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Old 26-03-2014, 02:06   #16
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Re: can we calculate capacity with limited information

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Originally Posted by Stu Jackson View Post
Because it simply doesn't work that way. What goes OUT is easy: amperage times time. What goes back IN is determined by the battery acceptance....
Its far far far more complicated than that - because, as you say to MoncSail, "it simply doesn't work that way".

Battery monitors are an essential tool on a boat to help with the OPs problem. They try to work out the battery State of Charge but they can do a very bad job. You must tell them three important characteristics of the battery first, the capacity of the service bank, Peukert’s constant for the batteries being used which adjusts the actual discharged Ah values depending on the size of the discharge current, and you must also enter the “efficiency” of the battery at accepting charge. Wet cells may be only 75% efficient whereas AGMs may be 98%. So you might have to put 140Ah into a battery to raise its Ah count by 100Ah. (This is not the same as Battery Acceptance rate)

If all these values are not input correctly it will upset the Ah count accuracy, but worst of all these values change as the batteries age so the BM will become more and more inaccurate.

The answer is a SmartGauge which only uses voltage and very clever algorithms to calculate the State of Charge of a battery, which is all you really need to know. It doesn't need to know the capacity of the battery, only the type. The more it learns over time the better the accuracy.

Search the Forum for lots more on Battery Monitors and SmartGauge. I have both and for me the SmartGauge is magic. Its claim of accuracy to less than 1% seems true. You do need a digital amp meter as well so you know what is happening with the systems, but a SmartGauge and an amp meter can still cost less than a GOOD battery monitor - certainly here in the UK.
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Old 26-03-2014, 02:48   #17
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Re: recovering battery abuser another mistake?

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was a standard feature of a $500 solar controller, I didn't know it could do it till after as I chose it for different reasons
Your one-liners would be more helpful if you added more information. I assume your standard controller doesn't have a shunt, as I was describing, to measure the actual state of charge of the battery.

Your current setting control can be useful, but can also be confused by other chargers since it isn't measuring the current going into the battery.

As I said it is an "expensive" controller because it can accept 60 amps or more. With the addition of the FLEXnet dc adapter and shunt it can be converted to a battery monitor and control the charger Float mode. As far as I know there are no other controllers at 20 amps or less that use current to control the drop to float mode.
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Old 26-03-2014, 18:44   #18
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It may just be that simple

Stu, It may just be that simple. I = E/R. A simple equation. During the absorption phase of charging the voltage stays constant (14.8 Trojan recommended), so what changes is the battery resistance. The battery resistance increases as it is charged. That resistance change is predictable. At least I think it is. In fact Trojan uses the same charge profile for all of it's flooded batteries, with a note that time and current changes with battery size (capacity). However, the slope of the curve is the same. My question essentially is, could a charger manufacturer take advantage of the slope of the curve being the same no matter the capacity of the battery.

Sailinglegend, I have an Amp-Hours+2 battery monitor, arguably the first of the real battery monitors. The only thing it wants to "know" is when is the battery considered full. "when the battery is above (set full voltage) Volts, and the current (going in) falls below (set current recommended at 2% of capacity) Amps, for five minutes, the meter considers the battery full". Once the battery is "full" any additional amps into the battery are deleted when discharge occurs. That is how it determines efficiency. It knows when the battery is full, it knows what amps went out, and it knows that more amps had to go back to get to "full". Pretty simple. Back home, I don't think we would call that a very clever algorithm, we would just call it arithmetic. The battery charger knows the current going out, so no need for an expensive shunt, and it knows the applied voltage. But, I must say that your point concerning the house requirements does throw a wrench into my thinking that a smart charger may have a chance at determining when a battery is full, therefore the switch to float when it determines the absorption current curve over time. I am not sure I am willing to give it up just yet, because I do not think we have answered that question yet.
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Old 26-03-2014, 20:14   #19
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Re: recovering battery abuser another mistake?

Measuring a charging profile and a discharge profile isn't much use, firstly the relationship between terminal voltage and current flowing is very non linear. It also varies non proportionally with changes in load current. Hence for it to work you'd have to characterise the battery at a wide range of charge and discharge cycles and interpolate between them.

Have a look at 2rd order electrical models of a LA battery to se what I mean. There are both real and complex impedances etc etc involved

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Old 29-03-2014, 19:10   #20
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charge curve is not linear

firstly the relationship between terminal voltage and current flowing is very non linear. It also varies non proportionally with changes in load current. Hence for it to work you'd have to characterise the battery at a wide range of charge and discharge cycles and interpolate between them.


Maybe that is exactly what we need? The relationship is not linear. If the curve shape is the same no matter what the capacity is, but the amount of current to create the curve is dependent on the capacity (more capacity, less resistance for the same charge level) maybe a "smart charger" could figure that out. These guys are selling these chargers as being able to figure it out. Surely they know something?
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Old 30-03-2014, 00:34   #21
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Re: charge curve is not linear

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...These guys are selling these chargers as being able to figure it out. Surely they know something?
They know nothing! Well they all think they do, but they all lie when they tell us our batteries are charged when their charger drops to float mode.

