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Old 20-12-2012, 06:08   #16
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Re: So, how battery and electricity do I need?

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12V. Have to adjust by factor of 2 from 24 V.
Just to clarify: To adapt Jimbo485's rule of thumb for 24V, the relationship between batteries and daily consumption stays the same but the solar capacity in Watts should be 8x rather than 4x the daily consumption in AH.
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Old 20-12-2012, 07:49   #17
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Wow, certainly lots to learn here. Lots of good info. Thanks for the basic info as it is what I was looking for rather than overcomplicated electrical theories.

I'm looking at getting a boat (my first) for weekend sailing and the occasional 7-14 days offshore cruise with wife and kids. I hate running the engine if I can help it and have no generator. Kids will require tv time and some other electronic conveniences more than me and wife, but it should not be tremendous demands either. I was thinking a 400 amp hr bank, but that was simply a guess pulled from thin air. I asked about alternator size because I wanted to maximize charging capacity in the least time of engine running. Same with solar.
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Old 20-12-2012, 09:25   #18
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Tell the kids television will not work on the boat. Cheaper than providing power to feed it.

My mother in law came by our boat and asked where the tv was. We told her it was home as it did not belong on a boat. She then asked us what we do while we sail. Funny that.
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Old 20-12-2012, 09:44   #19
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Re: So, how battery and electricity do I need?

Years ago (before flat screen TVs), a soft-spoken and mild-mannered friend of mine complained that his 14-year old son did nothing but watch television and was failing in school. He said he had threatened to take away the TV, but thought his wife would never let him do it. He asked me what he should do.

I told him what to do and he did it. He bought a 3/4 axe, walked slowly into the room wearing googles and carrying the axe while his wife and son were watching the TV, calmly told them to cover their eyes, and then he axed the TV. Neither wife nor son said a word. Neither asked about buying another TV.

He reported that his sex life immediately got better. The son graduated second among his high school class. He bought a TV for the wife a few days after the son left for university. Sex life went back to crap.

Your windage may vary.
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Old 20-12-2012, 10:39   #20
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Re: So, how battery and electricity do I need?

Our family wife and two kids 12 ad 14 have a tablet, laptop which plays dvd's for the kids on rainy times, 3 ipods, sirrus am/fm/cd stereo which is on and off throughout the day the chart plotter garmin 441 and vhf which is on all the time, hand held vhf x2 which are battery charged 12v plug ins. I have about 600 amp hours in battery's and 2 85 watt solar panels, my outboard has the charger on it but is very small 8 amp if memory serves, anyway long story short, with this i can stay basically plug in free and run everything for 2 or 3 cloudy days, if sunny every day the i can keep the plug in cooler running all day and off at night as it cools slightly to conserve or it can drain it right down.
another thought as well could be wind gen, if your doing alot of sailing per say, this can also charge up more as while under way you could be blocking your panels and reducing your recharge.
either way get out and enjoy
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Old 20-12-2012, 10:45   #21
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Re: So, how battery and electricity do I need?

My suggestion, to keep it dead simple, with no newbie-confusing technobabble that makes perfect sense to technically competent sailors but possibly not to the OP, is two banks of group 29s. Two to a bank, for 4 group 29 batts total. These are IMHO the largest size that is easy to lug around by onseself, and easy to find a place to install. A two-bank battery switch for switching between banks. This is assuming you use an electric starter for the engine. Without the need for dependable start amps, you could go with a pair of 29's. That is a start point. Try to live within the limitations of this bank, and if you can't, expand it. AFTER looking for bad connections, small wire that should be replaced with large, bad switches and breakers, and other things that rob your electrical system of power.

I don't use a fridge away from the dock, and my Atomic starts pretty easy, and I get by okay with a pair of group 29s. Just sayin.

If you can afford more and have space for more, get more. More amp hours make life aboard more pleasant.

