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Old 12-10-2012, 05:42 PM   #1
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Batteries for Solar project

Need advice on the batteries. I'll only have room for two batteries so I'm thinking 2x 6v in series. I was reading on some trojan batteries at 245 amp hours each (best I remember). Would I be just as well served to go get a couple 6v deep cycle golf cart batteries from Sams Club? I'm not wanting to break the bank for "the best" but I want something solid. From what I've read and my simple math I'm thinking two of these will suffice very well for lights, water pump, watching a movie, charging cellphone, charging kindle, etc. I'm guessing I can run the gas heater ok overnight if I have to though.

From what I've read I'm pretty sure I won't be running coffee maker, microwave, hair dryer, band saw, or a gigawatt flux capacitor any time soon.
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Old 12-10-2012, 08:33 PM   #2
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Just remember that when hooked in series the voltage doubles but not the Amp Hours; in parallel, the Amp hours double but not the voltage.

So your two 6 volt Trojans will make 12 volts but still have only 245 AH.
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Old 12-10-2012, 08:50 PM   #3
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Yes, 245AHr will be plenty for the usual power draw...lights, pump, some TV and heater. If you have good sunlight, and a properly sized solar system, you should have no problems and might even be surprised how much power you do have. I'm glad I went for the T145's even before the solar panels.
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Old 12-12-2012, 10:44 AM   #4
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Well, would I be better off going two 12v batteries in parallel for a two battery setup then? All of the reading I had done convinced me of the 6V path. I don't remember reading what Herk just said about the amp hours in series. Of course I could have conveniently overlooked it though.

I'm wanting to get rolling on the project but I'm anal retentive about trying to avoid bad infrastructure if possible. It's the Sys/Network admin in me.
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Old 12-12-2012, 12:00 PM   #5
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one issue I ran into with parallel batteries, 12v, is that the reduced impedance caused my charger to constantly be in the bulk charge mode. this in turn would cause the batteries to "boil off" the fluid. there are fixes for that though, battery selector switch for one.

Anyway, double 12's marine batteries are just a little lighter in weight, cheaper per battery, easily replaced and if one fails, you keep going.

6'ers are more durable, hold more capacity per pound, and should last longer. plus, to the stock charger, they look like a single 12 volt battery.

If you are serious about going boondocking you will end up with real deep cycle batteries. whether its a real deep cycle 12v batteries or dual 6 volters it's up to you.

I have never regretted my T145 purchase. But I did regret my dual 12v marine batteries from trip #1.
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Old 12-12-2012, 03:56 PM   #6
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Originally Posted by RPAspey View Post
one issue I ran into with parallel batteries, 12v, is that the reduced impedance caused my charger to constantly be in the bulk charge mode. this in turn would cause the batteries to "boil off" the fluid. there are fixes for that though, battery selector switch for one.
Not sure what that is about; but it could be that the setup was wired such that the internal resistance varied between the cells of the bank.

Care must be taken to use as near identical batteries with identical cycles as possible in order for the batteries internal resistance to be the same. If you use different batteries (manufacturer, life, or size for example), the difference in resistance will result in one battery working and charging "harder" than the other.

Look at the batteries in the diagrams and you will see what I mean about capacity differences between 6 and 12 volt systems.
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Old 12-12-2012, 04:11 PM   #7
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Quote:
Originally Posted by herk7769 View Post
Not sure what that is about; but it could be that the setup was wired such that the internal resistance varied between the cells of the bank.

Care must be taken to use as near identical batteries with identical cycles as possible in order for the batteries internal resistance to be the same. If you use different batteries (manufacturer, life, or size for example), the difference in resistance will result in one battery working and charging "harder" than the other.

Look at the batteries in the diagrams and you will see what I mean about capacity differences between 6 and 12 volt systems.
Herk where do you find all these graphics? Surely you can't stay up all night drawing these things!
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Old 12-12-2012, 04:13 PM   #8
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I forgot to mention there are great and informative.
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Old 12-12-2012, 04:25 PM   #9
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Herk where do you find all these graphics? Surely you can't stay up all night drawing these things!
If you liked those; here is how to wire several banks of cells for equal resistance, and therefore equal charging and use) between battery banks.

While the depiction shows 6 - 6 volt batteries, the white boxes around each pair can be considered as 1 12 volt battery and the external wiring is the same for 3 12 volt batteries in your bank.

PS - these graphics were not created by me - they were found online and copied into the "Herkbrary" and used as needed to help explain concepts and answer specific questions of our members.
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Old 12-12-2012, 05:20 PM   #10
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the 12v batteries were new from one of those battery warehouses. They were wired correctly. As it was explained to me, years ago batteries had a higher impedance than those in the last few years. Today's consumer grade batteries have a more sponge like makeup so as to keep the capacity yet lower the lead content. It has something to do with EPA regulations or some government regulations. Anyway the new makeup causes a change in impedance. So, a older charger that might charge correctly with a older battery, or a single new battery, could overcharge a parallel pair of modern batteries. The impedance would be just too low.

A couple of things here: First, the batteries were NOT commercial quality. Second, the original charger was a simple 2 stage, bulk and trickle.
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