How big of a battery bank do I need?

[kmacdonald]

I think you will use less than 150 amp hours a day if you use your wind vane. The autopilot and refrigerator are the big consumers. LED lights can be disregarded their consumption is so little. VHF and chartplotter use some but you dont need to have them on most of the time. (When offshore) charge a laptop maybe 5 amp hours a day. You could do with a 200 amp hour bank. Two 6V golf carts would be fine.

Pizzazz has the right idea also. Figure 30 to 80 SOC usage and replace batteries every 2 or 3 years. 50 to 100 SOC is a myth. Accept the facts and plan accordingly.

[Peeew]

As others have described above one big issue is that fla batteries are really only usable from about 50% to 80% due to slow acceptance rate of charge and long time needed for absorb/float. One nice thing about lithium or the firefly batteries is how fast they charge, so they will accept what your alternator puts out, and the ability to more deeply discharge without harm. Obviously all the solar, wind, Genset etc charging you can reasonably use is best. But I was really surprised at how effective upgrading batteries to modern chemistries helps.

[TrailerCruiser]

Is there additional things I need to consider (Electrically) if I went with Lithium-ion? I'm trying to figure out if I need a bigger alternator, regulator, etc?

[Peeew]

I went with firefly carbon foam batteries. They have similar performance to lithium. I’m sure some that know lithium better can help compare. Due to the fast charge acceptance I didn’t want to burn up my 120 amp alternator or belt so I did an easy swap for the Balmar external regulator that has temp probes and programmable loading. Some people have swapped out to wide belts and pulleys if you don’t have that already. These were all fairly simple, and I’m not an expert by any means. Some chargers will need to be programmed for proper charge profiles. I would suggest considering these before deciding on what to pick. But I’m happy with my choices.

[Dockhead]

Originally Posted by TrailerCruiser

Is there additional things I need to consider (Electrically) if I went with Lithium-ion? I'm trying to figure out if I need a bigger alternator, regulator, etc?

Read the LiFePo4 thread.


If you go with drop-in LiFePo4 units, like the Battle Born ones, then you don't need to do too much -- basically just (a) make sure your mains charger profile is suitable; (b) make sure your alternator regulator charger profile is suitable (you will need an external regulator); and (c) make sure your alternator is protected from being burned up by the high acceptance rate. If you have a stock car-type alternator this is a good time to upgrade.


If you buy bare LiFePo4 cells then you have to build the infrastructure for that -- BMS, cut-offs, right controls for charge sources, etc. You can read all about that in the thread. This is the way to go -- much cheaper and much more flexible, than drop-ins, but it's a rather more involved installation.

[admiralslater]

I have a similar load to the op’s . I currently have 550 amp firefly battery bank . When I first installed them I had 600 wats of solar which on a good day could get the bank back up , but if there was a cloudy patch it struggled . After increasing charging capacity to 960 watts I have a much better balance .
If you don't have the capacity to bring them back up to full every or at least most days ,it does not really matter how much capacity you have you will eventually will have dead batteries. I just fitted a high capacity alternators with serpentine belts ,well worth the expense

[Ken Fry]

Originally Posted by StuM

For crying out loud, how many times does it have to be said.


It's AMP HOURS per day, not AMPS!


And they are abbreviated to Ah, not a/h!

Amp is a RATE of consumption, not a quantity of energy.

This stuff drives me nuts, too! I was scanning through this thread to see if there were any posts with correct terminology, and yours is the first.

If people took a little time to understand the concepts, then there would be very little need for threads like this one. I hope we can all agree that there should be no need for a thread that begins with this question: "I need to go to an island 100 miles away, and my boat will go 20 miles per hour, while burning 2 gallons per hour. How long will it take me to get there, and how much fuel will I use? "

Some of the answers might be (if this thread is a indication) "You cannot get there! You can only go 20 miles." or "You need an engine five times as big, because you need to go 100."

You correctly point out that the amp is not a quantity of energy. However, you seem to suggest that Ah might be a quantity of energy, which it is not. A 100 AH 6 v battery and a 100 AH 12v battery store different quantities of energy. The first can supply 600 Wh of energy; the second can supply 1200 Wh. This distinction is important when talking about 6V golf cart batteries, which have half the energy capacity of a 12 volt battery of the same Ah rating.

These distinctions become important especially in modern small boats, in which some things run on 12 V, some things on 24 V, some on 120 VAC and some at 240 VAC. (More variety: Lithium cells are often purchased in 100 Ah increments, but at 3.3 volts, so such a cell has about 1/4 the energy capacity of a 12V 100 Ah battery).

To illustrate the confusion that ensues regarding using Ah as a measure of energy (which would imply that the amp is a measure of power, which it is not): One poster here said that a 40 amp alternator is "nothing." But the alternator in a Honda 2200 generator is rated at 18.3 amps at 120 volts. Many people would consider 18.3 amps "something". There are many small boats for which a 2200 watt generator can supply all electrical needs. If 18.3 amps is "something, then 40 amps can't be "nothing", can it?

[StuM]

Originally Posted by Ken Fry

You correctly point out that the amp is not a quantity of energy. However, you seem to suggest that Ah might be a quantity of energy, which it is not.

An over simplification in this case. I didn't want to go "the whole hog" yet again.


https://www.cruisersforum.com/forums...ml#post1933764

More variety: Lithium cells are often purchased in 100 Ah increments, but at 3.3 volts

3.3 or 3.2? Depends on who is selling them and what they are
Most LiFePO4 cells used in boats seem to be rated 3.2 these days

[Ken Fry]

[QUOTE=StuM;3142668]An over simplification in this case. I didn't want to go "the whole hog" yet again.


https://www.cruisersforum.com/forums...ml#post1933764

I enjoyed your "whole hog" version!

