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Old 16-10-2020, 14:33   #16
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Re: House Bank Sizing Question

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Not a direct answer, but I have priced up every type almost of battery including a tesla battery...

I am either going to go for a tesla 24v battery. Or lifep04. Size of the bank and ability to deep discharge without worry, super low internal resistance means everything is easier.

Its taken me months of research and review reading, and more research. You won't see me post the install till next year because I'm currently on 12v and tesla is 24v, but when I do I will post figures etc to justify it ��

I hope this helps in some way!
Will really appreciate reading results of your research and hopefully some real-life testing also, if possible. But if Tesla battery is only 24V, no 12V available, this might deter most folks from using them. It would seem to be too expensive to convert an existing complete 12V system to 24V. Battery chargers, inverters, reefers, watermakers, anchor windlass, bow thruster, all the electronics including VHF and HF gear: I think that list is already over $40 Grand.
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Old 16-10-2020, 15:31   #17
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Re: House Bank Sizing Question

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Originally Posted by Dsanduril View Post
Well, since this seems to be expanding a bit, I use two values to calculate bank size; typical (daily) depth of discharge (DoD - i.e. capacity used) and maximum occasional DoD.

For LA batteries and 365 boat living I like to see daily DoD at or less than ~20% because that gives the best cycle life. I also like to use ~50% (or maybe 60%, depends on frequency) as the worst case DoD. Using some round numbers for ease of calculation:

My usage is 50Ah/8 hours (that's 150Ah/day). I have solar that can easily handle all daytime loads and bring the batteries back to full on a good day. So, I start discharging at 4pm and start charging at 8am. That gives 16 hours of discharge = 100Ah. For 20% DoD that gives 100/0.2 = 500Ah bank size. With nice sunny days all the time that's all I need.

Estimating the worst case becomes trickier. If I have no solar production then at 4pm on day 1 I am -150, and at 8am on day 2 I am -250. If I again get no solar production, at 8am on day 3 I am -400. Say that I'll fire up a diesel charging source in that case. 400Ah/0.5 (worst case DoD) = 800Ah bank size. It's going to take some charging time to get that 400Ah back in the batteries.

Impossible from a distance to know what use patterns someone has and what charging profiles are available and likely. But if you put those numbers together you can come up with a reasonable way to estimate bank size. In this example 500Ah would be minimum and 800Ah would be preferred. What fits (both physically and the wallet) then start to come into play.

The best money you can ever spend on batteries is reducing your usage so you don't have to buy the batteries. Better refrigeration, LEDs, low power TV - whatever is your biggest power user, look at lower power alternatives and see if replacing something is less expensive than the batteries you need to buy to power it.
What I must be missing is the added complication of 50% usefulness of LA Batteries.

So in our case our total daily usage is 124 AH. Our house batteries are 4 FLA T105's = 450ah capacity. Yet we see that they are down well below 50% SOC after 124ah daily load. (12.1v)

So, from my perspective the most I can use of my 450 AH battery is 124ah, or only 1/4 the rated capacity.

OK, disclaimers:
I get a bit better performance the first two or three days after getting fully charged on shore power. The performance slowly deteriorates over time. The scenario I just described occurs after about two weeks on the hook. After three months it requires more hours to bring the batteries up to14.2 and they are rarely above 12v after 12 hours of night time usage (60ah). I know that coming up t 14.2v in a daily charging cycle with the engine is not fully charging these batteries.

So doesn't this mean people need more capacity than the formula (daily ah/.4) would indicate?
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Old 16-10-2020, 16:12   #18
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Re: House Bank Sizing Question

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...So doesn't this mean people need more capacity than the formula (daily ah/.4) would indicate?
Well, the first question I'd ask is how sure you are of the voltage measurement at the battery terminals, without load? But, having said that...

