Help on battery choice

[palmsandpines]

It looks like I will need two 12v 150 amp batteries that I will wire in series for a small 400 amp system. I would like to know a few options (brands) that would meet these requirements. Thanks for your thoughts!

[Sunking]

You have a whole lot of homework to do because you really have no idea what you are doing or know anything about batteries. Two 12-volt 150 AH batteries wired in series is 24 volts, but is only 150 AH. I have no clue how you came up with 400 AH. Secondly if you really need 24 volts @ 400 AH you would not use 12-volt batteries. Well you could like most people do trapped inside a 12 volt box.

My gut says you really do not know what you want or need. So you had best do a lot of homework, or else you will loose a lot of money. If you do your homework and find out what it really takes, you will likely decide it is not a very good idea. 99% of folks who come here grossly underestimate what it really takes. Many by a factor of 10 meaning they spent $1000 and find out it takes $10,000 and discover they lost $1000. FWIW a 24 volt 400 AH battery is going to cost over $1000. Example 4 of these batteries will cost $1344 plus shipping charges on 600 pounds of toxic material. Keep in mind you will need to replace then in 2 years or less. Once you learn how to care for them your second set might last up to 5 years.

Does that get your attention?

[palmsandpines]

Well a neighbor (electrician) and I worked this out, but maybe very wrong from what you are saying. I have a Grape 400 Watt system (very small). I'm looking to supply a Dometic CFX-35US fridge. My thoughts were to operate my system on 24v to decrease the size of the wiring needs, so that is why I said in series. So for someone with little knowledge, how best to proceed on answering the questions, calculations and homework? There must be already built schematics for this simple system as there has to be hundreds or thousands out there.

[Sunking]

Start by reading stickies. Do not make the mistake of buying something before you know what is required. All components must be matched and made to work together, You have no idea if 400 watts of panels are enough or not. What I can tel you is a 400 watt panel locked you into a 24 volt 500 watt Inverter and a battery no larger than 175 AH that will give you around 1 Kwh per day usable. Neither you or I have any idea if that will work or not. My experience and educated guess it is not enough. .

Off Grid Design
Battery Tutorial
Inverter Tutorial and the rest of the stickies in the Off-Grid section. Once you read all of them should answer most of your questions including the most important question you should be askingg yourself: Do you really want to do this now that you know what it takes.

[John Galt 1]

Since the Dometic CFX-35US appears to be a high quality thermo-electric cooler that draws about 85 watts when cycling and doesn't have any start up surge beyond the fam motor you're inverter looks ok if you want to run it off of 120v but I think that cooler can also run off of 12v and 24v DC so you really don't need the inverter.

I'd suggest a little more than a 300-400 amp hr battery if you plan to run it for more than 36 hrs in very hot weather. At this point we don't know how much it will be cycling so it my run for a week in cooler weather with the small battery but only go for a day to two in hot weather.

150 amp 12v batteries are rare and very heavy. You'd probably be happier with four 6v batteries.. As far as what brand and type (lead acid vs AGM) you could spend as little as $500 and as much as $2000. How mobile do you want to be and what is your budget? Also how long do you want this cooler to run during warm weather?

[Sunking]

Please accept my apology and delay. Took me a while to find the specs on your fridge. Is this the fridge? If that is the unit, what you have proposed should work just fine and good to go.. .

Would you be interested in solar electric thermal Tumblers to go with your ice chest. They will keep your drinks hot of cold. They start at $1000. Just let me know if you are interested, I have them and ready to ship. Just call 1-800-Dum-Bass and ask for Dan. If Dan is not available ask for either Ben Dover, Dewey, Cheetum. & Howe

[Amy@altE]

This is probably the math your electrician did. At 24V, that draws 3.2A. 24V x 3.2A = 76.8W. The tricky thing to figure out is how frequently it runs. Is it always drawing 78W, or does it cycle like your fridge at home. Guessing it running 50% of the time (and guessing is very dangerous when calculating for solar, you need to know for sure, but I'm just guessing for this example), 76.8W v 12 hours = 921.6 watt hours (Wh). I don't know where you are, so another dangerous guess, says 4 sun hours, assuming (also dangerous, wow, I'm living on the edge today) you are not running it in the dead of a cold winter, where ever you are. The 400W panel x 4 sun hours x .6 losses = 960Wh. So, that's just barely enough, if all of my guesses are right. For battery bank, 922Wh x 3 days without sun x 1.3 temperature compensation (again, guessing) x 2 (50% DoD) / 24V = 300Ah, 24V. So the battery bank the electrician suggested is half the size needed, unless they didn't figure on any days without sunshine, as they had 24V 150Ah.

