Just finsihed reading your very interesting thread....and I look forward to following it in the ..... months to come as it looks like you are on quite journy. Similar to what I did, just not quite to your degree.
I see you are considering getting a generator. However, I suggest that before you do, you reconsider solar. No, solar dosn't charge fast, but your batteries will love you for giving them this treat (nice, slow, even charge all the time). And solar works in the fog reasonably well as long as you don't expect full output...especially at your latitude. And, with your battery bank, you should be able to deal with a few hours of fog (used to live in S. Cal and SLO so have seen my share). Don't forget the federal tax credit too.
Anyway, just my two cents worth.
Time to go pick up my 21ea 55 gallon drums that I plan to fill with water for thermal mass in my greenhouse (sort of like a BIG battery bank......)
Thanks Steve. I'll have solar before I have a generator unless we end up getting a MH first. I want to get at least 200+ watts, even if we sell the trailer. It would be nice to not have to plug in at home (although I'd probably still plug in for an overnight boost charge and let solar top off next day) and an automatic, periodic "equalize" function would be cool too.
You won't need to ever plug in at home unless you won't be home for more than a day or two..... or you park under cover. I would recommend that you stay away from the automatic equalization. If you need it (I suspect this would be rare once you have solar), select it manually.
Of course, if you are going to sell your rig, it really dosn't make much sense to put on solar. Sorry if I missed that earlier in the thread.
I have a much smaller system than you do (~460 A Hr battery and 300 watts solar), but I do camp in fairly cool conditions (frequently below 20 degrees F and often in the snow and/or rain) and have yet to use my new Honda generator. Of course, we are not big power users...though do use the microwave on occasion. Now that summer is comming, it's about time to tuck the trailer in for a few months and go back to a tent...or stars...over my head at night.
Steve,
When we come home from a trip it's typically in the late afternoon or evening. Solar wouldn't come close to recharging before nightfall. Considering the expense of the batteries, I won't let them sit in a partially charged state especially on nights that are below freezing. That's my reasoning for hooking up to a charge for at least one evening. And come to think of it, I might even plug in until the charger goes into float cause there simply won't be enough current to recharge quickly off of solar at least during the winter.
I agree that it isn't good for batteries to be be stored, partaly discharged, in freezing temps (like close to zero). I assuned (perhaps incorrectly) that you were in Southern California. But if you are in a different, much colder, location then you may indeed need to plug in upon returning home from winter trips IF your batteries are still low after driving home.
My experience has been that, since I installed solar, my battery bank has always been fully recharged within 24 hours of returning home from winter camping (in the snow) trips. And usually, my batteries are fully (within 5%) recharged by the time I return home from a trip anyway, due to both solar and alternator charging while traveling. I have determined this state of charge by measuring specific gravity with a temperature compensated hydrometer and also with a battery monitor that I ocassionally reference to the specific gravity.
The only time I plug the trailer into shore power at home (other than when testing out other systems) is when I am preparing for a winter trip and I want to run the furnace all night to keep the water and food in the trailer from freezing...so I can start the trip with full batteries...
Again, this has been my experiece with my system here in Bend (~ 45 degrees latitude). Due to conservation efforts, my power use is fairly minimal so my batteries seldom get very low when on trips anyway. Your system will, of course, be diffeent. You will have different power demands and battery size as well as a different angle of solar radiation (latitude} and weather conditions.
BTW, I do not tilt my panels as I don't like climbing on the roof when it is snowy and/or icy. I felt that it was cheaper (than falling off the roof) to just add more watts to compensate.
I hope this helps you with your decision to get (or not get) solar panels when you have the rig you plan to keep for awhile.
The problem is, mena wants to do a minimalist install with around 200 watts. That's not enough for the size of the battery bank, unless they are separated into twin banks and charged alternately. (one bank on odd days and one bank on even days).
200 watts may be enough to meet his daily needs with no inverter or furnace use. It is enough over a two or three day period to return the bank to fully charged when in storage mode.
The freeze point may be a red herring, as I doubt mena ever gets lower than 12.2 volts.
