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Old 12-17-2017, 07:42 PM   #1
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12V 35AH Golf Cart Batteries for Solar System?

Hey there,

I'm completely new to this and it feels like I'm trying to learn another language. I could really use some help and guidance when it comes to figuring out if the setup I'm planning will be compatible.

I purchased four 100W solar panels, a 40A MPPT charge controller, a 3000W pure sine wave inverter (I'm planning to add more panels when I can afford it.)

Here's my question:Will 12V 35AH golf cart batteries work with this system, and how many would I need? I was thinking of using 6-8 of these batteries and running them parallel, but I don't even know if that would be the thing to do.

Any help is super appreciated!

Thanks!!!
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Old 12-17-2017, 07:54 PM   #2
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Originally Posted by zm1994 View Post
Hey there,

I'm completely new to this and it feels like I'm trying to learn another language. I could really use some help and guidance when it comes to figuring out if the setup I'm planning will be compatible.

I purchased four 100W solar panels, a 40A MPPT charge controller, a 3000W pure sine wave inverter (I'm planning to add more panels when I can afford it.)

Here's my question:Will 12V 35AH golf cart batteries work with this system, and how many would I need? I was thinking of using 6-8 of these batteries and running them parallel, but I don't even know if that would be the thing to do.

Any help is super appreciated!

Thanks!!!
The usual batteries people use are the 6V golf cart batteries.

Wire two in series, then the two pairs in parallel for 12V. Four of these would give you 450 Amp Hours of capacity, and last years if you can give them at least 14.8V for the bulk charge section.

http://www.trojanbattery.com/product/t-105/

The AIMS inverters will do this.
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Old 12-17-2017, 08:33 PM   #3
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Originally Posted by Twigg View Post
The usual batteries people use are the 6V golf cart batteries.

Wire two in series, then the two pairs in parallel for 12V. Four of these would give you 450 Amp Hours of capacity, and last years if you can give them at least 14.8V for the bulk charge section.

T-105 | Trojan Battery Company

The AIMS inverters will do this.
So is a single 12v worse than 2 6v? I'm also having some issues understanding amp hours, or at least my understanding is very minimal.
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Old 12-17-2017, 08:59 PM   #4
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So is a single 12v worse than 2 6v? I'm also having some issues understanding amp hours, or at least my understanding is very minimal.
2 x 6V, or multiples thereof is simply the most common arrangement.

Most 12V batteries marked "Deep Cycle" or "Leisure" are simply beefed up plates in regular starting batteries. Those Golf Cart batteries are not that. They are made for deep discharging, and they are 225 AmpHours at the 20 hour rate.

Key to using them is a charger that can deliver 14.8 volts as one of the three steps in the cycle. Actually, with temperature monitoring they will charge at up to 15.3 volts.

Chargers that are restricted to 14.4 volts will never fully charge them, even though the meter will say they are at 100%.

An Amp Hour is the supply of 1 amp for 1 hour.

You add up all of your expected usage by working out the power consumption of everything over a 24 hour period. That gives you the total number of amp hours you consume in a day.

With 4 of those batteries you have 225 amp hours to play with as you don't want them discharged below 50%.

Plug your appliance into a Kill-A-Watt device and run it normally for 24 hours. It will tell you the exact number of amp hours consumed. This is especially useful for fridges, and you will be surprised at how frugal modern domestic fridges can be.
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Old 12-18-2017, 08:25 AM   #5
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This helped me a lot. Thank you so much!
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Old 12-18-2017, 09:36 AM   #6
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There's a lot of opinions around 6v vs 12v batteries. I'd like to say that the biggest reason to go with 6v is its's easier to carry two 50 pound batteries than one 100 pound battery.

Batteries are all made of cells. Lead acid batteries use cells of about 2v each, so the primary difference between a 6v and 12v is that the 6v has 3 cells and the 12v has 6 cells.

It gets more complex beyond that. Construction differences in plates matter. If you're comparing heavy plate 6v in series to light plate 12v, the 6v is clearly a better setup. And the opposite is also true.

Connecting groups of batteries together can multiply any battery weakness. When you connect in series, you get the combines voltage of both batteries, and the lower of the amp capacity. Connecting in parallel, you get the sum of the amperage at the lower of the voltages, and your higher voltage battery will always be trying to charge the lower voltage one. Any time you group batteries together its pretty important they be equal in specifications and health.


Your typical Group 31 deep cycle at Walmart isn't going to be a good house battery. As mentioned, it's a slightly better performing start battery. As you look at better quality batteries you'll see AGM, which is preferred for these types of application. Compared to the typical wet cell batteries, they can handle higher charge and draw rates, they last much longer, are fully maintenance free without off gassing. Many of those gold cart packs will be AGM.

I went with a 200AH 12v AGM and for my usage it's plenty of capacity for my bus. All my lighting is low wattage LED, and everything is run from DC power except my freezer. I can go for several days without sunshine. It's critical that you know your power needs before you start spending money, and take any steps you can to reduce/optimize those needs (hint: avoid running anything from an inverter!)
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Old 12-18-2017, 09:47 AM   #7
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The generally-accepted wisdom on the Northern Arizona Wind & Sun forum from the solar experts there (who know much more about anything solar than I probably ever will!) is that flooded lead-acid batteries should ideally be charged at between a 5% to 13% charge rate. Anything less than 5% and you run the risk of long-term deficit charging that will eventually kill the batteries due to plate sulfation. Anything over 13% will boil the batteries dry, or worse. So, first thing you should do is calculate all your loads, and that will tell you how much battery capacity you'll need, then using the 5-13% rule you can calculate how much PV is needed. The NAWS forum has plenty of good threads to read about this. (Or just do what I did - carpet the whole roof with as many solar panels that fit! Fortunately 2kW of panels just happens to charge eight golfcart batteries at the upper end of the 5-13% range. I'll probably have more power than I'll need for most of the year, but that's OK.)

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Old 12-18-2017, 09:59 AM   #8
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Lots of panels is great if you're relatively stationary and can be in full sun at all times. If you're mobile, dealing with at least partial shading will dive your power fast. Even s splatter of bird poop on a panel can have a serious effect on your generating ability.

Since they're a bunch of cells connected in groups, you have the same caveats as with batteries.. In series you get the sum of volts at the lowest amps. In parallel you get the sum of amps at the lowest voltage.

If you take a typical panel like the Renogy 100W Mono panels I use, they have 36 cells per panel. The panels themselves use a combination of series and parallel groupings, and then connecting panels together does one or the other or both. Shading a single cell is a big deal.
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Old 12-18-2017, 11:12 AM   #9
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Lots of panels is great if you're relatively stationary and can be in full sun at all times. If you're mobile, dealing with at least partial shading will dive your power fast. Even s splatter of bird poop on a panel can have a serious effect on your generating ability.

Since they're a bunch of cells connected in groups, you have the same caveats as with batteries.. In series you get the sum of volts at the lowest amps. In parallel you get the sum of amps at the lowest voltage.

If you take a typical panel like the Renogy 100W Mono panels I use, they have 36 cells per panel. The panels themselves use a combination of series and parallel groupings, and then connecting panels together does one or the other or both. Shading a single cell is a big deal.
Shading of a single cell is less of an issue with modern panels than it used to be. That said, they work better if the entire panel is in the sun.
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