Wednesday, September 1, 2010

HowTo: Using a Watt Meter

Using the Hobby King X1 Watt Meter

The instructions in the package are pretty inscrutable, so here's a quick HOWTO.

Basic Idea
  • This thing sits between your battery and your ESC.
  • It measures voltage, amperage, and wattage.
  • It has a HOLD mode that keeps the highest values.
  • When it's set up, you fiddle with your props, motors, etc, and see the power requirements of various setups.
  • You can send it aloft to record the flight's peak power requirements.
 Setting Up
  • The unit doesn't come with any power connectors, so you need to attach your own.
  • The wires labeled IN attach to the battery.  Put a male power connector here.
  • The wires labeled OUT attach to the ESC.  Put a female power connector here.
  • Black wire = Neutral (-)
  • Blue wire = Hot (+)
Turning It On
  • Plug the unit into a battery.  Whatever battery you use to fly a plane is fine (the manual says the voltage rage is 8-30V, but it seems to work fine with 2S batteries as well, as seen below).
  • The display of the unit will turn on.
  • If you use a 2S battery, you will see something like this:
  • Voltage (U=7.93V).  Over time this will go down, as your battery discharges.
  • Amperage (I=0.1A)
  • Wattage (P=1.0W)
Trying It Out
  • Attach a motor to your ESC.
  • Plug your ESC into a receiver.  It's OK if there are servos attached.
  • Attach the OUT wires to your ESC.
  • Your setup should power up and work as normal.
  • The power levels should go up a bit, since you're running servos and a receiver.
  • Wiggle your servos.  You will see the numbers jiggle in response.
Testing a Motor
  • Make sure your motor is secure, and bring the speed up.
  • You will see the amperage (I=) and wattage (P=) increase.
  • Bring the speed back down.
  • You will see the values decrease back to the original values.
  • The voltage may have gone down a bit, since you've been using some power to run these tests.
HOLD mode
  • HOLD mode will measure the Peak values.
  • To turn it on, click the HOLD button.
  • Rev your motor and bring it back down a couple of times.
  • You will see these peak values displayed. Rearranging the order a bit, they are:
  • P 14.3W -- maximum power (wattage).  This is the peak power output of the battery.
  • Up 7.71V -- voltage when P was at max.
  • Ip 1.9A -- amperage when P was at max.
  • Im 1.9A -- maximum amperage, even if it didn't correspond to P above.
  • Um 7.84V -- the minimum voltage of the time period.
  • Click HOLD again to go back to instantaneous mode.
Flight Mode
  • If your plane is big enough to carry a couple of extra ounces, you can attach the meter between the battery and ESC in your plane, set HOLD mode, and find out your peak usage aloft.
Manual Calibration Mode
  • If you have a good quality multimeter, you can adjust your unit's readings.
  • Depress HOLD for three seconds and you will be in adjustment mode.
  • Measure an unloaded power source with both the watt meter and your reference multimeter.
  • Use the ADD and SUB menu items to make the two units agree.
  • SAVE will of course save your calibration.

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