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Owen Kellogg
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# Posted: 22 Dec 2012 11:43am
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Here's a quick overview of my set-up:
I've got 4 Marine-type deep cycle batteries powering my cabin. They're Energizer brand from Sam's Club. They're the biggest ones at about 110 amp-hours each. I've had them for about 2 years. They're all stored outside the cabin in an insulated cabinet.
I have them "segregated" with separate panels (100 watts to each panel - 400w total) and charge controllers to power different things:
One battery powers my 12v water pump and fans to circulate heat from my wood stove.
One battery powers mostly my LED lights and a small charger for small AA, AAA and D batteries.
The last two are wired parallel for my "fun stuff" - a small 7" TV, mp3 speakers and a laptop that I watch movies on.
I stay at my cabin about 5 - 6 nights a week. I monitor each battery set with LED voltmeters. Every evening when I first get to the cabin, all meters are reading 13 volts. Sunlight hours still seem to be plenty for charging. The two batteries that power the "essentials" seem to hold up well in the evenings, but I've noticed my "fun stuff" pair seem to drain much more quickly as the weather gets gradually colder. Often, I have to cut my entertainment a little short before the batteries drain down below 12v.
They seemed to hold up much better in warmer weather, and I hope this is normal for cold seasons, as I'd hate to have them going bad only after 2 years.
Is this expected for cold weather? I'm in the "experimental phase" with solar, and I have no problem expanding my system if I need more power this time of year.
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razmichael
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# Posted: 22 Dec 2012 12:33pm
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I'm sure you will get some more detailed responses but the general rule is that battery capacity goes down as temperature goes down and increases as temperature goes up (however battery life is the reverse). A couple of sites that provide a bit more information:
12 Volt Side of Life Part 1 and Trojan Batteries Charging . Both these sites have a lot more very useful information and show the the change based on temperature is not trivial!
You may have noticed that many charge controllers either include or have an option for an external temperature sensor that can be used to track the temperature of the batteries - especially if they are at a different temperature than the charger (which sounds like it may be the case for you). This allows them to compensate better for temperature. I also suspect that your batteries are hybrid deep cycle/starter batteries.
Curious - why split the system up the way you did? I can see some advantages but also a number of disadvantages as well.
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MtnDon
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# Posted: 22 Dec 2012 02:39pm - Edited by: MtnDon
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Lead acid batteries have their capacity (amp-hours) stated for a standard temperature of 77 F. For sake of simplicity I call it 80F. As razmichael mentioned the effective capacity is lessened as the temperature drops. At 60 F we've lost 8% of the capacity stated on the label. At 30 F we've lost 22%, 10 F brings us to a 33% loss. At -10 F 48% of the nice warm summers day effective capacity is nowhere to be found. Those temperatures are that of the electrolyte, not the air temperature. If the batteries are insulated and are being charged and depleted there will be some warming from the chemical reactions involved.
The good news is the lead acid battery will live longer when it At 0 F if the voltmeter reads 12 volts under no load, the battery is 75% depleted. That will shorten the battery life, negating any gains in longevity brought by the cold temperatures.is cold. Note that a hydrometer with a thermometer to permit adjustments for temperature is the only truly accurate method for gauging the state of charge.
I too wonder about the split battery system you have in place. To my mind you would have an overall more efficient system if you connected the batteries in one bank. That is, IF, they are of relatively the same age.
When it comes time to replace them you will also be better off with using 6 volt golf cart batteries. They have thicker plates and survive discharge and recharge cycles much better.
Also as razm stated, you eill get much better charging with a charge controller that includes the battery temperature sensor. That can also prevent the charger from overheating the batteries in hot weather. That too reduces battery life.
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SE Ohio
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# Posted: 23 Dec 2012 07:46am - Edited by: SE Ohio
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I noticed similar results with my single (powers lights only) 12 V deep cycle battery that I kept under the cabin. It didn't like the cold. I've since brought it inside to keep warm, but charge outdoors due to potential for flammable outgassing. Future plans are for an indoor airtight battery box that vents outdoors. An upgraded charge controller (have Harbor Freight solar setup) may also be in my future, along with the golf cart batteries! My battery often drops below 12 v per the controller readout.
I suspect that Owen's battery banks are separate in order not to have all of one's eggs in one basket, so to speak. I have a separate (and smaller) 12 volt battery to power my stereo, as I play this all day and don't want to drain power away from my already feeble light system.
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TomChum
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# Posted: 23 Dec 2012 12:33pm - Edited by: TomChum
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Quoting: MtnDon To my mind you would have an overall more efficient system if you connected the batteries in one bank
Agreed (if "about the same" age). Plus it's much simpler, and simple is good.
If you have a generator, I would put them all together in one bank, and use a generator to recharge the whole bank in one shot, whenever they get to 90%. Get a smart charger that can put out about 40A, so you don't waste gas & time. Charge with generator in early evening, so the solar can finish in the daylight. There may be a better way, but that's what I do currently.
I see that you have systems that could run a battery way down, probably the reason you want one bank remaining useful..... Is this working out?
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Owen Kellogg
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# Posted: 23 Dec 2012 01:28pm
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Thank you, everyone for your replies and advice. The question about my battery set-up has been answered also. As SE Ohio said - I don't like all of "my eggs in one basket." Also, my 4 batteries are different ages, so it all works out well. I like the set-up, and honestly, I'd feel a little nervous if everything was tied together.
SE Ohio - If you don't mind me asking - where in Ohio are you? I'm in Northern Ky, right across the river from Cincinnati. It would be nice to network with local off-gridders. EVERYONE I know thinks I'm crazy. 
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SE Ohio
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# Posted: 23 Dec 2012 04:38pm
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Owen,
My main address/job is in Columbus; off-grid cabin is in Vinton County. I'm about 20 miles from Athens. There are quite a few Vintonians on this website (names escape me).
It has been a few years, but I've lived in Erlanger and Cincinnati in your general area. Originally from Lexington (I've moved around a bit).
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