Calculate how to size a resistor for following circuit?

Have a DC supply that varies from 48-54VDC that is supplying a relay that works between 12-48VDC. We have a 475 ohm resistor in series to drop the voltage but we continually keep blowing up the electronic relay. We are now looking at connecting a zener Diode (39V 1W) and keep the series resistor. Will we need... show more Have a DC supply that varies from 48-54VDC that is supplying a relay that works between 12-48VDC. We have a 475 ohm resistor in series to drop the voltage but we continually keep blowing up the electronic relay.

We are now looking at connecting a zener Diode (39V 1W) and keep the series resistor. Will we need to change the size of the resistor?

Could someone show me how to calculate this?
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