Hello.
I have a car transformer. Car outlet, (12v, 15A max) to 120v (500W on box). There ia a temperature controller ( XH-W3002) to add to control the transformer's fan. Adding it to the same output doesn't function. So, the same problem to solve: 2 outputs from 1 input. Can you please, give some ideas.
Thank you very much.

 

Use DC-DC converter?

 

Try installing a big fat Capacitor to the 12V Input of your Converter.
Something on the order of ~10,000uF @ 16Volts.

You probably have a Noise-problem,
caused by the Converter,
interfering with the Electronics of the Thermostat.
.
.
.

 

Fist of all, I do not understand the description. What is a "Car Transformer"????
Could you be meaning an inverter: 12 volts DC in and 120 volts AC Out?? or would it be like a battery charger: 120 volts AC and 12 volts DC out???
IF it is an inverter 12 volts at up to 15 amps in, that equals 180 watts in, so 500 watts out is a fiction. That would imply about 275% efficiency of the inverter device. Not Likely!!
So use a 12 volt fan to cool that device and avoid the problem.

I have two inverters that use 12 volts in to deliver 120 volts out, 400 watt and 800 watt units. They each consume about 10.35 amps to light a 100 watt incandescent bulb.