Equalization

[admiralslater]

Originally Posted by bvimatelot

Proof reading, and maybe grammar, are quite important too!

I would like to claim I did that on purpose.

[DefinitelyMe]

[QUOTE=a64pilot;1934894]

Originally Posted by sailinglegend

Yep,
Your right, I talked to him as well and agree with the numbers you posted.

Now you say, fully recharging is not feasible on a cruising boat, so which one of the other regimes are you going to be able to achieve, and how?
A marina at least once a week? I agree all LA batteries will suffer from not being fully recharged, some more than others, but all of them's life will be shortened.
Now Lifeline AGM's cost around 300% more that golf cart FLA's, and if you cannot recharge them daily, will not last any longer.
So what are you getting for having paid three times as much?

I can't afford that, so I'm doing the impossible and recharging them to 100% every day I have good sunlight, and will run the generator when I don't, as I can't afford $900 to $1,800 a yr battery budget.

I still say if you can't fully recharge an AGM, you don't want AGM's

I've seen people who fully recharge AGM's every cycle get as much a ten years out of them, but if I can't get at least five, I can't make them make sense myself.


Sent from my iPad using Cruisers Sailing Forum

Based on my experience with lifeline you are getting what you pay for. I've had golf cart batteries in the past and they were OK but didn't last more than a few years. I replaced them 8 years ago with 2 lifeline batteries and the performance i'm getting out of them is still excellent.

My lifeline batteries are actually defective. I was having a problem with deposits forming by the negative terminals so i sent a picture to the manufacturer and they immediately came back and told me it was leaking terminals. Must have been a bad batch. By the time i did this they were outside warranty, but the company nevertheless agreed to replace them at a heavily discounted price. Furthermore, they agreed to honour that agreement if and when I finally start to see a problem with performance........ which i haven't.

For me, this is why they are well worth the extra cost compared to golf cart batteries.

[Maine Sail]

Originally Posted by blackswan555

I can not agree with the above, Battery life is gauged in cycles which are not taken into consideration here, or temperature, or load, eg Is this once a day ? week ? Month? 2190 to 3285 cycles ? not out of AGM :-)

Then you would be disagreeing with Lifeline battery directly. Lifeline battery is owned by the Godber family. Justin's last name just happens to be Godber. Perhaps the only person more qualified to make a statement like that would be Dave V. Lifelines chief engineer. That statement from Justin is an estimation of typical life based on many years of actual experience with these batteries in the marine environment not based on white coat, white glove "lab" data.

Once these batteries leave the lab they are subjected to the abuses Justin outlined:

"*Fully charged after each discharge. Estimated life: 6-9 Years.

*Fully recharged at least once a week and equalized once a month. Estimated life: 4-6 Years.

*Only recharged to 85% and equalized once a month. Estimated life: 2-4 years.

*Only charged to 85% and never equalized. Estimated life: 1 year."


If you treat them, as in one of those four scenarios, that is what you will likely get as a rough time frame estimate. The vast majority of marine batteries, no matter what brand, barely make 150 cycles and this is because they are abused and not charged properly not necessarily because they are bad batteries...

Originally Posted by blackswan555

EQ, Be very careful with EQ'ing any sealed battery with both your voltage & temp, Equalising is not really the proper term as it really refers to flooded lead acid's & involves a temperature monitored over charge involving lot's of gassing, Get to that point on a sealed battery, And you have a mess,
Over the last years I have noticed manufactures of "Sealed's" (Gel/SLA/VRLA/AGM etc, they are all a lead acid, Just it is suspended in a gel etc) Starting to use the Equalise word, Some started with calling it "A Conditioning charge" "Maintenance charge" or similar, usual recommendation was 12 to 24 hr's at absorb V, Temp compensated,
In the last few years more of them are calling EQ (I guess as the major downside to sealed is not being able to EQ, That was affecting sale's & reputation ?)
Tim

Lifeline uses the word conditioning charge but it is 15.5V for up to 8 hours temp compensated. I equalize lots and lots of Lifeline batteries and it does net longer life for those who abuse them in a PSOC environment. Other brands of VRLA batteries can not be conditioned or equalized at that voltage but Lifeline batteries can. Some AGM batteries such as Odyssey or Northstar allow much higher absorption charge voltages which tends to fight off sulfation at each charge cycle and in a PSOC environment seems to work fairly well. Firefly AGM's use a patented carbon foam construction and don't need equalization and yet remain highly sulfation resistant.

