battery bank configuration

[libra]

Hi      I had (past tense) a battery bank of 30 agm batteries in 3 banks of 10 for a 24v system. These were used 12v 75 ah from a call center. I had each bank connected as two in series for 24v and 5 pair connected in parallel with heavy copper bus bar. The 3 banks were rack mounted and close together withing 3 -4 feet of the main connection to the generator. Since there was copper bus bar I connected the pos and neg of each bank bank to the main connection, not pos at one end and neg at the other end of each bank.
I have a computer controlled charger that cuts in when the battery bank drops to 24.4 v  and charges till the bank reaches 25.5v.
I usually never go more than two days without the batteries getting recharged to 27,4v from the wind generator.

I recently lost most of the batteries (12 left) due to ? but some batteries were dead but many were 11.5v . There was no pattern of failure. The farthest ones had some good batteries in series with a low ones so am at a loss to see where I went wrong or if this was just old age.

The remaining bank of 12 batteries are still connected 2 in series and in parallel with copper busbar for a 450 ah system BUT the pos and neg are at each end of the bank. I can't see that with hvy busbar each battery wouldn't have gotten an equal charge but not taking chances.

Appreciate any comments

Libra

[luv2weld]

The first thing I would check is the charger.
If that is OK, then look at the connections.

If the charger is taking them to 25.5, then the wind generator is taking them to 27.4, is there any possibility
that you were over charging them???
Is it possible that the wind generator was charging them too fast??

I have never worked with AGM batteries so I have  no idea. Just thinking of things that may have caused a problem.

Ralph

[thirteen]

maybe check and see if one batteries is heating up more than the others you might have one battery drawing more the others causing an unbalanced system and I agree check all connections. Just and idea

[libra]

There is a charge controller that dumps excess voltage to a dump load at 27.6 v and the charge is never over 20amps over 30 batteries should be no problem there.

Libra

[theshadownose]

I know that a bus should have low resistance,  but if each group  was in a line, with the charger and inverter on one end, then there will be uneven charging to at least some degree-  looking at  http://www.smartgauge.co.uk/batt_con.html    ,  they were doing there calculations based on 35 MM cable, and still got the battery closest to the load doing 2x the work of the battery at the far end, and that was a 4 deep series;  if I read correctly your series are each 5 long, which would compound the issue even with lower resistance.

[Bushwhacker]

Shadow, thanks for the link, it's a great read (and saved to favorites).

Not to hijack the thread, but wanting more informed minds than my own to weigh in...

With the mess of cable required to achieve equal lengths from each battery to the buss bar and/or charge/discharge point, doesn't the field around each cable come into play with the field of other cables it crosses paths with or runs parallel to?

What I am getting at is the field of energy that a DC clamp meter can read MUST interact with other fields of energy around other cables. If you ran the + and - buss bars fairly close together (2"?) wouldn't there be losses incurred? If an insulated + cable crossed within an inch of the path of a - buss bar wouldn't that change the charge/discharge pattern?

Please bear with me because I really don't understand the electrical side of RE very well and want to understand it better.
BTW I posted this here because I think it is still on topic about wiring battery banks.

[RP]

With DC there is no "field" in the sense that you're probably thinking.  A DC clamp on Ammeter reads the magnetic field around the wire and this is no more of a drain on the power than the permanent field around a magnet.

High frequency AC creates a field around conductors (radio!) but this is insignificant at the frequencies and power levels usually encountered here.

A much more relevant issue to having buss bars close together is the likelihood of an accidental short circuit from a metal tool or loose cable lug.

[Bushwhacker]

Not to worry about me putting buss bars close together, I just used that as an example. Due to the design of my battery rack I will be running both + and - cables side by side and was worried about power losses due to the magnetic fields around the cable.

Thanks for the explanation.