How to prevent output voltage spikes
A current limiter is probably the most straightforward way to do this. Check out this answer: https://electronics.stackexchange.com/a/229893/106823

NB that transistor should be AFTER the load coil. Also pay attention to transistor base voltage versus current, you have a lot more current than the 20mA LED circuit. You're probably looking at 0.7V, not 0.6V. 

You can also implement this with a mosfet as well but a transistor may be easier to pull off.