# off grid battery question



## smaj100 (Oct 17, 2012)

I know this is a much debated topic. I am looking for suggestions from a practical standpoint. I have a small wind turbine that will provide power to a remote shack. 

My question is my local farm store has some giant tractor batteries that are similar in price to marine/deep cycle batteries. I am planning on 2-4 in parrallel initially and eventually expanding to an off grid system in the house. The tractor batts are 1000 cca where the marine ones are 550-650 cca, group 27. Are these apples-apples or different critters?


Thanks


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## forluvofsmoke (Jan 27, 2012)

Dedicated cranking batteries are not a good choice for long-term energy needs. They will fail prematurely, as they are not designed or intended for that type of service. They are designed to throw out massive amounts of energy for a very short duration, then, be recharged in a very short time.

Deep cycle batteries will handle the rigorous discharge and recharge cycling much better over long time periods than cranking batteries...this is what they're designed for...lower current draw over long time periods and slower recharge rates, which is typically what will be found with off-grid systems.


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## Viking (Mar 16, 2009)

For about six years we've been using four 225 amp hour 6 volt golf cart batteries in a series/parallel connection for total of 12 volts and 450 ah in our motorhome. This set up is charged by four 100 watt solar panels and has performed far better than I had expected. Just last summer I finally replaced all four batteries as I had added two new batteries to the existing batteries which were already a number of years old. Actually the two I had added were still working good but I wanted to have all batteries fresh. A lot of people say that AGM batteries are the best as they are sealed and will not seep acid while charging but they are far more expensive, I only paid about $80 each for the golf cart batteries at Costco. As for seeping I just mount them in a heavy duty poly battery box that I installed hose drains for any seepage to go on the ground. I have enough trust in these batteries that I'm going to use them on a solar system for our home that will be used as a backup or even off grid if needs be. That being said I may check into a forklift battery as sometimes they can be picked up reconditioned at a decent price, not fun to move them around but they sure have a lot of amp hours of power.


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## seanallen (Nov 13, 2012)

@Viking: whatever you do make sure the batteries are good quality. I recently had to re-wire a guys house that had burned. He had installed a solar set up, and instead of getting good batteries he bought cheapo rebuilt automotive types. Wound up costing him a small fortune when one of them blew up and torched his house. Insurance wouldnt pay off because he didnt use a licensed contractor or the proper components. I would strongly suggest keeping the battery bank isolated from your house.


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## Viking (Mar 16, 2009)

seanallen said:


> @Viking: whatever you do make sure the batteries are good quality. I recently had to re-wire a guys house that had burned. He had installed a solar set up, and instead of getting good batteries he bought cheapo rebuilt automotive types. Wound up costing him a small fortune when one of them blew up and torched his house. Insurance wouldnt pay off because he didnt use a licensed contractor or the proper components. I would strongly suggest keeping the battery bank isolated from your house.


The Costco batteries are of excellent quality, it's just that the last set I bought was from a major battery company that charges about $20 more each for the exact same battery only with their label on them. The battery bank will be isolated in fireproof container. I had a electrical license years ago and use the Code book for any wiring I do. I worked for Square "D" Electrical Company building electrical control systems and buss work and with that background I tend to overbuild things and so if anything goes it will be a fuse or a breaker. My wiring is at code or better because I value what I've built. And yes I've seen batteries explode, it's amazing how powerful hydrogen gas is for such a small area that's in the top of the cells when it blows.


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## Viking (Mar 16, 2009)

As to heavy duty high amp hour batteries like are in our motorhome, I have great respect for their power and in using hand tools around them I use absolute caution. There is probably enough power in them to be able to weld pretty thick steel, just don't want it to be a wrench in my hand.


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## seanallen (Nov 13, 2012)

Im glad to hear that!! I love Square D products. Its the only brand i install in my new construction contracts.


