The “Myth” of 100% by Midday

[noelex 77]

Originally Posted by sailorboy1

And even today the short charger using generators may be getting the best cost:benefit for their setup. My current 640W solar setup would buy 3 sets of new batteries. So if I "only" get 3 years more out of the batteries using the solar it doesn't really pay off very much in the big picture.

I don't understand about "over charge". The batteries only take what they can, doesn't matter if the generator/charger could supply a lot more.

For me the benefits of a good solar installation, where it is practical, is doing without the generator. The lack of noise, maintenance, heat, vibration, plus the improved reliability is the focus rather than the cost difference. There are of course drawbacks associated with solar, but I am not a fan of generators, although they are sometimes required. Even if a generator is necessary, solar can help reduce generator run time and while this is rarely cost effective some of the benefits already mentioned apply.

Battery charging when using the generator will be governed by the settings on the battery charger. Adjusting these settings to inappropriate values can result in over or undercharging the battery.

[sailorboy1]

Originally Posted by noelex 77

For me the benefits of a good solar installation, where it is practical, is doing without the generator. The lack of noise, maintenance, heat, vibration, plus the improved reliability is the focus rather than the cost difference.

I agree!!!!!

Talked myself out of it 1.5 years ago till the above became more important than the $$$$

[noelex 77]

Originally Posted by conachair

But from daily real world monitoring guessing nearly everyone goes to float too early

I don’t agree.

Many generator based charging settings go into float earlier than optimum and many solar systems go into float later than optimum. This is because the default absorption times on battery chargers are usually similar, or even the same as the default absorption times on solar regulators despite very different charge rates.

The above is only a generalisation. Absorption longer or shorter than optimum can be seen with both types of charging depending on the individual system and settings.

Providing the charger or controller has adjustable settings, these anomalies are easily fixed, but few people adjust absorption time so the programmed setting is often not ideal. Fortunately there is a reasonable amount of latitude in absorption time so achieving a perfect result is not as critical as setting the correct voltage set points.

[daletournier]

Haven't I read the likes of Mainsail saying that it takes 6-8 hrs to dribble in the last 10%,(achieve end amps) if I've read this correctly how can the batteries on a normal cruising boat be full by 9-10am......hes wrong?

[sailorboy1]

Originally Posted by daletournier

Haven't I read the likes of Mainsail saying that it takes 6-8 hrs to dribble in the last 10%,(achieve end amps) if I've read this correctly how can the batteries on a normal cruising boat be full by 9-10am......hes wrong?

It’s the difference between actual truth and practical cruiser truth

[Stu Jackson]

Originally Posted by sailorboy1

It’s the difference between actual truth and practical cruiser truth

Good approach. And Dale's right, too.


Here's why, from Maine Sail:


Why Going to Float is NOT Full


which says:


Full is when the battery gets to 2% of its amp hour rating.
Actually 2% or less AT ABSORPTION VOLTAGE/14.4V +

AT ABSORPTION VOLTAGE is the part everyone tends to forget. Just because you are in float does not mean the battery actually got full. There are far too many dumb "smart" controllers, chargers, regulators that use simple egg timer programs that may NOT match your bank for the proper transition to float from absorption...

Less than 2% AT FLOAT voltage is not always full unless it previously attained less than 2% at 14.4V +........

It should also be noted that 2% is not technically full for many banks but is rather "cruiser full", which means close enough to deem it full.

[conachair]

Originally Posted by noelex 77

I don’t agree.

We must chat with different people at happy hour then

The majority just leave the default settings on the solar regulator which are cautious to begin with , that's before half the energy doesn't even make it to the batteries but goes on house loads.

[noelex 77]

Originally Posted by conachair

We must chat with different people at happy hour then

The majority just leave the default settings on the solar regulator which are cautious to begin with , that's before half the energy doesn't even make it to the batteries but goes on house loads.

Yes, I agree most leave the default absorption time setting on their solar regulator, but the absorption time for solar regulatators is generally too long rather than too short.

The more energy that goes to house loads and the less that goes to the batteries, the slower the charge rate. A slower charge rate results in a shorter not a longer absorption time. This is opposite to what most people would predict, but if you think about the charging algorithm this obviously must be the consequence of reducing the charging rate. A simple example is a charge rate lower than the required end amps. In this case the ideal absorption time is zero.

Many get this wrong and want a longer absorption time with a low charge rate and a shorter absorption time with high charge rate. Perhaps it is a good thing, in many cases, that the absorption time is not adjusted from the default, as most want to adjust the setting the wrong way.

[conachair]

Originally Posted by noelex 77

Yes, I agree most leave the default absorption time setting on their solar regulator, but the absorption time for solar regulatators is generally too long rather than too short.

