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395ah batteries to light a shop

 
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Hello,
I live off grid in middle tn. I recently upgraded my flooded lead acid batteries to lithium because I thought the old ones had died after 5 years of use. Turns out only 1 of them died and it was taking down the whole string. I would like to put 2 6 volt 395 ah batteries together to provide lights in a shop. I know I will need 1 or 2 solar panels, a charge controller and an inverter or 12 volt lights. My worry is the 395 ah rating of the batteries. will this be to much just to run some led lights? What size wire should I use coming off of the batteries. I used 2.0 wire when they were powering a house but this seems overkill for lights. But I dont want to burn out the lights with to much power. Any advise would be great.

Thanks
 
pollinator
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Do a bit of research across the internet, you will be amazed at what information is out there.
Try;
- How many lights for a building sized xxxx  xxx
- how long will LED lights run with 395aH batteries?
- What cable sizes are best with 12V?
You cannot burn out globes with too much power, they will only draw what the globe needs.
BUT, you can burn out the wire if its not large enough, or have lights running dull for the same reason.
LED globes use very little power, so overloading may not be an issue.
 
Rocket Scientist
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Hi Troy; Big Welcome to Permies!
I've been 100% off grid since 1983.
A pair of L-16 battery's is plenty to use in your shop. A pair of 150 watt panels a  charge control and a smaller pure sine wave inverter are all you will need.
You can not overpower anything with 12 volt, unless it is a 6 volt item.
Here is the thing. Right now you would like some light in your shop.  Soon... since its lit up in there... you will want to plug something else in.
So, I recommend that you wire your shop with lights and outlets just like you were hooked up to the street power.
A small breaker box for your A/C use.  Your panels only need light wire, the battery's need the same heavy wire you used in the house to connect to the inverter.  The inverter to the breaker box can be much smaller.
This way your shop is set up, to just plug in standard work tools. No need for expensive 12 vt tools.

I know you  have these battery's left over and just want to use them.  
I assure you that if you do as I suggested and make your shop 110vt you will be much happier 20 years down the road and it helps for resale later if you go to move.
solar-hydro.JPG
[Thumbnail for solar-hydro.JPG]
 
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Troy Smiddy wrote:Hello,
I live off grid in middle tn. I recently upgraded my flooded lead acid batteries to lithium because I thought the old ones had died after 5 years of use. Turns out only 1 of them died and it was taking down the whole string. I would like to put 2 6 volt 395 ah batteries together to provide lights in a shop. I know I will need 1 or 2 solar panels, a charge controller and an inverter or 12 volt lights. My worry is the 395 ah rating of the batteries. will this be to much just to run some led lights? What size wire should I use coming off of the batteries. I used 2.0 wire when they were powering a house but this seems overkill for lights. But I dont want to burn out the lights with to much power. Any advise would be great.

Thanks



The size of the battery bank does not matter as much as how much you are going to discharge them between recharging. ah, won't burn out lights, over-voltage will. I would imagine you are going to need several led light strips which will add up in wattage, if 1 light strip is 100w it will draw 10amps per hour through an inverter, so try to get lights that run off 12vdc directly and use a buck converter to limit voltage to 12vdc. Depending on what you want to bring your battery capacity down to before recharging will determine how long you will be able to run the lights, and not ruin your batteries, let say you did not want to discharge past 70% then you are only really using 115ah of that 395 capacity, but you will need panels that can recharge that 115amps back into the battery in a reasonable amount of time during the day. You will need a few hundred watts of solar panels to recharge the 115ah used within approximately 5-8 sun hours.
 
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One way to look at this is how many watts of panels will you need to make all the power you consume.
Another way to look at this is how many watts of panels will you need to keep your batteries happy.

Though related, they will not be exactly the same value.

I tend to think batteries are your single most expensive component, so you should scale your system to how to keep the batteries healthy.  As a general rule of thumb, you want to charge at a certain rate related to the capacity of your battery.  Those would be....

A low rate of 1/20 of C or 0.05C.  At 12V that works out to be  395Ah X 0.05C X 13V charging X 1.2 fudgefactor = 308W.  Call that 1 300W panel.  This rate may or may not keep up with demand.  Expect it to take two days for a full charge.

A medium rate of 1/10 of C or 0.1C.  At 12V that works out to be  395Ah X 0.1C X 13V charging X 1.2 fudgefactor = 616W.  Call that 2 300W panels.   This rate may keep your batteries fully charged every day.

A high rate of 1/8 of C or 0.125C.  At 12V that works out to be  395Ah X 0.125C X 13V charging X 1.2 fudgefactor = 770W.  Call that 3 260W panels.  This rate will charge fast, and still provide a bit of power on less than optimal days, when there's some cloud cover.

You can get cheap 250W grid-tie panels now in the range of 50-55$ per panel, so there is no good reason anymore to not try to maximize your wattage.  With a good MPPT controller, you could wire three 30V panels in series to feed the controller, which will transform the raw high solar voltage down to the 13-14V your batteries need to charge.  I personally would go with the third 1/8C option.
 
pollinator
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I would recommend this tool ->  

https://www.ebay.com/itm/203274121451?epid=9019357854&hash=item2f5414f0eb:g:aeAAAOSwxCVgItdJ

It helps to get an idea of how much power various items pull,   and helps to know how much storage you need.

I would advise on your lithium batteries, to not charge them when it is freezing, as it can destroy the batteries, if they are kept warm then they are ok.

I am on the verge of going off grid  I have had my power shut off for about 2 weeks now,  only thing left is my dryer, and I am getting close to having a solution for that.

Has been years getting here, but very close now.

Also note there are useful tools on the web that help you to figure out capacity of what you  need.      Also be aware of where your inverter will cut off at lowest voltage.

https://www.batterystuff.com/kb/tools/solar-calculator.html

 
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