How do I check voltage? - RC Groups
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Jan 19, 2004, 05:56 AM
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How do I check voltage?

Just got a volt meter, how do I check and see what my motor is pulling? With a Mini AC 1215-16, 12x6 prop and 7 cell 1050 Kan batteries, I get about 6 minutes flying. I want to see how many volts this motor is pulling with this prop. What do I need to do?


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Jan 19, 2004, 07:26 AM
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sarge's Avatar
I think your motor is pulling exactly as many volts as your batteries are providing. I may have this all wrong, but I believe that the usefullness of a voltmeter is in determining how many volts your pack still retains after use. Gives you an idea if you are running into the area of damage to the pack. A multi meter is used to determine how many amps your motor is drawing, which shows if you are getting max efficiency out of your motor/prop combo, if your are in danger of burning up your ESC, and if you are drawing at a rate too fast for your battery. The short answer to your question is that you place the probes on the "+" and "-" terminals of the motor. You may be able to determine if the pack voltage is dropping too rapidly by comparing the voltage at the motor, under load, to the voltage at the pack, not under load. My appologies if I got this all wrong.
Jan 19, 2004, 07:51 AM
Trying to defy gravity...
jimsky's Avatar
Electronics Basics:

Voltage - The sourcing potential provided by the electro-chemical reaction of the battery. Voltage is always measured "ACROSS" two points. Like the "+" and "-" of a battery.

Example - The voltage measured across the battery was 9.6 volts. Here the meter (configured to measure voltage) is placed in parallel with the battery.

Current - A measurement of the magnitude of electron flow. The amount of voltage applied to a circuit divided by the resistance of the circuit will yeild how much current will flow through the circuit. Current is always measured "THROUGH" something, since current flows through a circuit path; like water through a hose. No circuit path, no current flow.

Example - The current flowing through the motor was 5.2 amps. Here the meter (configured to measure current) is placed in series with the motor circuit.

Jan 19, 2004, 07:52 AM
Registered User
Thanks, I meant to ask how to check if the motor was drawing to many amps I guess.
Jan 19, 2004, 09:34 AM
Trying to defy gravity...
jimsky's Avatar
Your meter will need to be a "multi-meter", meaning it has to have the ability to measure current in addition to measuring voltage. And the current measuring capability of the meter needs to be matched for the anticipated current you intend to measure.

Typically there will be three inputs on a meter. The "Common" is used for both voltage and current measurments. The "+" input and the "Common" is used to measure voltage. The "A"input and the "Commom" is used to make current measurments.

To make a motor current measurment you will need to disconnect one wire from the motor, it really doesn't matter which one. Configure the meter to measure current. Place one meter probe on the wire you disconnected from the motor, the other meter probe connect to the motor terminal. The meter is now in series with the motor, completing the current path and measuring the motor current.

It really doesn't matter which probe connects to which point, if it's "backwards" you will just get a negative symbol infront of the current display.

Crank up your plane and make your motor current measurment.

Jan 19, 2004, 10:17 AM
TDI Abuser
flyinghigh's Avatar
put the probes on the + - of the motor I thought he was running a mini AC isnt that like a 3 phase AC brushless setup?correct me if Im wrong please
you need to also make sure your multi meter can take the amps your about to read.Most are rated for 10,I believe
Jan 19, 2004, 10:31 AM
Trying to defy gravity...
jimsky's Avatar
My mistake...what I detailed is only good for a regular DC, two terminal motor with brushes.