The more energy that goes to house loads and the less that goes to the batteries, the slower the charge rate. A slower charge rate results in a shorter not a longer absorption time. This is opposite to what most people would predict, but if you think about the charging algorithm this obviously must be the consequence of reducing the charging rate. A simple example is a charge rate lower than the required end amps. In this case the ideal absorption time is zero.

Many get this wrong and want a longer absorption time with a low charge rate and a shorter absorption time with high charge rate. Perhaps it is a good thing, in many cases, that the absorption time is not adjusted from the default, as most want to adjust the setting the wrong way.

Don't actually understand what you,re saying there.... WIth default switch to float (which is often too quick imho) , the reg will switch to float thinking the batteries are charged whereas half the energy hasn't actually gone into the batteries but the fridge and laptop. The batteries are far from fully charged. With solar float will do next to nothing before the sun goes down.

[nwdiver]

Size of the battery and panel input are rather important........700 watts solar into 440 with regular cooler, night lighting and iPad recharge in the PNW in summer, full by noon making water by 1......

[noelex 77]

Originally Posted by conachair

Don't actually understand what you,re saying there.... WIth default switch to float (which is often too quick imho) , the reg will switch to float thinking the batteries are charged whereas half the energy hasn't actually gone into the batteries but the fridge and laptop. The batteries are far from fully charged. With solar float will do next to nothing before the sun goes down.

You are not alone getting this the wrong way around.

Let’s look at at simple, but realistic example.

If we assume a 500AHr battery bank. Suppose we also decide the ideal end amps is 1%, with an absorption voltage of 14.7v. The details do not matter. I am simply trying to pick reasonable values.

So using the above data the charging should ideally drop down to float when a charge current of 5A (or less) is entering the battery and at the same time the battery voltage is 14.7 v (or higher).

Lets assume the solar panel can produce a constant 10A and there are no loads (everything off). Not very realistic, but this keeps things simple and is easy to understand without effecting the outcome.

When solar charging begins the battery voltage will rise. The bulk phase. The battery voltage will eventually hit 14.7v. This is the start of the absorption phase and the absorption time countdown will begin. At this stage the battery is accepting 10A well above the 5A required for ideal point to drop down to float. The voltage will be regulated to maintain the required 14.7v absorption voltage, but the battery current needed to maintain this voltage will gradually fall as the battery SOC rises. After some time the battery will become more charged and the current will have dropped to 5A while the battery voltage stays at 14.7v. At this point the end amps have been reached and the charger should ideally drop to float. The time taken between 14.7v and 10A and 14.7v at 5A is the ideal absorption time. The actual time is not important but lets take a guess that this might take 30mins.

So in this case with a 10A charging current the ideal absorption time is 30 mins for our example.

Now lets turn on a 5A load and repeat the experiment with a battery and solar panels that are identical.

The charging current entering the battery is now only 5A. The bulk charging time will be much longer. The lower current will cause the battery voltage to rise more slowly, but eventually the voltage would reach 14.7v, the start of the absorption phase. As soon as the absorption phase is reached the end amp criterion has been reached. The voltage is 14.7v with a 5A current entering the battery. So the ideal absorption time is zero. As soon as the absorption voltage is reached the end amp criterion has been met.

So the lower charge current (or higher load) has resulted in slower overall charging, but a shorter ideal absorption time. A much longer bulk time, but a shorter absorption time is the net result. The absorption time has dropped from 30mins with a 10A charging current to a 0min absorption time with 5A charging current.

A higher charge current entering the battery needs a longer absorption time. A lower charger current entering the battery needs a shorter absorption time.

Most solar charging is at a lowish charge rate or at least a charge rate lower than produced by the alternator or battery charger. People imagine this means the absorption charge should be correspondingly longer, but this is wrong. The lower charge rate means a shorter adsorption time is more appropriate.

Some people are wrongly extending their solar absorption time settings, even to the extent of using an infinitely long period, when solar generally requires a short absorption time.

[a64pilot]

Originally Posted by noelex 77

You are not alone getting this the wrong way around.

Let’s look at at simple, but realistic example.

If we assume a 500AHr battery bank. Suppose we also decide the ideal end amps is 1%, with an absorption voltage of 14.7v. The details do not matter. I am simply trying to pick reasonable values.

So using the above data the charging should ideally drop down to float when a charge current of 5A (or less) is entering the battery and at the same time the battery voltage is 14.7 v (or higher).

Lets assume the solar panel can produce a constant 10A and there are no loads (everything off). Not very realistic, but this keeps things simple and is easy to understand without effecting the outcome.

