Battery Bank Sizes on Sail Boats

[Rustic Charm]

HI,

Please excuse me for starting a new thread when there is such a lot on Batteries all ready. But I'm struggling with the time it's needed to struggle through so many.

Would people mind posting what size battery banks you have on sail boats. How many batteries in your house bank, what size are they and what's the total amp hours.

Also, is your set up heavy electronics or light. If you know what your daily amp usage is that would be great too.

As I'm on my first boat, and I'm about to renew all my batteries I just want to get an idea of what others use and how successful your size bank is.

[Ex-Calif]

Weekend warrior

Capacity - 3 X 70ah AGM = 210ah. ~100 useable

Usage - ~60 amps in a 7-9 hour day sail

Instruments, autopilot, vhf & transponder

[Rustic Charm]

Thanks Ex - C, you seem to have a small boat do you or just very good in conserving energy?

I found this on the Westmarine site as a very rough guide. Does it look about right?

30' boat200Ah house bank35' boat300Ah house bank40' boat400Ah house bank45' boat500Ah house bank50' boat600Ah house bank

[Thin Line]

37 CSY

8 6v golf cart batteries
920AH @ 12v
460AH usable @ 12v

Absolutely overkill for my usage, but I'd always rather have more and not need it. My batteries are hardly ever, if at all, below 12.7/12.8.

[Rustic Charm]

Originally Posted by Thin Line

37 CSY

8 6v golf cart batteries
920AH @ 12v
460AH usable @ 12v

Absolutely overkill for my usage, but I'd always rather have more and not need it. My batteries are hardly ever, if at all, below 12.7/12.8.

Do you have two banks or one bank?
A bank of 920 or 460?

[Ex-Calif]

Small boat yes. The energy hog is the autopilot - it consumes about half that budget.

And that guide as West Marine notes is an "extremely rough guide."

BTW - You will get a lot of responses from people saying what works for them - It is largely irrelevant to you unless you operate your boat like they do.

Maybe you can tell us what you want you "whole energy system" to do

For example - I am redesigning my system for 3-5 days of off the grid independence with about a 70-100 amp/day appetite for power.

If I told you what I am doing it may have no relevance to what you want your system to do.

[Rustic Charm]

Originally Posted by Ex-Calif

Small boat yes. The energy hog is the autopilot - it consumes about half that budget.

And that guide as West Marine notes is an "extremely rough guide."

BTW - You will get a lot of responses from people saying what works for them - It is largely irrelevant to you unless you operate your boat like they do.

Maybe you can tell us what you want you "whole energy system" to do

For example - I am redesigning my system for 3-5 days of off the grid independence with about a 70-100 amp/day appetite for power.

If I told you what I am doing it may have no relevance to what you want your system to do.

Well, basically I just want to make sure I have enough amps to not damage my new batteries (when I buy them shortly) by draining them too much during the night. I'm not sure how this will come out but I have the following devices, which I'm doing up a list of what power they use. But that will take a little while. I've already changed all my internal and Nav lights to LED.

I'm not sure what my alternator is, I'll check on that. I also have an 80watt solar panel but intend on getting a second 80w to replace a rusted out one I had.

Windlass
Autopilot
Autopilot ST60
Bilge pump
Bilge pump panel
Wind Ins
Depth
Speed
Chartplotter A
Chartplotter B
VHF radio TXT
VHF Standby
Gas Alarm
Head
Water pump
Shower pump
Wash down
Radar


Lights
Anchor light
Nav lights
Tri colour
Steaming
Stern
Cockpit
Cabin x 1
Cabin x 6
Nav table
Engine light
Fwd flood

Other
Heater
Fridge
Lap top
Charging mob
Fans x 1
Fans x 4
Television

[mitiempo]

The larger the battery bank the less they will be drawn down for a given usage. Because of this they will last longer. The larger bank will also give you more amp hours than their rating suggests. For example 100 AH battery is rated at a 20 hour rate - 5 amp draw for 20 hours. If you use 3 amps it will provide more than the 100 AH rating. The opposite is also true - if you use more than 5 amps you will get less than 100 AH. The larger the bank you can reasonably fit the better you are as far as life of the batteries is concerned. You will also have a greater reserve with a larger bank if you are unable to charge or are anchored and don't want to - for example you do not want to run the engine and the weather is not good for optimum solar charging.

I will have a bank of 4 golf cart 6 volt batteries - 484 AH. My usage is not high so I doubt I will get to 50% very often.

[Rustic Charm]

Originally Posted by mitiempo

The larger the battery bank the less they will be drawn down for a given usage. Because of this they will last longer. The larger bank will also give you more amp hours than their rating suggests. For example 100 AH battery is rated at a 20 hour rate - 5 amp draw for 20 hours. If you use 3 amps it will provide more than the 100 AH rating. The opposite is also true - if you use more than 5 amps you will get less than 100 AH. The larger the bank you can reasonably fit the better you are as far as life of the batteries is concerned. You will also have a greater reserve with a larger bank if you are unable to charge or are anchored and don't want to - for example you do not want to run the engine and the weather is not good for optimum solar charging.

