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Step 10 Testing and debugging

Connect the batteries and inductor, and push the button. If you are near something heavy and made of steel, like a fridge, filing cabinet, car, etc., you should hear a chirp. If you hear this chirp, you can pretty safely assume it's all working OK.

If the fuse blows, remove the inductor and replace the fuse. If it still blows, you have a short somewhere, such as a backwards diode or blown MOSFET. It can be a real pain to find which one.

If the fuse only blows with the inductor in place, the inductor may be too short. Add more turns.

If the fuse blows with a properly sized inductor, one more possibility is that something is wrong in the timing/control circuit, or a diode is backwards, or a MOSFET is fried. If the inductor is left connected to the battery, the current can ramp up beyond 5A very quickly. At 8 kHz, there is not enough time for the current to ramp too high. If you have access to an oscilloscope and know how to use it, great. If not, you can use a voltmeter to make sure the H-bridge is putting out AC. Remove the inductor and measure voltage at the device output. There should not be a significant DC offset.