Q - Pro/Cons - configuration of Batt to create 24VDC?

[hamitduk]

Ok

I have 12 6 VDC 235AH gel Cells, need 24VDC.

The question, what are the Pros/Cons of banking them in the following Configs?

4 - Banks of 6VDC, 3 Batts each bank
2 - Banks of 12VDC, 4 Batts each bank
3 - Banks of 24VDC, 4 Batts each bank

any suggestions on protection, a fuse on each bank, Fuse in each bank (APC inserts in between Batts), or just at the output?

Hami

[rossw]

I have 12 6 VDC 235AH gel Cells, need 24VDC.

4 - Banks of 6VDC, 3 Batts each bank
2 - Banks of 12VDC, 4 Batts each bank
3 - Banks of 24VDC, 4 Batts each bank

Or you could do a hybrid.

+24 ---------------------
          B1     B2      B3
           |       |         |
           +-----+-------+
           |       |         |
          B4    B5       B6    
           |       |         |
           +-----+-------+
           |       |         |
          B7     B8      B9
           |       |         |
           +-----+-------+
           |       |         |
         B10   B11     B12
          -------------------------- gnd   
        

The interconnects arcoss (eg, B4-B5-B6) should help keep them better balanced.
The potential difficulty here is how you fuse them. A fuse in series with each battery as it joins on to its interconnect would be the only practical way, but thats a dozen fuses - plus a larger one to protect the main cable to your inverter.

(Edited: meant to show the ground connection off the right hand side)

[fabricator]

This is what mine looks like I have 12 volt batteries though, this allows you to use 4 awg to the buss bars 24VDC Series Bus.pdf (146.86 kB - downloaded 203 times.)

[hamitduk]

I'm thankful for the responses, but I was hoping for was the logic behind in the selection also?

Hami

[rossw]

I'm thankful for the responses, but I was hoping for was the logic behind in the selection also?

I thought "The interconnects arcoss (eg, B4-B5-B6) should help keep them better balanced." covered that?

[fabricator]

On mine the cables come from opposite ends of each string which helps keep things balanced.

[wpowokal]

Personaly I would have 3 banks fused at positive and negative ends if terminals are exposed, if not exposed then just the positive end, reason, if something shorts across two banks but not at an equal voltage point then the negative fuse will limit fault currents.

I know we all believe we it will never happen.

I had 8 banks of 2V batters for 10 years and ballance was never an issue, I know it is in text books but in the real world one checks individual battery voltages and specific gravity and equalises if required. Sure some of my  banks received/gave more current than other, principally because of their age but the system voltage is what works for me.

If one had two water tanks, say one was 1000 gallons and one 2000 gallons but the same height at the base and top, connect these together and draw water off, they will give their share at aproximatly 2:1 within the connecting pipe limitation, equally batteries within cable limitations (resistance).

With more than one string you need to be prepared to monitor your batteries which will show up any discrepencys before they become a problem, even in a single string monitoring mid point voltage is a valuable tool for indicating any discrepancy.

Just my perspective from an old fool who has done it.

regards Allan