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Old 30-07-2020, 08:21   #76
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Re: Best batteries for $2k budget

200AH in a 800AH bank is the last 25% and the bank starts at 75% SOC
200AH in a 600AH bank is the last 33.3%, and the ban starts at 66.6% SOC

Given a battery charger capable of putting out at 100% capacity 100 amps and that each bank could accept that till it reaches the mysterious 80% state of charge point. Then the battery acceptance just drops as a function of the internal resistance of the battery and varies as a % of capacity, which the bank doesn't matter.

800ah X (80-75%) = 40ah, divided by 100 amp = 0.4 hours = 24 minutes
600AH x 1(80-66.6%) =80.4ah, divided by 100 amp = 0.8 hours = 48 minutes

After that point it is assumed each battery bank will accept charge amps less than 100 amps and be self limiting and each will charge at the same rate. Let's say it takes 4 hours to go from 80% to 100%m that means the 880ah bank takes 4H 24m and the 600ah takes 4H 48m. So it takes longer to fully recharge the 600 ah bank to 100%.

Is it worth debating? You decide.
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Old 30-07-2020, 08:24   #77
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Re: Best batteries for $2k budget

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That might be where you and Dockhead crossed wires.
Could be. We all tend to look at things in our own context and misunderstand what is actually being said. We often "read in" whats not there. I'm not very good at articulating the points I'm trying to get across either.
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Old 30-07-2020, 09:05   #78
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Re: Best batteries for $2k budget

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200AH in a 800AH bank is the last 25% and the bank starts at 75% SOC
200AH in a 600AH bank is the last 33.3%, and the ban starts at 66.6% SOC

Given a battery charger capable of putting out at 100% capacity 100 amps and that each bank could accept that till it reaches the mysterious 80% state of charge point. Then the battery acceptance just drops as a function of the internal resistance of the battery and varies as a % of capacity, which the bank doesn't matter.

800ah X (80-75%) = 40ah, divided by 100 amp = 0.4 hours = 24 minutes
600AH x 1(80-66.6%) =80.4ah, divided by 100 amp = 0.8 hours = 48 minutes

After that point it is assumed each battery bank will accept charge amps less than 100 amps and be self limiting and each will charge at the same rate. Let's say it takes 4 hours to go from 80% to 100%m that means the 880ah bank takes 4H 24m and the 600ah takes 4H 48m. So it takes longer to fully recharge the 600 ah bank to 100%.

Is it worth debating? You decide.
It could be. That's why PSOC cycling is reasonable if you only charge LA batteries with the main engine alternator. Firefly batteries would be a reasonable choice then or even better---lithium. With lithium you could cycle between X and 100% SOC relatively quickly with a large alternator. People try to do that with AGM's and it doesn't work well. AGM's don't last in a PSOC environment.

With LA batteries and enough solar the high output alternators have little benefit if trying to cycle from X to 100% SOC. Trojan recommends 10 to 13% of Ah capacity charging rate. Above that and the battery will reach absorption at a lower SOC than when charged at a lower rate. Very little time will be saved. The bottom line is that a high output alternator is not very useful if you don't PSOC your LA batteries.

Solar is a game changer with LA batteries. Free energy all day. Less battery capacity needed because solar is used during the day. You only need to store enough energy for the night. I know some people won't have solar because of the looks so LA with PSOC use or Lithium might be the better option.

In reality I think most people don't think about it much and more is better rules. A combination of cycling strategies are used and new batteries are purchased when needed. It's not the most cost effective method but seems to work just fine for most.

Naturally ones daily energy requirements also play a factor.
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Old 30-07-2020, 10:23   #79
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Re: Best batteries for $2k budget

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Naturally ones daily energy requirements also play a factor.
Unless you have a battery that is "ok" with partial state of charges, LFP or Firefly, I don't even think it matters. If you are an off the grid cruiser batteries will be good for maybe 4-5 years. If you have a big enough bank compared to your needs maybe you can call it 6-8 years by ignoring the lost capacity because it isn't affecting you yet.
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Old 30-07-2020, 10:27   #80
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Re: Best batteries for $2k budget

So kmac are you saying itís better to drive to Pskov than 100%??
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Old 30-07-2020, 10:53   #81
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Re: Best batteries for $2k budget

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So kmac are you saying itís better to drive to Pskov than 100%??
It depends on your circumstances and your priorities. I'm saying you need to understand all options and the different price points of each to make an informed decision.

