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Thread: Off grid battery plant for weekend cabins

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    Default Off grid battery plant for weekend cabins

    I am looking for experience of those who leave thier batteries for extended time in the winter and how thier batteries fare?

    I am installing a large-ish system but will only use it in the summer. I have not had any issues with my genset batteries or other vehicle batteries if I don't forget to leave a good charge on them. Is this the same approach I should take or am I asking for yearly replacements?

    George

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    Moderator bkmail's Avatar
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    George,
    We simply charge our batteries up before we leave. As long as they are topped off, no problem. Also, donít drain Ďem completely before you charge them up. They survive temps in the -40 range with no problem doing it this way.
    When we return, we let the batteries warm up before using them as well. Itís worked for us so far and we have batteries that are a couple years old.
    BK

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    Batteries with a good charge are quite resistant to freezing. Get familiar with battery bank maintenance and battery bank equalization. I equalize before I leave for extended periods. You'll learn that freshly equalized batteries maintain their charge better than when not equalized. I also think the addition of a solar panel, even a relatively small one, tickles the system and keep the batteries healthier.

    Good batteries that are designed for off-grid power systems should easily last well past 10 years. My current Exides are about 15 years old. When I change them I'll spend the extra and use Surrette. More money, better batteries, longer life. In the end the more money part is offset by better performance and longer life.

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    I'd say get a small solar panel. Just before you leave, fully charge them, disconnect everything except the small panel, and you should be good. Mount the panel vertical so the snow doesn't cover it. The actually wattage for the panel would depend on the size of your bank. You want just a small amount of power going in to offset self-discharge but not so much that you start boiling off water (assuming these are flooded lead-acid batteries).

    The freezing point of a fully charged battery is around -75F. If it is only half charged the freezing point is around 5F. Quite a difference.

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    Just an fyi... when you size the bank based on your load make sure your only discharging 35% or 40% max otherwise you will kill your batteries in 5 years instead of 10. (or therabouts) They have a set number of full discharge cycles before they are toast. Let's say you have a battery bank with 200cycles of life, you can fully discharge them 200 times. If you discharge to 50% you will extend that to 400 recharge cycles If you size your system correctly you may extend the life cycle by only dicharging 40% or even better 35%. Makes for a better return on investment.
    Lead acid is the most economically viable at the present, gels and AGM sealed stuff is ok, but you need to be precise with the voltage you are charging them at. 14.1Volts DC is the nominal voltage for a 12V system, anything over and they will cook off the electrolyte in them with no way of replenishing it. Same goes if you plan on using them alot (heavy charge discharge every day or two). Make sure to equalize them and burn off the sulfates from the plates once a month or so. Your charge controller or inverter should have this feature built in so you either push a button once a month or set a schedule and it does it automatically depending on the sophistication of the unit.
    Here is a calculator I use http://www.advancepower.net/advcalc.htm to help size a system. Let me know if I can help out a bit as I set systems up for folks on the side and have lived off-grid for about 10 years off and on.

    Regards,

    Mountaintrekker

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    I've never seen a solar charge controller that was capable of equalizing by overcharging. The use of solar panels greatly diminishes the need for equalizing when compared to a generator-dependent battery storage system. My system started with generator charging and I added solar initially to help keep the batteries fully charged to reduce sulfating of the plates. Battery bank maintenance depends on the system that charges it.

    Here's a good article about batteries. It's one of the better ones I've seen. http://www.backwoodshome.com/articles2/yago95.html

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    Mr. Pid,
    I have two Xantrex charge controllers, a model 40 and 60 which have buttons on the side that allow the system to equalize via overcharging. I think my friends Outback does it as well. If you are discharging your bank regularly down to the 60% level you are going to sulfate. I have discussed this with the reps and engineers with Trojan and Surrette and they tell me the same thing. Solar may help keep the levels up, but it all depends on how often and how far you are bringing the bank down and back up.

    Mountaintrekker

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    If you have a 40A and a 60A controller, how big is your array? My inverter's equalization mode requires about 8 hours using a 6kw generator at 12 and the charger is rated at 120A. How does your array do that reliably? I never knew solar equalization existed but I don't know anyone with an array that could push it, either.

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    Google , batteryMINDer , it's a maintainer/ Desulfanator . T

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    Quote Originally Posted by pacific23 View Post
    Google , batteryMINDer , it's a maintainer/ Desulfanator . T
    That needs 120v AC power. You could use it with your genset, but it isn't worth anything over the winter while you are away from a place not tied to the grid.

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    Quote Originally Posted by Mountaintrekker View Post
    Just an fyi... Regards,

    Mountaintrekker
    hey you seem to know a bit on batteries all I'd like to know is I am setting up a ham radio and am going to power it with a deep cycle and a trickle charger should I leave the charger on all the time or could that damage the battery
    Visions Steel/841-WELD(9353)
    "Rebellion is in my blood, I was born an American"
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    If the trickle charger is fully automatic, then you will be fine. they shut off automatically when the battery reaches a certain charge, and kick back on when they discharge passed a certain point. If its an actual battery maintainer (which is for maintaining a charge rather than recharging a battery) then that is what they are designed for. Just hook it up and forget about it.

    Solar panels seem to be the most logical way to keep remote battery banks maintained. Solar panels generally do not have enough to charge the batteries, but they will maintain them. If the batteries discharge even a little bit, then they risk freezing and busting (even if the plastic case isn't busted, the lead plates inside the battery can separate and short out).