My real world experience with Lifeline batteries, many hundreds of them, mirrors that range of what Justin of Lifeline suggests pretty darn closely. 6-9 years plus is pretty good life for the boater who cares to treat his/her batteries well.

[a64pilot]

If you have gotten eight years out of them, then I believe your fully re-charging them daily?

See the only thing with AGM is I believe you have to have the whole system in place to support them and get the advantages from them, a high amp alternator with three stage regulator able to be set for the appropriate voltages per stage, enough Solar with a charge controller that can be set, and ideally a big shore power charger that is itself able to be set for AGM, then buy the batteries.

But buying AGM knowing your not able to fully recharge them, but relying on equalizing them every so often, your not going to get the best out of them that way, and you will significantly shorten their life.

[sailinglegend]

Originally Posted by a64pilot

I just put in a 660 amp/hr lifeline bank in.......
It's my understanding that you only equalize if you can't fully recharge every cycle......my goal is to fully recharge them daily.

In post #3 you say you put in 660 Ah of Lifeline, yet you seem to be dismissing them heavily!

Equalization is needed to break down the Lead Sulfate crystals that are produced every time a battery is even partially discharged. It's part of a chemical formula that, among other things, produces water which reduces the SG of the electrolyte and results in the Lead and the Sulfuric acid combining to form Lead Sulfate. Charging reverses the process. The problem is that if not fully re-charged some Lead Sulfate crystals stay on the plates and over a week or more harden and need a high voltage Equalization charge to convert them back to Lead + higher SG Sulfuric Acud. The longer they are left the harder the crystal become and the harder it is to remove them with equalization. So after a month there will be some crystal which form permanent sulfation which reduces the life of the battery.

Originally Posted by a64pilot

...Now you say, fully recharging is not feasible on a cruising boat, so which one of the other regimes are you going to be able to achieve, and how?

These were Justin's thoughts not mine. He has posted the worst case scenario were people only ever charge to 85%, which is unfortunately far too many people. The problem with his article us that there are lots of other regimes in between that will make a huge difference to the life of the batteries. Charging to 95% will make a big difference to his figures - most will NEVER get to 100% without going onto shorepower for maybe 24hrs.

Originally Posted by a64pilot

Now Lifeline AGM's cost around 300% more that golf cart FLA's, ..... So what are you getting for having paid three times as much?

Here in the UK Lifeline AGMs are les than twice as much as Trojans. If you've got Lifelines then you know the difference!

20% faster charging over a full cycle.
Potentially much much faster charging with larger charging sources.
No need for battery boxes.
Smaller than most sealed batteries for same Ah - Lithium are much much better!.
No maintenance other than checking cables and connections.
Can be regularly Equalized unlike other sealed batteries.
Can be mounted in any position - my starter battery has been 11 years in the bilges.
My House bank is nearly 11 years old and as a Liveaboard for 10 years it has NOT been regularly charged to 100%.[/QUOTE]

Originally Posted by a64pilot

..... so I'm doing the impossible and recharging them to 100% every day I have good sunlight, and will run the generator when I don't....

As Justin and others have said its almost impossible to get to 100% every day with solar. Even if you get to 85% with a generator you may still only have 5 hours of good sun left in a day. You may think you are up to 100% when a little green light comes on but you could still be well short of this. That last few % could take hours and hours after the charge controller has dropped to Float. With your 38 Island Packet you surely can't have enough 'real estate' to mount enough panels?

