Off grid battery charging for small mine

[Crab_Cake]

I am planning a mining expedition to a very remote region of Idaho. I will probably be staying there the whole summer and am going to build a cabin to run off of solar. The mine is at about 6000 feet and it is very sunny there the whole summer. Winter isn't an issue as I will be back home in Washington.

Here is a rough list of what I would like to run:

• Some 12v LED light bulbs
• A charger for Nintendo DS, Sony PSP, walkie talkies, and my iphone (for GPS)
• CPAP device. It will run for about 7 hours per night and take about use about 7ah per night.
• A 30ah battery that powers a piece of mining equipment will have to be recharged every other day or so.

I was thinking of getting 3 or 4 deep cycle 35ah batteries. Whats the minimum solar watts that I would need to keep these batteries charged? Thanks for the info!

[Mike90250]

You are going to have to measure the rest of your loads, before we can begin to calculate what you need to charge them.

I think you are better off, for a summer, to get 6v golf cart batteries, wired in series, to create a 200AH 12V bank (2, 6V 200ah batteries) 30 ah batteries are handy to carry around, but don't really store much.

First guess, erring on the safe side, would be at least 300w of panels. Maybe 400. just to keep it all charged up. Don't want the cpap to fade out at midnight !

And you are facing double losses, charging your main batteries, and then charging the little ones, so that adds another 20% or so.

[Crab_Cake]

You are going to have to measure the rest of your loads, before we can begin to calculate what you need to charge them.

I think you are better off, for a summer, to get 6v golf cart batteries, wired in series, to create a 200AH 12V bank (2, 6V 200ah batteries) 30 ah batteries are handy to carry around, but don't really store much.

First guess, erring on the safe side, would be at least 300w of panels. Maybe 400. just to keep it all charged up. Don't want the cpap to fade out at midnight !

And you are facing double losses, charging your main batteries, and then charging the little ones, so that adds another 20% or so.

Really?

I must not be understanding this correctly.

This kit right here is a 60watt and 4 amp unit. http://www.amazon.com/Sunforce-50048...2636031&sr=8-1

Lets say it produces 3.5 amps, wouldn't that charge a 30ah battery in like 10 hours? Lets say that I use an average of 15ah per day. Are that many watts really required?

I can spend about $500 tops on solar equipement. I don't need any AC power, it just has to keep those batteries charged.

[Bala]

Really?

I must not be understanding this correctly.

You are correct, you do not realize that by the time you account for actual panel output, (not what the specs say), and losses from the charge controller, that size panel array would basically just keep good batteries charged if they were under no load.

On the positive side you have come here before you purchased so as mike suggested you need you need to work out your real loads if you want real advice on a system that will supply you what you want.

I mayhave to rethink your $500 budget if you want a system that will work for the summer. not just the first week or two.

[TnAndy]

Really?


Lets say it produces 3.5 amps, wouldn't that charge a 30ah battery in like 10 hours? Lets say that I use an average of 15ah per day. Are that many watts really required?

It will produce that 3.5 amps for maybe 2 hours out of a day.....maybe......morning and afternoon are going to vary from nothing on one end up to about that 3.5 around noon, and then back to nothing on the far end of the day. Just because it's daylight doesn't mean you get solar power.

You're also not allowing any for cloudy, rainy conditions. Sun may shine a LOT there in the summer, but you will get some crappy solar days too. You have to allow for that as well.

I'd go 100w per battery, minimum.

[Wy_White_Wolf]

I....[*]CPAP device. It will run for about 7 hours per night and take about use about 7ah per night....

I think you may need to recalculate this. My BIL's CPAP takes 1.5 amps at 120volts. Over seven hours that would be 1260 watthours or 105AH on a 12v battery bank. You will need a much bigger system than people are talking about. Figure at least a 750AH @12v battery bank and @500 watts in array just to handle it. Propably need to increase that by at least 50% to handle everything else.

WWW

[Mike90250]

... wouldn't that charge a 30ah battery in like 10 hours? ...

Almost, there are system losses you have not accounted for, and that 10 hours will occur over at least 2 days, even assuming 5 good solar hours per day...
See chart below, only 3 good hours of production, the rest of the day has little energy. If you re-aimed your panels 3x a day, you could get a bit more. Solar power is NOT very dense.
SGV_3.8.jpg

[Sunking]

I agree with WWW, my wife's CRAP uses 120 VAC @ 1.5 amps also. If ran for 8 hours per night uses 120 volts x 1.5 amps x 8 hours = 1440 watt hours. To generate that much energy with solar in Idaho summer insolation of 6.3 hours with system losses added in would take 450 watts of solar panels. In addition would take about 475 pound battery or 600 Amp Hours @ 12 volts. That is only for the CRAP machine and nothing else.