You would be better off spending a little bit more money for a more efficient fridge that is designed to be run off solar, like a Sundanzer DCR50 50 liter fridge. It only needs 114Wh a day, a fraction of the one you are looking at. www.altestore.com/store/refri...gerator-p7189/

[palmsandpines]

John, Amy and Sunking, Thank for your replies and helpful info. I'm very much a novice at this and as Sunking said, I don't want to make expensive mistakes. The goal would be to run the fridge for 24 hours a day for up to a month. So, what I'm trying to do is to generate enough power to charge the batteries for nighttime discharge and charge and run the fridge during the day. I don't expect it to run all of the time; I expect it to cycle as needed. Sunking that would be the fridge and I don't know anything about "tumblers" and will need to research. Amy I will look at another fridge. We live 40 miles out of Seattle so we do get our share of cloud cover. I have not bought a fridge yet or batteries, but I do have the 400 amp Grape system. Thanks again!

[Sunking]

Palm the devil is in the details. I am trying to get your attention so you do not get ripped off. Dude spending $500 on a Ice Chest and powering it with Solar battery is being gang raped. $500 will buy a quality ice chest and a whole lot of ice. If you fully discharge the battery at night, will destroy the battery in a few short months.

The tumbler was a joke to make you think about what you are doing. A Tumbler is an insulated large cup you buy at any five and dime store for $2.

[Amy@altE]

Do try to keep the terms straight to avoid confusion. The Grape is 400 watts, not amps.

The SunDanzer fridge uses 114Wh a day (in 90F temps, so it will use less most days). Your 400W solar array can generate, worst case with 1.6 sun hours in Seattle in the winter 384Wh. So you have 3x more solar than needed. (400W x 4.48 x .6 = 1075Wh in the summer). 114Wh x 3 days x 1.3 temp x 2 / 24V = 38Ah 24V battery bank. Compare that with the fridge you are looking at. By spending $100 more on a good fridge, you save hundreds on your battery bank. And you could have gone with a much smaller solar array, but that ship has sailed.

The 400W solar array can send 16A to the battery, if you want an optimal charge rate of C/10, that's 160Ah, which may be where your electrician got that battery size. If you don't use all of your solar panels, you could go with a smaller battery bank. Or if you do use all of the solar, and the 160Ah battery bank, you can use the system for more than the fridge.

[PNPmacnab]

I don't really believe those Sundanzer numbers at all. True if you never take food in or out. You'll get tired of that small fridge rather soon. I run a 7CF freezer as a fridge. It was never said what the actual use for this is.

[Sunking]

I don't really believe those Sundanzer numbers at all. True if you never take food in or out. You'll get tired of that small fridge rather soon. I run a 7CF freezer as a fridge. It was never said what the actual use for this is.

All appliance energy ratings are make believe dreamed up in lab conditions. Like MPG your mileage may vary unless you are 80 years or older and still allowed to drive on Sundays only on the way home from church. That is why they say ESTIMATED.

[Amy@altE]

If you look at the "fridge" he was looking at getting, it is a cooler. A chest fridge is at least as useful, and opening the top as opposed to a door will limit the cold air loss when opening.

[PNPmacnab]

I live with a chest fridge, do you?. You still loose some cold, it always starts up after lifting the lid. You are still taking food out and putting it in and that takes energy. It is easy to believe numbers till you actually try it. Their numbers are crap.

[Amy@altE]

I live with a chest fridge, do you?.

Just for my kegorator, you know, the important stuff . Of course it is not opened much, just to change the kegs, so totally different animal. But again, he's currently looking to power a 25" x 16" x 16" cooler, so I'm not proposing something radically different from what he's looking at. If that's what he's looking at, I'm guessing this is not a full time situation. I have a friend living in a yurt who has that small Sunfrost model, I'll check with him if he's been able to measure actual usage.