When I repeatedly connect and disconnect the power source, eventually the fan dies. I lost multiple fans this way already. I'm not sure if it happens on the connect or disconnect. When the first fan died I thought that water might have killed it, but it happened twice more with a different, waterproof fan. Once there was a burning smell.
I thought that maybe an inductor in the pump produces a voltage spike when the power gets disconnected, burning out the fan in the process, and that the addition of a flyback diode might prevent that.
When I measure the voltage across the pump in isolation while disconnecting the power, I see the voltage spike shown in the screenshot below. I expected a negative spike but I see a positive one, and it seems a flyback diode won't help with that.
- What could be the reason for this spike?
- Could it be responsible for burning out a 12v fan (or should the fan be able to tolerate this duration and/or level of spike?)
- how could I fix it?
Update: One commenter recommended a 10000uF capacitor but the largest I had around was a 470uF one rated at 50V. I tried that, and it fixed the problem, no more voltage spikes.
Out of interest I also checked if the fan produced any spikes that might damage the pump. It did produce some small negative spikes on power down but the magnitude seemed harmless. I quickly checked if a flyback diode would help and it did, but I ended up not adding that to keep it simple.