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Old 12-19-2012
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How do I know how much I need?

I am trying to learn a little about electrical consumption, demands, and needs. I know very little about it, so that is why I am posting here.

1. First thing is, how do I figure out how many amp hrs would I consume, ballpark figure, so I can figure out how much of a battery bank do I need?

2. Any links to where I can read basic info on batteries, which and how many, chargers, how to charge, how much to charge, how often to charge, to what level discharge, how to figure what size alternator to use based on needs and size of battery bank, etc?

3. Adding solar. How do I figure what size do I need, what type of charger and controller, etc.

Thanks in advance.
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Old 12-19-2012
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Re: How do I know how much I need?

dg,

There's plenty on the net about this -- but it'll take a good bit of time to wade through it all.

As you can guess, your numbers will depend on what you've got on the boat.

The best way to work it all out is to methodically list every item that draws power, then figure out how much it will need for a 24 hr period. Consult your manuals (or find e copies of them on the net) for the data. If you can't find the manuals, there are approximations in most energy budget worksheets that'll get you close.

Tally up all of the amp hours needed for a 24 hr period, then at least double the number to get your recommended minimum battery bank capacity.

Once you figure out the size bank you need, then come back and ask about alternators

BTW: Get a copy of Nigel Calder's Boatowner's Mechanical and Electrical Manual; it will serve you well and will likely become one of your most used references. Well worth the investment.
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Last edited by PorFin; 12-19-2012 at 10:56 PM.
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Old 12-20-2012
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Re: How do I know how much I need?

This is my seat-of-the-pants solution: I don't want to buy any bigger more expensive batteries, I really don't want to buy and install a bigger alternator, and I can't afford huge solar panels (wouldn't have enough room anyway). Therefore, I keep my systems to a minimum, and plan on engine charging with the help of a solar panel, as needed.

Just depends on if you want the horse to pull the cart, or the cart to pull the horse... I guess my cart is leading the horse.
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Old 12-20-2012
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Re: How do I know how much I need?

Quote:
Originally Posted by Barquito View Post
This is my seat-of-the-pants solution: I don't want to buy any bigger more expensive batteries, I really don't want to buy and install a bigger alternator, and I can't afford huge solar panels (wouldn't have enough room anyway). Therefore, I keep my systems to a minimum, and plan on engine charging with the help of a solar panel, as needed.

Just depends on if you want the horse to pull the cart, or the cart to pull the horse... I guess my cart is leading the horse.
Hmmm

More like same cart ...same horse....think Ill do without the air conditioning and the radio
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Old 12-21-2012
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Re: How do I know how much I need?

Quote:
Originally Posted by PorFin View Post
BTW: Get a copy of Nigel Calder's Boatowner's Mechanical and Electrical Manual; it will serve you well and will likely become one of your most used references. Well worth the investment.
If you seriously want to know - this is the resource you really do need!

PorFin is correct!

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Old 12-22-2012
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Re: How do I know how much I need?

For question # 3 - solar panels - Use the 'rule of thumb' of 40 - 45 amp hours generated per each 100w of solar panel, provided you have a good PMW - or better yet a MPPT controller.
What that really means is figure on 35 if you are north of NY, 40 for the mid-atlantic and 45 on a sunny day down south.

From that you can pretty well see that if you are sailing along on autopilot and instruments (3ah for the a/p, 1 for the radio (just listening) and another 2 for the displays (wind, depth, speed) etc..) you can easily consume 60ah (6 per hour) in a ten hour day.
Meanwhile, you won't make that much on a 100w panel.That's worse case because the a/p only draws 3 when it's cranking the wheel/rudder around. Trim those sails .

If you have a refridge that draws 12v look up the spec's (or use 4.5amps as a base line) then figure if you have a stock insulation set up you are cycling (on, full draw) at least 40% of the time. That's highly dependent on your specific set up.

Figure 1amp for lights, 1 for fans, 1-2 for the stereo and if you have powered water pressure just toss a 2 or 3 in the count. Don't forget things like your propane sensors, cell phone plugged into a 12v, bilge pumps - and mostly that huge drain from the anchor light (can be up to 2amp per hour unless you have a LED one).

Remember that unless you have upgraded your alternator (provided you have one) it's not really putting out the rated amps unless you are running at 2/3 rpm - most stock alternators are 55 amp, at idle or slightly above you are lucky if you are actually getting 15-25 amps out of it. That's a lot of diesel to get your batteries back to 80/85%. 20 minutes of motoring to get back to the slip/mooring does NOT charge a battery bank that has been used all day.

The best way to take out the guess work is to install a monitor (properly) - and actually see what you use. Search for posts by Maine Sail here on sailnet, he's got the full install and use thread.

FWIW, taking your average need and doubling it doesn't always work. You should instead truly try and make your bank 3 times your estimated need.
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Old 12-22-2012
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Re: How do I know how much I need?

When in doubt about finding answers to long, basic, complicated questions like yours, it would do you well to check out West Marine's Advisors, either in their printed catalog or their online versions. Scroll down to electrical: The West Advisor: West Advisor Articles

You could also Google "energy budget" - which is also included in the WM Advisors, or you can read this: Energy Budget

Or buy a book or two or go to your library if it has a reasonably good collection - smaller libraries usually don't have a stock of good boating books, some larger ones do. But Google is your friend.

There simply aren't that many different loads on boats, and newer LED lights/lamps makes a tremendous impact on energy use/loads. Like a 10:1 ratio!!!

$$$-saving? Don't buy anything but simple wet cell batteries.
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Old 12-23-2012
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Re: How do I know how much I need?

I don't know any other way to do this except trial and error.

I've seen some people who claim to use math to figure it all out, but I've heard of very few people who had a complete working system that was designed with math that had stayed true to its initial design.

