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Onan Generators

This page was last updated on May 18, 2026.

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D. W. Onan & Sons

(The focus of this page is the early history of the D. W. Onan Company, and its history as it became a supplier of mechanical refrigeration for the transportation industry, using sources not previously readily available. Sources include a wide variety of internet searches, online newspapers, and current websites and abandoned websites, and industry trade magazines at Archive.org.)

Founded by David W. Onan in 1920 (or 1918, or 1925, sources differ), the company initially focused on small power plants for rural homes before branching out into engine-driven generator sets. While Onan is best known for its generators, the company designed and produced its own air-cooled engines for a wide range of applications. In the late 1940s and early 1950s, Onan engines were sold to manufacturers of truck refrigeration units, making them a crucial component in the transport of perishable goods during that era.

From the Minneapolis Times, March 29, 1943.

Onan had started his business of manufacturing specialized automobile repair equipment in 1918 while he was still employed since 1909 at the local Reinhard Brothers company. By 1919 he was superintendent of their Electrical Repair Department. At the Reinhard company, Onan employed 50 mechanics, finishing 100 to 125 repair jobs per day. These were solely repairs of automobile electrical components. In January 1920 Onan hired his first employee, a clerk who worked on the first floor of the same Onan home where the shop was located in the basement. In November 1920, due to the growth of his as-yet unorganized company, Onan rented space in a nearby to handle the increased business. In late 1922, Onan quit his job at Reinhard to run his business full-time, but Reinhard continued to pay his as a consultant to visit their facility to ensure its continued smooth operation. At age 36, in December 1922 Onan was making enough money to buy his own building, located on Royalston Avenue, which was to be the home of the company for many decades after..

Beginning in March 1926, newspaper ads show that the D. W. Onan & Sons company was the manufacturer of the "Onan Safty Saw," a gasoline-powered portable table saw, with contractors and homebuilders seen as their market. By mid 1927 the company had shipped 6,600 versions of the saw. The design had come about by Dave Onan seeing the need for a portable saw in the use in his own factory that was manufacturing and shipping of specialized automobile repair equipment, mostly in the need to provide standardized shipping crates. The saw business very soon grew larger than the automobile repair equipment business, which he had started in his basement in 1918. The saw was first offered with an electric motor, but to expand it market, Onan added a Briggs & Stratton gasoline engine for building sites that lacked electrical service. The "Safty Saw" remained in production until just before World War II.

The first newspaper ad for the "Onan Electric Light Plant" made by D. W. Onan & Sons appeared in March 1928. This was in response to a need stated in summer 1926 by a friend of Onan's who needed a small portable gas-powered generator for use in his cabin. This resulted in a string of events for the Onan company that started with tools to repair motor cars in 1920, quickly switched its focus to the "Safty Saw" in 1926, and before a decade had passed after its start in 1920, Onan was producing generator sets, a product the firm has stayed with ever since. This change in focus for the company fulfilled two of David Onan's twelve points of philosophy of operating a successful company; point eight: concentrate on one-product, and point nine: meeting a need.

Onan and his 16-year-old son took up the challenge by coupling a single-cylinder Briggs & Stratton gas engine to a Master electric motor from the Master Electric Co. of Dayton, Ohio. The Master motor was converted from a motor to a generator. In spring 1927 they delivered the prototype of the new generator set to Onan's friend for testing. After some tweaking of the design of the coupling between the engine and generator, they named the finished design, the "Onan Ten-Lite Generator" from the generator's ability to furnish power to ten 30-watt lights. In late 1928, the original direct-current generator was converted to an alternating-current generator, and the new AC version became the first gasoline-powered AC generator in the country. In late 1929, Onan worked with a radio manufacturer to offer a free radio with the new generator, which boosted sales of both the generators and the radios for both companies.

Also in 1928, the Onan company known as the D. W. Onan Company, became the D. W. Onan & Sons Company when Onan added his two sons to the company organization. In 1946 the company was incorporated as D. W. Onan & Sons, Inc.

Onan began manufacturing its own engines and generators in 1931, moving away from the Master motor and Briggs & Stratton engine, and became a leader in producing gasoline engines in the 5 to 40 horsepower range. They were among the first to introduce features like pressure lubrication, aluminum cylinder blocks with cast-iron sleeves, and replaceable bearings in small engines. By the 1950s, they had also entered the diesel engine market.

