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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 09-02-2008
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New Battery System

I hope this isnt a "which boat is right for me question" If it is any direction to a link would be appreciated, I did search but also did not want to revive an old link..I will be very specific.

I have a 36ft boat with the standard 2 12V batteries (one house and one starting - the automotive type) This is obviously in serious need of a new battery system especially for the house. I have asked around for quotes and what the suggestions are on the best system. As a newbie on the electrical side Im not sure who to trust in terms of requirement and costs...so to Sailnet we go....

My power draws are quite simple with standard fridge and freezer (im assuming standard draw), stereo, and house lights. I would like to be able to have enough juice for 3-4 days at anchor..including charging a laptop/cellphone on occasion...is this realistic without solar panels or wind gen?

Im told the 6V deep cycle (golf cart) type would be best and to bridge? them ie. putting 4 together while maintaining one 12v automotive battery dedicated as a starting battery...and upgraded alternator and an invertor.

ANY opinions would be appreciated that could help me determine which is the best setup for my needs and approximate costs for supplies and labour....


Thanks
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Old 09-02-2008
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sorry... In addition I was also told I would should have a monitoring system and isolator. I have the standard 1-2 or both...
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Old 09-02-2008
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artbyjody is just really nice artbyjody is just really nice artbyjody is just really nice artbyjody is just really nice
Are you doing this yourself or hiring someone? Personally, I stay away from golf cart batteries and go with Marine gels that meet my requirements...Do a detailed search using google "batteries sailnet" - tons of info.. good luck
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Do you have shore power for charging between trips? is your refrigerator/freezer 12 volt or 120? You need to figure your amp use for the refer and all other power use first and go from there.
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Old 09-02-2008
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Might I suggest that you first install a battery monitoring system on your existing house battery. A Xantrex XBM or LINK 10 is all you need. This is the only way you'll be able to accurately know how much power you use per 24 hours.

Once you know your average power usage you can then build a system around those parameters. Fridge/freezers are notorious consumers and there is NO average as every installation is entirely different. Things like insulation, ice box cu/ft, door position is it top or side opening, the amount of warm food or beer you toss in, did it run at the dock all week or are you firing it from warm up every Friday night etc. etc. all play into the fridges consumption and efficiency.

Some fridges, when properly cooled, will run as little as 50% of the time but some others will still run 70% of the time. When you fire it up for the first time and load it with food it may run as much as 80-90% of that first 24 hours.

I hope your getting my point that only a dedicated battery monitor will tell you how efficient or inefficient your fridge is.

For grins let's say you guess your fridge draws 5.5 amps per hour and runs 80% of the time. That is 4.4 amps per hour over 24 hours or 4.4 X 24 = 105.6 amp per day for just the fridge. Now lets throw in an extra 70 amp hours of use for everything else and your at about 175 amp hours per day.

Now you want to go for three to four days, will figure four, and you look like this 175 X 4 = 700 amp hours of use!!

Considering that a battery bank should never be discharged bellow 50% of capacity, and you'll rarely ever get it charged back beyond 90% or so running the engine, you'll need a bank of about 1500 to 1600 amp hours. That is freaking HUGE!!! Actually it's 14 6V golf cart batteries or 14 group 31 12v Deep cycle batts..

Or you could buy a monitor and find out for real that in 24 hours you only really use 90 amp hours per day and your bank gets drastically smaller..

A battery monitor should be the first step as it can save you HUGE money. My buddy Charlie spent well over 2k on a wind turbine, Balmar alternator and 4 six volt batteries with associated wiring and gear.

His last purchase was a battery monitor. To say the least he was very surprised to find out that he only used about 25-30 amp hours per day not the 100 he had guessed on. He could have saved a lot of money by buying the LINK 10 first not last...

Figuring current draw on some stuff such as lights is simple but variable items such as fridges, autopilots, stereos, TV's and laptop computer chargers are tough to guess on.

My Mac, while plugged in, burns anywhere from a low of about 2.2 amps to over 7 running through a small inverter and it's very dependent on what I'm doing on the computer as to how much current it draws. If I'm running PhotoShop it rarely ever dips bellow 5 amps but if I'm surfing the net it hovers in the low 2 range..


Get in about five or six average days, with the monitors ah consumption re-set each 24 hours, and monitor those numbers and base your system on that..
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Last edited by Maine Sail; 09-02-2008 at 10:38 PM.
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Lets assume you use a very minimal 100amp hours a day at anchor. This means 4 days at anchor will require 400 amp hours. Batteries should never be discharged beyond 50% so that means you need 800 amp hours of batteries or 3x8D's at a minimum. Chances are you have no room for that much battery on your boat. (Each of those are 150lbs!)
So...you are faced with getting a SMALLER battery bank and need a way to charge it at anchor. Lets assume you can fit three group 31 batteries and build a bank of around 350 amp hours. You'd have to spend some time each day charging them to put back in the 100 amp hours you'd use. Options:
1. Get a large (90-100amp) alternator and 3 stage regulator and AGM batteries that can ake a fast charge...Run the engine for an hour a day while you are out on the hook...or use the motor time cruising to a new spot to do the same thing.
2. Get a Honda type generator and LARGE 3 stage battery charger and run the generator for an hour or two a day. Standard wet cells or 6V's would be fine in this set up.
3. Buy a solar and/or wind set/up with at least 400 watts of solar panels 200 watts with a wind generator. Battery bank should be wet cell and around 400amp hours.

I favor option #1 given your cruising style.

You should also get a XANTREX Echo Charger to charge your start battery and a Link10 or 1000 to monitor the state of your battery charge and amp hour usage.

