Patient Warming Blanket Heater

Project and Challenges

Our client wanted to design a very compact warming product for use in operating rooms worldwide. Marketing indicated that there would be very great acceptance of the device if it could be very small. The heater needed to ramp up in stages, and the product had to be very safe.

The heater in this product would provide warm air into a garment surrounding the patient during and after surgery. It was imperative that this compact product operates safely in a sensitive environment like the Operating Room with oxygen nearby and the patient connected.

Since the product needed to be such a small size, there was very little room for the heater. A space of 1.8" x 7.5" x 0.8" is all that was available for a heater in the most desired product configuration. To accommodate 1400 watts at 240 volts and squeeze in safety devices would be difficult - especially with adequate electrical spacings for CE approval.

Solutions and Their Impact

Farnam was able to design a heater that would fit this space without compromising the needed rate of airflow. We designed the heater so that integral mica dielectric / thermal insulators would line the plastic duct and act as heat shields.
We implemented a design with three circuits which allow the heater to ramp up to 1400 watts in stages. The three circuits are powered up in a sequence of 200 then 400, and then 800 watts. The in-rush current is controlled by this gradual and progressive process.
A snap-acting over-temperature thermostat protects against excessive temperature build-up.