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Old 15-10-2007, 23:02   #1
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??? about electrical consumption/battery power/solar/wind

I am new to cruising and and this forum. I have a question or two about how to setup my electrical system. I am planning already but have been told my expenditure of energy will be too much. I have a general understanding of this sort of thing but I probably have much to learn. . . so here goes. . .

I am purchasing a 34' yacht that I plan to live aboard and sail the Islands with my wife. I wanted to have a laptop based nav system, radar, a 32"LCD TV, DVD, a mini refridgerator/freezer combo (stats said 3.8 amp draw), a microwave, plus the normal lights, winches, etc. I was planning a 4 battery system with Trojan golf cart batteries. This would be somewhere near 900 amp hours. So does this mean with my batt. fully charged I can steadily draw 10 amps from them for 90 hours? That is almost 4 days. I plan to get a couple solar panels and a wind gen. I don't see that I will be pulling anywhere close to 10 amps around the clock. . . the fridge would be the only thing that would run constantly. . . at 3.8 amps that would mean I could go for almost ten days? Is this correct? Wouldn't the solar/wind replenish the other energy I use, say watching a movie for 90 minutes, the nav gear, etc.???? am I way off base? How long should I be able to go without charging up on the shore? Also, will the altornator on my small (27 hp) engine actually recharge the bank or will it just maintain the current under a load? Thanks for input, Dustin
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Old 16-10-2007, 00:17   #2
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Dustin - it would be hard to write an entire primer on DC electrical systems with multiple charging systems in this forum although I think I did one a while back, it was unweildy.

Generally you want to use no more than half the available battery storage capacity. Running the batteries dead is detrimental to them over the long haul.

In reality you want to design a charge system that meets or exceeds your daily needs.

Imagine the battery like a dam and the river is the charge supply. If you pull more out of the dam then ever gets replaced eventually the dam runs dry. The dam is there to smooth out the flow so you don't get floods and droughts and also to provide reserve capacity when you can't replensih for a short period.

So it all starts with your consumption and it pays to be conservative. You will learn how to conserve as you spend more time on the boat but you will always be up against the power equation.

900 amp hours is about 450 max usable. You will have inneficiencies in your systems due to resistance as things naturally corrode and deteriorate over time. 10% is a very optimistic estimate. Also any time you convert from DC to AC through an inverter you will have inneficiency and heat losses. I'd guess that you will have no more than 380-400 usable.

So that fridge would run for 100 hours or about 4 days if you used no other power. Incandescent bulbs are wicked power sinks. The bigger the LCD the bigger the draw. I reckon your system will run 3 days max without replenishment.

So you need to put in 125 amps per day. That can be a combination of solar, wind, engine alternator and or generator.

The next problem is where to get 4 X 12V batteries that will supply 225 AH each. Those are some big muthas...
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Old 16-10-2007, 00:19   #3
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Hi Dustin,

You dumped a lot of info here. But, not to be negitive, I think you may want to get more info on battery usage.

One does not want to drain the battery more then around 30%. 1) It would put a heavy load on you altenator to recharge. 2) Taking it down too far takes some of the longevity from a battery.

The microwave, reserve for when your tied up with shore power. And it sounds as if you'll need a 2000 watt inverter.

The TV/DVD- chances are you will not watch underway unles kids are aboard.

Winches- power?? Not on a 34' boat unless you plan on turning your motor into a genset.

Wind gen's need about 15 kt of wind to put out max power and if your going with the wind while sailing, the windgen isn't going to put out anything.

Water generators are a good thing but expensive and easily disrupted (catches weeds and stuff).

It takes a lot of $olar panel$ to produce the type of current your taking about.

Every boat is different but the best thing is to get out there (once you get the boat) with a good monitoring system and see what it can take and then set your useage/means around that. Reserving your power for the important things like navigation instruments, auto pilot and bilge pumps has a higher priority.

Sailboats under 45' will have a lot of power restrictions. Having big batteries isn't the answer unless one has a way of recharging them.

But that is one advantage of powerboats, they constantly have an ongoing power source, until that motor quits.

Hopes this helps ...................................._/)
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Old 16-10-2007, 06:41   #4
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Dustinp,

All good advice above.

Just a note: you said "4 Trojan golf-carts". I assume you mean the T-105s which are rated at 225AH each. Four of these 6V batteries in series-parallel would give you 500AH @ 12VDC, not 900AH. This would mean that you'd have a maximum usable capacity (@ 50% of total capacity) of 250AH.

