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Old 09-24-2012, 07:54 AM   #1
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SOC advice

I assume SOC is state of charge. Am I right? I am keeping track of the house batteries with a digital Volt/Amp meter wired directly to the battery bank. Please recommend a brand name meter/s and how to hook it or them up? Assume they will be digital since one needs two decimal
places for a good reading. Do you use a fuse inline? Does the length of wire run alter the read out? I probably would be satisfied to just monitor the house bank, hence one would do. I am going to change the charger out this winter so I can leave it on all the time.
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Old 09-24-2012, 08:04 AM   #2
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Here's a link:

Wiring & Installing A Battery Monitor - SailboatOwners.com

FF has posted somewhere in the archives on buying the pieces for a lot less money.
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Old 09-24-2012, 10:31 AM   #3
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OK, Xantrex linkpro or link light.

Battery Chargers | LinkPRO Battery Monitor | Xantrex

This unit counts amp hours in and amp hours out keeping track of your batteries state of charge.

I've used this exact product on several boats and think its a must have item for any boat.
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Old 09-24-2012, 10:59 AM   #4
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My Victron is a great unit as well. Easy as heck to install and use!

Victron BMV 602 Two Bank Battery Monitor

How to article:

Installing A Battery Monitor Photo Gallery by Compass Marine at pbase.com

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Old 09-24-2012, 11:31 AM   #5
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Using the voltage reading of your battery bank will only be an approximate indicator of the state of charge. And you have to let the batteries rest with no charge or discharge for several hours before even attempting it. Even so I don't think you can get any closer than 20% this way.

But having said that, it is cheap. Google 12 dc meters. Don't assume that digital is more accurate than a good analogue Blue Seas 8-15 V meter for about $30. Wire to your battery terminals with at least 18 gauge wire and put a 5 amp fuse near the battery in the positive wire.

As others have said, a battery monitor that measures amps and volts and integrates amps over time to give amphours in and out is best for cruising boat.

But if you are a casual overnight cruiser then the DC meter will work ok.

David
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Old 09-24-2012, 02:04 PM   #6
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Highly recommend the Victron monitor suggested at post #4...A simple volt meter is near-useless in comparison.
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Old 09-24-2012, 02:17 PM   #7
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The Coot has a Victron BMV-501 battery monitor (square device to the right of the inverter multicontrol) for the single house bank.

http://www.victronenergy.com/upload/...attMonitor.pdf

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Old 09-24-2012, 04:52 PM   #8
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[QUOTE=djmarchand;104827.

But if you are a casual overnight cruiser then the DC meter will work ok.

David[/QUOTE]

It seems that the voltage in the battery bank will read lower when it is under a discharge load with no charge load going in. If that is the case reading the voltage should be on the conservative side. Did that make sense?
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Old 09-24-2012, 05:18 PM   #9
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Moonstruck:

Yes if there is a discharge current, the voltage reading will be lower than if the battery has been at rest for several hours thereby providing a conservative indication.

When I was cruising full time I didn't have a working battery monitor (and Xantrex couldn't help me get my new monitor working right!!) but with about 3 amps of discharge current I used 12.0 V as my 50% SOC indication instead of 12.1-12.2. It seemed to work out ok.

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Old 09-24-2012, 05:31 PM   #10
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Moonstruck:

Yes if there is a discharge current, the voltage reading will be lower than if the battery has been at rest for several hours thereby providing a conservative indication.

When I was cruising full time I didn't have a working battery monitor (and Xantrex couldn't help me get my new monitor working right!!) but with about 3 amps of discharge current I used 12.0 V as my 50% SOC indication instead of 12.1-12.2. It seemed to work out ok.

