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Old 16-01-2014, 07:38   #1
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LiFePo batteries

Sorry if this is already covered in the existing thread but the search returned to many results. Really long threads too!

I want to install 400ah at 24 volts. My available space requires I configure this as 2 banks next to each other. Like 2 8d side to side.
My question is am I better to use.
2 12v 400 ah series
2 24 v 200 ah parallel

Many thanks
Paul
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Old 16-01-2014, 07:55   #2
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Re: LiFePo batteries

Neither. Figure out a way to connect the two "Banks" into one, so that you have one 400ah 24v bank. eight 400ah 3.2v cells, or 16 200ah 3.2v cells. If they are 200ah cells, you should have eight sets of two, that are in parallel, then theses sets are connected in series.

Chris

Edit: I realize reading again you may have been trying to communicate this setup with your #1 choice.
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Old 16-01-2014, 08:11   #3
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Using 200Ah cells or 400 Ah cells works well, but you need to make sure that the connections are done correctly.

When using more than one cell to reach the desired capacity, then you have to connect the smaller cells in parallel first and then connect them to the desired battery voltage. Never make two 24V-200Ah batteries and then connect them in parallel.

Keeping the individual cell voltages between 2.9 and 3.5 V (May vary slightly with manufacturer) is the key to a long life. Making two separate batteries of 24V200Ah each gives you 16 individual cell voltages to monitor. Making one battery with cells paralleled first gives you 8 cell voltages to deal with. You just halved the potential points of failure. Also, when in parallel you get a chance to have a strong cell help a weak cell and even things out.

Most importantly, never charge to absolutely full (3.8-4.0V per cell) and never discharge to absolutely empty (below 2.8V). All these voltages are under a conservative loads as usual in house bank applications. That means about 20-200 A from your 400 Ah battery.

A number of real application tests by users here on CF have shown that for a 12V battery 13.8 V charge is safe and gets you to +95% full. The good thing is that these batteries do not have to be fully charged ever to enjoy a long life, as lead acid have to on a very regular basis. LiFePo like it better to hang around the middle.

Hope this helps.

Rolf
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Old 16-01-2014, 12:02   #4
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Re: LiFePo batteries

Thanks, this is what i meant to do in the series option. intend to fit the as per attached sketch, into 2 aluminum boxes about 60kg each.
Will feed with about 8-900W of solar plus 4 kv generator for back up.
System feed 2 x 2500W Mastervolt invertrs 1 at 110v 1 at 230V
Charger is mastervolt 100A 110/230 V.

Not installing myself but trying to prep the space.
Many thanks
Paul
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Old 16-01-2014, 13:24   #5
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Why cant you have two 4s packs and then parallel for double Ah??
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Old 16-01-2014, 13:38   #6
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Re: LiFePo batteries

That would get you 12v, not 24, which the OP needs.

Chris

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Why cant you have two 4s packs and then parallel for double Ah??
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Old 16-01-2014, 13:41   #7
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Re: LiFePo batteries

That diagram will work, as long as the cable between both sets is sized for low resistance, which generally means short and fat.

Chris

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Originally Posted by Steel sails View Post
Thanks, this is what i meant to do in the series option. intend to fit the as per attached sketch, into 2 aluminum boxes about 60kg each.
Will feed with about 8-900W of solar plus 4 kv generator for back up.
System feed 2 x 2500W Mastervolt invertrs 1 at 110v 1 at 230V
Charger is mastervolt 100A 110/230 V.

Not installing myself but trying to prep the space.
Many thanks
Paul
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Old 16-01-2014, 15:20   #8
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Sory i meant 8s. Why cant you have two 8s packs and then parallel them?
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Old 16-01-2014, 17:10   #9
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Quote:
Originally Posted by d design View Post
Sory i meant 8s. Why cant you have two 8s packs and then parallel them?
Because that is asking for trouble. Too many points of potential failure. The weakest cell determines your capacity in this configuration too. Remember, you want to check each cell voltage. Checking 8 vs 16 cells makes a difference in equipment.

Better parallel two cells together, and put 8 ( 2p4s) into one box each. Now you are putting together two 12V batteries in series to make a 24V one.

Get a Junsi Celllog (about $25 from Hobby King) to show you all cell voltages.
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Old 16-01-2014, 23:33   #10
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Because that is asking for trouble. Too many points of potential failure. The weakest cell determines your capacity in this configuration too. Remember, you want to check each cell voltage. Checking 8 vs 16 cells makes a difference in equipment.

Better parallel two cells together, and put 8 ( 2p4s) into one box each. Now you are putting together two 12V batteries in series to make a 24V one.

Get a Junsi Celllog (about $25 from Hobby King) to show you all cell voltages.
Thanks for info
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