Most boat owners start with one system and then take it through a series of evolutionary steps to end up with what they really want and need. Sure, maybe you can do some math and get lucky, but I wouldn't bet too much money on that. Chances are the system you start with isn't going to be that close to the system you end up with, but you have to start somewhere!

Instead of using too much math to figure it out, I'd start talking to other boaters who have similar kinds of equipment on their boats and see what kind of system they have, then copy that, leaving as much room as possible to change it after you gain some experience with it.
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Old 12-25-2012
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Re: How do I know how much I need?

Quote:
Originally Posted by wind_magic View Post

1. I don't know any other way to do this except trial and error.

2. I've seen some people who claim to use math to figure it all out, but I've heard of very few people who had a complete working system that was designed with math that had stayed true to its initial design.

3. Most boat owners start with one system and then take it through a series of evolutionary steps to end up with what they really want and need. Sure, maybe you can do some math and get lucky, but I wouldn't bet too much money on that.

3a. Chances are the system you start with isn't going to be that close to the system you end up with, but you have to start somewhere!

4. Instead of using too much math to figure it out, I'd start talking to other boaters who have similar kinds of equipment on their boats and see what kind of system they have, then copy that, leaving as much room as possible to change it after you gain some experience with it.
wd and others,

1. Trial & error---Most people had to do it that way in “the old days” because they didn’t have a) any clue; b) relatively expensive ammeters; c) didn’t understand battery chemistry and acceptance: the fact that batteries take longer to recharge than to discharge. Most of us now know how to do it without trial and error: by doing an energy budget. What comes OUT of a battery bank consists of only two things: the load and the duration of the load. Those are the ONLY two “variables” which are easy to estimate – which is why it is called a BUDGET. I think you are seriously confusing an energy budget and a system design.

2. I think you’re confusing an electrical system DESIGN with the simple addition of more batteries in the house bank. The most simple system design for a majority of recreational boaters are two banks, a house and a reserve bank with a 1-2-B switch which most people already have, with the alternator output to the house bank (and not avoid having to use the switch just add a parallel relay to charge the reserve bank). “…true to its initial design…” seems incorrect to me, since if one “designs” a system, please advise what changes? The reason I ask is that a number of us have figured out a simple system and have been promoting it for over a decade or two. After initial installation, we and many others have done nothing else, other than flipping ONE switch and using our boats! I designed our system 14 years ago, “met” Maine Sail on the internet, discovered that we shared the same design concept and have been promoting it. My electrical system is UNCHANGED since 1999, works great, and the ONLY thing I changed were seven year old batteries.

3. Math has NOTHING whatsoever to do with a SYSTEM design. The only variable is the amount of house bank size you choose to install.

3a. See 3 above. Even if the boat is new, it is rare to find one initially set up as described above. Perhaps that is why you may think people have to change things. If they have “discovered” our references to the simple, easy to operate electrical system DESIGN, then the only variables are the size of the house bank and the size of the wiring in between the components. A larger boat will need bigger wires simply because the wire runs are longer – assuming the same system design, and same size alternator. If you start out with a good system DESIGN, there’s not much to ever have to change.

4. “Too much math???” --- Huh? Not really true, unless you have found someone who uses his boat the same way you do (for great extremes, compare an anchor out vs. marina-hopper). What the energy BUDGET does is help you to properly size your house bank. Then buy a good energy monitor and you can see how accurate your budget is. The system DESIGN is a completely different issue, and these “Basic Wiring Diagrams” are pretty good, and are the ones referenced in earlier posts.

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com
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Last edited by Stu Jackson; 12-25-2012 at 02:07 PM.
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Old 12-25-2012
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Re: How do I know how much I need?

Stu,

I appreciate your thoughtful and polite response to my post, thank you.

Without getting into a debate over what a substantial change is and isn't, I would say this -- the basic design is simple, and shared by most, solar panels, wind generator, shore side chargers (often used with the generator), alternator, etc, with chargers, into a bank, connected to loads. Throw in the fuses, cabling, etc, and I think we are all basically using the same design. But, that wasn't what I was talking about ...

What I was talking about is what you mentioned as a minor change, that being the addition of batteries, more panels, etc. In my opinion that isn't usually a minor change at all. If you want to add a panel you are often going to be changing the way you have your panels mounted to accommodate, it is the rare person who thought ahead and just happened to leave empty space next to their panels for an extra one or two panels, usually you end up redesigning the mount and doing it over. Same for batteries, it is the rare person that thought ahead and made extra space for more batteries, or batteries of a different design, that doesn't have to go back and create a new well for their batteries, redesign whatever system they are using for tie downs, and all the rest. At some point when you are adding capacity you are probably going to have to change your fusing, often have to upgrade your wiring to handle more amps, often change your chargers out because you reached capacity on them, sometimes upgrade your shore side charger to allow for more amps because your larger battery bank can accept a bigger charge, etc.

I don't think I know anyone who hasn't made changes like that, often substantial changes, and often resulting in a complete rebuild. Yeah, sure, it is still just panels, through a charger, to a bank, to an inverter ... but almost every system out there has that basic design.

Edit - I forgot to mention the math. I don't mean to make it sound like the math is totally useless, I just meant to convey that I don't think it matters that much in the sense that it rarely leads to the final design (battery capacities, number of panels, etc) that the boat owner ends up with. I know that is the case in many electrical systems, it seems like just about everyone has ideas about how they'd do it "next time", because few who have experience with their system seem to feel it has reached some pinnacle. Contrast that with a water maker, most people who install a water maker never have to touch it again except for maintenance, they don't sit around with pen and paper imagining how they'll change it on their next boat.
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Last edited by wind_magic; 12-25-2012 at 02:16 PM. Reason: Edit
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