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How can I get wattage measures?

Old 11-28-2005, 06:39 PM
  #1  
arizonajoe
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Default How can I get wattage measures?

I'm very slow on elec. I need to learn how to obtain wattage info. Is there anybody out there who can help me? I can get a meter to show me how many I'm running,but telling me how or why is what I need to know.
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Old 11-28-2005, 07:04 PM
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Bob_CO
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You need to plug a watt/amp meter in-line between the battery and the ESC in order to measure the current. You can get one like this. http://www.horizonhobby.com/Shop/ByC...?ProdID=AST101 But there are several brands on the market currently.

Edit: Here is another brand. http://www2.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML
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Old 11-28-2005, 07:16 PM
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Elfwreck
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Hey now,
Right, get a watt meter, I know, you said you figured that part out. Also get a tachometer. There are several good ones out there, I use a Glo-Bee. Hook up the watt meter, switch on the power, let it run a few moments and watch the initial voltage drop, hold the tach to the prop and note all the numbers. Change props, take new readings. Do this with a range of props suggested for your motor combo. Also try different brands of props, youi'd be amazed at the differences.
Now, go out and fly the model. Change props, fly again, repeat. Take notes. How do the wattage changes alter the flight? Do different props at the same wattage fly differently? How much do rpm changes effect the flight? You're now learning what these numbers mean. How you apply them comes as you gain experience and notes.
RobII
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Old 11-28-2005, 09:25 PM
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Matt Kirsch
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arizonajoe,

Could you try to better explain what it is that you are looking to achieve?

Watts is a measure of power, the metric equivalent to Horsepower (746 Watts equals 1 HP). Electric Watts or mechanical Watts, it's the same unit. Put 746 Watts of electrical power into a motor, and you will get 746 Watts of mechanical power out, ignoring losses. It takes so much power to make a plane of a certain weight fly in a certain way, so many mechanical Watts to turn that propeller... Because it's a direct translation from mechanical to electrical, and so easy to calculate electrical Watts (Volts times Amps), we work with electrical Watts almost exclusively.
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Old 11-29-2005, 01:14 PM
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arizonajoe
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Thanks alot guys. I'm on my way to understanding elec.R/C. Double thanks to Mr. Kirsch, V x A = W was what I needed to know to get me over a bump in my path.
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Old 11-29-2005, 02:16 PM
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Matt Kirsch
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Careful there, AJ, you're going to make me start thinking I'm clairvoyant or something
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Old 11-29-2005, 08:45 PM
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Rugar
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Originally Posted by Matt Kirsch View Post
Careful there, AJ, you're going to make me start thinking I'm clairvoyant or something
LOL @ Matt
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Old 12-21-2005, 12:17 AM
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davidej
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Another basic question from a beginner:

That is fairly straightforward for a brushed motor but what about brushless motors? How can you measure the amps?

David
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Old 12-21-2005, 01:06 AM
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ForestCam
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volts x amps = watts

All can be done with your basic multi meter.

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Old 12-21-2005, 01:16 AM
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davidej
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Yes but how do you measure the current which is divided between three wires - I assume that each carries an AC 120 degrees out of phase.

David
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Old 12-21-2005, 01:20 AM
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ForestCam
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You don't, you measure it between the battery and the ESC.
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Old 12-21-2005, 01:24 AM
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davidej
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As easy as that!

Thanks.

david
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Old 12-21-2005, 01:25 AM
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Big_Bird
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Originally Posted by davidej View Post
Yes but how do you measure the current which is divided between three wires - I assume that each carries an AC 120 degrees out of phase.

David
David, I really don't know why you would want to measure current on the output of the ESC unless you are interested in motor winding imbalance or .... Most of the time people are interested in supply current to the ESC. Please elaborate.
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