Electromagnet 02

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I built a new electromagnet. This time I used a variety of coil and battery arrangements, used a very sensitive scale to measure the relative strength of the magnet, and tested the lifting power to its maximum. The two coils I used were the primary coils from identical microwave oven transformers (MOT). I believe they are about 100 turns each, so wiring them in series essentially makes a 200 turn coil. It's important to make sure the coils are close to each other and that the turns are going in the same direction.

Video


Details

These are the arrangements I tried:

  • 1 coils, 1 battery
  • 1 coils, 2 batteries (series)
  • 2 coils, 1 battery
  • 2 coils, 2 batteries (series)
  • 2 coils, 6 batteries (series)

Using the "weight lifting" method, I got rough relative measurements of the strength of the magnetic field. This was done by placing a 115.76 gram piece of steel (piece of a MOT core) on a scale and taring it (setting the scale to zero). By placing the magnet at a set distance above it (44.83mm from magnet to steel piece) I could partially lift the steel piece and a negative value could be seen on the scale. This is a very crude, unscientific way to compare the strength of different magnet designs.

Magnet chart.png

Again, these are relative measurements and the numbers don't mean anything in an absolute sense. The 2 coil 6 battery arrangement lifted the metal weight off the scale entirely, and so the measurement was invalid. I also felt the 2 coil 1 battery arrangement was trivial. I did not include these data in the graph.

Some people asked me, "Why don't you use a switch?" There are several reasons:

  1. For 1 or 2 batteries, there is very little danger and a switch is unnecessary.
  2. For 3 to 6 batteries, a switch is not as safe as a "chicken stick" (in my case, a 3 foot long PVC pole).
  3. Arcing will still occur in a switch and my hand will be closer to it.
  4. It could ruin the switch while offering no benefit.
  5. I was not concerned about damaging the batteries; I got them for free because they were already from a damaged lot.

Some people asked if I should wire the batteries in parallel. In my experience, doing so results in a weaker magnetic field. I may make a video on why that occurs. The quick explanation is that the coils have resistance, and as long as resistance doesn't increase then increasing the voltage will also increase the current, but voltage also helps overcome the resistance of the wire allowing more current to flow. Putting batteries in parallel increases potential current, but the lower voltage means it doesn't have as much "push" to carry the full amount of that current through the wire.

As mentioned, these batteries were from a lot of damaged batteries, so they cost me nothing and it's not a waste. I took the bad ones to a proper battery recycling drop-off.

DSC00322.JPG

The limit of the weight I could lift was dictated by my desire to not make a massive hole in my floor. I also wanted to push the magnet to the failing point, so I opted to use a single coil and 2 batteries in series. I used a wooden plank as a lever and was able to just barely lift 209 pounds (94.8 kg) before the magnet started to let go. At this time, I can only speculate on how much weight I could lift with more coils and more batteries. Unfortunately, I don't have a yard or a garage to do my experiments.

Links

Check out my first Electromagnet project: Electromagnet 01