IMHO it is better to cycle to a PSOC if you are using fossil fuel to do the LA charging and a high output alternator won't charge a LA battery to 100% SOC much faster than an alternator that can deliver 10 to 13% of battery capacity. Engine run time is WAY more expensive than batteries.
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Old 30-07-2020, 11:11   #82
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Re: Best batteries for $2k budget

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Charge efficiency drops significantly as SOC increases. The larger bank, 800 Ah, drops to 75% SOC after consuming 200 Ah. The 600 Ah bank drops to 66% SOC. The smaller bank will charge at a higher average efficiency. That's why a lot of people chose to cycle between 50 and 80% SOC. Not only the acceptance rate drops way off above 80% SOC, the efficiency also drops.

80% SoC is not a magic number where a bank hits the CV stage but many people assume it is.

When or where you hit absorption or constant voltage during the SoC curve is 100% dependent upon how much charge current you have. Bulk charging (CC) is extremely efficient, even with FLA batteries, storing upwards of 98% +/- of the energy delivered to the battery. CV is a diminishing efficiency and why it takes so long to fully charge a lead acid battery as SoC rises.

A low current charge source, such as solar, may not hit absorption or CV until the mid 90's as a % SoC (bulk charging all the way into the mid 90's) and up to this point nearly every Ah delivered is getting stored. On the flip side your alternator may hit the CV point at 75% SoC or even lower if big enough.
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Old 30-07-2020, 11:15   #83
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Re: Best batteries for $2k budget

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80% SoC is not a magic number where a bank hits the CV stage but many people assume it is.

When or where you hit absorption or constant voltage during the SoC curve is 100% dependent upon how much charge current you have. Bulk charging (CC) is extremely efficient, even with FLA batteries, storing upwards of 98% +/- of the energy delivered to the battery. CV is a diminishing efficiency and why it takes so long to fully charge a lead acid battery as SoC rises.

A low current charge source, such as solar, may not hit absorption or CV until the mid 90's as a % SoC (bulk charging all the way into the mid 90's) and up to this point nearly every Ah delivered is getting stored. On the flip side your alternator may hit the CV point at 75% SoC or even lower if big enough.

80% would be typical with a 0.15C or 0.2C charge source, wouldn't it?


What you describe is a fight between speed and efficiency, right?


As someone above said, few will care about efficiency, we care about speed -- because it's the hours of running the charge source, not the small incremental use of horsepower, which costs money and which bothers us. Right?
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Old 30-07-2020, 11:40   #84
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Re: Best batteries for $2k budget

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80% would be typical with a 0.15C or 0.2C charge source, wouldn't it?
It really depends upon the battery. Thicker plate flooded batteries will hit CV earlier and with lower current than a deep cycle AGM but a TPPL AGM will hold off CV to a slightly higher SoC than other AGM's.....

What you describe is a fight between speed and efficiency, right?[/quote]

There's no fight if used appropriately...

-Use high speed (alternator generator etc.) for the bulk & early absorption early in the day

-Use low speed (solar, fuel cell, wind etc.) for the remainder of absorption and long taper

If you know how much current your PV array can provide just shut down the dino-juice charging when acceptance has dropped to or near that level (minus domestic loads). Now you have the ideal charging set up. The alternator is used really just for bulk/fast charging and possibly a bit of early absorption then the low current trickles the bank the rest of the way towards 100%.

Course if you have LiFePO4 you can just run the engine enough to put what you need for your daily energy back into the bank, and no more.

We don't even use our solar array any more, it's mostly shut off, as 30 minutes a day of engine run time covers us. We don't even begin to think about charging until we get down towards 80% DoD. The only time we use the PV is perhaps to extend our stay at anchor beyond three-four days and we don't want to hear the engine during that time. With lead acid it was always a struggle staying in the upper SoC range and trying for 100% as often as possible.. Don't miss that at all..
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Old 30-07-2020, 11:51   #85
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Re: Best batteries for $2k budget

There's also this gem from Nigel, written about 20 years ago, still true as far as I know.


IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?
(By Nigel Calder - I DIDN’T write this!!!)

The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.

LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.

This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.

Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 5% increase in life expectancy using exactly the same batteries!

But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!

There are two immediate conclusions to be drawn from these figures:

1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries.

2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle).

