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Old 14-07-2014, 12:42   #16
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Re: Battery bank sizes on sail boats

We've gotten by with 2x220 amp 6v wired in series for 220 amps at 12 volts. We are light users, no refrigeration, no video or entertainment center, wind vane self steering. Have two 130 watt solar panels that more than keep the batteries charged when the sun shines. Did run the batteries down to 12v on a TransPac when the sun didn't shine for 10 plus days of the passage. Was running the plotter and AIS 24/7, using the computer lightly, HF radio for net check-ins and sending a couple of emails a day, and lighting is all LED. Once the sun came out, the batteries slowly charged back up. Never turned the engine on to charge the batteries on the 14 plus day passage though was thinking about before the sun came out.

Am adding refrigeration so will add another set of GC 6v batteries for a total of 440 amps at 12v.

Refrigeration and autopilot are the real energy hogs.
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Old 14-07-2014, 12:56   #17
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Re: Battery bank sizes on sail boats

I have 460AH in 2 banks that always connected. Boat has all the normal toys (refrigeration, chart plotter, autopilot, stereo). The normal daily load running in daylight is about 100AH, night + day sailing 130AH (used during the night as normally would have started the dark fully charged from solar), sitting on anchor/mooring 70AH.

Unlike a lot of posters my autopilot doesn't seem to use a lot of power. I balance my sails so only have 5 degrees or less rudder and run with the response set at 2 out of 10, so it only normally is using 2-3 amps.
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Old 14-07-2014, 12:59   #18
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Re: Battery bank sizes on sail boats

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Originally Posted by HansSolo View Post
41' boat with moderate to heavy electronics
4 6v batteries
800 Ah @ 12v
Can you elaborate - how do you get 800 Ah from 4 - 6V batteries?
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Old 14-07-2014, 13:01   #19
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Re: Battery bank sizes on sail boats

40' Weekend warrior and seasonal cruiser. Boat lives on a mooring and we're on the hook when we cruise. The energy hog is refrigeration which is on full time whether we're aboard or not. Underway, the AP is the big user. We have 4X6V golf cart batteries with 460Ah charged by 2X125 watt solar panels.

You show a windlass, hot water and a heater. The windlass and hot water are big energy users, but we never use the windlass without the engine running and never heat hot water with electricity. Our Espar diesel heater is a significant energy user, but we don't use it a lot.
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Old 14-07-2014, 13:07   #20
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Re: Battery bank sizes on sail boats

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Originally Posted by S/V Illusion View Post
Can you elaborate - how do you get 800 Ah from 4 - 6V batteries?
Maybe something like Surrette S530 6V 400 AH Wet Battery
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Old 14-07-2014, 15:39   #21
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Re: Battery bank sizes on sail boats

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Originally Posted by S/V Illusion View Post
Can you elaborate - how do you get 800 Ah from 4 - 6V batteries?
TeddyDiver nailed it.
Rolles S-530. Each battery is 6v 400ah wired in series and parallel that gives us 800 ah at 12v
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Old 14-07-2014, 15:54   #22
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Re: Battery bank sizes on sail boats

House bank 4xT1275 ( 12vTrojans) 4x150amps = 600 amps
one start battery
39 foot Ben393
Use about 75 amps a day mostly the fridge.
cruise 6 months a year
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Old 14-07-2014, 16:13   #23
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Re: Battery bank sizes on sail boats

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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.
This.

It's all a matter of what your daily usage pattern is, and what power generation you have. Putting gobs of batteries on your boat is potentially just a waste of money. Sizing it to your needs, so that you discharge to @50-60% on average, will give you the longest battery life but it will not give you the lowest annual cost for batteries averaged out over time.

Of course this is a generalization, and for some or even many sailors having a larger reserve, based on how they use their boat, is prudent. For example if you take longer passages offshore without alternative power generation, having a larger bank gives you a margin of safety if your engine can no longer generate power.

I have 4x125 amp hours, divided into two banks, no starting battery. This is what the boat came with and it has worked well for me. I alternate banks each day and have found given my usage that gives me the optimal discharge/recharge pattern for daily use. I did replace the batteries when I bought the boat, and expected that when the new ones kicked the bucket I would potentially redesign the system based on my usage patterns/needs and some other best practices. Still analyzing what that will be.

