The “Myth” of 100% by Midday

[a64pilot]

If the link doesn’t work, select return to menu, pick a month, I used July and December, then pick a panel orientation, I picked horizontal flat panel cause most boats panels don’t track the sun, or none that I have seen anyway.

Then out of curiosity pick two axis tracking flat plate to see just how much more power can be had by tracking, it’s phenomenal.

[Kenomac]

I must not be “Joe Average,” we use only 40-50ah during the overnight hours; which is closer to 10-12.5% of total capacity and far from 33%; maybe that’s the reason we have no trouble getting back up to 100% via solar alone on any given sunny day.

Like I’ve written many times on this forum, efficiency and management are the key components of a successful install, not... hanging additional cheap solar panels.

[a64pilot]

Ken, is that 40 to 50 AH at 24V? If so then of course that equates to twice that at 12V, and likely puts you right in the middle of AH use.
Nolex is very efficient, and I’d suspect may be in cold water which makes a difference with refrigeration. But I’d bet that their refrigeration size is smaller than average and or more efficient than average for their size boat too.
They may be so far North that they only see a few hours of total darkness this time of year too, maybe no total darkness?
You have a 400AH+ bank at 24V? So close to 1000 AH at 12V? If so that is above average I’d guess, but maybe not for a 50+ ft boat.

All of this isn’t really hard, you can get an average estimate by adding your total 24 hr consumption up, then if meets or exceeds your average Solar output, your in the hole, average Solar output is usually 1/3 or your rated power in watts, but use AH, so you having 450W will output on average 150 AH at 12V or 75 AH at 24V.
Now that’s average, not average for July and December, but average over a year, it varies a lot by month.
Seeing as how you use 50 AH during the night and you don’t cook or make water at night, it’s going to be tough to not use more than 25 AH in the day to keep from going into a hole.

So, therefore you must be making well more than average output from your panels or your going in hole, one or the other, or of course are making up the shortage with engine alternator or generator.
I’d suspect both, it’s July so your making more than average, and surely you motor some, I’ve heard it’s called the motorterranian after all, or run a generator occasionally?

[Kenomac]

Originally Posted by a64pilot

Ken, is that 40 to 50 AH at 24V? If so then of course that equates to twice that at 12V, and likely puts you right in the middle of AH use.
Nolex is very efficient, and I’d suspect may be in cold water which makes a difference with refrigeration. But I’d bet that their refrigeration size is smaller than average and or more efficient than average for their size boat too.
They may be so far North that they only see a few hours of total darkness this time of year too, maybe no total darkness?
You have a 400AH+ bank at 24V? So close to 1000 AH at 12V? If so that is above average I’d guess, but maybe not for a 50+ ft boat.

All of this isn’t really hard, you can get an average estimate by adding your total 24 hr consumption up, then if meets or exceeds your average Solar output, your in the hole, average Solar output is usually 1/3 or your rated power in watts, but use AH, so you having 450W will output on average 150 AH at 12V or 75 AH at 24V.
Now that’s average, not average for July and December, but average over a year, it varies a lot by month.
Seeing as how you use 50 AH during the night and you don’t cook or make water at night, it’s going to be tough to not use more than 25 AH in the day to keep from going into a hole.

So, therefore you must be making well more than average output from your panels or your going in hole, one or the other, or of course are making up the shortage with engine alternator or generator.
I’d suspect both, it’s July so your making more than average, and surely you motor some, I’ve heard it’s called the motorterranian after all, or run a generator occasionally?

I’ve remained in the same anchorage for the past 10 days, so no motoring has taken place. This photo was taken today at 5pm and I think it trumps your words of doubt.

I refer you back to the first paragraph in post #1.

[sailorboy1]

it always has to be become some type of competition and/or argument debate over the electron (or hole) storage boxes

[a64pilot]

Ken, you use between 40 and 50 AH at night, have you calculated your daily consumption?
Your water maker, what’s it’s amp draw?
I’d assume it’s about 19 or 20 amps. At 12V. So three hours of it is 60 AH, again at 12V. We can use 12 or 24 or course, just can’t mix the two.
I have no doubt that your battery monitor is saying your fully charged, no doubt at all.

This isn’t magic or rocket science, first thing you have to have of course is make more power than you use, second thing you have to have if a lead acid bank is at least a 6 hour period of making significantly more power than you using.
Flooded and Gel are of course way more tolerant of not being fully charged every day, every now and again is fine for them, reason why my next bank will most likely be Gel.