We are not trying to scare you off, but we seriously think you have grossly underestimated your true needs, and overestimated what solar can do. Secondly if having electric power is critical, you are also going to need a generator and AC battery charger. Otherwise if you get a cloudy day or two you will have to shut down and go dark and wait until you have had a couple of sunny days to recharge.

[Mike90250]

re:CPAP power consumption

For camping use, I had to calculate my Respironics nightly usage. I used a kill-a-watt for 8 days, and averaged about 75 WH nightly

At 12V that's 6.25 Ah {zipped spreadsheet attached}

I ended up getting a mid-size automotive jump start pack [my review @ amazon] , with no air compressor, and I figure I'm taking it's the 18ah internal battery, down 30 or 40%. I only run 1 night, and then recharge it. (how can they claim 450 amps from a 18ah battery? - it's the peak power just before it melts)

[s.xavier]

The small little kit works for small applications and small loads. Once you take into account different loads, the system will not work for what it is you are doing... I'm also sure if you are going into a mine 6000 ft and running out of power would be a bad idea Spend a few extra dollars and buy something in the range of 400w- 500w for a solar powered system. A good place to start is to spec out and compare the price & performance of solar modules which will make sense for your budget and provide enough power to power what it is you are doing.

Mike is right, you will need probably 300w and above. Always evaluate what you need and the power demand rather than have your budget dictate what you need. Running out of juice out in the field is a waste of time and money (and your blood pressure rise when you go - "DOH!")

First guess, erring on the safe side, would be at least 300w of panels. Maybe 400. just to keep it all charged up. Don't want the cpap to fade out at midnight !

Really?

Lets say it produces 3.5 amps, wouldn't that charge a 30ah battery in like 10 hours? Lets say that I use an average of 15ah per day. Are that many watts really required?

I can spend about $500 tops on solar equipement. I don't need any AC power, it just has to keep those batteries charged.

[Sunking]

To pile on the $500 you mentioned on another forum is not even going to make a down payment on what you need. Try maybe $5000 or more.

One thing that strikes me as really odd is this is for a gold mine right? Wouldn't that require some fairly significant pumps to move large volumes of water?

[Crab_Cake]

I think you may need to recalculate this. My BIL's CPAP takes 1.5 amps at 120volts. Over seven hours that would be 1260 watthours or 105AH on a 12v battery bank. You will need a much bigger system than people are talking about. Figure at least a 750AH @12v battery bank and @500 watts in array just to handle it. Propably need to increase that by at least 50% to handle everything else.

WWW

http://www.cpap.com/cpap-machine/CPAP.com-Lithium-Ion-Battery-Pack.html

This site says their 6.7ah battery will run my unit without humidifier for 7 .7 hours. so I figure I will be burning around 7-8ah per night.

[Crab_Cake]

To pile on the $500 you mentioned on another forum is not even going to make a down payment on what you need. Try maybe $5000 or more.

One thing that strikes me as really odd is this is for a gold mine right? Wouldn't that require some fairly significant pumps to move large volumes of water?

Well its pretty small scale.

This is the only real powered equipment I will be using this season.

http://www.ebay.com/itm/260900650133?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_500wt_1413

Its a battery powered trommel. The seller told me a 16ah battery will power it for about 2 days. Thing is I am not going to be running it all the time. I will probably be loading up 5 gallon buckets and once I have a few filled with dirt I will then use the trommel and process them into a sluice in the river. Once thats done I will turn it off and go back to loading dirt. Probably run it for 4 hours a day at most.

The other stuff is just for convenience. The nearest town is an hour and half away so I would like some type of entertainment in the evenings if I'm by myself. Mostly lights to read books, maybe a bit of power for my nintendo DS. I can probably charge the DS and my iPhone in my truck.

So my idea was to have 3 or 4 mid-size batteries. Like 30-45ah. I would leave two batteries attached to the cabin to charge all day. Nothing would be drawing power during the day. I would use the third battery for a day or two and then swap it with one of the other batteries. Use that one for a day or two and repeat the process.

I could also increase the size of the battery bank. I was going to get a generator but after doing research I would have to run it for 6-8 hours per day to charge the batteries. I thought that solar would be a better solution but maybe I was wrong.

[Sunking]

Crab cake I hope you understand if you discharge any lead acid battery more than 50% will ruin it. For solar systems you design to only discharge a max of 20% per day for two very good reasons

1. to give you 2.5 cloudy days
2. Extend battery life for more than a year.

[Crab_Cake]

Crab cake I hope you understand if you discharge any lead acid battery more than 50% will ruin it. For solar systems you design to only discharge a max of 20% per day for two very good reasons

1. to give you 2.5 cloudy days
2. Extend battery life for more than a year.

Yah I did read that somewhere. I was hoping that deep cycle batteries could withstand the charge cycle for at least a season.

Thanks so much for this information, I really appreciate it. In your opinion what would my best bet be? I could raise my budget to about $750 max but that's about it.

I am researching other forms of power, in particular a DC generator, but they are so freaking expensive.