With your 660Ah bank you would still need 100Ah to get to from 85% to 100%. To do this you need to put in more because of charge efficiencies. With a new AGM bank that might mean only 102Ah is needed, with an old FLA bank that could mean as much as 140Ah needs generating to raise the bank by 100 Ah. As the SOC gets closer to 100% the charge efficiency falls off dramatically. So because of charge efficiencies you may really need to generate 300Ah or more to get to 100% charged.[/QUOTE]

[a64pilot]

I'll try to answer most of your questions to the best of my ability.

Yes, I have Lifeline Batteries, 660 amp hr total, split in two banks, 440 House, 220 starting, although I may combine with the battery switch to all.
I am not dismissing AGM, or in particular Lifeline, just want to state my opinion that you can't just take your FLA's out and stick AGM in and expect good results, not even if you equalize every now and again, you need to fully recharge them every cycle to get the most out of them, and you need to upgrade your charging system as well, it's a bunch of money to do this, but if your going to get the most out of them, you need the whole shebang.

The whole 85% thing comes from another very well respected figure on electrical boat systems, who I will not name but sort of supports the discharge to 50%, charge to 85%, because above 85% is a point of diminishing return due to charge acceptance, but you can get to 85% pretty quick. This is bad for all LA batteries, but apparently even more so for AGM's.

Street price for Lifelines here in the US is three times the cost of Costco / Sam's club golf cart batteries, which is the cheapest price I have found, I am comparing price wise to the cheapest battery available, not the best, the cheapest. Yes that is like comparing a BMW to a Kia, but the Kia does work.

Now as I just installed them recently and am just now getting a handle on my consumption, it seems that overnight I used 12% of the 440 amp hr bank, I'm not tracking amps, I'm using a Smart Gauge, which I am led to believe is accurate as anything out there. That left me discharged to 88% and should have meant that I used 55 amp / hours, which is right about where I had figured I'd use.
It took 2 hours for the shore power charger to get me to 98% and float voltage.

Now charge acceptance rate does fall dramatically the closer to 100% you get, but your wrong with the 300 amp hr thing, it will take only about 120% of the amp / hours you used to fully recharge, just the closer you get to charge, the less amps a battery will accept, you can't slam it in like you could at the start of the charge, you have to trickle it in.
Using 120% as the number, I have to make 66 amp / hours on top of my daily usage to recharge my batteries to 100%, so if during the day I use another 66 amp / hours, then I need to make 132 amp / hours.
Now this is where I may mess up, so check my math, I hate amp / hr, so I'm going to convert to watt / hr. 132 amp / hr at 14V is 1848 watt / hr?

I have 750W of panels now, assume I only get 50% of rated power for 8 hours a day.
Thais is still 2,800 watt / hr? I only needed 1900, so I have a surplus, in theory and at this point it's all theoretical as I am not yet out there doing it, but I have two more panels if I need them for a total of 1,250W if I have to go there.

I have three 250W panels over my dinghy on the davits now, in theory I can mount two more over the Bimini, three if I had to, but I think 750W will get me what I need

[hellosailor]

"Does this mean that other brands don't need EQ. Or that they don't accept it. "
Typically it means that "other" brands of AGM battery will overheat and vent, and ruin themselves, when that much voltage is put into them.
Supposedly, you won't need equalization because the AGM construction doesn't allow sulphites to form and fall to the bottom of the battery, correct recharging habits will keep them trapped right next to the plates, or prevent them from forming. The contrary argument is that that's all a nice theory, but in real life you "should" still equalize. Which would make you pretty much only a Lifeline customer.
Kinda like buying mattresses and tires...

[sailinglegend]

Originally Posted by a64pilot

.....Now charge acceptance rate does fall dramatically the closer to 100% you get, but your wrong with the 300 amp hr thing, it will take only about 120% of the amp / hours you used to fully recharge, just the closer you get to charge, the less amps a battery will accept, you can't slam it in like you could at the start of the charge, you have to trickle it in......

EDIT:
You are not fully understanding Charge Acceptance, or Coulombic Efficiency or Charge Efficiency. This means, as you rightly suggest, you need to put in maybe 120% of the Ah needed to achieve a 100% charge to overcome the battery inefficiencies......but!