If you are anchored or docked a lot without shore power, get a wind charger. Great supplement to solar, even if it is a little expensive for the juice you get from it.
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Old 20-12-2012, 14:07   #22
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Re: So, how battery and electricity do I need?

By all standards and comparison, my kids are actually far above and beyond the average or most when it comes to playing video games and electronic stuff. iPods, laptop, and phones are all 12v, so no great electrical usage there. Not entirely sure, but I think even the TV/DVD player is 12v as well. I am also not talking about 12 hr/day of TV, but rather 1-2 hr at night while playing a movie before bedtime. I'm also realistic in that there is only so much they will do at ages 8 and 10 in a boat with me or me+wife. Some conveniences have to be accommodated or pretty soon I am going to be sailing solo. Everything is a compromise of sorts.

To some degree, the cost of adding a few batteries is not going to break the bank. Solar may be way down the road though.
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Old 20-12-2012, 14:20   #23
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Re: So, how battery and electricity do I need?

you can get a 85 watt kit from Costco or Sams for around 300 it will take the strain off at anchor. It was my first solar set for a couple years and I just upgraded Christmas gift to me... Any solar will put a charge back so a $90 panel will at least recharge some of the usage during the day, and on those days where your being a tourist the charging is even better as you shut everything off when your gone. so anything is better then nothing
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Old 20-12-2012, 15:35   #24
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I personally found the book "Energy Unlimited" written by Reinout Vader very informative. A big plus of this book is that it's free.
Order the book
(Reinout Vader is the managing director of Victron, a brand that will be familiar to many here)
A very good primer is available on teh Victron site. I have a link to it but am working from iPad today. It really is useful in planning a mid-sze boat plan.

I approach from "both" directions.

1/ How much would I "like" or "need"
2/ How much can I generate (reasonably)

'With this approach I find the median or average cruiser is "comfortable" with 100 amps a day - not including air conditioning but including fridge and moderate use of a watermaker.

My personal bank size rule of thumb is 4 times the daily consumption with a target never to consume more than 50% of available capacity. i.e. 400 amp hour capacity. Add 100 a/h for each additional day you think you need to be independent from charging - engine or solar or wind. If you want 3 days reserve you would look at 600 a/h - 400 + 200 (2 days)

Charging - You need to replace what you consume. Plan to generate 100 amps a day with solar, wind and engine. For "top up" reserve if you went a few days without sun, the engine is flexible charging.

Cut fine white hairs, make a science project out of it. Study Pleukerts and charge rates and all that if that is your thing and I don't begrduge that it is a "thing" to a lot of folks - batteries are expensive and taking care of them is a good idea.

I am a fan of the current consumption worksheet but I also agree that until you get on the boat and live it you won't really know what your personal habits are going to be.
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Old 20-12-2012, 15:46   #25
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Re: So, how battery and electricity do I need?

I have A 32'' 12 VOLT TV AND 12 VOLY SATLITE SYSTEM It really does not use that much power
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Old 21-12-2012, 02:21   #26
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Re: So, how battery and electricity do I need?

One additional idea is the addition of a simple battery monitor when you install the new battery combination, there are several device which give you accurate usage data, time to discharge, time to fully charge and state of charge. This takes the guess work out and is a low cost proven approach.
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Old 21-12-2012, 07:00   #27
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Re: battery monitor

dgasmd- I highly second the battery monitor - I was surprised how useful it was to know how much power we were using and the actual state of the batteries. And about battery banks - it seems the consensus is to have only one house bank,but larger as you are only going to charge to about 80% using the Atomic 4 alternator for only an hour or 2 each day. Remember you are also going to have to charge the starting battery for at least a few minutes depending on how quickly your Atomic starts. I love my gel cells but normal lead acid bats are less costly. Also note that gel and AGM require different charging rates than normal lead acid. All the solar controllers have a setting for gel and for AGM as well as lead acid.
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Old 23-12-2012, 06:32   #28
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Re: So, how battery and electricity do I need?

I sort of agree with the throw the spreadsheet away argument.