When solar charging begins the battery voltage will rise. The bulk phase. The battery voltage will eventually hit 14.7v. This is the start of the absorption phase and the absorption time countdown will begin. At this stage the battery is accepting 10A well above the 5A required for ideal point to drop down to float. The voltage will be regulated to maintain the required 14.7v absorption voltage, but the battery current needed to maintain this voltage will gradually fall as the battery SOC rises. After some time the battery will become more charged and the current will have dropped to 5A while the battery voltage stays at 14.7v. At this point the end amps have been reached and the charger should ideally drop to float. The time taken between 14.7v and 10A and 14.7v at 5A is the ideal absorption time. The actual time is not important but lets take a guess that this might take 30mins.

So in this case with a 10A charging current the ideal absorption time is 30 mins for our example.

Now lets turn on a 5A load and repeat the experiment with a battery and solar panels that are identical.

The charging current entering the battery is now only 5A. The bulk charging time will be much longer. The lower current will cause the battery voltage to rise more slowly, but eventually the voltage would reach 14.7v, the start of the absorption phase. As soon as the absorption phase is reached the end amp criterion has been reached. The voltage is 14.7v with a 5A current entering the battery. So the ideal absorption time is zero. As soon as the absorption voltage is reached the end amp criterion has been met.

So the lower charge current (or higher load) has resulted in slower overall charging, but a shorter ideal absorption time. A much longer bulk time, but a shorter absorption time is the net result. The absorption time has dropped from 30mins with a 10A charging current to a 0min absorption time with 5A charging current.

A higher charge current entering the battery needs a longer absorption time. A lower charger current entering the battery needs a shorter absorption time.

Most solar charging is at a lowish charge rate or at least a charge rate lower than produced by the alternator or battery charger. People imagine this means the absorption charge should be correspondingly longer, but this is wrong. The lower charge rate means a shorter adsorption time is more appropriate.

Some people are wrongly extending their solar absorption time settings, even to the extent of using an infinitely long period, when solar generally requires a short absorption time.

This whole dissertation is why a timer to control absorption will never work, it can’t work, unless you have the exact same Solar output every day and the same loads every day. You just have to get as close as you can I guess.
For some reason Solar controllers won’t go to measuring how much a bank is actually accepting and dropping to float then. it’s not hard or even that expensive to do so, all it takes is a shunt, you likely already have one.

So if you go the timer route, and for most that is the only option, you decide based on your best guess how long to set it.
Every charge source I have right out of the box drops to float well in advance of when it should, all four of them. My Sterling Pro charge Ultra near as I can tell can’t be adjusted, you have to turn it off and back on again.
I don’t walk up and start talking batteries to people. But when it comes up, I’ve only met one person that has a clue, the rest assume when the green light comes on, they are fully charged, many don’t even know that, they run the engine for an hour a day, and because it cranks, that must be working. But they all are using it in default program, or often it’s whatever the installer set it at, and I’d bet very few do anything but install.
Only charge source I have that hits it dead on is My Magnum inverter, it can be set to drop to float when acceptance rates hits .5% or any other percent. I use .5 % as I have a Lifeline bank.

This is why I would like to have a switch to drop to float and just control it myself for my alternator and Solar.

Small engine mode on the Balmar doesn’t set to float voltage, I don’t think. It only reduces current output, which if your fully charged is just your house load, reducing it won’t change anything.
Mark Grasser’s Alt controllers have a force to float switch, which does just that, flip it and the alternator outputs float voltage, so you can leave the dock fully charged and not be at absorption voltage until the timer times out.

[Kenomac]

Apparently, I over-estimated our overnight usage on an earlier post. Looks like our overnight draw is around 30Ah at 24v which is only 5% of our total house bank. So this picture was taken at 7:15am, and we will probably be even with solar covering the fridge draw by 8am, with no trouble getting back to 100% by around 12 noon today on solar alone.

Very similar numbers to noelex77. This number also includes the extra cup of coffee produced in order to provide the .4Ah number for weavis.

The myth has been busted.

[Kenomac]

Did I mention, that we have the hot water issue figued out? Yes, 10 gallons of piping hot water are produced onboard daily without the use of any fossel fuels. Solar takes care if that issue as well.

It’s now 8am and as you can see by the photo, we have now gone positive and are in charging mode. The juice has begun to flow back into the battery bank as the solar production has now overcome the fridge useage/draw.

[Simi 60]

What are you using for hws?
On a sunny summer day our solar copes with charging up a 47 gallon 240v hot water system but in summer, we rarely need it.
In winter, so low sun, we need to give it and the batts a 1 hour genset headstart in the am and a solar finish.

At ten years of age the rheem hws is probably getting close to death so looking at a smaller version of same.
13 gallons here for $400

https://www.bunnings.com.au/dux-50l-...eater_p5104141