We all can observe the Charge Acceptance rate falling as the SOC gets above about 85% and the battery has reached its constant Absorption voltage of 14.4v or above. The closer the battery gets to 100% SOC the current falls to almost zero.

The Charge Efficiency of the battery is a figure that says how much of the energy put into the battery is actually converted into stored Ah. Most good/more expensive battery monitors have an option to input the charge efficiency of the bank. 85% is the default value. FLAs are about 85% efficient, your AGMs are maybe 98% efficient.

BUT, and this is the big but, the charge efficiency is very non-linear and the value quoted is the overall value for a bank starting at 50% discharged and reaching 100%. The attached graph from PowerSonic AGM batteries shows how the efficiency changes depending on the SOC.

The importance of this is dramatic if you are using Solar to fully recharge your batteries as the guys at Sandia National Laboratories, Photovoltaic System Applications Department have discovered in this research document.

http://www.otherpower.com/images/sci...Efficiency.pdf

I quote:
'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.'

What this all means is the closer to 100% you get then the charging current has less effect, which is why there are probabaly not enough hours in the day for Solar to fully recharge your batteries. If you don't get to 100% SOC at least every two weeks then your batteries will start to sulfate and die prematurely.

At 100 Ah battery is considered fully charged when it is taking 0.5 amps at 14.4v. The problem is you may never see this voltage and current combination because the charge regulator will have switched to a much lower Float voltage long before the battery is up to 100%. You can force the charger back into Absorption voltage by turning it off and back on again to check the actual charging current.

[zboss]

Originally Posted by sailinglegend

20% faster charging over a full cycle..

Is this actually true? I have never gotten a straight answer from anyone regarding this.

My panels only put out about 30 AMPS max so I can't take advantage of the high acceptance rates of AGM's unless using our 175 AMP alt.

If we have two sets of batteries one lifeline/firefly AGM (you pick) and one traditional trojan lead acid - both discharged by 150 amp hours... should I expect the AGM's to reach something like 90% or 95% full faster than the trojans?

[a64pilot]

Originally Posted by sailinglegend

With your 660Ah bank you would still need 100Ah to get to from 85% to 100%. To do this you need to put in more because of charge efficiencies. With a new AGM bank that might mean only 102Ah is needed, with an old FLA bank that could mean as much as 140Ah needs generating to raise the bank by 100 Ah. As the SOC gets closer to 100% the charge efficiency falls off dramatically. So because of charge efficiencies you may really need to generate 300Ah or more to get to 100% charged.

[/QUOTE]


Nope I understand charge acceptance rate, what I disagree with is this statement that you have to generate far more than you pull out to recharge a battery. I believe you only have to generate approximately 120% of what you used.
It's not that you are continually putting in say 50 amps to a battery, it's that as the battery gets higher in it's SOC, it can only accept lower charge current, you aren't using 50 amps but only 5 going into the battery, your only using what the battery can accept. It's not that you can't make enough electricity to fully charge a battery with Solar, it's that it takes longer to fully charge a battery than you have available sunlight, maybe.

Now if you were pulling down to 50% SOC that may be true, but my little experience is that if I have a larger bank that I discharge only 10% or 12%, it fully recharges faster than if I pulled the same number of amp / hours out of a smaller bank, but cycled the smaller bank more deeply.
And yes I will cycle the CB to put the charger back into absorption and force to float when I see the batteries are fully charged, realizing of course I have a 5 amp draw going into the fridge, so battery acceptance is 5 amps less than the charger display.


I don't know why but it seems I can use 50 amp/hours out of a 440 amp/ hr bank and recharge it faster than if I used 50 amp / hours out of a 100 amp / hour bank.

I assume it's because the charge acceptance rate of the smaller bank is less

[a64pilot]

Originally Posted by zboss

If we have two sets of batteries one lifeline/firefly AGM (you pick) and one traditional trojan lead acid - both discharged by 150 amp hours... should I expect the AGM's to reach something like 90% or 95% full faster than the trojans?

Assuming your charger has an equal or higher capacity than the batteries can accept, then yes it is true.