Based on experience and computation, I'd guess this would give you about 2 days or less without charging. Solar panels or a wind generator would help, of course, based on their sizing and on the waters you intend to sail.

On a 34-footer, four T-105s is a pretty good size battery bank. You might be able to squeeze in a few more AH by using the taller Trojans (same footprint, but taller and more expensive). Or, maybe, adding two more. I have six T-105s (675AH) as my house bank on a 42' sloop and find that to be a comfortable size (with elec refrig, radar, laptop, LCD, instruments and lights, inverter, etc.).

Charging batteries is a key concern. They last much longer if you keep 'em as fully charged as you can. Chronic undercharging will reduce battery life and is expensive in the long run.

Some charge options to consider include a big engine alternator (100A or more) with a smart regulator (e.g., Balmar MC612 MaxCharge); solar panels; wind generator; separate generator; and a big charger or inverter/charger, with a charge capacity of at least 75A.

Bill
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Old 16-10-2007, 06:58   #5
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Dustinp,

In the real world you only rely on 35% of your battery capacity. This is because batteries last longer if drawn down only to 50% and when you recharge, the last 15% takes all day to put back in so you generally stop at 85% full. In a 400 amp bank, 200 amps would be your 50%. First time you use the batteries from fully charged you could use 200 amps. Then you charge them up to 85% your batteries are back up to 340 amps, now you can only draw them down 140amps. If you're anchored for long periods 140 amps would realistically be your maximum if you recharge daily. Of course other factors come into it as the batteries age and the wiring deteriorates but this is a general guide as nothing works to theory in the real world. I rely mostly on wind for charging and sometimes I can get the batteries right up but a few days without wind, when I use my Honda I only bring them up to 85%. I only have about 450 amps and find it best to run the Honda daily in those circumstances. An hour a day'll do it for me as my usage is under a 100 amps per day and i have a 100 amp charger.
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Old 16-10-2007, 09:36   #6
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A few points of points. You only want to discharge your batteries down to 50% max. When you start taking them below 50% charge you SIGNIFICANTLY reduce the life of the battery. Most manufacturers have a chart of the relationship between state of discharge and the number of charging cycles a battery will take before they approach failure. So you're probably looking at cutting in half the time between charges.

Charging is usually, at best 90% effective. So, you have to put back in more than you take out. Factor that into your recharge calculations.

While cruising, I found it VERY inconvient to have to rely on shore power to top up the batteries. There are a number of discussion on gensets, and portable generators, I'd recommend you browse them. They will provide valuable insight. There are also numerous discussions about wind, solar, high output alternators, and towed water generators. All make for outstanding reading.

I'd also recommend Nigel Calders books. There are a couple that have excellent discussions about sizing and configuring on-board power systems.

So in summary,

I think you are off base somewhat.

Probably 3 days before having to top off, but that is REALLY subject to many variables that are hard to predict. Also, it is impracticle to count on shore power while cruising.

27 hp for charging source is A LOT, relatively speaking. You'd have to get a high output alternator to fully utilize the engine capacity. 200 amps would be about as high as most folks think is practicle. But, interesting math here, If you use 120 amp/hours a day, you need to put it back, regardless of the size of your battery bank. 120 amp hours would require .x hours to put it back. Now we'd have to get into charge exceptance rates and all that to really figure out how long it would take...

The smaller alternators are about 50 amps or so, they would allow you to cover your current usage and put some charge back into the battery, while your engine is running.

Good luck!
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Old 16-10-2007, 10:10   #7
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Quick sizing rules:

Solar panels are rated with full sun, so use about 8h instead of 12 hours at about 80% of rated amps for (clouds etc).

Into the batteries you will lose 85%, out you will lose another 85%,

Derate wind even more cause when you stop you don't want to be in a windy place.

So say you want 450 ah. That is 450/.85/.85= 622ah for 8 hours 77 amps.

A Solar panel about 32 inch X 42 inch will give about 9 amps so you need about 8 or 9 of those.

Bear in mind I am used to BC and may be derating a bit too much cause it is pretty mountainous and rainy.

Your battery have to last 24h - 8 h= 16 hours but really at a low demand time so 450 ah/.5 (as above) = 900 ah for the day but really 900*16/24=600 ah.

Most sailors have battery banks that are too large and solar panels that are to small, hence they have to run the generator.