The question of partial state of charge (PSoC) greatly complicates the whole discussion. In calculating you have to at least estimate how often you will get to 100% SoC. For myself, I define 100% SoC as 14.xV (where 'x' varies a little bit from manufacturer to manufacturer) and input current < 1% nominal battery capacity (tail current). Trojan says that T105s should get to 14.8V, and using 1% they would be full when the charge current gets to 4.5A at 14.8V. There is some latitude in the tail current definition with values ranging from 0.5% to 3% (2 to 12A for your T-105s) depending on who you ask. On older batteries it can be hard to get below 2% sometimes, they may take that amount of current essentially forever.

That kind of charging is nearly impossible to get with an engine/generator charging system - you can only get it with a dockside battery charger or solar/wind that can provide the long, slow taper. You'd drive yourself crazy trying to get there with engine/generator charging (on a sailboat anyway - a powerboat underway is a whole different scenario).

If you don't get to 100% SoC reasonably often then you will build up hard sulfates on the battery plates and start to lose capacity. That's when an alternative chemistry can come into play, LiFePO4 or Firefly Carbon Foam AGM as examples. Both of these can deal with chronic PSoC much better than regular flavors of LA.

For our own system, we have the luxury of having about 900W of solar for charging. In the tropics/sunny climates on most days our batteries switch to absorption/voltage regulation between noon and 1 and we probably reach the tail current of 1% on > 50% of days. Usually also no more than 3-4 days between reaching that tail current. During the summer here in AK it's a bit more hit-or-miss but we still get there at least once a week. So we pretty frequently get to a true 100% SoC.

If you can't ever (or rarely) get that 100% SoC then you'll see the behavior you describe. What you're really seeing is that at the end of each charge cycle you're at more like 80-90% SoC, and so you have to start your calculations from that point. Pretend your bank is a 400Ah bank (90% SoC), take out 124Ah and you're at 275/450 = 61% SoC. Take 124Ah out of an 80% charged bank and you're at 50% SoC. How often and how fully you can charge your batteries makes a huge difference.

And then to complicate it even more, pretty much every battery loses some capacity with each cycle. Even my EV battery (Li-ion) was only warranted to hold 80% of its initial capacity through the life of the warranty (3 years I think).

If you keep adding all those factors into your bank sizing then pretty soon you end up with a bank that is really large.
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Old 16-10-2020, 17:04   #19
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Re: House Bank Sizing Question

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Originally Posted by Dsanduril View Post
...What you're really seeing is that at the end of each charge cycle you're at more like 80-90% SoC, and so you have to start your calculations from that point. Pretend your bank is a 400Ah bank (90% SoC), take out 124Ah and you're at 275/450 = 61% SoC. Take 124Ah out of an 80% charged bank and you're at 50% SoC...
Thank You, very interesting (we've all read many threads about battery capacity over the years but your very lucid explanation is the most understandable I've read).

But what I am really getting at is that since we've heard that going below 50% SoC is tough on the FLA batteries (and that below that point the voltage is pretty low anyhow) then it means to me that in usage such as I have described I'm really only getting about 124Ah realistically out of my 450Ah battery.

After a long period away from the dock I'm limited to cycling between 80% and 50% SoC on most days meaning I get about 30% of the battery's capacity.

All of this adds up to: Without much bigger solar array or some other way of getting a lot more charging a user can only count on 30% of their FLA batteries' capacity.

So for users like me, who must cycle between 80% SoC and 50%SoC the formula should be:

Daily Consumption / .3=AH Required

If you use 124Ah it is 124/.3=413Ah

And this is for one day's capacity.
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Old 17-10-2020, 13:18   #20
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Re: House Bank Sizing Question

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Will really appreciate reading results of your research and hopefully some real-life testing also, if possible. But if Tesla battery is only 24V, no 12V available, this might deter most folks from using them. It would seem to be too expensive to convert an existing complete 12V system to 24V. Battery chargers, inverters, reefers, watermakers, anchor windlass, bow thruster, all the electronics including VHF and HF gear: I think that list is already over $40 Grand.
Ah this is the fun part, so you can run 24v to 12v converters relatively cheap 60a is about £80 this will run most of the auxiliary bits on a boat you can have more in series if need be (old autopilot)

Most solar chargers are 12/24v so my existing wind generator and solar will work.