[darylat8750]

Handy Bob http://handybobsolar.wordpress.com who lives remotely and has lived in a camper off grid for years seems to think (if I understand it correctly) that having excess battery capacity results in less efficiency because every battery has a certain threshold of charge current that has to be exceeded before any actual charging of the battery takes place. He advocates a balanced system with enough battery capacity to operate above 50% battery capacity and enough solar to fully recharge every day. He also notes that most systems that he has seen use inadequate wire sizes and have shade issues.

I just went for the Duracell golf cart batteries. I have easy access for servicing them and the cost benefit ratio just makes the most sense for my use. I need to put the next additional $ into solar rather than more expensive batteries. If my golf cart batteries last 5-6 years (last ones lasted 6 years with at least 20% of the time on the hook + some abuse) The cost either per cycle or per year is pretty good. I do spend about an hour every two months servicing 8 of them.

[a64pilot]

There has to be a point of diminishing returns with batteries, there is with everything.
But, from what little I have leaned your better off not cycling your batteries lower than 75% SOC. That gives you reserve capacity for times when you may need it, and by reducing depth of discharge, your extending battery life.
I guess there are two schools of thought, one is to determine very accurately your electrical consumption and size your bank and charging sources just right
The second is where I'm at, determine if possible electrical use, but then build in a rather large cushion to cover things you may not have thought about.

[Maine Sail]

Originally Posted by sailinglegend

EDIT:
You are not fully understanding Charge Acceptance, or Coulombic Efficiency or Charge Efficiency. This means, as you rightly suggest, you need to put in maybe 120% of the Ah needed to achieve a 100% charge to overcome the battery inefficiencies......but!

We all can observe the Charge Acceptance rate falling as the SOC gets above about 85% and the battery has reached its constant Absorption voltage of 14.4v or above. The closer the battery gets to 100% SOC the current falls to almost zero.

The Charge Efficiency of the battery is a figure that says how much of the energy put into the battery is actually converted into stored Ah. Most good/more expensive battery monitors have an option to input the charge efficiency of the bank. 85% is the default value. FLAs are about 85% efficient, your AGMs are maybe 98% efficient.

BUT, and this is the big but, the charge efficiency is very non-linear and the value quoted is the overall value for a bank starting at 50% discharged and reaching 100%. The attached graph from PowerSonic AGM batteries shows how the efficiency changes depending on the SOC.

The importance of this is dramatic if you are using Solar to fully recharge your batteries as the guys at Sandia National Laboratories, Photovoltaic System Applications Department have discovered in this research document.

http://www.otherpower.com/images/sci...Efficiency.pdf

I also have that paper and there are some very good take-aways from it. You often quote AGM's as being 98% efficient (Lifeline says 102-110% needs to go back in in their literature) but this is really pretty much marketing fluff, that will rarely if ever be achieved on-board a boat. It is usually only achievable, in the lab, at very low charge rates, or when quoting bulk efficiency, not the total efficiency. In order to achieve anywhere near 98% efficiency the charge rate would need to be far lower than we usually have or would want on boats....

The higher the charge rate the lower the overall charge efficiency. On boats we tend to want fast charging thus our AGM's will not be anywhere near 98% efficient unless the bank is very large and being charged by a rather small solar array. On boats we have a mix of charge sources capable of high efficiency (low current eg; solar) and charge sources that will be lower efficiency (high current).

Key Point #1
"Battery charge efficiency is also a function of charge rate, with lower rates resulting in higher efficiencies. The larger battery will be operating with a lower charge rate, which will result in higher charge efficiency. A decision on increased array size must be made with full knowledge of charge efficiency at the actual charge rate being employed."

What this is saying is that of you want the highest efficiency charging you will need to charge very slowly to achieve anywhere near the high 90's in efficiency. As you accurately state we simply do not have the time in a day to do this at the rates that will result in the highest charge efficiencies. This is why the one-two punch of alternator or inverter/charger for bulk and solar for absorption & finishing makes the most sense.

Key Point #2
"It is generally understood that battery charge efficiency is high (above 95%) at low states of charge and that this efficiency drops off near full charge. However, actual battery charge efficiencies are often stated as though efficiency is linear across all states of charge, with general guidance that it drops off at higher states of charge."

