Relay, max voltage on the coil

[Dimitree]

hi everyone
I'm using this relay:
Takamisawa RY-12W-K

Datasheet:
http://www.fujitsu.com/downloads/MICRO/fcai/relays/ry.pdf

however instead of 12V, I'm supplying more or less 16.5V on the coil. While it works, I'd like to be sure that it won't melt over time.
So can anyone help me understand how should I calculate the max voltage I can supply to the coil using the infos on the datasheet?
thank you

[Gus]

Use Ohms law to calculate a series voltage dropping resistor you have the information on the PDF

Then calculate the DC power rating for the resistor

[R.G.]

Gus is right. I might use a 4V or so zener, but a resistor works fine and is cheaper.

However, it is possible that it will not melt. This datasheet, unlike some other manufacturers', does not explicitly tell you the maximum voltage or dissipation in the coil. The coil resistance is 960 ohms. the nominal power is V²/R = 144/960 = 0.15W. At 16.5V, the power is 16.5*16.5/960 = 0.284W.

In the Specification table, Coil Section, line for "Nominal power (at 20C)", it lists 150 to 300mW. 284 is less than 300, so if I read that right and guess correctly, 284mW is OK, if very close to the edge.

Also, in "Characteristic Data", second table "Coil Temperature Rise", for a coil power of 0.3W, it shows a 30C temperature rise. Back in the Specification table, Coil section, it lists operating temperature for this one as -30C to +90C. While that number is probably an external operating environment temperature, it shows the coil is safe from burnout at 90C. So if your coil rises 30C, and the operating environment around the relay (that is, the air temperature around it) is less than 60C, I'd say you're fine.

This is guesswork and intuition based on an incomplete datasheet.