David
David, that has paralleled my experience. With any significant discharge current going out, my voltage meter will read about .2 volts lower.
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Old 09-24-2012, 07:28 PM   #11
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Anybody who thinks they can use voltage as a substitute for a SOC meter is either kidding themselves or simply doesn't know any better. You can buy a Trimetric for well under $200 and they're dead simple to install so the real question is "why wouldn't you?"
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Old 09-24-2012, 08:21 PM   #12
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Anybody who thinks they can use voltage as a substitute for a SOC meter is either kidding themselves or simply doesn't know any better. You can buy a Trimetric for well under $200 and they're dead simple to install so the real question is "why wouldn't you?"
Didn't say I wouldn't. Just discussing the digital voltage read out. $200 is chump change. I have been checking out the various SOC meters. Because we have in the last year or so changed out cruising style, we are checking out a lot of things. Thanks for mentioning Trimetric.
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Old 09-24-2012, 10:09 PM   #13
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Appreciate the discussion. Our boat sits at the dock much of the time. The only thing we have drawing current at the dock is a bilge pump and that is infrequently since the shafts don't drip after at the dock for a day or two. Rain water intrusion is minimal. Boat only cost us $25,000 and we did have work to bring it up to functional use, which is different than most of yours. Understand $200 might be chump change for a Sabre 42 owner but for us, considering our use and need for battery monitoring, or lack there of, I'll hard wire to a Harbor Freight $2.00 VOM before we got all out for a true SOC system. I could have been more specific and indicated I was looking for an inexpensive meter I could locate at the helm or such and hard wire. I'll check out the referenced volt meteres, $15 to $20 is our chump change reference. Thanks
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Old 09-24-2012, 10:56 PM   #14
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If the boat sits at the dock most of the time then SOC is likely irrelevant to you anyway so your solution will probably serve you well. Just don't kid yourself when away from the dock that battery voltage will tell you much about SOC unless you're prepared to go to some extremes to take your readings.
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Old 09-24-2012, 11:39 PM   #15
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Quote:
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I'll check out the referenced volt meteres, $15 to $20 is our chump change reference. Thanks
Sorry, Fighter Pilot, that was not intended specifically for you. As you know $200 can go pretty fast on a boat. I also did not mean that I would not consider fairly carefully any addition to the boat that requires cutting holes. That being said, I think the best value for the money is the Victron monitor. It seems the simplest by far to install, and I like the simple way to move between functions. Now, I have to decide if the one or two bank model is needed. The two bank model is $40 more, but I can't see a real need to monitor a starting battery. Maybe I should. Maybe not. At any rate a SOC meter will probably be added when the 3 stage voltage regulator is installed.

When I said that we had changed our cruising style, I was referring to the fact that we have decided we like anchoring as much as possible. We upgraded our dinghy, so now Lou's feet don't get wet. We can also now transport 4 adults. That makes anchoring a much easier proposition. We like cruising with just the two of us, but we also like to share the boat with friends and family----especially the grand children. As they start into the college age we will see less and less of them.

On another note, I was checking into satellite TV, but when we moved the boat to South Florida we found so many digital broadcast channels that we don't think we need satellite. Now, I just have to learn to speak Spanish to be able to watch all those channels.
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Old 01-10-2013, 09:48 AM   #16
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A question for you tech savvy guys. My set up is two 80 alternators. I just had them checked out at the alternator shop. They say they are really good. The current setup is one on the port engine is dedicated to the house battery bank. The starboard engine alternator is dedicated to the starting and bow thruster. The banks are completely isolated unless a battery switch is turned to parallel them. I like keeping the starting bank isolated to keep from house use discharging it.

The bow thruster is hardly ever used. The starting bank recharges quickly, and the volt meter drops to float. Is there any way to add the starboard alternator to the house bank for charging only? With a total of 160 amps max on tap, it would be a shame to buy another alternator, unless they can't be tied together for charging only.
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Old 01-10-2013, 10:05 AM   #17
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A question for you tech savvy guys. My set up is two 80 alternators. I just had them checked out at the alternator shop. They say they are really good.
Don, why do anything to a perfectly fine and standard setup? Mine is identical, except for larger alternators. I have separate BMKs (Magnum shunts OMG!) for both house and start batteries to give me something to watch. In a pinch I assume you can always run your genset to charge the lazy/low bank.
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Old 01-10-2013, 10:15 AM   #18
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In a pinch I assume you can always run your genset to charge the lazy/low bank.

Thanks. You are correct, and that is what I have been doing. I have a 12KW NL generator and a 60 amp Charles battery charger. I just thought that I was wasting a lot of alternator potential. The icemaker and fridge both run through the inverter, so the port alternator could use a little extra help to cut down on generator time which is usually about 3 hours per day at anchor.
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Old 01-10-2013, 10:22 AM   #19
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Don: Call Ample Power in Seattle. They have many alternator/voltage regulator combinations available.

Dual Alternator Controller
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Old 01-10-2013, 10:50 AM   #20
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Greetings,
Mr. Moonstruck. Seems you have two starboard engines. Hey....is this one of those four engine set-ups I've heard about? No worries, I think I know what you mean. As far as "wasting" alternator power I think the alternator only produces the amount of power called for so if you battery is fully charged, it produces zero. Leave it like it is until such time you get a larger alternator for the house bank or talk to Larry M's contact.
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