And herein lies the issue with Ah counters... They apply a number for CEF that is linear. I have data, at very high charge rates (.46C), showing AGM efficiencies, when brand new, in bulk charging of over 96%. The key word is BULK.

*All batteries discharged to 11.7V then recharged for exactly 1 hour at .46C than discharged back to 11.7V and Ah's stored data-logged. The bulk charge storage efficiency is below.

Odyssey AGM - 46A Charge, Removed 44.69Ah back to 11.7V = 97.15%

Firefly AGM - 50.6A Charge, Removed 49.75Ah back to 11.7V = 98.32%

Lifeline AGM - 48.3A Charge, Removed 46.56Ah back to 11.7V = 96.4%

Deka AGM - 48.3A Charge, Removed 46.45Ah back to 11.7V = 96.17%

Once you hit absorption this changes. As the batteries age, and sulfate, this changes...

Key Point #3
"The testing reported on here examined a single sample of the Trojan 30XHS battery. This is a 12-volt, flooded, lead-antimony battery rated 130Ah at the 20 hour rate by the manufacturer. Testing in PV applications, where charging is rarely in accordance with manufacturer’s recommendations, indicates that this battery has a “PV capacity” of about 100Ah, and that is the value that will be used as this battery’s capacity in this paper."

So this is the same battery as the Trojan SCS-225 that many boaters use on boats. Sandia is acknowledging that one of the main issues with batteries in solar systems, which actually no different on boats, is that;

"charging is rarely in accordance with manufacturer’ s recommendation".

In regards to that statement they reduce the usable capacity to 100Ah from 130Ah!! I know some of us have been harping on under & improper charging for a long while, you & myself included, but it is always great to see Sandia National Labs also acknowledge this major shortcoming not just by owners of the batteries but this is a major shortcoming of the entire industry building charge equipment...

Key Point #4
"Full recharge (as opposed to the partial charges used to charge the battery with a specific number of Amp-hours) was performed by bringing the battery voltage to 14.8 volts and then maintaining regulation voltage (14.8 volts) by tapering the current for 10 hours."

This is perhaps the most salient point in the entire paper. At a low charge rate (remember this is a 130Ah battery so a 3.3A charge rate is 0.025C or a 2.5% charge rate based on labeled Ah capacity. Even at this extremely low charge rate (which should be more efficient) in order to achieve a truly full battery it was held at a 14.8V absorption voltage for TEN HOURS.

It takes a LONG time to fully charge a lead acid battery!!!!!!!!!!!!!

Honestly, who out there has the ability with solar to not only attain 14.8V but then hold it there for TEN HOURS and do this each day? The answer is a trick clearly....

Key Point #5
"After the initial regime of 10 full charge/discharge cycles, the battery was charged with 68Ah which was estimated to result in about 65% SOC, or that would provide about 65Ah on discharge. The 68Ah charge actually resulted in an average discharge of 65.9Ah. After the battery was charged with 68Ah, it was then discharged to determine the amp-hours available, and charge efficiency was calculated."

This battery was discharged fully to 10.5V then recharged until 68Ah's had been returned. They netted 65.9Ah's when discharged back to 10.5V.

This makes for a flooded battery bulk efficiency, at a low charge rate, of 96.91% of the energy put in taken back out. Like above, bulk is very efficient...


Key Point #6
"Clearly, the use of assumed charge efficiencies in the range of 80% will not result in a fully charged battery when this battery is expected to operate in the upper 20% of it’s state of charge. It is expected that these results will hold up well for other deep-cycle flooded lead-antimony batteries as well."

What this means is that those of us sizing banks to operate in the 80% SOC and higher range, for the longest cycle life, will have MUCH, MUCH lower charge efficiency than the often stated 80% etc... Much lower than you would if you cycled from 50% to 100% SOC which is where the 80% efficiency number tends to stem from. If you are sized to be operating in the upper SOC range, shallow cycling, the bottom line is don't use 120% as your return Ah because that will not net you a full battery.