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    Solar has worked for me for 15 years and as I mentioned before I'm on the same batteries. The solar contribution to those batteries is zero from about November 1st to March 1st and my batteries do fine year after year, even to now as the batteries are nearing the end of their life and don't maintain a charge like they did when they were younger. When we use the cabin in the winter we recharge with a generator. A couple of hours with the generator will recharge a couple of days of inverter use. As long as the battery bank is above 12.5 volts I don't have any concerns about the cold and the next trip in the cold batteries power the cold cabin just fine. As the batteries warm they perform even better. By mid summer we can leave with the batteries in the 12.1 range and return a week later to find the charge at 13.9, and I have a small array. Solar works great when the sun's out. In summer the generator isn't needed.

    Battery Minders work great on my 4 wheeler. My solar battery bank wouldn't benefit from a little maintainer at all. Desulphating large battery banks is done by sustaining an overcharge, not by maintaining a level charge to prevent small battery sulphation like battery minders do. My solar battery charger runs the charge voltage up to around 15v and holds it there for a couple of hours before it switches into float charge mode. Even with 120A output it takes quite a while to get the battery charge that high, too. While the battery voltage is up in the high 14s the acid in the batteries is churning and bubbling and off-gassing. That's when the desulphating happens. It's a process that needs to be monitored and it takes all day. This king of "equalization" is required to maintain the health of battery banks. It's much different that maintaining the charge of your 4 wheeler or boat battery.

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    Quote Originally Posted by NRick View Post
    That needs 120v AC power. You could use it with your genset, but it isn't worth anything over the winter while you are away from a place not tied to the grid.
    They have one with a solar panel too.

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    http://www.batteryminders.com/batterycharger/home.php

    They have two with a solar panels too.
    http://www.batteryminders.com/batter...--p-16139.html
    http://www.batteryminders.com/batter...--p-16140.html

    They do not DE-SULPHATE by over charging the battery as said above, it's done by PULSE . The one I have pulses 5ma to 200ma and it has in one week brought back a group 24 12V Deep cycle/Start battery that I had in my boat for 2 years [ I traded out both of my batteries for AGM's] then sat on the floor for a year. I put a load tester on it and it now shows good.
    The lawn mower and tractor batteries are next.

    Your mileage may vary.

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    Ah, didn't see the solar option. However, I don't think you need to spend the money on the minder for what George wants to do, just get a small 5 or 10 watt panel and connect directly to the battery bank. The idea is just to keep an already fully charged and maintained battery bank at 100% charge while they sit for six months. It doesn't take much, and a 5 watt panel simply can't overcharge a big battery bank. Hence, no need to spend money on a small controller. I'm assuming he will already have a charge controller on the main solar array and for charging with the generator.

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    It has been mention that all you need to do to keep a battery from freezing is to put a full charge on the battery and disconnect the battery incase there a problem with a parasitic drain and I agree this is what George should do.

    It has also been mention that a battery will self discharge over time, this is true if the battery were stored at temperatures above 40* for a very long time not just 5 or 6 months. So there is no reason to keep charging a battery in the winter.

    Mr Pid, mention that his solar panels put out zero power from November to March so I donít see how 5 watt solar panel would work.

    In order for a controller to control the charge going into a battery it needs to draw power from the battery 24/7, putting a constant drain on the battery when it not charging. I would think (know) this would be more than what the self discharge would be.

    In several of the new cars, trucks and atvís power from the battery is used to run the electronics after the ignition switch is turned off. If you park the vehicle for a long time and do not disconnect the battery you will have a dead battery. This is why a person would need a batteryminders, assuming you were too lazy to remove a battery lead or throw a battery switch.

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    Member pacific23's Avatar
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    MacGyver, here ya go ....

    Question: Why Do Batteries Discharge More Quickly in Cold Weather?

    Answer: The electric current generated by a battery is produced when a connection is made between its positive and negative terminals. When the terminals are connected, a chemical reaction is initiated that generates electrons to supply the current of the battery. Lowering the temperature causes chemical reactions to proceed more slowly, so if a battery is used at a low temperature then less current is produced than at a higher temperature. As the batteries run down they quickly reach the point where they cannot deliver enough current to keep up with the demand. If the battery is warmed up again it will operate normally.

    One solution to this problem is to make certain batteries are warm just prior to use. Preheating batteries is not unusual for certain situations. If the battery is already warm and insulated, it may make sense to use the battery's own power to operate a heating coil. It is reasonable to have batteries warm for use, but the discharge curve for most batteries is more dependent on battery design and chemistry than on temperature. This means that if the current drawn by the equipment is low in relation to the power rating of the cell, then the effect of temperature may be negligible.

    On the other hand, when a battery is not in use, it will slowly lose its charge as a result of leakage between the terminals. This chemical reaction is also temperature dependent, so unused batteries will lose their charge more slowly at cooler temperatures than at warmer temperatures. For example, certain rechargeable batteries may go flat in approximately two weeks at normal room temperature, but may last more than twice as long if refrigerated.

    As batteries sit they WILL sulphate , that's where the MINDER comes in [ used with the solar panel in the day light/summer] handy to extend the life of your batteries .
    If you will use Google and search things like Battery discharge or Battery maintenance instead of guessing or going by old wifes tails yall would get farther ahead on battery maintenance/longevity.

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    I was thinking about this thread this weekend at the cabin. The solar panels are holding snow and have zero output. The batteries hadn't been actively charged (generator charged and equalized) since October. It's been kinda cold this winter and the batteries responded normally when I switched the inverter on even with the battery temps in single digits. Of course they got better as they got warmer. And this with batteries that are old. I did run the genie to put a fresh charge to them.

    My solar array stays connected all year. No problems with parasitic drain.

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    Mr. Pid, sounds like you have a good set up and know how to maintain your stuff.

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