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## cowboyhermit (Nov 10, 2012)

First things first, CCA is meaningless for your purposes, unfortunately auto type batteries are often not measured in amp hours which is what you need. If you are comparing 6 volt versus 12 remember that a 6 volt battery will have 1/2 the power with the same amperage ([email protected][email protected])
Sometimes they will have a "reserve capacity" listed and you might be able to compare that way.
With a deep cycle battery you are able to use more of the power without shortening the lifespan considerably so you have to factor that in as well.
All that being said many have had good luck with large "tractor batteries" I have personally converted our tractors and heavy machinery to use regular automotive types instead due to high failure rates and price.
If I couldn't justify the cost of agm I would stick to marine deep cycle or low to moderate cca automotive batteries (not recommending the automotive batteries unless you have a really reliable brand with a reasonable price like I have here)


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## cowboyhermit (Nov 10, 2012)

Sorry, am scatterbrained atm. What I was trying to say is that batteries designed to have high cranking amps are built very differently from ones designed for long slow cycles. High CCA batteries are often the worst for deep cycle.


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## smaj100 (Oct 17, 2012)

They did have golf cart batteries available for the same price as the marine/deep cycle batteries. I'm gonna have to consider locating the batteries outside. I don't need the shack burning down, especially since we aren't there all the time or close by...


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## cowboyhermit (Nov 10, 2012)

I have charged all kinds of batteries over the years from cheapo to agm and gel, have used manual chargers, vehicles, every way you can charge, even had someone hot swap a battery in a truck and put on clamps with reverse polarity. I just took a box full of batteries in to scrap ($1000) this summer, many were cracked, bulged etc.
Never in all that experience have I had a battery explode or come close to causing a fire. If I use an enclosure it is metal and vented so risk is very low, have used plastic on machines where fire was not a concern.
That being said I don't like batteries in the house, even though it gets -40 here all the time, just easier outside in an enclosure or shed.


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## Viking (Mar 16, 2009)

smaj100 said:


> They did have golf cart batteries available for the same price as the marine/deep cycle batteries. I'm gonna have to consider locating the batteries outside. I don't need the shack burning down, especially since we aren't there all the time or close by...


Over the years I've used marine/deep cycle batteries, mainly on our travel trailer, but they really didn't hold up well to deep discharges. From what I've read on them is that they are the happy medium between real deep cycle batteries and high amp cranking batteries. People often use them for electric trolling motors and they seem to do pretty good, but for off grid batteries one really needs to use high amp hour deep cycle batteries. Some of the GC-6 golf cart batteries are now rated at 230+ amp hour. If you don't know about amp hour rating all that it means is that a 230 amp hour battery will supply a 1 amp draw on it for 230 hours. These batteries have a lot of lead in them and weigh close to 70 lbs.


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## cowboyhermit (Nov 10, 2012)

Sorry to mention again but to avoid confusion because most people are used to 12v, the batteries Viking mentioned would be equivalent to a 115Ah 12V battery.


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## Viking (Mar 16, 2009)

cowboyhermit said:


> Sorry to mention again but to avoid confusion because most people are used to 12v, the batteries Viking mentioned would be equivalent to a 115Ah 12V battery.


I have to respectfully disagree here as I believe you are thinking of Ohms Law where amperage drops as voltage rises. In the case of amp hour ratings two 6 volt 225 ah batteries in series will produce 225 ah of usage time. Go to: www.wholesalesolar.com and look at the Battery Banks page.


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## zombieresponder (Aug 20, 2012)

Viking said:


> As to heavy duty high amp hour batteries like are in our motorhome, I have great respect for their power and in using hand tools around them I use absolute caution. There is probably enough power in them to be able to weld pretty thick steel, just don't want it to be a wrench in my hand.


A typical automotive starting battery has plenty of power to use for welding. Many, many trail fixes have been made on broken 4x4's with the battery, jumper cables, and some welding rods. The downside is the risk of battery explosion and no ability to control the current.