Continually operating above 80% SOC results in charge efficiencies as low as 50%..... While AGM batteries would fair better they will still be quite inefficient if continually cycling in the the upper SOC range and this you won't find in the glossy marketing data..

Key Points #6
"This result has important implications to operational PV systems. That is, if a battery is partially charged for several consecutive cycles (for example, the array is marginally sized and there is a series of less than full sun days in the winter) the useable battery capacity decreases each cycle, even though the same amount of energy has been presented to the battery each day. This is the result of battery inefficiencies, electrolyte stratification, and sulfate buildup during these partial charges."

"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%.

"Charge efficiencies at 90% SOC and greater were measured at less than 50%"

What this means is if you PSOC (partial state of charge cycle) your usable capacity will continually "walk down" (get smaller) with each PSOC cycle.This is exactly what we saw with the Practical Sailor May 2015 "Fighting Sulfation In AGM's" test. Batteries need to get full as often as possible or you will permanently lose capacity. As you reach the 90% SOC range you will need roughly 2 Ah's to store just 1 Ah of usable capacity...

If you think your Ah counter is programmed to know or account for this non-linear efficiency, think again..

Key Point #7
"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."

Take away here is that your PV really needs to be sized at DOUBLE or more of your daily consumption to even begin to get close to a full recharge. 100Ah's consumed daily means an array capable of supplying 200Ah's each day. That said it would also require charge controllers that can hold absorption for a minimum of 6+ hours, of which very few can even be programmed to do. This is exactly where the old one-two punch of fast charging via alternator then finish charging with solar can get you to the highest possible SOC with the sunlight hours you have available.

When folks look at me and tell me; "My batteries are at 100% SOC by noon." It at least gives me a good chuckle......

Just my 2¢, don't spend it all at once...

[sailinglegend]

Originally Posted by a64pilot

Nope I understand charge acceptance rate, what I disagree with is this statement that you have to generate far more than you pull out to recharge a battery. I believe you only have to generate approximately 120% of what you used.

Please read my text again AND the link I gave you.

I agreed with your statement that you only have to generate 120% of what is used. I never said you needed more than that! My point is during Bulk stage the charge efficiency is very high - maybe 98%, but when the solar tries to top up past 90% SOC it will take a very very long time, because the small amount of current and Ah going in at this stage is mainly being wasted. Does that now make sense?

Originally Posted by a64pilot

I don't know why but it seems I can use 50 amp/hours out of a 440 amp/ hr bank and recharge it faster than if I used 50 amp / hours out of a 100 amp / hour bank.

I assume it's because the charge acceptance rate of the smaller bank is less

Amp/Hours should read Ah not amps per hour - see the very long thread on this!!!

Doubling the service bank size means it will be more efficient and accept more Ah more quickly from all charging sources during because it is the boost phase longer.

It takes a bit of very over-simplified maths to prove the point, but a 100 Ah battery that is discharged to 50% may accept 20Ah in the first hour during the boosts stage with a 20 amp charger, maybe 10Ah in the second hour during the start of the less efficient absorption phase, and the remaining 20Ah in another say 5 hours. Doubling the battery size to 200Ah, with the same charging source of 20 amps, will accept 10Ah into each battery in 1 hour, that’s 20Ah into the bank. In the second hour it will still store another 20Ah - still in the bulk stage. That’s 40Ah replaced in two hours, as compared to 30Ah with a single bank. In the 3rd hour it may still accept 20 amps into the bank because a single battery in the start of the absorption phase could accept 10 amps. That’s 60Ah in three hours. The key point is that for two hours it is still in the more efficient boost stage where the battery is taking all the current the charge source can give it. Note that the initial boost charging stage has captured 40Ah in two hours and 60 Ah in three hours. With the smaller bank it could only capture 20Ah in the first hour during boost and 30Ah after the second hour during the start of absorption. The third hour may add another 5 amps. That’s 35Ah with one batteries and 60Ah with two batteries. So a bigger bank will be more efficient and accept more Ah more quickly from all charging sources.