Compatibility with power inverters, UPS devices, and generators.
Question: Are the Herpstat's compatibile with UPS units,12vdc to 120vac power inverters, or generators?
The short answer:
Most computer UPS backup systems and 12vdc to 120vac inverters output a modified sine wave. A modified sinewave typically will not work with the components that proportional thermostat use to dim power. They will work with relay based non-proportional thermostats. In order to work with a proportional thermostat the backup system must produce a "True" or "Pure" sine wave. These systems are usually double the price of a standard UPS or power inverter. We also only recommend pure sine wave inverter based generators that are compatible with sensitive electronics like laptops.
The long answer:
Most proportional thermsotats use a Triac to control the AC output. This component gets triggered and turns off on its own once the AC voltage reachs zero volts. Common UPS systems or power inverters using "modified" sinewaves do not recreate the smooth curve sinewave that comes from your home outlet. Instead they spike the voltage 120vac positive, then drop to zero, then spike to 120vac negative. Because of this there is no way to dim the power. Also in my testing the triac typically will not turn off properly and stays stuck ON once its triggered. In order to have a proportional thermostat work properly off a battery powered (or gas generator for that matter) device it has to output a "True" or "Pure" sine wave. These systems recreate the correct smooth arced sinewave just like your home power. Because of the extra components and technology they are usually double the price.