It doesn't sound like you've checked out SmartGauge yet. Their website tells you a lot about the problem - but of course it doesn't tell you about the algorithm it uses to make SmartGauge work. It has a relay that could be used to turn an external charger to float mode - if chargers had that facility.

SmartGauge is a very very simple device with only two wires going to the house battery that only measure the voltage, but there's a 34 page manual that comes with it!!!! It does what it says on the tin.
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Old 30-03-2014, 01:28   #22
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Re: recovering battery abuser another mistake?

I decided not to comment because there is already too much disinformation in this thread...why add more.

OP, beware of what "you are learning."

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Old 30-03-2014, 02:35   #23
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Re: recovering battery abuser another mistake?

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I decided not to comment because there is already too much disinformation in this thread...why add more....
Not a very useful posting, especially from someone who has only contributed once to this Forum in the last 12 months.

Your knopwledge of the subjects here is demonstrated by one of your postings on a thread entitled:

"things you've tossed off the boat that others think are necessary"

Dozens of "how-to" marine-related books. All those refrigeration repair books and electrical books and other that people said we just had to have. Carried those heavy books for 2 years and tossed them before crossing the Pacific. Never opened a single one and wasted well over a thousand bucks.

If you think there is dis-information here - and that happens all the time on most threads - then stand your ground a make your point. I am always willing to learn and have my errors corrected.

There are always different points of view on ALL subjects to do with sail boats, but one-liner postings that make no further contribution are not welcome here.
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Old 06-04-2014, 10:43   #24
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Smart chargers not any smarter than us?

OK folks, I have come to some kind of conclusion on this subject and I appreciate your help in making this determination. My conclusion is that smart chargers may be clever, but they do not have enough information to be at the head of the class. This experience is also another example in my experience book that manufacturers will do or say just about anything to get you to buy their product, and when they essentially say to you that it is just too complicated for you to understand it probably is not that complicated. Be very leary of any manufacturer that has an "algorithm". Having said this, I spent some time at the boat 3 weeks after the install of my new charger. Based on every test I can make, open voltage 13.27, and specific gravity 1.265 to maybe 1.275 (depending on my ability to read my $7.00 hydrometer) my batteries appear to be charged to at or very close to 100%. I did an equalizing charge (recommended by some at commissioning) and I have documented this as a baseline. So, while I am not pleased with the information provided by the manufacturer, so far the charger seems to be doing what I bought it to do, or at least close to it. But, I will keep an eye on it, watching closely as it charges during the absorption phase, and see what the charging current is when it switches to float. On occasion, I will test the sg, and if my full charge sg falls much, I will equalize. As Regan said, Trust but verify.
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Old 06-04-2014, 11:04   #25
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Re: recovering battery abuser another mistake?

OK, for starters, I agree that there are a lot of opinions here, some a bit off base. My thoughts in brief:

1-- AGM, Gel, and Flooded batteries (FLA) are all LEAD ACID. Using that term for flooded batteries only is part of the confusion. Nicad, Lith, etc are not LA... Nothing here applies to them...

2-- Trojan, Lifeline, Rolls and other manufacturers have lots of engineering info on their websites that is worth study.

3-- Genesun, Outback, Victron, Mastervolt and others do as well.

On this forum, the real experts are MainSail, Bill Trayfors, and a few others (some might kindly say me..). There is no magic here, just a lot of well established science and engineering... Some study is in order for new boaters or those who aren't getting 5-7 (or more) years out of their battery banks.

So...

Manage your discharge rates to no more an 50% for max life. AGM's in particular can be taken lower but at shorter life 500 cycles to 80% discharge or 800 cycles to 50% discharge as an example for Energy1 per their literature. You'll make your own choice based upon how you cruise.

Fully charge your LA batteries to manufacturers' spec's at least every two weeks, this is critical for AGM especially.

Equalize your FLA batteries when hydrometer readings show variance noted by manufacturer.

Most modern chargers can do that... I personally like the new Sterling/Pro Mariner models, Victron, Mastervolt, and, if you can equalize with solar or other means, Iota.

Solar, a LOT of it, wi a good, configured MPPT controller, is your friend.


And, to quote Bill, batteries don't die, they are murdered...

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Old 06-04-2014, 11:57   #26
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When do battery chargers float?

OK Scott,
But, this thread was not really intended to be about batteries, it was intended to ask how battery chargers protect our batteries. I agree that information relating to the charging needs of flooded lead acid batteries is available, and fairly consistent. The problem as I see it is the lack of information, and perhaps misleading information from charger manufacturers, specifically as to the point at which they switch to float voltage.
I too agree that there have been a lot of opinions here, some of which are a bit off base. Some may have been provided by me. This may be a good indication that we continue to need to answer the question of how chargers determine when to switch to float voltage. If you are going to depend on your charger to take care of your batteries, you need to know. By using a fancy algorithm is not an acceptable answer. I have decided that my charger is "trying" to take care of my batteries, but I will be watching it closely in the future, and taking steps to make sure my batteries are treated as the battery manufacturer states.
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