The inverter is replacement though, tesla gives 240ah @24v between 18-25v i have found 24v inverters that will run from that

Engine alternator is 12v, sterling sell a 12v to 24v battery charger 60a.

Anyway sorry I'm taking over your thread! I will start another one when I have all the info

Question, reefers? Are we talking e cigarettes?

Thanks for the input 😁
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Old 17-10-2020, 13:21   #21
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Re: House Bank Sizing Question

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Originally Posted by wingssail View Post
What I must be missing is the added complication of 50% usefulness of LA Batteries.

So in our case our total daily usage is 124 AH. Our house batteries are 4 FLA T105's = 450ah capacity. Yet we see that they are down well below 50% SOC after 124ah daily load. (12.1v)

So, from my perspective the most I can use of my 450 AH battery is 124ah, or only 1/4 the rated capacity.

OK, disclaimers:
I get a bit better performance the first two or three days after getting fully charged on shore power. The performance slowly deteriorates over time. The scenario I just described occurs after about two weeks on the hook. After three months it requires more hours to bring the batteries up to14.2 and they are rarely above 12v after 12 hours of night time usage (60ah). I know that coming up t 14.2v in a daily charging cycle with the engine is not fully charging these batteries.

So doesn't this mean people need more capacity than the formula (daily ah/.4) would indicate?
Are you running a charge regulator on your alternator? Engine can fully charge any bank but a standard one won't without a decent charge controller have a look at sterling electronics
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Old 17-10-2020, 14:52   #22
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Re: House Bank Sizing Question

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Are you running a charge regulator on your alternator? Engine can fully charge any bank but a standard one won't without a decent charge controller have a look at sterling electronics
We have a high output Balmar Alternator (130A) regulated by a Balmar ARS-5 regulator. We have fully explored the settings for various stages of charging, (times and set points) and have tracked the charging profile quite methodically with various settings.

What we find is that the amps coming into the batteries tapers off pretty sharply after an hour of "bulk" charging (to use Balmar's terminology), even at a steady 14.7 volts alternator output. (The battery is seeing 14.6v due to loses in the long cable run.) As the battery voltage comes up gradually to the 14.6 set point the amperage acceptance rate drops to around 45 amps. After an additional 30 minutes the batteries are taking around 20-30 amps.

According to Dsanduril these FLA batteries won't be fully charged until the amps being accepted is down to 1-2% of the nominal, which I think he means, for us, is about 4-5 amps.

I am not sure how many hours of charging that would be, but it's way more than we are willing to do each day. So we settle for about an 80% SoC.

This is where I see the difficulty lies in charging with an engine driven alternator. The same thing would be true with a gen-set. FLA batteries apparently take many hours of charging to achieve 100% SoC. Big solar systems may be able to supply that kind of voltage and amperage over a period of many hours, as can shore power based battery chargers.

Where it works for some cruisers, (perhaps many) is that they usually run their motors whenever they are underway; sailing is not standard practice. A six hour motor trip can charge an FLA battery. Also, many cruising boats have large solar arrays built over the sterns of their boats, also contributing to charging efficiency.

But for many years we have avoided motoring that much or building a solar array on the back of our boat. Instead we live with cycling our batteries from 80% to 50% each day, getting only a fraction of the potential amp-hours of which the battery is capable. it does work for us however, and surprisingly, I am only now, after 34 years, learning actually what is going on: we never hit 100%Soc while at anchor or sailing.
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Old 17-10-2020, 17:15   #23
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Re: House Bank Sizing Question

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... it does work for us however, and surprisingly, I am only now, after 34 years, learning actually what is going on: we never hit 100%Soc while at anchor or sailing.
I donít want to show both our ages, but thatís pretty much how it used to work for all of us. The only charging source was the auxiliary engine and you simply didnít run it enough to get a full charge. There are tons of threads here that will tell you thatís the best way to quickly murder your (LA) batteries, and there is some truth to that, but a lot of boats have spent a lot of time cycling between 50 and 80% SoC because thatís the reality of charging only from the engine.

