Beard at 20:04, 11 May 2018

2018-05-11T20:04:52Z

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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 =

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= 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.

[[File:Magnet_chart.png|frameless|300px]]

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:
# For 1 or 2 batteries, there is very little danger and a switch is unnecessary.
# For 3 to 6 batteries, a switch is not as safe as a "chicken stick" (in my case, a 3 foot long PVC pole).
# Arcing will still occur in a switch and my hand will be closer to it.
# It could ruin the switch while offering no benefit.
# 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 <i>also</i> increase the current, but voltage also helps overcome the resistance of the wire allowing more current to flow. Putting batteries in parallel increases <i>potential</i> 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.

[[File:DSC00322.JPG|frameless|300px]]

The limit of the weight I could lift was dictated by my desire to <i>not</i> 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]]

Electromagnet 02 - Revision history

Beard at 20:04, 11 May 2018