This will depend entirely on the resistance of the relay coil. Chances are it will be fine if the relay is designed to operate on less than the 0.5 amp current of your source. Most relays that are rated at a particular voltage will function just fine on 3/4 of that voltage. You might for the fun of it put a mA meter on the relay and see exactly how much it draws at 24 volts. Post back what you find as I am interested in your results.