[noelex 77]

Originally Posted by conachair

Wouldn't a better measure of full charge be when the acceptance current levels off? If they are accepting 1% the 2 hours later are accepting 0.5% and another 2 hours later still accepting 0.5% could they really be charged at 1%? Possible that will change with age and temperature?

Anyway, I can just get my 225Ah 2 x T105s charged from around 80% to full before sunset with 300W of solar, or what was once 300W with some shading. Pity I can't find a screenshot from at anchor but this shows the current leveling off on the mains from slight discharge. I take level current acceptance as fully charged and set float to bulk @ 14.9V. From happy hour charts I doubt many people actually get to fully charged very often.

The state where a lead acid battery has first reached its maximum SOC is difficult to to determine.

The strict definition is the point where the battery capacity is no longer rising. But this requires the battery to be be fully discharged so the capacity can be correctly measured.

When the above point is reached the battery will still be accepting a small amount of charge especially at higher voltages. It is easy to mistake the acceptance of this charge as energy that is increasing the battery capacity, but at some point the energy will be just converted to heat etc without any rise in SOC or the available capacity.

The difficulty is in defining this point.

It is an intriguing theory, but I do not see how the point where the end amps is no longer reducing would always, or even usually correspond to 100% charge. I would have expected the point you have described would relate more to point where the equilibrium between the batteries ability to dissipate excess charge energy in form heat and other waste products was reached at the particular voltage temperature etc.

Most battery manufacturers recommend end amps at absorption voltage of around 1-3% as the optimum point to drop down to float, although this varies considerably with battery chemistry and even individual manufacturers. Many cruising sailors suggest, with I think sound logic, that a more aggressive settings of around 0.5-1% is optimum. The deliberate overcharging, over the manufacturer’s recommendation, is deemed better than the risking uncharging. However, some users routinely continue well past this level, with the mistaken belief that energy entering the battery is always continuing to raise the SOC.

It is very hard to deliberately reduce and effectively throw away power even if this may be better for long term battery life. The screenshot in post #1 is a good example. 4A is still going into the batteries. To reduce this by dropping down to float voltage at this point seems wasteful even if this is beyond the point where the battery manufacturer recomends the transition to float voltage should occur.

The above only touches the surface of a complex subject. My post blurs the important distinction between when to drop to float voltage and when full SOC is reached. These two factors are not necessarily the same.

Most cruisers only need to check their battery charging is dropping down to float at, or at least near, the recommended end point current for most charge cycles. It is also important to check the charging voltages are correct for the battery chemistry and battery temperature. Measure these voltages at the battery.

[Kenomac]

Originally Posted by a64pilot

Ken, you use between 40 and 50 AH at night, have you calculated your daily consumption?
Your water maker, what’s it’s amp draw?
I’d assume it’s about 19 or 20 amps. At 12V. So three hours of it is 60 AH, again at 12V. We can use 12 or 24 or course, just can’t mix the two.
I have no doubt that your battery monitor is saying your fully charged, no doubt at all.

This isn’t magic or rocket science, first thing you have to have of course is make more power than you use, second thing you have to have if a lead acid bank is at least a 6 hour period of making significantly more power than you using.
Flooded and Gel are of course way more tolerant of not being fully charged every day, every now and again is fine for them, reason why my next bank will most likely be Gel.

Check out the Spectra 380c and Solbian specs for yourself, you seem to be the resident expert on just about everything these days.

https://www.solbian.eu/img/cms/PDF/SP_eng_06.pdf
https://www.spectrawatermakers.com/us/us

[Adelie]

I believe the myth leaves out the assumption many people make that the bank is at 50% to start. Different folks make different assumptions about state of battery at the beginning of the day and consequently argue about whether an outcome is possible when they are actually arguing about different things.

If you have a very large bank and panel nameplate capacity compared to demand then being at 100% in the AM is not really hard or unusual.

If your overnight usage puts you at 50% it's going to be hard to be at 100% until 6-9 hr after sunrise.

[a64pilot]

.5% isn’t above all manufacturers recommendations. But is for some of not many.
If your manufacturer has a recommendation then of course go with their recommendation, my bank that happens to be .5%.

There are two reliable ways that I know work to determine SOC when under charge, one is specific gravity, the other is tailing charge current.
What other means exist? You can amp count, but on average for a bank in very good condition it takes between 102% and 106% of used amps to be returned to be fully charged, and well more for an older possibly previously abused bank.
Most of us occasionally abuse our bank, often by accident, I have by both significantly overcharging by relying on the charger timer to disengage equalizing voltage and by a power pedestal’s circuit breaker going bad and my bank being discharged by refrigeration until the voltage dropped so low that the compressor wouldn’t start.
Then again due to a family emergency that had me abandon the boat for months on a mooring and leaving the Solar controller to drop to float when it wanted to.
On return the Smart Gauge said SOC was 85%, but it charged to 100% quicker than it should.

