chaosMurphy's blog archive for September, 2007 - RC Groups
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Archive for September, 2007

# Watts up and no smoke

Posted by chaosMurphy | Sep 23, 2007 @ 08:25 AM | 6,815 Views
To share an observation, some nickel knowledge
and first hand experiments with respect to
model airplane electric motors.

How I got more speed for less AMPs;

Volts equate to speed.
Amps equate to duration.
Watts equate to work accomplished (Watts per pound).

Watts equal Volts times AMPs
(10V X 15A = 150W)

Two box store digital multi-meters.
Picture and diagram below.

With respect to propellers;
Shorter and/or less pitch usually equate to fewer AMPs >at full throttle<
AND higher rpm, more speed.

Smaller props develop higher rpm for two reasons;
1) less mass accumulated on the motor
2) fewer AMPs mean more Volts (in the form of power) available to the motor due to less internal power waste building up nothing but heat inside the battery and ESC.

Empirical static test proof … different propellers;
post 7 in order to selected a prop that was most efficient AND not blow my motor or ESC or puff lipo at MAX throttle.

Battery discharge specification is based on its internal resistance and how much heat it can dissipate before smoke is generated.

The higher the AMP flow through ‘any’ resistance the more heat generated.
Power (in Watt) equals AMP [squared] multiplied by resistance.
IF a component (battery for this example) has an internal resistance of 0.2 Ohm then power waste at 15 A discharge is 15 X 15 X 0.2 = 45 Watts of nothing but heat.

Gramps :>)

# Measure WATTs

Posted by chaosMurphy | Sep 09, 2007 @ 10:18 AM | 7,121 Views
Jim,
I can not figure how to post images to your PM
'text' was sent in PM to you.

Gramps