FOR BATTERY LONGEVITY, A SINGLE LARGE (HOUSE) BANK, THE LARGER THE BETTER, IS PREFERABLE TO DIVIDED (HOUSE) BANKS.
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Old 30-07-2020, 11:55   #86
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Re: Best batteries for $2k budget

Quote:
Originally Posted by Maine Sail View Post
It really depends upon the battery. Thicker plate flooded batteries will hit CV earlier and with lower current than a deep cycle AGM but a TPPL AGM will hold off CV to a slightly higher SoC than other AGM's.....

What you describe is a fight between speed and efficiency, right?
There's no fight if used appropriately...

-Use high speed (alternator generator etc.) for the bulk & early absorption early in the day

-Use low speed (solar, fuel cell, wind etc.) for the remainder of absorption and long taper

If you know how much current your PV array can provide just shut down the dino-juice charging when acceptance has dropped to or near that level (minus domestic loads). Now you have the ideal charging set up. The alternator is used really just for bulk/fast charging and possibly a bit of early absorption then the low current trickles the bank the rest of the way towards 100%.

Course if you have LiFePO4 you can just run the engine enough to put what you need for your daily energy back into the bank, and no more.

We don't even use our solar array any more, it's mostly shut off, as 30 minutes a day of engine run time covers us. We don't even begin to think about charging until we get down towards 80% DoD. The only time we use the PV is perhaps to extend our stay at anchor beyond three-four days and we don't want to hear the engine during that time. With lead acid it was always a struggle staying in the upper SoC range and trying for 100% as often as possible.. Don't miss that at all..[/QUOTE]


I hear you! I have zero solar -- considerations of windage; and we started racing this year. So that struggle you describe is ours. We are a great use case for lithium.
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Old 30-07-2020, 12:25   #87
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Re: Best batteries for $2k budget

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I hear you! I have zero solar -- considerations of windage; and we started racing this year. So that struggle you describe is ours. We are a great use case for lithium.
Lithium would be your best option but it needs an externally regulated high output, high performance alternator with the associated expense.

Firefly batteries with PSOC cycling would also be good with less demanding charging capabilities. I'm not sure of the charging characteristics of Fireflys so you would need to check on that but PSOC cycling is their strong point.

And maybe the most cost effective would be LA batteries with PSOC cycling and a stock alternator or fairly inexpensive upgrade. MaineSail has lots of options for any of the configurations and stellar advice.
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Old 30-07-2020, 12:37   #88
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Re: Best batteries for $2k budget

I got my three L16 Fireflies in today.
Not $2,000, but hopefully I won’t sweat the 100% SOC thing, In truth it wasn’t really very hard to achieve, but maybe the Fireflies will last longer. I should be cycling them down to 66% each night and achieve a full charge most days.

I too have surveyed many cruisers, and it seems that no matter which chemistry they have that five years is pretty much of an average, even Gel.
My lifelines showed significant capacity loss right at five years, they still charge up fully and hit full charge at about the same number of hours and if I wasn’t tracking capacity, I’d think they were still fine.
I think that people who get real long lives out of their bank have large banks when compared to their usage, and don’t consider their banks bad until they have lost so much capacity that they are waking up with nearly dead batteries, but they may have lost 2/3 capacity.

On edit, one thing I’m wondering and haven’t found out, will my original Balmar smart gauge work with the Fireflies?
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Old 30-07-2020, 12:47   #89
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Re: Best batteries for $2k budget

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I hear you! I have zero solar -- considerations of windage; and we started racing this year. So that struggle you describe is ours. We are a great use case for lithium.
I believe people like you are the poster child for a generator and Lithium, however I’m not so sure about the huge charge rates I see some say that you can charge Lithium at, Lithium may will accept some high C rates, but my experience with other formats is that it will reduce the life. High rate charging gets then hot, and no battery does well with heat.
Just as the you can cycle Lithium up to 80% regularly, that will also I believe reduce life.

Use the middle third of capacity and they will last a very long time, maybe never have to replace them.
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Old 30-07-2020, 12:51   #90
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Re: Best batteries for $2k budget

I don't know that there are right or wrong batteries because it depends on how you use them. We're happy with golf cart batteries, they last 6 years or more and are cheap. Our bank is large ~1,100 amp hour and we draw it down about 6/8% a day. After 3/4 days we are down 20/25% so we run the genset for 3/4 hours, make water and let the solar panels bring it back to 100% by days end. A couple more solar panels would probably keep us at 100% but running the genset every 3/4 days allows for a healthy water budget (1,000 gallons per month). This works for us but if we were in a place that wasn't as sunny and we had easy access to water then a lithium battery would maybe be a better solution.
For the OP with a budget it's tough to beat golf cart batteries and some solar.
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