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# How to determine current in a DC motor?

## How to determine current in a DC motor?

(OP)
Hi, I am having difficulty trying to figure out current and resistance in a simple DC half motor I made. Any help would be greatly appreciated. I built a half motor which consists of a coil with 10 loops made out of 20 gauge magnet copper wire . The coil sits inside 2 paper clips that are connected directly to a d cell battery. One paper clip is on the positive side of the battery and the other paper clip is on the negative side. The coil only conducts half of the time as I only sanded the bottom half of each lead of the coil. I tried to figure out the current draw by the motor by calculating the resistance of the coil and then using ohms law. The 10 loop coil is 5 feet in length. I looked at an online chart and saw that 20 gauge copper wire is 10.13 ohms/1000 ft at 20 degrees C. From this I calculated my 5 ft coil to be .051 ohms as follows.

10.13 ohms divided by 1000 ft = X divided by 5 ft
therefore X = .05 ohms

Next I used ohms law V=IR to calculate the current draw.

1.5V = I(.05 ohms)
I = 29.4a

I felt that this answer of 29.4a is wrong because I did not feel a D battery could supply that much current. When I test my motor with a digital multimeter, I get 3a when the motor is spinning and .5a when I hold the coil from spinning with the sanded coil leads conducting. What I would like to know is what is the correct way of determining the current draw for this type of motor and how is ohms law (V=IR) used. Thank you.

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