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View Poll Results: at what state of charge do you decide to recharge your batteries
at 95% 2 5.88%
90-95% 2 5.88%
85-90% 1 2.94%
80-85% 2 5.88%
75-80% 6 17.65%
70-75% 1 2.94%
65-70% 5 14.71%
60-65% 2 5.88%
55-60% 5 14.71%
50-50% 5 14.71%
40-50% 2 5.88%
30-40% 0 0%
20-30% 0 0%
10-20% 0 0%
less than 10 or when I need a jump to start the engine 1 2.94%
Voters: 34. You may not vote on this poll

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Old 03-06-2012, 05:43   #1
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Battery state of charge

I have this feeling that I keep my batteries charged more than really needed. Not that there's anything wrong with this overall. But I wonder what others are doing. So time for a poll ....
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Old 03-06-2012, 06:04   #2
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Re: Battery state of charge

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Originally Posted by Don Lucas View Post
I have this feeling that I keep my batteries charged more than really needed. Not that there's anything wrong with this overall. But I wonder what others are doing. So time for a poll ....
Don,

1. You can't really keep your batteries charged "more than really needed"...anything less than a full charge will result in loss of capacity over time. The further from a full SOC, the faster sulfation and other undesirable things occur.

2. Not to rain on your parade, but it really doesn't matter what SOC others aim for, especially when you consider that many/most boats abuse their batteries -- knowingly or not -- and reports of battery longevity are virtually meaningless.

As MaineSail and other professional battery/power system workers have said repeatedly, most boaters simply don't understand their electrical systems well enough to make intelligent choices about charging.

Bill
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Old 03-06-2012, 06:12   #3
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Re: Battery state of charge

I think a lot of crusing boats with extensive solar are tending to fit too many AHrs in their house bank. The draw with solar tends to me much less a lot of the load is taken by the solar panel output.
I have decreased from 600 AHrs to 400 and I think minimum *battery running*costs would be close to 200AHrs. This is despite running a Watermaker plus all the usual crusing stuff. *I connect to shore power only every couple of years.
Solar is getting cheaper, so people are fitting more panels. Devices like LED lighting and low powered tablets are reducing battery consumption.
Despite this people seem to be fitting larger battery banks.
The adage that a larger battery bank will last longer than a smaller one is as true now as it ever was, but it needs to applied with some caution and tempered with the thought that a smaller battery ubank will often be cheaper to run, as well as reducing weight and increasing storage.
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Old 03-06-2012, 07:03   #4
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Re: Battery state of charge

I found this table in the link below showing max energy out of a battery over its lifetime is around 40% discharge. They multiplied amp-hours out of battery for a certain discharge depth times the expected number of discharges you get for that depth.

http://www.google.com/url?sa=t&rct=j...hc4Iec482JlNyg

Part of table in above link:
DD___ total amp-hours out of battery over lifetime
30% 132,000
40% 148,000
50% 145,000
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Old 03-06-2012, 07:34   #5
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Re: Battery state of charge

I didn't place a vote in the poll because I don't find myself making a consistent decision. I'm often recharging by the consequence of my wind generator, solar panels, using my propulsion engine, my 7KW generator or even having a shore power cord to a dock. With the activity of these five modes of charging, paired with my miserly use of 12VDC, I'm rarely put in the position of deciding to recharge the batteries. When I do make such a decision it comes with an "idiot light" that catches my attention when the capacity drops to 80%, but this is not a common event. More than 90% of my 12VDC draw is consumed by my freezer/refrigerator. If I were to prepare for a long term with recharging supplied by my solar panels and wind generator alone, by turning off my freezer, my batteries would remain "topped off".
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Old 03-06-2012, 07:41   #6
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Re: Battery state of charge

i try to allow mine to drop nicely before charging up---but is difficult with solar power keeping them topped off. no i didnt vote in poll.
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Old 03-06-2012, 08:42   #7
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Re: Battery state of charge

The way we sail there is no way to say X%. We have solars (but not every day is sunny) and then there is the alt (but we never/hardly ever run the engine only to charge the batteries). We may be 100% Monday 50% Tuesday back to 95% Wednesday.

So my happy guess is our batteries spend their short lives in anything between 100 and 50 of charge. And then we buy new batteries.

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Old 03-06-2012, 11:05   #8
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Re: Battery state of charge

The question really should be "When do you NEED to start recharging?"

50%
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Old 03-06-2012, 11:09   #9
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Re: Battery state of charge

no that's NOT the question!
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Old 03-06-2012, 11:15   #10
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Re: Battery state of charge

Whatever it is when I get around to running the engine! That's probably 50% on many days. Pretty hard to quantify it really. If the wind was blowing like stink then the wind gen reduces the charge time. IF we're headed to town first thing in the am, then the batt's would be really low by the afternoon when we return.
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Old 03-06-2012, 11:19   #11
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I never decide to recharge anymore. I've delegated that decision-making authority to my PWM solar controller and batteries.

I do, however, monitor their behavior with a battery monitor, and with periodic open circuit voltage and specific gravity testing. So far, I haven't needed to overrule any of their decisions.
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Old 03-06-2012, 11:35   #12
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Re: Battery state of charge

Quote:
Originally Posted by Don Lucas View Post
I have this feeling that I keep my batteries charged more than really needed. Not that there's anything wrong with this overall. But I wonder what others are doing. So time for a poll ....
Don

I am curious how large your battery bank is, what type of batteries they are, how you charge and what you are basing your decision on re overcharging.
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Old 03-06-2012, 12:27   #13
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Re: Battery state of charge

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Originally Posted by mitiempo View Post
Don

I am curious how large your battery bank is, what type of batteries they are, how you charge and what you are basing your decision on re overcharging.

I'm not really looking for any advice on what I do. But my house bank is 460 amps FLA and i like to keep it above 80%. At least every couple of weeks I charge them to 100%. When I left my boat today the house bank was at 90%, which it will still be at next weekkend when I go back. If I had AGM I would have to fully charge before leaving each time in order for them to last.

For the most part I can keep my batteries above 80% just with the motoring out/into the mooring field and wherever I may have gone for the weekend (normally above 90%).

I will say that in the past before I had a monitor that I charged based on voltage. I now know in those days I was charging more than needed because the displayed voltage when systems are running is not a good indication.

So this is just a poll to see what others are doing. Not on how I should run my electrical/battery system.
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Old 03-06-2012, 12:37   #14
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Re: Battery state of charge

All batteries are best kept fully charged. In the case of flooded batteries they will sulphate if not fully charged as often as conveniently possible.

re your feeling - no, I don't think you are keeping your batteries charged more than really needed. Probable not fully charged often enough.
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Old 03-06-2012, 12:46   #15
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Re: Battery state of charge

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re your feeling - no, I don't think you are keeping your batteries charged more than really needed. Probable not fully charged often enough.
Everything is a comprise. Balance of the reduced battery life compared to the extra wear and tear on the engine and the cost of the fuel plus the hassle of going to get it. I prefer in the long run to buy batteries a year or so earlier because I let their SOC be a little less, than to put the wear on the engine just to charge them all the time (plus the current 2 hour round trip to get fuel).

Now this is just my current equipment and will be different in a few years when time to sail off.
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