I had an aquarium air pump which broke down a couple of days back as it got water inside it. I knew the electromagnet inside it has been damaged. Even though I could have bought a new one. I thought of experimenting to fix it.
I had seen online that an electromagnet can be made from a transformer. And decided to give it a shot. I followed this video Electromagnet from a Transformer, and used an E-I Laminated core transformer 
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As shown in the video I disassembled the laminated core, stacked the Es together and placed it in the winding.
On turning it on it did act as expected,as an electromagnet ! I placed it in my air pump, and it even pumped air. It sparked and got damaged shortly after though.
I will be honest I did few changes in the design though, knowing the air pump used to work at 5W,still I went with a step down 12V 1A transformer (For no reason). Later replaced the stacked Es with the previous electromagnet core which used to be in the air pump(It resembled in shape and size, and was easier to fit in the air pump casing).
Can you please help me with knowing where I went wrong with this, I am still new to electronics and really to want to know more about it ?
Best Answer
If the transformer sparked it is most likely due to the wires shorting on the core, and they were probably damaged when you reassembled the transformer. Transformer windings are usually covered with a thin enamel on the wires.
If it was something else sparking, you probably did not match the voltages of the core and the required voltage of the air pump and too much voltage was given to the air pump.