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Old Nov 23, 2014, 05:35 PM
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Custom Battery Packs

Batteries in a series have their benefits. However, charging them can be a pain. Right now, I have two 5ah 4s lipos connected in a series. I looked into buying a 10ah 8s battery, but it gets darn expensive. I checked out cheapbatterypacks.com and their custom battery pack tool. For 8 LiFE cells already packed with any connector I want is only $40! But "you get what you pay for" keeps popping up in my mind. What are your thoughts?
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Old Nov 23, 2014, 06:17 PM
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Do you have a charger that will charge 8S?
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Old Nov 23, 2014, 06:21 PM
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Do you have a charger that will charge 8S?
Yes. Up to 12S.
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Old Nov 23, 2014, 06:27 PM
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What is the intended purpose of this battery? Are your current batteries adequate for your application? If so, I'd simply use them in series and then reconfigure and charge in parallel as a 4S, 10Ah pack. Either that or hard wire in series for both usage and balance charging.

You do realize that the 'custom LiFe battery' from CBP is only 1.4Ah and rated for 1C continuous current draw?
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Old Nov 23, 2014, 06:34 PM
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What is the intended purpose of this battery? Are your current batteries adequate for your application? If so, I'd simply use them in series and then reconfigure and charge in parallel as a 4S, 10Ah pack. Either that or hard wire in series for both usage and balance charging.

You do realize that the 'custom LiFe battery' from CBP is only 1.4Ah and rated for 1C continuous current draw?
I need the battery to power the 5055 Turnigy SK3 270KV 60A motor. As for the LiFE battery, its fine for the 1C, since the total draw would be 8C (eight 1C cells) times 10AH = 80amps, and the motor only uses 60 amps.
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Old Nov 23, 2014, 06:39 PM
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Your math needs a little rework here...

1C for a 1.4Ah battery is 1.4 amps, not 80 amps. The current sourcing ability of a single cell does not magically change by placing more in series (or parallel, for that matter). e.g. - You would smoke the custom pack in a right hurry if you attempted use it to operate the described motor in your model.
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Last edited by mrforsyth; Nov 23, 2014 at 09:13 PM. Reason: spelling
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Old Nov 23, 2014, 08:33 PM
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Originally Posted by mrforsyth View Post
You're math needs a little rework here...

1C for a 1.4Ah battery is 1.4 amps, not 80 amps. The current sourcing ability of a single cell does not magically change by placing more in series (or parallel, for that matter). e.g. - You would smoke the custom pack in a right hurry if you attempted use it to operate the described motor in your model.
OK. I guess my math was a little off :insertsarcasm:

So to be clear, adding more cells in a series DOES NOT change the overall C rating? For example, if I added eight 1C cells in a series, the total C would still be 1C, not 8C?

So my calculation would be wrong if calculated the amperage this way:

1.4Ah*8 (since I will be using 8 in series)*8C(Added 1C for each cell added)=89.6A

Would the right equation be:

1.4Ah*8 (since I will be using 8 in series)*1C(C does not change even if more cells are added)=11.2A
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Old Nov 23, 2014, 09:11 PM
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No, 1.4Ah * 1C discharge rate = 1.4A. Add more in series and it's still 1.4A of available current. Voltage does go up however so the available power will increase by virtue of the higher voltage.

If connected in parallel, total current does indeed go up. 8 cells in parallel will increase available current to 11.2A, as you've described. However, voltage will not increase so total available power will be no greater than if connected in series.
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Old Nov 23, 2014, 09:57 PM
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No, 1.4Ah * 1C discharge rate = 1.4A. Add more in series and it's still 1.4A of available current. Voltage does go up however so the available power will increase by virtue of the higher voltage.

If connected in parallel, total current does indeed go up. 8 cells in parallel will increase available current to 11.2A, as you've described. However, voltage will not increase so total available power will be no greater than if connected in series.
Thanks so much! I get it now. I feel so blonde.
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Old Nov 24, 2014, 03:30 PM
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A123 batteries (the original Lithium, Iron Phosphate chemistry) will power flight motors as they are a 30C continuous output, but are generally quite a bit heavier than a similar size LiPo, do not come in a prismatic cell type and the biggest cell you can get right now is a 2500mah.

It's pretty much impossible to duplicate the power output vs. size/weight of a LiPo when used for our RC purposes....
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