My experience has been that, since I installed solar, my battery bank has always been fully recharged within 24 hours of returning home from winter camping (in the snow) trips. And usually, my batteries are fully (within 5%) recharged by the time I return home from a trip anyway, due to both solar and alternator charging while traveling. I have determined this state of charge by measuring specific gravity with a temperature compensated hydrometer and also with a battery monitor that I ocassionally reference to the specific gravity.
We're not heavy users but we use a decent amount of power. We have yet to get below 85% SOC though.
This is probably where we'll disagree and get into some OT territory. I'll just say that my batteries aren't full until my SG is at my baseline (which has changed recently). I don't go by what the chargers say as they're mostly wrong. And I have 4 charging sources I can use. The battery manufacturers current documentation (I have not read any manuals for CC's recently though) seems to support an overcharge being needed to return the bank to 100% after cycling. With the right amount of solar, batteries don't seem to need any overcharging from what I read and hear but I don't believe that. I do live in SoCal but I live in the higher elevation desert that gets into the 20's at night in the winter so battery freezing is an issue.
PT, thanks for that chart. That's good to know! Regardless, my batts will be on a charge. I'll know for certain they won't freeze that way. BTW, I have let them sit overnight fully charged in freezing temps without a charger hooked up so I'm not completely neurotic. Self-discharge isn't as catastrophic as you're saying based on a test I ran on stratification (where I failed to know what that really was...I get it now). I let my batteries sit for 5 days without a charger and they never went below 1.275 (58F/14C, 12.8V). Start of that test was 1.300 (63F/17C, 13V). If you go by voltage, that's almost 1%. If you go by SG, that's almost 1%. Quite a bit better than 1% per day.
pianotuna,
Great chart, thank you for sharing. I especially like the last sentence where it "implies" that self discharge will decrease with decreasing temperature. Makes sense to me.
mena661,
Something to keep in mind is that, while it may get to the 20's for a few hours, does it stay that way long enough to impact the batteries? I don't really know your climate that well (lived near the beach when in So CA) but suspect it dosn't because you have so much thermal mass in your battery bank that will take quite some time to change temperature. You may want to put a thermomenter inside your battery some cold morning to verify this experimentally.
Sometimes we engineering types can get too wrapped up in theoretical, rather than empirical, data (just ask my poor wife who has to live with me). It's fun, but managing all the variables can become a "challenge" at times. So I would respectfully suggest that you consider getting a solar panel (or more) and just give it a try. You will either be surprised at how well it works...or you will confirm your analysis. Either way, the proof really is "in the pudding". You could mount the panel(s) so they could be easly moved to a different rig should you wish to in the future. Based on the size of your battery bank, and my guess on the way you like to do things (the right way...like me), you may want to spring for a controller that can handle 600 to 800 watts so you have room for expansion if desired. I am, of course, assuming you have sufficient roof area for the panels(s).
Something to keep in mind is that, while it may get to the 20's for a few hours, does it stay that way long enough to impact the batteries? I don't really know your climate that well (lived near the beach when in So CA) but suspect it dosn't because you have so much thermal mass in your battery bank that will take quite some time to change temperature. You may want to put a thermomenter inside your battery some cold morning to verify this experimentally.
Fun indeed! I suspect you are right here because when I took the 1.3 reading, the batteries felt really cold so I wonder if that really is a new baseline. I am planning to buy an IR thermometer sometime but that test will have to wait till next winter. We only get a couple of months of that kind of temperature (lows in the mid 40's currently). And to answer your question about temp, typically during the coldest part of winter, the temp will drop to near freezing around 10 pm and be in the 20's before we wake up. By 8am it will be above freezing.
I won't buy a large solar setup for the way we camp. We're weekend warriors (3-4 days tops) and it's just not necessary. Batteries take care of everything we do with room to spare. If we were half or full timing off grid or even taking longer trips more often, then I'd definitely do at least that much. We can do at least mid 400W and possibly up to 700W (three 230W panels).
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I do live in SoCal but I live in the higher elevation desert that gets into the 20's at night in the winter so battery freezing is an issue.
