Serial vs Parallel

[RichardMid]

I have a system that requires 600Ah at 12V. I have done some serious battery shopping, and found two options:

1.I can either use four 6V330Ah batteries, and connect two sets of in series and those two in parallel or
2.I can connect four 12V230Ah batteries in parallel.

The 2nd setup will be able to deliver more, but that is not required.

The first option looks more attractive because the physical size of the batteries are smaller, and space is a major issue.

I want to know if there is a trade-off between the two setups as the batteries are to be charged and discharged 24 hours a day for long periods. The batteries are of the gel cell type.

Are there advantages or disadvantages of charging batteries in series?

Thank you
Richard

 

[IRstuff]

What is the discharge rate? Will the 6V series resistance support your specified rate?

As for charging, there would seem to be some potential issues regarding the series connection and preventing overcharge/undercharge.

TTFN

 

[felixc]

IRstuff, since the gel-cell batteries are made of isolated 2V cells connected in series, why would two 6V batteries be more of a problem than one 12V battery?
I'd be more afraid of directly paralleling batteries. Maybe it's just a feeling. Please correct me if I'm wrong.

 

[IRstuff]

They may all be 2V cells, but there's nothing to indicate that the 6V cells are constructed the same way as the ones in the 12V battery.

And, in either approach, he's paralleling batteries. He still needs to come up with a scheme for ensuring that the weakest branch doesn't drag down the whole show.


TTFN

 

[RichardMid]

The maximum discharge rate is estimated at 10A. I cannot get the internal resistance of any of the batteries I am considering...

I think that the difference in internal resistance between the different batteries will be small enough not to cause any major concerns, but I need to get samples in order to verify that.

I am more concerned about what will happen if I get a failure as the batteries will operate in very remote locations and the cost to get somebody there to replace the battery will take time and cost alot, and the loss of revenue will be significant.

With the series configuration I am concerned about what will happen in case of a battery failue, because an open circuit failure will mean only 6V available on which the equipment cannot run, and a short sircuit failure will mean a 6V in parallel with 12V which gives 4V which is not enough.

The parallel configuration is more resistant to failure as a open circuit failure will cause the batteries to deliver less current, but at the same voltage only with less standby time. A short circuit failure will cause the system to go down though.

To summarize: A failure in the serial config will cause the system to go down no matter what, and in the parallel config it will only go down if it is a short sircuit failure.

Are there statistics which compares short circuit failure rates with open circuit failure rates?

 

[felixc]

Lead-acid batteries tend to short when they are deep-discharged too often with a strong load. They will tend to lose capacitiy and open with aging. Gel-cell manufacturers claim that they immproved this. Perhapd they do have data to support their claims. There's a lot of power involved in your setup. I'd be really afraid to leave it without any data logging or monitoring system to see the trends especially if the good condition of the batteries seems to be so important.