Excess charge current must be converted into heat, nothing else is logical, however that amount of current is tiny, so it can’t amount to much heat. When fully charged my charge current at equalization voltage, in my case 15.5 V for a 12V bank is about an amp. This is of course about 15 watts, 15 watts spread put over a few hundred pounds of lead isn’t much, I’ve watched my bank temp of course and it doesn’t change in a 5 hour equalization cycle.
So there is more going on than just heat of course, because I don’t think anyone would say that if you leave a 12v bank at 15+ volts continuously that your going to ruin it, cause of course you will. The class will off gas and dry up. But it’s not heat that is causing that.

Actually I don’t think excess current is converted to heat, not necessarily I think it’s consumed in the phase change of water to hydrogen and oxygen?

[noelex 77]

Originally Posted by a64pilot

It’s not for you that those of us that say you can’t get there with Solar alone, it’s for the guys down in the Bahamas in December who’s Solar Charger drops to float every day around Noon
.

I have not sailed the Bahamas so I am not familiar with the insolation during December in this location.

In many locations 100% by noon is not realistic during the winter season. In Scotland you would probably need an array similar to one pictured below .

However, a genuine 100% by noon is certainly achievable in many locations, for at least some of the year. The statements made on Cruisers Forum are frequently that the only possible explanation for hitting 100% by noon is that the poster is wrong, mistaken, doesn’t understand the settings, or battery charging in general etc, is not correct.

Even 100% before 9am is not impossible as my example shows.

[Kenomac]

Originally Posted by noelex 77

I have not sailed the Bahamas so I am not familiar with the insolation during December in this location.

In many locations 100% by noon is not realistic during the winter season. In Scotland you would probably need an array similar to one pictured below .

However, a genuine 100% by noon is certainly achievable in many locations for at least some of the year. The assumption made by many members on solar threads that the only possible explanation for hitting 100% by noon is that the poster is wrong, mistaken, or doesn’t understand the settings etc, is not correct.

Even 100% before 9am is not impossible as this thread shows.

Apparently, it’s easily achievable in Italy, Croatia, Montenegro and Greece during the summer months, as I’ve witnessed it first hand on many occasions... even daily.

[a64pilot]

Yes, I guess we need to put the myth of solar charging being fully charged by noon right up there with the myth of hull speed wouldn’t you say?

Under the right conditions both are myths, right?
Under the right conditions there are no absolutes, people have even fallen from airplanes miles high with out a parachute and walked away. Death from falling from 30,000 feet isn’t assured, but it’s almost a certainty.
So I guess telling some one that if they jump out of an airplane from six miles high that they will die isn’t true as some have survived?
https://en.m.wikipedia.org/wiki/Vesna_Vulović

[noelex 77]

Originally Posted by a64pilot

.5% isn’t above all manufacturers recommendations. But is for some of not many.

O.5% end amps is recommended by a couple of AGM battery manufacturers (Lifeline and Trojan) but I cannot think of any flooded lead acid battery manufacturers that recomend anything this low.

Rolls advises 2-3% for flooded batteries (0.7% for AGM and gel). Trojan 1-3% for flooded batteries.

0.5% is often quoted in this forum, creating the impression that this is a typical number from most battery manufacturers. However, if you look up the data this number is on the low side.

I have some sympathy for setting aggressive charging settings, but it is incorrect to conclude that 0.5% is a typical manufacturer’s recommendation, especially if you do not have AGM batteries. Many manufacturers recommend a cut off current that is two, three or even six times larger, as the above examples show.

As i indicated earlier 0.5-1% is not a bad number. With my gel batteries I usually aim for around 1% in summer and a little lower in winter.

[sailorboy1]

Originally Posted by noelex 77

The statements made on Cruisers Forum are frequently that the only possible explanation for hitting 100% by noon is that the poster is wrong, mistaken, doesn’t understand the settings, or battery charging in general etc, is not correct.

It's all in the details and understanding what is being talked about. Lots of times on CF that "not by noon battle" is about 98% verse 100% that is more about internet people are here to prove they are RIGHT

For most of us our batteries don't live on a bench in a lab.

Wasn't long ago that the rule was to operate your battery between 50-75% SOC as the balance between live costs and charging costs.

As long as the lights work and the beer stays cold all is good.