How can I calculate the Amps  
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How can I calculate the Amps - 5/13/2008 1:09:46 PM   
cutarug


 

Posts: 26
Joined: 7/11/2006
From: , AUSTRALIA
Status: offline 		I have a geared brushless in a glider and I want to check the amps incase I blow the speed controller and BEC.
The prop is 16 x8, gearbox is 3:1, RPM is 4600, motor is 26 turn 2209 1130kv 15A Turnigy Outrunner,battery 4C 2100 LiPos.
Can any one estimate the amps from these results so I can be sure a 18A speed controller will be O/K.
       Post #: 1

RE: How can I calculate the Amps - 5/13/2008 7:25:40 PM   
Dr Kiwi


 

Posts: 1067
Joined: 12/4/2002
From: Chattanooga, TN, USA
Status: offline 		If you are getting 4600rpm I fear you must be drawing more than Motocalc predicts - thus too much for the 15A motor and too much for an 18A ESC - that is a HUGE prop for a 45g motor! [The Turnigy motor is not in the Motocalc database, but the Hyperion is fairly close, though based on my testing of "Turnigy/Hyperion pairs" probably more efficient than the Turnigy]. My feeling is that this tiny Turnigy is a 150W max motor, and you are wanting to put 250-300W through it!

Motor: Hyperion HP-Z2209-26; 1120rpm/V; 0.65A no-load; 0.119 Ohms.
Battery: Thunder Power TP2100 (ProLite) (15C); 4 cells; 2100mAh @ 3.7V; 0.018 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Direct; 16x8 (Pconst=1.17; Tconst=1) geared 3:1 (Eff=80%).
Airframe: Anything you want.
Motor Amps = 18.9
Motor Volts = 13.3
Input (W) = 251.3
Loss (W) = 89.9
MGbOut (W) = 161.4
MotGb Ef(%) = 64.2
Shaft Ef(%) = 57.8
Motor RPM = 12402
Prop RPM = 4134
Thrust (oz) = 54.2
PSpd (mph) = 31.3


I really feel you should borrow a Whattmeter and actually measure the amp draw!

< Message edited by Dr Kiwi -- 5/13/2008 7:28:23 PM >

_____________________________

Dr Phil Millener, Chattanooga, TN

(in reply to cutarug)
       Post #: 2

RE: How can I calculate the Amps - 5/14/2008 10:46:03 AM   
cutarug


 

Posts: 26
Joined: 7/11/2006
From: , AUSTRALIA
Status: offline 		Thanks for the calcs Dr Kiwi.
I only have the motor on for 30 sec or so and by your figures it should unload in the air and be about 17 amp.
I don't want to cook the speed controller and the BEC so I will keep the otor runs short and get a 30 A controller.
Last thing I expected was a reply form a Kiwi in Chattanooga.
I beleive they are restoring the train station there but the rail line is no longer running ,what a shame.

(in reply to Dr Kiwi)
       Post #: 3

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