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A li-po question

Old 02-20-2014, 08:18 PM
  #1  
green river rc
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Default A li-po question

Is two 2 cell 4000mAh li-po packs wired in series the same thing as 2 4 cell 2000 mAh li-po packs wires in parallel? Would this be enough battery for a 40 size plane (Sig Smith Miniplane) powered by an E-flight 46?
Old 02-21-2014, 03:42 PM
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Dr Kiwi
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Both set-ups come out as "4s 4000mAh"... so, yes, they are the same. Whether or not this gives you the power you need for a .40-size aircraft with a power 46 depends on the prop size you choose and the flight time you desire.

Here are two scenarios from E-flite, both of which, conveniently, assume a 4s configuration.... but BOTH of them push the motor well over its rated 40A continuous rating, so I'd reduce prop size somewhat to keep the amp draw within the stated "40A continuous" limit. [12x8/12x6 maybe, at least to start with, to determine whether performance is going to be adequate.

Hangar 9 Ultra Stick 40 ARF (HAN1675 / HAN1690)
[TABLE]
[TR]
[TD]Option 1:[/TD]
[/TR]
[TR]
[TD]Motor: Power 46[/TD]
[/TR]
[TR]
[TD]ESC: Castle Creations Phoenix 60 (Standard settings with 12V Soft Li-Po cutoff and no brake)[/TD]
[/TR]
[TR]
[TD]Prop: APC 13x8E[/TD]
[/TR]
[TR]
[TD]Battery: Thunder Power PRO LITE 6000mAh 4S3P (THP60004S3PPL)[/TD]
[/TR]
[TR]
[TD]Flying Weight w/Battery: 5.8 lb[/TD]
[/TR]
[/TABLE]

[TABLE="width: 450"]
[TR]
[TD]Amps[/TD]
[TD]Volts[/TD]
[TD]Watts[/TD]
[TD]Input Watts/Pound[/TD]
[TD]RPM[/TD]
[/TR]
[TR]
[TD]51.5[/TD]
[TD]14.4[/TD]
[TD]745[/TD]
[TD]128[/TD]
[TD]8250[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD]Expect very strong performance with very short takeoff rolls and a great balance of thrust and top speed. Average duration is approximately 12 to 20 minutes depending on throttle management.[/TD]
[/TR]
[/TABLE]


[TABLE]
[TR]
[TD]Option 2:[/TD]
[/TR]
[TR]
[TD]Motor: Power 46[/TD]
[/TR]
[TR]
[TD]ESC: Castle Creations Phoenix 60 (Standard settings with 12V Soft Li-Po cutoff and no brake)[/TD]
[/TR]
[TR]
[TD]Prop: APC 13x8E[/TD]
[/TR]
[TR]
[TD]Battery: Thunder Power PRO LITE 4200mAh 4S2P (THP42002S2PPL x2 in series)[/TD]
[/TR]
[TR]
[TD]Flying Weight w/Battery: 5.4 lb[/TD]
[/TR]
[/TABLE]

[TABLE="width: 450"]
[TR]
[TD]Amps[/TD]
[TD]Volts[/TD]
[TD]Watts[/TD]
[TD]Input Watts/Pound[/TD]
[TD]RPM[/TD]
[/TR]
[TR]
[TD]47.4[/TD]
[TD]14.1[/TD]
[TD]670[/TD]
[TD]124[/TD]
[TD]8220[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD]Expect strong performance with very short takeoff rolls and a great balance of thrust and top speed. Average duration is approximately 8 to 15 minutes depending on throttle management.[/TD]
[/TR]
[/TABLE]

Last edited by Dr Kiwi; 02-21-2014 at 08:14 PM.
Old 02-21-2014, 04:42 PM
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green river rc
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Thanks, Dr Kiwi. This is my first electric build and I'm a little green on all the electric optins these days, it gets a bit overwhelming. I have always been a bit confused as to what voltage with what size motor and how it affects run time and such. In the old days we would just "gas and go"!
Old 02-25-2014, 09:39 AM
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aeajr
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Dr Kiwi has give you excellent advice. As this is your first electric build you might find this helpful:

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm

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