On the batteries...go cheap flooded deep cycle cells UNLESS you go for the large engine alternator and can take advantage of the quick charge capability of AGM's.
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Quote:
Originally Posted by halekai36 View Post
Might I suggest that you first install a battery monitoring system on your existing house battery. A Xantrex XBM or LINK 10 is all you need. This is the only way you'll be able to accurately know how much power you use per 24 hours.

Once you know your average power usage you can then build a system around those parameters. Fridge/freezers are notorious consumers and there is NO average as every installation is entirely different. Things like insulation, ice box cu/ft, door position is it top or side opening, the amount of warm food or beer you toss in, did it run at the dock all week or are you firing it from warm up every Friday night etc. etc. all play into the fridges consumption and efficiency.

Some fridges, when properly cooled, will run as little as 50% of the time but some others will still run 70% of the time. When you fire it up for the first time and load it with food it may run as much as 80-90% of that first 24 hours.

I hope your getting my point that only a dedicated battery monitor will tell you how efficient or inefficient your fridge is.

For grins let's say you guess your fridge draws 5.5 amps per hour and runs 80% of the time. That is 4.4 amps per hour over 24 hours or 4.4 X 24 = 105.6 amp per day for just the fridge. Now lets throw in an extra 70 amp hours of use for everything else and your at about 175 amp hours per day.

Now you want to go for three to four days, will figure four, and you look like this 175 X 4 = 700 amp hours of use!!

Considering that a battery bank should never be discharged bellow 50% of capacity, and you'll rarely ever get it charged back beyond 90% or so running the engine, you'll need a bank of about 1500 to 1600 amp hours. That is freaking HUGE!!! Actually it's 14 6V golf cart batteries or 14 group 31 12v Deep cycle batts..

Or you could buy a monitor and find out for real that in 24 hours you only really use 90 amp hours per day and your bank gets drastically smaller..

A battery monitor should be the first step as it can save you HUGE money. My buddy Charlie spent well over 2k on a wind turbine, Balmar alternator and 4 six volt batteries with associated wiring and gear.

His last purchase was a battery monitor. To say the least he was very surprised to find out that he only used about 25-30 amp hours per day not the 100 he had guessed on. He could have saved a lot of money by buying the LINK 10 first not last...

Figuring current draw on some stuff such as lights is simple but variable items such as fridges, autopilots, stereos, TV's and laptop computer chargers are tough to guess on.

My Mac, while plugged in, burns anywhere from a low of about 2.2 amps to over 7 running through a small inverter and it's very dependent on what I'm doing on the computer as to how much current it draws. If I'm running PhotoShop it rarely ever dips bellow 5 amps but if I'm surfing the net it hovers in the low 2 range..


Get in about five or six average days, with the monitors ah consumption re-set each 24 hours, and monitor those numbers and base your system on that..
Good idea...I will definately look at taking that route first.

Artb - thanks I did locate a couple of articles after I posted which I will read through.
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I wouldn't get too overly concerned about some of the amp hrs quoted here over a 4 day period as this fails to consider that most people, if only to heat the water, will run their engine, genset or portable generator sufficiently long enough to replace much of their daily power use.

If you don't want to buy a battery monotoring system which isn't always as precise a measure as marketed, you can get a fairly good approx of your typical daily usage by simply monitoring your existing ammeter throughout the day and doing a simple energy budget to calculate an avg daily use. If you know your existing charging capacity or intend to upgrade it, you have the rest of the story.
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Quote:
Originally Posted by k1vsk View Post

If you don't want to buy a battery monotoring system which isn't always as precise a measure as marketed,
Hmm interesting considering my XBM is reading exactly the same draw as what my $250.00 Fluke meter tells me.

I have found my XBM to be very, very precise. Items with specific draws such as light bulbs, LED Sensibulbs, or my ACR relay read exactly what they are spec'd to be.

On toeh boats I've also owned a Link 10 and a Link 20 and they too were as accurate as my Fluke on amps in and out and voltage. The algorithm for battery state of charge is just that an algorithm and as such may not be as accurate but I never go by the 80%, 50% or state of charge scale. I use my ah's consumed scale, simple math, and know what my bank consists of.

It's nice to look over and see +45 amps going back in from my alt or +4.5 amps from my solar panel or a +1 amp charge while under sail with no engine and the autopilot, plotter and stereo on while still charging the battery due to solar.. It's also nice to see it flashing "BATTERY FULL"...

BTW I also have an analog DC Amp Meter, AC volt meter as well as a digital DC Blue Seas Volt meter. I have my analog amp meter wired only into the panels consumption so I can compare what I'm taking out and what I'm netting in by comparing the XBM to the analog AMP Meter.

I have since replaced that Link 10 with the XBM:
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Last edited by Maine Sail; 09-02-2008 at 11:32 PM.
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Quote:
Originally Posted by halekai36 View Post

BTW I also have an analog DC Amp Meter, AC volt meter as well as a digital DC Blue Seas Volt meter. I have my analog amp meter wired only into the panels consumption so I can compare what I'm taking out and what I'm netting in by comparing the XBM to the analog AMP Meter.

I have since replaced that Link 10 with the XBM:

That looks like one clean setup...two questions that the articles I have read dont answer:

1. It states to never discharge a deep cycle below 50%..is there an audible alarm or does it just require regular monitoring..I wouldnt have solar panels or wind gen so this may occur with an incoming charge.

2. The maint guy at my yard recommended building a bank of 6V (golf cart type)which doesnt seem to be a popular choice on sailnet but rather either flooded or gel 12V..can you explain why you would or wouldnt go with 6V.

Thanks again for all your help guys...Im learning..Im learning...
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