How the PEPI® Model J Became the World’s Most Versatile Thermal Control

We’ve been in the thermal control business a long time. Our first product to become popular was the Model B with a sealed case. It came out in 1963 as a functional solution to a motor protection problem facing one of our clients who manufactured electric motors. This product is still manufactured today. In the beginning, material costs were low, so the entire emphasis was on performance and reliability. Since silver has excellent electrical conductivity, we used it for the electrical contacts of the Model B. Back then silver cost about four dollars an ounce, now it costs over twenty, but today’s appliance and motor manufacturers are demanding lower prices. You do the math.

When manufacturers first began facing more low price pressure from Asia, the challenge became how to cut costs while still maintaining reliability. We couldn’t control the prices of silver, but we could change our product designs and manufacturing techniques to cut costs. If you look back on the evolution of our thermal controls you can see how the route to the Model J Series was pre-ordained. We wanted to find a better starting platform to expand various types of functionality for our devices.

The Model J snap action platform allowed for fully automated production and, therefore, turned out to be an ideal combination of reliability and low cost. But, really the Model J’s versatility, made the other two possible. By designing the Model J with a wide variety of bimetal snap action elements, it became a reliable solution for more applications. More applications meant higher sales volume leading to lower manufacturing and material costs. For many years we’ve called it the Swiss Army Knife of thermal controls. Our ultimate success can be measured in the number of different functions available within the Model J Series family. At the present time, there different versions with wide differentials in temperature between the opening and closing temperature, narrow differentials, self-hold functionality, and non-resettable actions. That is a lot of versatility from a single product platform. This is the result of a series of design decisions and evolutions made at the beginning of the process.

When we started designing the Model J Series we quickly settled on the fold-over case design. It could be manufactured using fewer, fully-automated manufacturing steps than previous models. We first used the fold-over case technology with the Model A, our most popular creep action control. However, to this day, the Model J remains our only snap action device to use a fold-over case. 

At the same time, we made the conscious decision to continue using over-engineered, larger contacts to maintain performance reliability. We had already replaced riveted contacts with weld buttons contacts. They were easier to automate than rivet contacts without sacrificing performance. On the one hand, we were still using more silver than most of our competition at a time when the price was exploding, but maintaining reliability was as important to us as to our customers. Our big bet was that we could automate our manufacturing and improve our product designs enough to more than compensate for the additional silver.

The Model F, a forerunner to the Model J, used costly copper arms formed from strip material to complete the electrical circuit. With the Model J we replaced the internal copper arms with an all steel case and cover plate equipped with crimp terminals. We found the steel body performed just as well for a fraction of the cost of copper, and offsetting some of the price rises we were seeing for silver. 

Now, we could still take a bigger hatchet to material costs. There are certainly more economical bimetals and lower cost contacts available. However, thermal controls are a safety product. Malfunctions affect our customer’s reputation as well as our own, so we have rigid specifications for the materials we use. Most of the lower cost materials can’t meet those specifications so, again, there’s more pressure put on design and manufacturing efficiency.

The Model J has now been in heavy demand for over 25 years and is still one of the great workhorses of the thermal control industry. This is especially true among consumer product manufacturers who need to customize their thermal controls in some way to more closely match application needs. There are some customization steps we can take on our own factories, such as adding lead wires, or insulation sleeving, that help streamline our customer’s own manufacturing processes. 

Over the years, we have found other ways to cut costs while maintaining reliability. Some have been incorporated into the Model J design. However, the Model J remains our most popular snap action thermal controls. It is a jack of all trades and master of just as many.

Thermally yours,
Brandon Wehl