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Battery Bank ?
By 2windy, Section Storage Posted on Sun Oct 14, 2007 at 01:19:44 AM MST
How to hook up

I have 12 6-volt T-105's wired for 12 volts for my wind genny. My dumb question is , does it matter where I come off the batteries to go to the inverter? Should I be coming off the center, like 6 batteries on one side and 6 on the other side so I discharge them equally, or charge them equally, does this matter? Should I paraell 6 and 6 then series the 2 groups? I did some searches on battery banks but never really found anything on trying to equal the input or output of the bank.

Battery Bank ? | 8 comments (8 topical)

Re: Battery Bank ? (3.00 / 0) (#1)
by vincecastro on Sat Oct 13, 2007 at 09:45:02 PM MST

The best equal pull and charge would be to use the negative off of one end of your parallel bank then the positive on the extreme opposite end of the parallel circuit.

(I-) - - - - - - - - (WT-)
(WT+) + + + + + + + + (I+)

I = Inverter
WT = Wind Turbine

Hope this helps.

Vince

Re: Battery Bank ? (3.00 / 0) (#8)
by Ungrounded Lightning Rod on Mon Oct 15, 2007 at 05:14:07 PM MST

That's better, and balances perfectly when you only have two batteries paralleled. But with more than two the ones in the middle still loaf a tad.

Yes, I used to think it would balance them all. But I had it pointed out to me that it doesn't - and worked the math to confirm it. It's a lot better than feeding the end battery, or even the center one. But the batteries in the middle still see a somewhat bigger resistive voltage drop than the ones on the end, because they're seeing high current-produced voltage drop in both of their hookups. To balance perfectly you'd need the jumper cabling to get progressively fatter as you get closer to the battery with the fed terminal.

Best is to connect each battery separately to a common + and a common - binding post, using + and - cables for each battery that TOTAL to the same length as those for each of the others. This is equivalent to the tuned-thickness jumpers but a lot easier to fabricate. (For convenience the common binding posts can be one battery post each on the two end batteries.)

[ Parent ]

Re: Battery Bank ? (3.00 / 0) (#2)
by tecker on Sun Oct 14, 2007 at 05:15:53 AM MST

The impedance wise Idea is to design your buss wire to give the max allowable rate of your battery something like 450 amps for 25 minutes for the t105 .Then the bottle neck would be a single battery's impedance and this would be greater than the interconnecting wire .With this as your guide the charge getting to your batteries will certainly be equal and the 20 hour rate with 30 to 60 amp surges are not even close to the max discharge rate .If you are using small wire for your buss you could adjust where your charge enters the buss but the series connection of the 6 volt pairs is going to always be a bottleneck .I guess I rambled a bit .As long as your interconnect is thhn 4 or larger (about 150 amps freeair) you can be any where you want on the buss because the charge discharge rate is covered and the series pairs are the bottle neck .You might want to track the charge of individual batteries of your series pairs on a regular basis to be aware of the battery's health . And make shure the pairs are close on individual load test .That's the only problem area

Re: Battery Bank ? (3.00 / 0) (#3)
by 2windy on Sun Oct 14, 2007 at 08:23:42 AM MST

I have 2/0 cable for everything

[ Parent ]

Re: Battery Bank ? (3.00 / 0) (#4)
by spinningmagnets on Sun Oct 14, 2007 at 09:41:57 AM MST

Theoretically, If I had 4 large RE batteries sitting in a square formation, so my question didn't involve the actual physical moving of each...is there any benefit to "rotating" each batteries position in a parallel string, perhaps once a month?

Re: Battery Bank ? (3.00 / 0) (#5)
by spinningmagnets on Sun Oct 14, 2007 at 09:44:15 AM MST

(Newbie alert!) I apologize, I meant a "series string"

[ Parent ]

Re: Battery Bank ? (3.00 / 0) (#6)
by Chagrin on Sun Oct 14, 2007 at 10:47:56 AM MST

Parallel or Series it does not matter -- no reason to rotate.

[ Parent ]

Re: Battery Bank ? (3.00 / 0) (#7)
by tecker on Sun Oct 14, 2007 at 11:52:41 AM MST

If the batteries are matched the and load test healthy your good to go as a series string older batteries throw the the inpeadance (as they discharge) up faster and block current as they charge in the the series sting . Watch the voltage rise under charge if it jumps up in voltage load test it they should all load test with in a small margin after being fully charged to be effective in circuit charge and discharge.

[ Parent ]

Battery Bank ? | 8 comments (8 topical)

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