I will have a bank of 4 golf cart 6 volt batteries - 484 AH. My usage is not high so I doubt I will get to 50% very often.

Thank you.

And I've just checked I've got an 90amp alternator.

[HansSolo]

41' boat with moderate to heavy electronics
4 6v batteries
800 Ah @ 12v

[kas_1611]

If it helps with your decisions I have a 135AHr 12v house battery connected to the usual bunch of goodies. The real hog is the chartplotter but by reducing the backlight on this to about 55% dramatically reduces it's power draw without compromising the screen clarity.

With 2x35w Flexible solar panels on the bimini we often see the battery monitor indicating a charge even with the chartplotter on while sailing. We are in the Adriatic so do get bright near overhead sun around midday most days.

The only other real draw is the fridge but with internal insulation we have managed to get this down to a 10minute run roughly every hour so in fact it does not draw that much overall power (about 1amp/hr) so on anchor with the chartplotter off we still get a net charge over an hour.

All lighting is LED, internal and navigational. Changing the anchor light made a huge difference, not only is it brighter but it draws about 0.1amp!

So far this summer I have not seen the voltage drop below 12.4v overnight. As we are not on anchor/mooring bouy for more than 2 days the battery does get a regular top up from the alternator as we motor in/out of a bay/harbour and we have hooked up to mains power a couple of times in town harbours where available.

If we were planning to be away for longer I would consider doubling up my house battery to 2x135AHr, maybe increasing the size of the solar panels or adding a wind generator to the mix as well. However for what we are doing at present the current setup is more than adequate for our needs.

Keiron

[Neptune's Gear]

We have 2x 210ah gel hybrids. Lots of electronics aboard, use up to about 100ah per day when living aboard, including watching a movie on the PC. All lights are LED. We have a windgen and 70w solar, and a 80amp alt. Been with this setup 6 years, works well.

Sent from my Nexus 7 using Cruisers Sailing Forum mobile app

[noelex 77]

47 foot boat
400AHrs. We use as much as we can generate from solar. Lots in summer 120AHrs, not much in winter 50-80 AHRs

Battery bank size needs quite a few parameters to calculate optimally.
The most important factor is how you are going to recharge the batteries.

Batteries do not produce power they only only store it. Every AHr you use must be replaced (plus a bit more)

The method of charging and how you intend to use the boat makes a big difference to battery size. A boat re-charging from the engine battery, or generator for example will need a larger battery bank than a boat relying on solar. A boat with your requirements and equipment could get away with quite a small battery bank if you you only want to spend a couple of days away from the marina, but extend this to 5 Days and the results will be different.

First consider how you will replace the power you use. Your optimal battery bank size will flow on from this.

Many people fit very large battery banks because they claim, quite correctly, that increases battery life, but it should be remembered that the minimum battery bank cost per year is achieved with a bank where the average discharge is somewhere around 50%.

Fitting a very large bank that is rarely taken below a 85% SOC gives people a warm fuzzy feeling , but battery costs per year rise sharply over a smaller bank and while exchanging batteries less often is a nice compensation the fact that more need changing (and they are bloody heavy) offsets this somewhat.

You also need to consider the relative costs of a larger battery bank verses spending the additional money on energy saving devices, or on increasing your production.

It is difficult to predict power usage from just a list of equipment, but it you want to stay away from shore power for a reasonable length of time you are likely to be running the engine 1-2 hrs a day (in addition to the solar contribution) to charge the batteries. A large battery bank will only make a small difference to run time. I would be looking at ways to increase production and reduce consumption as a first priority.

[Snowpetrel]

2x N70Z's wet cells at about 90 amp hours each, 33 foot 2 x 40 watt panels PWM controller. No fridge, no chartplotter, no autopilot, and so no problems keeping them above 50%. About 5 years life full time living aboard on a mooring and at anchor. I Never had to run the engine to top them up, I just reduced my usage if I got a bunch of consecutive cloudy days. Laptop use had to be minimised, but now with a tablet instead I would have been fine.

[jcapo]

42' 24x7 live aboard on the hook. 720AH 6V Deka gels with 80AH to 150AH daily usage mostly the large reefer and freezer. Gotta have ice for the grog! 390W solar plus a Four Winds wind generator.

These batteries were 3 years old in May and they are down to less than 400AH capacity. My solar and wind is not enough to keep up with usage on cloudy calm days resulting in incomplete "mini" charge cycles. Lead acid batteries, flooded, gel, agm, want to see full or close to full charges for best life.

I will replace these gels with flooded golf cart batteries that are MUCH less expensive than gels these days. Shortened life due to bad charging practice won't break the cruising budget.