You donít need a giant solar array though, to try to get to 100%. If youíre willing to run the engine in the morning to do the bulk charging a reasonably small solar array can deal with the daytime loads and the charging taper. Itís all trade offs, and just about every boat is different.
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Old 17-10-2020, 21:33   #24
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Re: House Bank Sizing Question

Hi Guys, thanks for the info, both succinct and broader context. To answer your questions, I currently have AGM's in my house bank and they've given me more than 5 1/2 years of solid service, so my plan is to stick with them. As sailcrazy said "Lithium batts scare the *** out of me..." I do have a diesel genset which I could theoretically run until the cows come home, but I find about an hour both morning and evening to be tolerable. I believe my genset is original equipment on the boat (a 13 kW Onan which just celebrated it's 38th birthday, so its replacement is on the horizon, after my wallet recovers from the new house bank.) If a high output alternator is warranted on the new genset to keep the run time down, I'll go for it. As of now the genset is my only form of battery charging other than the engines.

I appreciate Dsanduril's differentiation between typical (daily) depth of discharge and maximum occasional DoD, which is the number I used for my load calculation, and the total was truly frightening. As tkeithlu said, I'm losing waterline just thinking about this. Dsanduril, re: post #8, when were you on my boat?? I'm now retired, so pushing the envelope from weekends to weeks.
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Old 17-10-2020, 22:25   #25
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Re: House Bank Sizing Question

Dsanduril is right on the money. No faster way to kill FLA batteries than not getting to 100%. We have two solar / battery systems. 12 v for starters and instruments and 24 house. Rolls 700 AH @24 VDC, 6x 285 panels. Schneider controller. NL 8kw gen set. Never at dock. No problems so no reason to go to Tesla. Keeping consumption is also the key. Iíd rather invest in production than storage. Been with Rolls batteries for decades and have seen them last 10 plus.
Big wire, very clean connections and low voltage drop also very important to a happy system. Itís the system, not one component thatís important.
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Old 18-10-2020, 04:48   #26
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Re: House Bank Sizing Question

Basic summary:

Cruisers routinely run their batteries between 50 and 80 percent full. If you're one of them, treating your boat to a "spa day" by being at a shore power point at least once a month, to allow "real" full charging, will help life.

As to not taking them down more than 50% capacity, that's all a matter of degree.

The best is to never have them leave full - but then you likely would not be cruising. Floor sweepers and other gear routinely discharge (typically a L16x battery, same footprint but twice as high and twice the amperage rating as a T-105 - and along with it, twice the weight) to 20% and then recharge (fully as they're plugged in for the other 16 or so hours not 'working').

Your FLA battery life will be a function of how many amp hours have been consumed, mostly, unless you're not bringing your bank up to a truly fully charged state on a frequent and regular basis, not how far you've drained it on any given occasion. Assuming you keep the water topped up, and the fully-charged state achieved regularly (and for most manufacturers, equalization at some cumulative AH use on a regular basis, which will help put sulfates back into solution and de-stratify the acid by virtue of the low-level boiling), you'll get a long life out of them.

That assumes, of course, that the bank is perfect when you install it; I had one bank which had one DOA (after some time on a 6V charger, the installing company brought me another), and, in the warranty period, each other successively failed, with the same center-cell dead. That DOA replacement was the champ of the later-obtained replacements, when it retained its full charge for many months while we waited until we got back to a dock where a new bank could reasonably be brought aboard (L16H-AC from Trojan weigh about 125# each and are about 17" tall, meaning they have to be lifted over the battery box to exchange), and it still showed 12.6V...
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