Voltage back flash? Can you help me understand that problem? I have a 12 volt system.
DC current in a motor, any winding or coil, produces magnetic energy which is how the motor/coil works. Actually all voltages/currents AC & DC produce a field around the wire in which they operate.
Especially in DC when the current in coil is stopped abruptly, switch, the magnetic energy field has to go somewhere. It produces a counter voltage which can do damage to switches, relays and other controlling devices. That counter voltage can be stronger than the initial supplying voltage by several times.
These voltage spikes are very fast.
These things must be built to withstand that backflash. The other option is to install another device, capacitor, to absorb that backflash and dissipate it over time as heat.
Or
use a diode which conducts only one way and allows that voltage to use the winding of the motor or coil to dissipate the energy as heat.
Infrequent use like your bilge pump gives some leeway for sizing but for frequent operation such as in a production plant it matters.
As a retired electrician I used to deal with this in my work.
In my case I did not expect frequent operation, hope not, but was just a matter of protection for the float sw., needed or not.
I hope my description makes some sense. It has now been a long time and I had to a bit of thinking.