Oh, 40' boat, live aboard, primary use of electric is instruments, navigation, communications, nav and cabin lights.
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Old 14-07-2014, 17:10   #24
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Re: Battery bank sizes on sail boats

Thanks everyone. This has been really helpful. I think I was planning on going too big. I havn't got all the figures to work out my overnight use yet but I'll keep doing that. But I do think I can go for four 120 AH AGM batteries with the separate 120 wet cell for a reserve. My ARC takes care of the charging. That gives me 480 on house which seems based on what you guys have to be more than adequate.
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Old 14-07-2014, 17:18   #25
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Re: Battery bank sizes on sail boats

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Originally Posted by tedsherrin View Post
Thank you.

And I've just checked I've got an 90amp alternator.
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Thanks everyone. This has been really helpful. I think I was planning on going too big. I haven't got all the figures to work out my overnight use yet but I'll keep doing that. But I do think I can go for four 120 AH AGM batteries with the separate 120 wet cell for a reserve. My ARC takes care of the charging. That gives me 480 on house which seems based on what you guys have to be more than adequate.
I think that's a good call, Ted.

Also think about your solar - You are way south (unless that's gonna change), you have 80 and are planning to replace the second 80.

If you could get a pair of 125s or something where the 80s are I think you will end up less reliant on the engine for charging.

My personal paradigm is wind power is good for higher latitudes but less effective the closer you get to the equator.
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Old 14-07-2014, 17:20   #26
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Re: Battery bank sizes on sail boats

Why AGM?

They are expensive, don't have the life cycles of flooded or even gel, and they don't like partial charges at all.
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Old 14-07-2014, 17:37   #27
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Re: Battery bank sizes on sail boats

Just keep in mind, even if you have a huge battery bank... sooner or later you are going to have to refill all those amps!
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Old 14-07-2014, 18:17   #28
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Re: Battery bank sizes on sail boats

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I think that's a good call, Ted.

Also think about your solar - You are way south (unless that's gonna change), you have 80 and are planning to replace the second 80.

If you could get a pair of 125s or something where the 80s are I think you will end up less reliant on the engine for charging.

My personal paradigm is wind power is good for higher latitudes but less effective the closer you get to the equator.
Replacing with two 125's is an option. Looks like I can pick two up for $500.

I did consider wind, for when I'm underway, but for a 'Silent wind', I'd be looking at $2300 which is a bit steep. I have just one major trip a year of up to four weeks duration (all the annual leave I can get) and other than that I'm only out over long weekends. But the 125's are certainly an option. I'll have to check and see what the capacity of my BP regulator is.
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Old 14-07-2014, 18:21   #29
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Re: Battery bank sizes on sail boats

Catalina 36

House Bank:
4 x Lifeline GPL-4CT (series/parallel for a 12-volt system)
Total: 440 AH at 12V (usable down to 220AH, then bulk-charge on alternator up to 350AH)

Starter Battery (emergency only, house bank can/does start the engine):
Some random 12-V West Marine cranking battery. Don't know/care about the capacity; as long as it can start the engine twice, it fulfills the mission profile.

I use a Magnum smart-battery combiner (probably a 30-A MOSFET with a couple of comparators/voltage divider circuits, gate driver, and voltage doubler).

All LED interior lighting and a 5-amp air-cooled fridge. Magnum MS2812 charger.

VERY happy with Lifeline/Magnum.
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Old 14-07-2014, 18:21   #30
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Re: Battery bank sizes on sail boats

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Why AGM?

They are expensive, don't have the life cycles of flooded or even gel, and they don't like partial charges at all.
I want maintenance free batteries and whether I get AGM or Maintance free wet cell,the prices are very similar. Exide 120AH I've been quote $285 each. A wet cell is $245. So I don't think they are that expensive.

As for life cycles and partial charging, well seems there is a lot of debate about that and if I make sure I have the means to keep them charged, e.g upgrading my solar for when it's on mooring and with my 90amp alternator for when I'm cuising, then a 480 AH bank should keep up.
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