A battery bank sized as above will take you through a couple of rainy days in a row.
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Old 16-10-2007, 13:45   #8
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thanks for all the great advice. . . I am looking into 6 or 8 Trojan T105's so that would put me at 660 or 880 A.H, correct? I am also looking to install a propane/AC/DC refer unit. . . manuf. told me it can run 30 days on 35lbs. of gas, and it consumes 108 AH per 24 hour period. . . is that really that much. . . I figure with the ability to switch it from LP to 110 to 12 V I can make a tank of propane last a long time. . . I am planning to add a few solar panels (3 Keyocera 170 watt/7.xx amp) this should replace a little over 100 amp hours per day, right. . . 40 gallons of propane would cost around $30. . . Do many cruisers use this as a method of energy? what about a propane hotwater heater?
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Old 16-10-2007, 14:30   #9
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As a rule of thumb for unshaded fixed solar panels in the tropics divide wattage by 4 to get average daily amp hours delivered and by 3 to get average sunny day input over time. You can increase this by 10-15% with the use of an MPPT chrger...so the best you will get in sunny weather from 100watts of panel ON AVERAGE is about 40a/h's.
Size your bank of panels accordingly.

Even in a 12 hour tropical day, you cannot expect more than the equivilent of 6 hours of full output due to significantly reduced angle of the sun once you are out of the 10-2 peak period and scattered clouds etc.

3 Kyocera 170 watt panels should give you around 125a/h's a day over time and ariybd 170a/h's on nice days. Apparently you don't yet have a boat but I think you may find some difficulty confguring a solar array that is 4 feet long by 9 feet wide on a monohullin the 35 foot range as you say you are looking for. Any shading of the cells can play havoc with the actual output. You may want to decide on a boat before you decide on a solar system.
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Old 16-10-2007, 14:45   #10
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Forget the propane refer. A consumption of 108AH per 24-hour period is considerably MORE than a simple 12V unit like an Adler-Barbour (50-80AH/day) which is absolutely reliable (mine is 24 years old) and which is quite inexpensive to begin with (about $1,000).

Propane is a problem on a boat. IMHO, it should ONLY be used with a good quality galley stove, with the proper sensors and remote shutoffs. Using it for refers and "instant" hot water heaters is potentially very dangerous. And, there are better solutions, so why do it?

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Old 16-10-2007, 14:45   #11
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So, just two panels may be adequate. . . I can mount them in different places right? They shouldn't have to be all next to one another. . . very true, I need to first buy my boat, but I am moving to FL to get the boat in 8 weeks and want to have all the knowledge I can to get it up and running quickly. Thanks, Dustin


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Originally Posted by camaraderie View Post
As a rule of thumb for unshaded fixed solar panels in the tropics divide wattage by 4 to get average daily amp hours delivered and by 3 to get average sunny day input over time. You can increase this by 10-15% with the use of an MPPT chrger...so the best you will get in sunny weather from 100watts of panel ON AVERAGE is about 40a/h's.
Size your bank of panels accordingly.

Even in a 12 hour tropical day, you cannot expect more than the equivilent of 6 hours of full output due to significantly reduced angle of the sun once you are out of the 10-2 peak period and scattered clouds etc.

3 Kyocera 170 watt panels should give you around 125a/h's a day over time and ariybd 170a/h's on nice days. Apparently you don't yet have a boat but I think you may find some difficulty confguring a solar array that is 4 feet long by 9 feet wide on a monohullin the 35 foot range as you say you are looking for. Any shading of the cells can play havoc with the actual output. You may want to decide on a boat before you decide on a solar system.
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Old 16-10-2007, 16:08   #12
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battries

Dustin,
the 4x6v 225amp/hr is a good size. Have you thought about AGM battery as they will charge more efficiently & be maintainance free. They are avail in the same case size.

regards Bill Goodward
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Old 16-10-2007, 16:38   #13
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I have, I am just considering the cost. . . I think I can the Trojan 105's for $125 each. . .

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Dustin,
the 4x6v 225amp/hr is a good size. Have you thought about AGM battery as they will charge more efficiently & be maintainance free. They are avail in the same case size.

regards Bill Goodward
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Old 23-10-2007, 16:20   #14
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what about a propane hotwater heater?
got to be Southern... we are the only people who heat hot water..
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Old 23-10-2007, 20:54   #15
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got to be Southern... we are the only people who heat hot water..
LOL, I guess you are right. . . I like my showers HOT!!!
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