electrical system chart - pls review - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-15-2007
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electrical system chart - pls review

I've been putting together what I think is an accurate view of the electrical usage on my new (new to me at least) sailboat. You can find it at
http://www.mattdpeterson.com/boat/electrical_system.htm

I've created it assuming average usage over the course of a weekend outting.

The exercise is being done to figure out the proper sizing of my batteries. I currently have 2 deep cycle 90 amp hour batteries (I think) connected to the standard off - 1 - all - 2 switch. I'm thinking that I need to connect those 2 as a single bank for house batteries and get a new starting battery (25 hp westerbeke diesel)

I don't yet have the inverter, microwave, or television. I also forgot to throw a DVD player into the mix.. so I assume that is probably another 50 watts or so.

I've made some assumptions on the wattage for the lighting, pumps etc.

does what I've put together seem reasonable?
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Old 07-15-2007
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You are way off on the stereo. That's because they lie about their wattage!
In any event...2-3 is typical draw of a car stereo type marine radio.
That will save you some juice!!
I also think you are overestimating most other stuff by a bit as well so I'd cut 20% off the total. I didn't notice a fridge in there. Icebox only?
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Old 07-15-2007
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It's a good exercise, though. Overestimating is not a bad thing, unless it kicks you into a heavier battery form factor and charging situation and your boat is sensitive or lacks the adequate space or access.
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Old 07-15-2007
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" I'm thinking that I need to connect those 2 as a single bank for house batteries and get a new starting battery"
This is a good idea--and the way things are often being done these days, instead of the old a/b banks. Among other things you get better life from the deep cycle batteries, because you are discharging them to less depth, and you can use a smaller cheaper starting battery, which won't hurt when it needs replacement. And it will last a long time, since it is only doing "SLI" duty. (Starting/Lights/Ignition, aka a car battery.)

I didn't check the numbers (have to scroll too much & I've had my share of sun and heat today, thank you) but would agree that stereos are most often loosely rated--and when the volume gets cranked and everyone is happy...it's a good thing to have a separate starting battery on the boat.

Seems like you're burning 186AH/day, plus another 200+ for the stereo. I like music sometimes too--but that's a heck of a power bill. If you figure that as 400AH per day, you'd want an 800AH battery bank to support it, so it was discharged only to 50% then recharged every day. How big a boat is this on??

I'd like into high efficiency stereo speakers (they vary widely, 10x from some to others) and find out what kind of amplifier the stereo uses. I don't remember the pros/cons of the different types but again--some consume 2x-3x more power than others, all the time. "Car" stereos usually are built with no regard for power consumption since there's an engine assumed. Some real sleuthing with some audio folks could cut that power use in half--without losing anything more than some cost up front.

And, it sounds like you seriously want a wind generator or other continuous power charging system to help defray that energy budget.
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Old 07-15-2007
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I'm a bit curious as to how large a boat this is as well. That number, nearly 400 amp-hours, seems to be pretty high, especially considering it doesn't include any refrigeration. Also, you can probably cut the amount the lighting uses considerably, by using CCF and LED-based lighting.
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Old 07-15-2007
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While attending the St Pete boatshow, I attended a session by the guy that owns Hotwire's Home Page. He handed out a sheet that listed *his* estimates on the power consumption of about 50 different items. In general your amperage estimates seem a little higher than his. The biggest discrepancy is the mast head light (2.1 vs 1 amp). His rule of thumb is 150 Amp Hours per day for a "typical" cruiser.
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Hey thanks guys.. I think I probably was overshooting when I saw what the number was.

Actually fairly scared me when i saw my calculation on the power requirements on the stereo. I didn't have any of the actual draw from anything other than the AC units and the stereo.. was just taking a stab at the lighting.

Unfortunately, no refridgeration yet.. for the weekends the ice box with 2-3 bags should suffice. I do have AC but I don't have any delusions of being able to use that anywhere but the dock.. although the heat would be nice out in a cove over the winter.

The boat is a 32' Islander on Lake Lanier in Georgia. I've had it for about 2 weeks and just intend on using it as a weekender. The goal is to get the juice that I can go out friday evening and come back sunday during the day.. standard 9 to 5 rules apply for work.

In all, I think I may try to go up to 2 120 Amp Hour batteries for the house. That, along with some engine charging I hope will suffice.. worse comes to worse I'll have the starting battery isolated so I can charge her back up and get back to the tunes.

Thanks all
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I agree with 150AH's as typical for a cruiser with refrigeration that is reasonably efficient. I think that people tend to overestimate daily usage since when on the hook, one tends to conserve energy. For example...
Lighting...using leds where possible and only turning on THE light you will be using...not lighting up the cabin. Since most people go to bed early on the water and wake up early lights might only be needed for 3-4 hours daily.
With a 2 person crew each using a 2amp light...that is maybe 15 amps a day. And that is if you are on the boat for the entire evening. Lots of folks use oil lamps too.
All of the other lights are either used only while the boat is underway and/or very sporadically (with the exception of the anchor light) and should not be figured into a daily use scenario nor should the instruments. Passagemaking is only a small part of cruising...on average 10-15% and much of that is done under power. Anchor lights with .2amp draw are widely used so the whole night can cost y0ou only a couple of amps.
You need to size your battery bank for your daily needs on the hook. Get a link 10 and wire it up and see what you ACTUALLY use before making battery bank size decisions.
It is the rare cruiser that exceeds 200 amp/hrs a day and many do quite nicely with refrigeration and STILL use under 100 amp/Hrs a day.
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You might want to look at using a percolator or coffee press for your coffee. Then you just use propane to heat the water and will use zero AH (and my wife said the coffee is much better!). Also, there are many things that you can cook on the stove instead of in the microwave. Popcorn cooked in olive oil in a pan blows away microwave popcorn. Many foods can be reheated in the oven, and the stove and oven tend to be a much gentler heat and less damaging to the food. Anyway, just a few thoughts to radically reduce your daily usage...
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I'd second using a coffee press...
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