not uncommon at the high end, and lots of other benefits to buying quality, like the ability to derate an 80A source down to 40 or 20A when desired.

Alt VRs very rare, but if an important charge source worth the investment.

One lower cost alternative if retrofitting is a single purchase of Sterling's B2B DCDC chargers, can then front-end control the profile fed by any old primary source.

[ramblinrod]

Originally Posted by Dockhead

A key question! Where do we get information to support this idea? Google doesn't help. It sounds like a good logical explanation, but where do we get this information? Calder doesn't write anything about it, and there's nothing turned up by Google.

I just told you. ;-)

Read up about amphorous vs crystalline lead sulfate.

There is your answer.

Don't let the lead sulfate harden.

How?

Don't leave it discharged too long.

The deeper the discharge the greater the sulfation.

The longer it sits sulfated the more it hardens.

The more it hardens the more difficult it is to reconvert.

Deep discharge with a long sit there, capacity tanks.

The active lead plate surface you started with is all covered up, and can't shake the lead sulfate off when you throw the charger on.

[conachair]

So anyone log & plot battery data?

If not it's like listening to an out of tune radio 3 rooms away compared to top of the range headphones

And really not difficult now for less than the cost of an ICW lunch
(plus a laptop of monitor to get into the Pi)

Just need a raspberry pi running openplotter, a ads115 voltage sensor, and ... that's it.

Signalk looks after the logging, install influxdb database and chronograf then in the signalk app store there's a store to influxdb app to store as many data sources as you want. chronograf makes looking at the data easy -


Only been running since last night so the second plot is the firist one delayed by an hour, other delay options available so you can compare yesterday or a week ago.

This would make a great opensource project if anyone was interested, design a pcb for a few dollars with sockets for voltage sensor, temperature sensors, barometer and an ESP8266 which could then send the lot over wifi to signalk.

[Dockhead]

Originally Posted by ramblinrod

I just told you. ;-)

You suggested Googling it.

Originally Posted by ramblinrod

Read up about amphorous vs crystalline lead sulfate.

Read up where? If you've actually done any reading yourself, can you give some cites? Doesn't need to be free Google material; anything. Thanks in advance for any leads.


Also, if you actually understand it yourself (and no shame if you don't; none of the rest of us do either), maybe you would enjoy explaining it in more detail.

[sailorboy1]

what are we now trying to "prove"?

[kmacdonald]

Originally Posted by sailorboy1

what are we now trying to "prove"?

The earth is flat!

[Zil]

Every one knows the earth is flat. It is just that the edge is very far away.

[thinwater]

Originally Posted by Wotname

Sorry to say you are wrong again
10.5V is 100% discharge in a 12V system.

50% is about 12V (depends on your preferred source of information)

Depends on the temperature. The biggest problems I have with capacity are in the winter, when some electronics begin warning of low voltage at 60% SOC (voltage will be slightly lower than table due to light load). The batteries may be below this table (20F or less) in the morning.

[evm1024]

Originally Posted by Dockhead

You suggested Googling it.

Read up where? If you've actually done any reading yourself, can you give some cites? Doesn't need to be free Google material; anything. Thanks in advance for any leads.


Also, if you actually understand it yourself (and no shame if you don't; none of the rest of us do either), maybe you would enjoy explaining it in more detail.

Here is a link to a paper that does address some of the failure modes of LA cells.

You are asking scientific questions and deserve scientific answers. Many of us have a layman's or technician's level of understanding and a few just think they know the answers and that those answers are simple (just google it).

But as the paper points out the term sulfation has at least 3 meanings and do not cover the range of common failure mechanisms in lead acid batteries. Things are not simple.

