Can I use a 4S1P in my NexStar EP?  
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All Forums >> Electric Aircraft Universe >> E-Flight Power Sources >> Can I use a 4S1P in my NexStar EP?
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Can I use a 4S1P in my NexStar EP? - 4/6/2008 5:11:40 PM   
Hypersprint


 

Posts: 59
Joined: 11/22/2007
From: Colchester, VT or Eustis, FL, USA
Status: offline 		The manual indicates that you can use either a pair of 8-cell 3600mah NiMH (which is what I currently use) or a 2S1P 3200mah AND a 3S1P 3200mah to make up a 5S1P setup. The stock prop is a 10x5 and the manual says to improve performance you can go to a 10x7. The motor is a RimFire 42-50-800. I was talking to someone the other day who said I could use the 4S1P 5000mah LiPo out of one of my trucks if I changed the prop to a 11x7. Is this correct? Is there a calculator or an equation to determine appropriate prop size or is this more or less by trial and error? For what my LiPo cost me it would be great if it could do double duty and run both.

Thanks
Robby

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RE: Can I use a 4S1P in my NexStar EP? - 4/6/2008 9:36:26 PM   
Matt Kirsch



Posts: 7087
Joined: 7/5/2002
From: Rochester, NY, USA
Status: offline 		You've got the right idea. The real question is, will the larger prop be enough to compensate for the reduced voltage, but not be so much that it overloads the motor, ESC, or battery?

A Whattmeter or equivalent tool to show Volts, Amps, and Watts while you test run the motor setup is invaluable. Take a base measurement with the original battery, then switch out to the 4S1P. Note how the Amps and Watts are significantly lower. Increase the prop size until the Watts start to get near the original measurement, but watch the Amps to make sure they don't exceed the rating on the ESC or motor. Your battery is good for 100+ Amps, so it's a pretty safe bet that you won't overload them.

(in reply to Hypersprint)
       Post #: 2

RE: Can I use a 4S1P in my NexStar EP? - 4/7/2008 8:11:12 PM   
Hypersprint


 

Posts: 59
Joined: 11/22/2007
From: Colchester, VT or Eustis, FL, USA
Status: offline 		Thanks Matt, very informative response.

Now I have to file a "Certificate of Need" with my wife, wish me luck.

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I Love To Fly - - - - - - - With both feet planted firmly on the ground

(in reply to Matt Kirsch)
       Post #: 3

RE: Can I use a 4S1P in my NexStar EP? - 4/7/2008 10:01:24 PM   
-pkh-



Posts: 2521
Joined: 5/28/2004
From: Emmaus, PA, USA
Status: offline 		His battery is good for 100A only if it is a 20C pack. I didn't see that he gave any details about his pack, other than its capacity of 5000mAh.

Power = Volts X Amps, so if you keep the current at the max limit for your motor, ESC, and battery pack, the 4S pack will give you 20% less power than the 5S pack. The only way to get the same power from a 4S pack as a 5S pack is to pull 20% more current with the 4S than the 5S.

< Message edited by -pkh- -- 4/7/2008 10:03:28 PM >

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Paul - Helis: Two Raptor 50V2s, Venture 30CP, Blade CX2
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(in reply to Hypersprint)
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RE: Can I use a 4S1P in my NexStar EP? - 4/8/2008 3:09:26 AM   
Hypersprint


 

Posts: 59
Joined: 11/22/2007
From: Colchester, VT or Eustis, FL, USA
Status: offline 		Sorry about that, the pack is a 20C.

Looking at the specs for my motor here: Rimfire 42-50-800

The bottom of the page, center column.

Configuration 3: a 10x5E prop at 13080rpm with a 5S times 40A equals 740 watts (current setup)
Configuration 2: a 12x6E prop at 9990rpm with a 4S x 50.2A = 743w

With all other things being equal would these 2 configurations have about the same performance? As I understood Matts post the goal would be to reach the same watt consumtion without the other specs going beyond the systems limits.

Do you know if the rpm's and Amps are calculated values in the above configurations or do they come from bench testing?

Is there a constant wattage when stepping from one pitch to the next ie: going from a 10x5 to a 10x6 add 50watts or going from one size to the next ie: 10x5 to a 11x5 add 100watts?

_____________________________

I Love To Fly - - - - - - - With both feet planted firmly on the ground

(in reply to -pkh-)
       Post #: 5

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