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## zombieresponder (Aug 20, 2012)

Viking said:


> I have to respectfully disagree here as I believe you are thinking of Ohms Law where amperage drops as voltage rises. In the case of amp hour ratings two 6 volt 225 ah batteries in series will produce 225 ah of usage time. Go to: www.wholesalesolar.com and look at the Battery Banks page.


This is correct. Wiring in parallel would give 450AH, but only 6V. Wiring in series doubles the voltage, but the effective capacity is unchanged.


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## cowboyhermit (Nov 10, 2012)

Sorry Viking but I don't believe I made any error.
[email protected][email protected]
It is easier if you convert to Wh, watts =current(amps)xvoltage


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## cowboyhermit (Nov 10, 2012)

Tried to find a concise explanation but the best I could find is this
http://techreport.com/forums/viewtopic.php?f=13&t=70203

http://www.wind-sun.com/ForumVB/showthread.php?15989-Battery-System-Voltages-and-equivalent-powersecond post down


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## Viking (Mar 16, 2009)

Go to: www.wholesalesolar.com click on Batteries in the right hand column, when this page comes up click on Battery Banks in the Batteries: Revelant Topics column. This page shows a list of battery combinations, the middle column with the blue lettering shows batteries needed to produce voltages and amp hours. I had to understand this to size my battery system for enough time for use each day. Amp hour ratings are based on how many hours a given battery will operate at a discharge rate of one amp per hour so no matter how many 6 volt 225 amp hour batteries are in series each battery will give 225 hours discharge at one amp. Now if this same battery gave a potential of 100 amps, then two in series the amps would be 50 at 12 volts, four in series 25 amps at 24 volts. Now if these batteries are paralleled the amp hour rating multiplies as Zombieresponder has mentioned. My system of four 6 volt 225 ah batteries are series/parallel and produce 12 volts and 450 amp hour. By the way this amp hour rating is to the usable voltage range, which is 10.5 volts where the inverter on the motorhome will automatically drop off line. Any lower than that cut off and the batteries won't get enough solar charging the next day for usage that evening. Amp potential and amp hours are two different things as one can have a high Cold Cranking Amp battery but it may not produce a very high amp hour potential due to plate design. No or low maintenance batteries have very poor amp hour ratings because the plates are made with calcium and in fact there are warnings of melting them for fishing weights or bullets due to very toxic gases that can form from high heats.


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## Viking (Mar 16, 2009)

Actually Cariboocoot on the Wind-Solar Forum explained it as I have.


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## cowboyhermit (Nov 10, 2012)

Sorry Viking, checked out the site you mentioned but I don't think it says what you think it does, or it is incorrect.

The amount of "energy" in one amp is proportional to it's voltage.
This means 1amp at 12V has the same "energy" as 2amps at 6 volts.

The best way to compare the amount of energy stored in a battery is to calculate the watt hours(Wh). To do this you multiply the amp hours by the voltage. If you do this it should quickly become apparent that a 200Ah 6V (1200Wh) battery equals a 100Ah 12V (1200Wh) battery in terms of total energy stored.

Maybe someone else can explain in a way that is more clear.


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## cowboyhermit (Nov 10, 2012)

Viking said:


> Actually Cariboocoot on the Wind-Solar Forum explained it as I have.


He did not, notice he says 2 6V 200Ah batteries=2 12V 100Ah batteries.

"Two 6 Volt 200 Amp hour batteries in series:
200 Amp hours @ 12 Volts.
One battery interconnection.
Even current flow through both batteries.
Six cells to check.

Two 12 Volt 100 Amp hour batteries in parallel:
200 Amp hours @ 12 Volts."


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## Viking (Mar 16, 2009)

Viking said:


> I have to respectfully disagree here as I believe you are thinking of Ohms Law where amperage drops as voltage rises. In the case of amp hour ratings two 6 volt 225 ah batteries in series will produce 225 ah of usage time. Go to: www.wholesalesolar.com and look at the Battery Banks page.