You will note in the clip below that lead sulfate crystal growth takes place over an extended time. Not overnight as has been implied. And that "sulfation" is not much in terms of a failure mode.

https://www.sciencedirect.com/scienc...78775303010681


Here is a clip from the paper:

“Sulfation” (second definition): This is the oldest and most discussed failure mode in lead–acid batteries. Essentially, lead sulfate crystal growth takes place over extended periods of time. Since lead sulfate is non-conductive, the crystalline mass tends to become passive to further electrochemical activity. If one measures the loss of battery capacity over time, the effect is indeed consistent with hard sulfation (and, at the same time, a number of other mechanisms). Teardown studies do reveal the presence of hard sulfation but it is usually not the failure mode for that battery. (1) This hard sulfation effect is considered to be irreversible but substantial discussion suggests that the conversion might be possible. However, battery failure is usually brought about for other reasons. In this connection, it has been observed that after a certain period of time under a deep discharge conditions, the recrystallization of lead sulfate could create a situation that makes it difficult to recharge the battery, if not impossible, with the usual charging method. This problem becomes more important as vehicles are equipped with electric motors and demand additional power. The new generation of vehicles with new start-up functions will probably increase the number of batteries “sulfated” as the additional power requirements act to discharge the battery during idle periods.

[ramblinrod]

Originally Posted by evm1024

Good discussion (when kept at a technical level).

There are peer reviewed papers out there that take a good look at FLA parameters under most all conditions.

In terms of charging efficiency it appears that the efficiency declines with increasing SOC. As noted in the paper charge efficiency vs SOC is non-linear and runs around 91% average for SOC between 0% and 84%. The charge efficiency is 55% with SOC between 79% and 84%. Clearly a decrease in charge efficiency with a higher SOC. Further the charge efficiency was less than 50% at SOC greater than 90%.

See:

A Study of Lead-Acid Battery Efficiency Near Top-of-Charge
and the Impact on PV System Design
John W. Stevens and Garth P. Corey
Sandia National Laboratories, Photovoltaic System Applications Department
Sandia National Laboratories, Battery Analysis and Evaluation Department
PO Box 5800, MS 0753
Albuquerque, New Mexico 87185-0753

https://xtronics.com/uploads/batpapsteve.pdf

Here is the clip:

CONCLUSIONS
A test procedure has been developed to allow the
examination of battery charge efficiency as a function of
battery state of charge. Preliminary results agree well
with established general understanding that the charge
efficiency of flooded lead-antimony batteries declines with
increasing state-of-charge, and that charge efficiency is a
non-linear function of battery state-of-charge. These
tests indicate that from zero SOC to 84% SOC the
average overall battery charging efficiency is 91%, and
that the incremental battery charging efficiency from 79%
to 84% is only 55%. This is particularly significant in PV
systems where the designer expects the batteries to
normally operate at SOC above 80%, with deeper
discharge only occurring during periods of extended bad
weather. In such systems, the low charge efficiency at
high SOC may result in a substantial reduction in actual
available stored energy because nearly half the available
energy is serving losses rather than charging the battery.
Low charging efficiency can then result in the battery
operating at an average SOC significantly lower than the
system designer would anticipate without a detailed
understanding of charge efficiency as a function of SOC.
During normal weather, capacity degradation will not be
evident, but it will manifest itself when the battery is
called on to provide the full purchased capacity, which
will be found to be unavailable. Extended operation in a
low SOC environment can also result in permanent loss
of capacity from sulfation if the battery is operated for
long periods of time without a sufficient recovery or
equalizing charge.
The impact of low charge efficiency at high states of
charge has the greatest potential impact on systems
where high energy availability is needed. Such systems
usually utilize large batteries to ensure energy availability
during the longest stretches of bad weather. This may
not provide the energy required if the PV array is
insufficient to provide a recovery charge for batteries at
90% SOC and above, where charge efficiency is very low.
Charge efficiencies at 90% SOC and greater were
measured at less than 50% for the battery tested here,
requiring a PV array that supplies more than twice the
energy that the load consumes for a full recovery charge.
Many batteries in PV systems never reach a full state of
charge, resulting in a slow battery capacity loss from
stratification and sulfation over the life of the battery

Thank you!

Excellent post.

I had not seen this before.

