Jan 13

Winding our own electromagnet

Max brought several electromagnets he made himself as well as wire and cores to make another.  His project to capture energy from soccer balls being kicked will use an electromagnet as part of the kick-testing jig, so he wanted to make a more powerful one.

We measured voltage, current, and pull strength for an existing electromagnet using first batteries and then a computer power supply.  In our excitement to measure, our recordings were disorganized.  Instead of an orderly table showing which electromagnet we were testing, the voltage, current and pull strength, we jotted down numbers haphazardly.  We will do better next time.

The results we got were, not surprisingly, contradictory.  With the first electromagnet, the batteries (two 6-volt lantern) provided 11.9V, 4.8A, and pull strength of 0.3 kg.  With the first electromagnet, the PC power supply (rated 12V, 15A) provided 11.6V, 10.8A, and 1.0 kg of pull.  We suspect our voltage measurement for the batteries because they provided less than half the current of the PC supply, so their voltage should have dropped to about half.  Could we have measured voltage before attaching the load? Early in the process, we introduced a second multimeter with higher current range (20A, not 10A), allowing us to measure voltage and current simultaneously.

Eager to wind a new electromagnet, we practiced poor science by not returning to explore the anomaly.  We used a power drill to wind 20 gauge wire onto an iron nail.  We did not measure or note the length of wire.  Photos show the crude mass we created.  Testing the new electromagnet with the PC power supply showed 11.1V, 1.43A, and 0.32kg of pull strength.  The new electromagnet had much more wire than the first, possibly explaining why less current flowed through and why, in spite of many more turns of wire, we got a third of the pull strength.  Not explained, however, is why the voltage would be lower (11.1V) than the first, high current, test (11.6V).

We ran out of time trying to unwind the electromagnet back onto the original spindle.  Excited to build something, we were careless with our data logging and did not make time to investigate anomalies.  It was a fun class, but we have plenty to learn from and not repeat.

IMG_3556 IMG_3557 IMG_3558 IMG_3560 IMG_3561

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