A modern live aboard yacht has so many extra bits I doubt you could work it out,

My gut feel is this.

I need about a 120 amp to 140 amp hr per day.

About 60% of my power goes to running my danfoss fridge. 6.5 amps in use 40% duty cycle. Measured with stop watch and clip on amp meter.

Next are the computers . Two laptops. The asus eee is about 1.5 ah 20 hrs a day.
Asus eee with video processor abot 3 ah 10 hours a day.

Fans we have 7 Camfro 757 fans. Usually two on. I estimate half a/h each.

Lights mix of fluoros and Led 3w to 18w in kitchen.

Music car stereo about 1.5 ah in use. .3 ah on stand-bye or 8ah for full day if not used. These phantom loads are crazy, So I turn it off with its own switch. It means you loose presets etc .

Plus we run a heap of a heap of other stuff. ie 1500 watt inverter. for printer, microwave, vacuum.

My belief is "do not be a boat that's stingy on power. " I hate being on boats were people follow you round and switch off lights, fans, devices etc".

Sure don't waste energy but to go without some thing you want on a boat is really bad for morale.

I power all this with 470 watts of solar which on a really sunny day will put in 26 to 27 ah into flat batteries. By afternoon on sunny day 18 to 23 ah.

To help with cloudy rainy days I added a aerogen 4 wind generator. This has been a fantastic addition. Absolutely useless in the tropics a lot of the time, but when it gets cloudy and stormy and solar input drops to a third. The wind gen starts kicking in between one and 3 ah. Multiplied by 24 hrs and it nearly makes up for the loss of solar.

Before I installed the windgen I would need to start my engine with 50 amp alternator and smart regulator every say 7 to 10 days.

Now with windgen its really rare only when we need vacuum cleaner thru inverter etc.

I would say if you can afford it a 70% solar 30% wind combination would be ideal in the tropics. Now that I have aerogen 4 I have thought about one less solar panel hanging off the back of the boat.

In the dry season when we have excess solar power we run the pur 35 watermaker almost every day for 4 to 8hrs as well to make between 20 to 40 litres of water. Its magical looking at the solar panels as the watermaker tricles water into a water drum. Again being on a boat stingy with water is also horrible for morale.

I have made detailed measurements and analysis of my devices power requirements and my usage and after 10 years afloat doubt i could accurately spreadsheet it.

For batteries I have 460 ah of truck batteries. I usually get 3 years out of them. I prefer n120 as they are easier to lift. I cannot imagine paying twice the price for trojans and getting 6 years out of them. A cruising boat is a horrible environment for batteries.

A short circuit, some thing dropped on them, forgetting to check water; running dry, faulty regulator over charging them, failing all by them selves early. Six years is too long a payback for me.

In my system I only use the batteries at night as wind solar powers everything during the day. So in theory I only need to power about 12 hours on batteries.

After about 2 days of cloud no wind I have to start the engine. Here in asia its only one month around October / november that is bad the rest is just a few days of cloud.

I am now delighted with my power system and now consider it a finished project and don't think about improving it any more.

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Old 23-12-2012, 07:00   #29
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Re: So, how battery and electricity do I need?

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For batteries I have 460 ah of truck batteries. I usually get 3 years out of them. I prefer n120 as they are easier to lift. I cannot imagine paying twice the price for trojans and getting 6 years out of them. A cruising boat is a horrible environment for batteries.

A short circuit, some thing dropped on them, forgetting to check water; running dry, faulty regulator over charging them, failing all by them selves early. Six years is too long a payback for me.

In my system I only use the batteries at night as wind solar powers everything during the day. So in theory I only need to power about 12 hours on batteries.

After about 2 days of cloud no wind I have to start the engine. Here in asia its only one month around October / november that is bad the rest is just a few days of cloud.

I am now delighted with my power system and now consider it a finished project and don't think about improving it any more.
You would get a huge improvement by switching to lithium phosphate batteries.
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