However, as soon as I started reading it my "BS" senses started tingling.

It should have been "peer" reviewed by a "technician".

When I look at this report (and others like it), a whole bunch of red flags start going off, and I ask myself,

"How well do the test parameters represent a real world condition?"

And then I ask myself,

"How might real world conditions alter the outcome."

How Well Do the Test Parameters Represent Real World Conditions?

So lets look at some parameters in this case:

Where I use the phrase "Educated Guess" below, I would have performed an investigation to confirm.

Lab Environment:

Battery was likely on a large heavy table, perhaps with a highly thermally conductive surface representing a significant heat sink. (Educated guess.)

Lab was temperature controlled to 72F (given).

Battery was not in a battery box (Educated guess).

Battery was in middle of large table with nothing around it. (Educated guess.)

Battery was exposed to normal lab environment air circulation or even more likely, under a ventilation hood. (Educated guess.)

Charge current was very low, C/30 (3.33 A) and fixed. (given)

The charge cycle can go on for as long as it takes for the battery to achieve 100% before the discharge cycle is started. At C/33 and 50% SOC start for a 100 A-hr battery, the charge cycle was likely 20 hours. (Educated guess.)

Real World:

Battery is likely in a plastic box, representing no heat sink. Any external or internal heat generated is not likely to be dissipated effectively. (Educated guess.)

Battery compartment not temperature controlled. Temperature will increase based on duration of charge cycle (both by self heating and nearby ICE operation, probably in communication with the battery space. (Educated guess.)

Before end of charge cycle, battery box internal would likely be 150F+ at 50% starting SOC vs 85F at 90% starting SOC. (Educated guess.)

Battery likely packed in very tightly with others, reducing ventillation and heat dissipation further. (Educated guess).

For lower SOC charging (to about 85% SOC) charge current would be C/4 (40-60 A), for higher SOC charging (85-95%) charge current would be variable from C/4 to C/30 declining, and for very high SOC, charge current would be variable from about C/40 to C/100.

The charge cycle is short and variable. When on shore power it can easily go on for 20 hours. When on ICE power it could easily be limited to 1 or 2 hours. Even on solar charge, (5 rated hours per day) this would require a much higher charge current resulting in much greater heat generation.

"How Might Real World Conditions Alter The Outcome."

Educated Guess:

The test parameters would keep the battery charging temperature much lower than would occur in a real world setting.

We know from other test reports that battery performance varies a great deal with temperature variation.

Charge efficiency is inversely proportional to temperature. The higher the temperature the lower the charge efficiency.

Storage capacity is proportional to temperature. The higher the temperature, the greater the storage capacity.

Battery self discharge is inversely proportional to temperature. The higher the temperature the faster the self discharge.

Battery life expectancy is inversely proportional to temperature. The higher the temperature, the fewer the charge/discharge cycles obtainable.

We also know that in the real world, the battery temperature during the charge cycle is likely to be much higher when the starting SOC is lower, and lower when the starting SOC is higher.

Conclusion:

Test results are inconclusive with respect to real world battery charge efficiency vs starting battery SOC due to lab environment conditions.

So, thanks for the post.

One more data source to consider, but not the "end all be all" one may think.

[evm1024]

Originally Posted by ramblinrod

Thank you!

SNIP

Anyway, as a result of this report my confidence in my previous post assertion that charge efficiency increases with SOC is slightly reduced (say 90% to 88%), but I wouldn't change my position based on this report alone, without evidence that the results represent what would happen in the real world, which I suspect they wouldn't.

So, thanks for the post. One more data source (of 1000s encountered) to consider.

I should point out that they say:

Charge efficiencies at 90% SOC and greater were
measured at less than 50% for the battery tested here

It appears that they do know (at least some) of the limits of their study.

Please cite the papers that you have authored and the studies you have participated in that support your assertion that charge efficiency increases with SOC.

I don't expect you to change your opinion - just back up your opinion with facts and not logic or conjecture.

Show me your data.