The only thing I should have said is that two 6 volt 225 ah batteries in series give you 12 volts and have 225 ah. I have four 6 volt 225 ah batteries that are tied two each in series then connected parallel giving me 12 volts and 450 ah. I have been considering adding two more series connected 6 volts to parallel my existing set which would provide 675 amp hours. I would also have to add another 100 watt solar panel to boost the charge rate for handling the extra batteries. I was talking about 6 volt batteries and not 12 volt batteries, if I was to use 12 batteries I would be hooking them up in parallel and I would have needed four 100 ah batteries to come close to the 450 amp hours I presently have. It may be that I've confused the issue by saying series/parallel connection.


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## cowboyhermit (Nov 10, 2012)

Viking, your last post makes perfect sense. The reason I have been harping on this is because I have seen MANY people confused by the difference in voltage. On the surface it looks like the 6V batteries have twice the energy when in fact they are equivalent. There are other reasons some prefer 6V batteries as well I just want people to be informed when they make a purchase. The fact that is so hard to find a clear explanation of the equivalence online is part of the problem. The solution is to convert to Wh and many batteries are marked this way but many lead acid batteries don't even have the Ah listed, then there is the fact of whether Ah is measured at C/20 or C/100
Am glad we could reach a consensus though 

I found a better explanation after the fact for anyone interested.
http://www.cleanenergybrands.com/shoppingcart/categories/Deep-Cycle-Batteries/%252d-Commercial-%26-Industrial/%252d-Flooded-Electrolyte-Batteries/

"Deciphering Capacity Specifications

Deep-cycle battery capacity is rated in amp-hours (Ah). The power equation dictates the relationship between amps, volts, and watts: A × V = W. When you add in the time factor for figuring energy capacity, the same holds true for the relationship between Ah and Wh: Ah × V = Wh.

To compare the energy capacity of batteries of different voltages, it's easiest to convert to Wh. For example, a 250 Ah,6 V battery has half the capacity of a 250 Ah, 12 V battery.

6 V × 250 Ah = 1,500 Wh
12 V × 250 Ah = 3,000 Wh"


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## cnsper (Sep 20, 2012)

Automotive batteries work fine for solar and wind applications but there is also a trick to it all. Never let the batteries get below 50% before you recharge them. If you do they will fail quickly. I have some that are 5 years old and still cranking. Other people will have them fail in less than a year because they discharge them too much.


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## Viking (Mar 16, 2009)

cnsper said:


> Automotive batteries work fine for solar and wind applications but there is also a trick to it all. Never let the batteries get below 50% before you recharge them. If you do they will fail quickly. I have some that are 5 years old and still cranking. Other people will have them fail in less than a year because they discharge them too much.


The manual that I got with our inverter-charger mentions discharges by 20% as being considered the optimal level for long battery life but says 50% discharges to be considered a realistic trade off between battery cost/life. Of course the greater the total amp hours one can have then it becomes easier to come closer to that 20% level.


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## Wellrounded (Sep 25, 2011)

cnsper said:


> Automotive batteries work fine for solar and wind applications but there is also a trick to it all. Never let the batteries get below 50% before you recharge them. If you do they will fail quickly. I have some that are 5 years old and still cranking. Other people will have them fail in less than a year because they discharge them too much.


We have been sourcing automotive batteries for our solar setup. Get them free from the local auto electrician, we check through all the batteries he has out the back for recycling and usually find 3 or 4 that are fine out of a pallet full. It's amazing how often they put in a new battery when it's not needed. There is no way we could afford a new battery bank, so for us automotive and a bit more TLC works well.


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## Boomy (Mar 17, 2012)

Wellrounded said:


> We have been sourcing automotive batteries for our solar setup. Get them free from the local auto electrician, we check through all the batteries he has out the back for recycling and usually find 3 or 4 that are fine out of a pallet full. It's amazing how often they put in a new battery when it's not needed. There is no way we could afford a new battery bank, so for us automotive and a bit more TLC works well.


My local Interstate Battery store sells recons for like $60. Bring in any size of auto battery for the exchange. So a tiny Toyota battery in exchange for a big 'old truck battery. Any size, same price...


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