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Watt meters

Old 08-19-2011, 04:56 AM
  #26  
Glacier Girl
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Racer, something else. DO NOT take an amp rating below wide open throttle (WOT)as fact.

In simplistic terms on a brushless set up, the esc turns on and off the power to each leg of the motor to regulate it's speed. How long the power is on, before it's shut off determines speed.

Where you can run into a problem is a watt meter averages it's readings.
Like it takes we'll say 10 readings a second. At WOT it's seeing 10 full amp draw readings. Below that, say half throttle, it takes the same 10 readings, but only sees half as many full amp draws. So it reads 5 full amp draws, and 5 zero amp draws, and when it gives you a reading you get the average, which in this case is 1/2 of the actual amp draw.

Like this. WOT, 50, 50, 50, 50, 50, 50, 50, 50, 50, 50. Reading is 50 amps.
1/2 throttle is 50, 0, 50, 0, 50, 0, 50, 0, 50, 0. Reading is 25. NOPE!

The motor is still pulling 50 amps, but it's not pulling it as often.

Folks get fooled into thinking if they run below WOT they'll be OK, on an under spec pack or esc or motor. And they soon find out it didn't work as they thought.
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Old 08-19-2011, 07:21 AM
  #27  
kyleservicetech
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Originally Posted by Glacier Girl View Post
Like this. WOT, 50, 50, 50, 50, 50, 50, 50, 50, 50, 50. Reading is 50 amps.
1/2 throttle is 50, 0, 50, 0, 50, 0, 50, 0, 50, 0. Reading is 25. NOPE!

The motor is still pulling 50 amps, but it's not pulling it as often.

Folks get fooled into thinking if they run below WOT they'll be OK, on an under spec pack or esc or motor. And they soon find out it didn't work as they thought.
Agreed:
As far as battery flight time is concerned, the flight time would be based on the 25 Amps if flying at 50% throttle.

But, as far as the ESC and battery is concerned, both have to be rated at the full 50 amps maximum throttle current, even if you never used full throttle current.

That also indicates you can't take a motor rated at 50 amps, put a big prop on it, and limiting throttle to only pull 50 Amps, when full throttle might be 120 Amps, as an example.

Has to do with the watts lost as heat in the windings being proportional to the square of the amps going through the motor windings. (Double the Amps, that results in 4 times more winding heat loss.)
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Old 09-11-2011, 06:32 AM
  #28  
Racer09
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well im back and the first flights were great. started with 4 min. flights and then move a min. at a time. looks like 9 is the magic number. The 4 min. fights only used about 10% 0f the battery.
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Old 09-26-2011, 12:27 PM
  #29  
Fast Guy
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If you have a Castle Ice ESC it has a onboard data logger that will tell you the amp draw, rpm, voltage and much more. You need Castle Link to get the data.
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Old 09-28-2011, 04:25 AM
  #30  
CT4
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I agree with Fast Guy CC Ice data logger is great gives max outputs as well as average and if you want a reading from any part of the curve the reader displays that when you place the mouse pointer on what ever line in the chart you want the reading from.
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Old 09-28-2011, 04:45 AM
  #31  
kyleservicetech
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Originally Posted by CT4 View Post
I agree with Fast Guy CC Ice data logger is great gives max outputs as well as average and if you want a reading from any part of the curve the reader displays that when you place the mouse pointer on what ever line in the chart you want the reading from.
Yes and you can also display multiple flights, plus zero down to a particular flight. And, blow up a portion of that flight by just using the mouse and draw a box around the area of interest.
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