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Old 11-06-2009, 11:53   #16
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With all due respect...measuring voltage when the battery has had a charge applied to it within the last 24 hours OR has recently been cycled gives a false state of charge reading. It is an excellent way to murder your batteries short of their useful life.
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Old 11-06-2009, 11:58   #17
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A simple voltmeter and a two way toggle switch will get you there without complication. Make a chart for depth of disccharge . ie: 11.5 volts =50% discharge etc. Or buy the monitors mentioned above...
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Old 11-06-2009, 13:09   #18
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Old 11-06-2009, 13:56   #19
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cheechako...no you cannot measure voltage to measure battery state UNLESS the battery is completely disconnected from the charging system and use for 24 hours. And 50% charge is 12.2V not 11.5.

Gonesail...that one is ONLY for use with Xantrex Freedom Inverter/Chargers and it controls them as well as monitors 2 banks of batteries....The Link20 is the right model for two bank monitoring if you do NOT have a Freedom you want to control.
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Old 11-06-2009, 14:56   #20
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I believe I said to disconnect the batteries. Is 23 too little? 25 too much? What if I miss the 24 hours by 10 seconds do I have to recharge and start over? Let's face it , the world isnt perfect. If it's a truly bad battery it will show up overnight. If it's a marginal condition, then he may have to delve into it further. Sorry the 50% was just an example.
DAKNO: Before you invest in a monitoring device, you should ask your self if you are in the KISS camp or the other camp. Either is fine, but if you search for the old discussion on this subject a few months back, you will find it goes on for many pages of opinions and also find posts from people asking how to make their fancy monitoring system actually work....... Just a fair warning..... having a complicated system wont put any more amps in your batteries .....
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Old 11-06-2009, 15:51   #21
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I'm sorry Cheechako but your explanation just won't do. You can get away with it when you disconnect all loads and/or chargers (wind generators, solar panels, battery chargers) for an hour or so and it'll give you an indication of the battery is bad or not. But state of charge?? within 20% precision is my guess. You need more than 10 hours complete battery rest for a more precise indication.

Most boats don't want to do without electricity for that amount of time but still want to know the state of charge. A $200 monitor is well worth it imo. I would skip bars and my beloved Cuba Libre's for a week or two if forced to make the choice ;-)

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Old 11-06-2009, 15:57   #22
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to each his own Nick! by my way of thinking "more than 10 hours " is overnight..... Remember, he's just got a 27 foot boat that sits on a mooring.... would you invest in a monitor or a solar panel?
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Old 11-06-2009, 18:31   #23
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guys, i don't want to get in a p*ssing contest here so ....

i'll just tell you that my trojan batteries are now four years old and still take a good charge. been using the voltmeter for all that time and it's never failed me.

i'm sure we could get into a scientific discussion about why some thousand dollar battery monitor works better than my voltmeter but all i can say is, in the real world, it works.

nuff said.....
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Old 11-06-2009, 20:29   #24
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But I didn't read that the OP is "just sitting on a mooring" (I re-read his post, it doesn't say so) and he didn't ask about a solar panel. I think a solar panel would be good on a mooring too, why not? I also fail to see why the length of the boat is a factor on the decision on which battery monitor to buy. The OP asked which monitor, not for anyone to belittle him as too small or cheap to get one. For all I know he's got more $$$ than <insert some famous millionaire, I don't know their names>.

onestep: you have good batteries but your method for checking them is flawed. It never mattered because your batteries are good, but your voltmeter will never show you how much capacity your batteries have. You will enter all science and history books if you find a way. Your real world is an illusion, and your thousand dollars must be from some island nation if you need that amount of them for a decent monitor.

Again, a voltmeter doesn't measure state of charge nor the actual capacity of your batteries; it measures the voltage at the point you connect it. That's why it is called a voltmeter. I will not explain how this works because it would be scientific ;-)

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Old 12-06-2009, 19:27   #25
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...and not to put too fine a point on it, if one reads all the caveats on ANY battery manufacturer's website, they all state that state of charge determined by the table that most of them provide is only accurate if the battery has not been charged or heavily discharged for 10-24 hours. MOST of them also will stipulate that, before taking the voltage reading, that a small load (reading light) be turned on for a few minutes to dissipate any surface charge effects.

If you do all that, then the voltage to determine SOC is fairly accurate.

This is fact...not esoteric science.

My opinion is, if a boater depends on his house bank for any significant period, than a battery monitor is essential and at $250.00 is a lot less expensive than replacing those expensive house batteries that were murdered by not monitoring SOC.

YMMV
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Old 15-06-2009, 07:06   #26
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I have 12 AGM batteries running my electric motors and an additional 3 "house" batteries. I need to know when the charge is "full" and when to recharge them. Since I could be motoring for 3 to 10 hours a day the chances are I could end up discharging dangerously low or over charging the banks if I don't monitor them closely. The need to have visual and audio alarms is high yet nuisance alarms would be highly stressful. The problem I have now is the Link-10 isn't even close to being accurate or easy to read for the complicated system I have. The ability to monitor the charge and discharge of a bank of batteries shouldn't be that hard or need to be that expensive but then again for me the cost to replace all those batteries do to lack of info is a hell of a lot more expensive than the average boater so I'm willing to put out a little more to save in the long run.
As a side note I left the dock under electric drives, sailed for 5 hours with the frig, freezer, navs, and radio running and returned under electric drive to the dock with more power than I started with. 0 Dino fuel used!

Steve in Solomons MD
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Old 15-06-2009, 08:06   #27
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Steve- First of all, congratulations on your zero carbon footprint (on a micro scale) cruise. Well done!!

I have been installing battery monitoring systems for several years. I recently found the SmartGuage site and started studying the extensive technical documentation provided on the science and art of battery charging/discharging aboard boats. They have dissected the subject very thoroughly and come to some startling conclusions:
1. Most shunt based battery monitors do not accurately calculate charge efficiency.
2. Peukert's equation is not readily understood.
3. Battery bank capacity, as entered into a shunt based battery monitor, is only correct when the bank is new (see #1 above).
4. As a result of these and several other factors, shunt based battery monitors lead a well meaning and thoughtful vessel operator to chronically discharge his bank to below 50% and chronically undercharge his bank to less than 100%.

Of course, SmartGuage has an answer for all of this and they make an excellent case for their product, even pointing out its limitations.

I have no tie to the SmartGuage company, and of this writing, have not installed any of these units. I will install one on the next large inverter/charger and house bank install that I do. I am pointing out their product as a possible source for a resolution to your Link 10 issues. (By the way, SmartGuage does answer their emails.)

Here is their link: SmartGauge Electronics - SmartGauge battery monitor

Hope this helps>
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Old 15-06-2009, 09:43   #28
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I think HprDRv just proved my point, just because a system is complicated and has a lot of bells and whistles, doesnt mean it's accurate or works. Many people think a digital meter (in any application) is more accurate because it shows 3 decimal places .... all that really means is that it's showing whatever inaccuracy it has built in..... to 3 decimal places!
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Old 15-06-2009, 09:55   #29
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inexpensive and far more reliable...

...than voltage checks.
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Old 15-06-2009, 09:57   #30
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Cheechako-
Sorry, HprDRv did not prove your point. Your basic premise has been, throughout this entire thread, that a DMM will provide an indication of the SOC of a battery bank. It will, but the caveats are so tough that this method is impractical on any type of vessel because of the limitations I and others have posted. What HprDRv has run into is the limitations of a shunt based battery monitor.
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