At least in the electrical world, the terms are generally understood worldwide.

In the mechanical world, things get more confusing. The slug, the unit for mass in the English system, is rarely heard, but is very useful for aerodynamic calculations. And given that multiplication is commutative, one could think that a foot-pound should be the same thing as pound-foot... but the first measures work and the second measures torque.

Humans!

[jimdelane]

A lot of good points have been made.
I assume that you will not be plugging into a dock every night. You use 150Ah per day that is 1800 watts @ 12V nominal. watts = volts x amps
Like a64pilot says - battery bank size does not change charge time. 1800 watts is the same whether it is out of a 300Ah bank or a 1000Ah bank. What battery banks size does affect is how long your batteries will last. Simply, if you have 100 cycle life, you can discharge your batteries 200 times before they are worn out. In real life, if you only discharge lead acids 20% they will last a lot longer than if you discharge them 50%. At 80% discharge, you will not see 100 cycles. Lithiums can handle a 80% discharge without damage to the battery. Battery chemistry does change charge time because lithium charge significantly faster than lead acid. Lithiums have 99% charge efficiency at 14.5v (more watts) whereas lead acid have 85% efficiency with a voltage and amp drop during absorption stage less watts).

Your solar panels will produce 350 watts per hour and if you get 8 hours of perfect sun = 2800 watts. However, I have never seen perfect conditions under sail. You do not have the best angle to the sun, sometimes the panels get shaded by masts or sail, sometimes there is not much sun.
Depending on the sun every day to charge your batteries is like depending on catching fish to eat. In either case, there is a chance of going hungry.
So figure you probably need at least 2 days worth of energy = 300 usable AH @ 12v or 3600 watts.
The size and weight of your battery bank depends on whether you go lithium or lead acid.
Lithium are 12.8v nominal and when you reach 50% you will still have 12.8v. Lithium can be safely discharged to 100% but 80% is where you start to see the voltage drop.
Lithiums have a 99% charge efficiency so every solar charge amp that goes into the battery. Lithiums are light weight. Lithiums are maintenance and corrosion free.
Lithiums will last 2000-6000 cycles.
You need a minimum of 200 Ah to meet your 150Ah needs.
200Ah 2560 watt hour = $1450 - $2000 60lbs
300Ah 3840 watt hour = $2200 - $3000 = 70lbs
400Ah 5120 watt hour = 2800 = 100 lbs
Sources:
AMPS https://lithiummarinebattery.com/
SmartBattery https://www.lithiumion-batteries.com/
LBP https://www.lithiumbatterypower.com

Lead acid are a nominal 12V and when you reach 50% discharge, they will have 12.2V. Lead acid batteries should never be discharged more than 50% or it will severely affect cycle life. The lower the voltage the more amps you need to get the 1800 watts of energy. With lead acid you have choices of flooded, AGM or Gel. Flooded and AGM are the most common lead acid batteries that are in boats. Do not buy the cheap batteries - go with Rolls, Trojan, Lifeline or some other quality battery. The difference is in the construction and materials and it is worth every dollar.
Lead acid batteries need to be maintained if you want them to last. They need to be fully charged regularly, perferably daily to prevent sulfation and electrolyte stratification. Keep the terminals clean and remove any corrosion regularly. Flooded batteries need to have water added on a regular basis. Lead acid batteries are heavy and every pound lowers your waterline, slows your boat and takes more fuel to push it. Lead acid charges at a max 85% efficiency and that goes down as the batteries get old, sulfate and lose capacity. Also AGM have about 20% less capacity than flooded.

Lead acid batteries will last 400-1000 cycles.
You need a minimum of 300Ah to meet your 150Ah needs
(4) Trojan T-105 Flooded 6v = 225 usable Ah (2700Wh) = 4 x $440 = $1095 = 248lbs
or (6) Trojan T-105 Flooded 6v = 338 usable Ah (4050Wh) = 372lbs
https://www.golfcartgarage.com/6-vol...05-4-pack-24v/
(4) Trojan T-105 AGM 6v = 217 usable Ah (2604Wh) = $1550 = 248lbs
or (6) Trojan T-105 AGM 6v = 325 usable Ah (3900Wh) = $2325 = 372lbs
https://www.ecodirect.com/Trojan-Bat...hoCItoQAvD_BwE

You can also consider using a
(2) 4D 12V = 210 usable Ah (2520WH) = $1230 = 248lbs
(3) 4D 12V = 315 usable Ah (3780WH) = $1845 = $372lbs

You have lots of choices - good luck

[StuM]

Originally Posted by Ken Fry

And given that multiplication is commutative, one could think that a foot-pound should be the same thing as pound-foot... but the first measures work and the second measures torque.

Humans!

Just another argument in favour of SI Units instead of confusing historical units which have different meanings depending on where they were used ( imperial v US gallons, quarts, pints and ounces being notable examples)

[StuM]

Originally Posted by jimdelane

You use 150Ah per day that is 1800 watts @ 12V nominal. watts = volts x amps
Like a64pilot says - battery bank size does not change charge time. 1800 watts is the same whether it is out of a 300Ah bank or a 1000Ah bank. ...
Lithiums have 99% charge efficiency at 14.5v (more watts) whereas lead acid have 85% efficiency with a voltage and amp drop during absorption stage less watts).

Your solar panels will produce 350 watts per hour and if you get 8 hours of perfect sun = 2800 watts.

Once again, despite the number of times it's been pointed out.



Every one of your uses of Watts is incorrect.

Please learn the difference between Watts and Watt hours before opining on power and energy matters.