The Great Depression hit Onan less than other companies, with numerous companies in the Minneapolis area going out of business completely. Onan's 1932 revenues were 65 percent of 1929 sales. Sales began to climb in 1933 and again in 1934, and exceeded the 1929 numbers in 1935, reaching four-times in 1939.

World War II brought growth for the company that Onan and his sons, and almost everyone else in the company could never have imagined. In 1940 they had produced 3,540 generators with 100 employees, and Onan and his sons were able to manage the company quite well. By war's end, Onan was manufacturing as many as 70,000 generator sets per year, with as many as 2,500 employees in five different plants in the Twin Cities area, was sub-contracting work to 82 other companies with 5,500 workers, and had annual sales as high as $50 million. From the beginning of 1942 through the middle of 1945 all of the Onan company's production went to the U.S. military and its allies. Onan produced both AC generators for lighting and other needs, and special DC generators to serve as battery chargers. The war also saw Onan expand from it original site on Royalton Avenue, into four additional sites in the Twin Cities area, bringing Onan production into an area equal to six city bocks. Engine production was also partially sub-contracted out to Continental Motor Co. in Muskegon, Michigan. There were 41 separate branches of the military ordering generator sets from Onan, ranging from 350-watt to 35,000-watt units. To fill the need, Onan produced 65 different models of generators and 40 types of internal combustion engines to drive the generators. Many of the parts going into the generator sets were made for Onan by more than 80 subcontractors.

The end of the war in 1945 brought an expected sudden cancellation of military orders, and drop in production, which in-turn meant severe lay-offs bringing the employee numbers down from 2,500 to 500 a year later. The blow was softened by the stock of parts on hand being readily available as civilian orders began arriving. Onan had gained a considerable reputation for reliability from the thousands of generators that had spread all over the globe, which translated directly into post-war sales.

After the war, Onan benefited from a federal mandate that new hospitals be equipped with standby power, along with growing demand for emergency generators for commercial and industrial buildings. Onan management also recognized that relying solely on generators risked stagnation, so in late 1946 the company decided to add to their product line by offering their air-cooled gasoline engines as a separate product line. Though Onan had long built its own engines for its line of generators, offering the engines separately soon proved to be a good decision.

The small gasoline engines were readily accepted by original equipment manufacturers for truck refrigeration, garden tillers, various types of pumps, small garden tractors, conveyors, and more. In 1946 Onan produced 60,000 units, mostly generators, but in 1947 production dropped by almost a third, to 41,000 units, 15,000 of which were non-generator engines. Without that engine production, the decline would have been disastrous.

In 1947 Onan management decided to produce a small diesel engine. The company saw a potential of heavy duty generator set that could be used where continuous running was a need. The Onan diesel engine opened an entire new market that was to play a vital role in the firm's future.

By April 1949 Onan was offering AC Power Plants in sizes ranging from 350 Watts to 10,000 Watts. The 10,000 Watt plants used a four-cylinder gas or Diesel engine. The 5,000 Watt plants used a four-cylinder gas engine. The 2,500 Watt plant used a one-cylinder air-cooled Diesel engine, and the 2,000-Watt plant used a two-cylinder air-cooled gasoline engine.

An Onan advertisement from December 1950 wrote that:

This is where the railroad application becomes part of the Onan story. The October 1953 issue of Industrial Refrigeration noted that the new mechanical refrigerator cars being built were using diesel generator sets to power the refrigeration units being installed as part of the new technology in railroad freight cars. The dominant builder was GM's Detroit Diesel connected to a GM Frigidaire refrigeration unit. The article noted that Onan was also part of the growing market.

The following comes from Ice and Refrigeration magazine, October 1953.

November 1953
Onan in AT&SF cars -- "Versatile electric power - 25,000 watts of it, runs Santa Fe's new Mechanical Temperature Control units now being performance-tested. The 30 cars are equipped with 25-KW generating sets of which ten are model 25 DCV-5E/344C, 25-KW Onan Electric Plants powered by IH Diesels. Another ten have Onan 25-KW generators run by Hercules Diesels. Each electric plant supplies power for one 15 HP, 3-phase, 220-volt electric motor for the refrigeration compressor, one 3 HP motor for the evaporator fan, one 5 HP motor for the fan which cools the engine radiator and condenser unit, and heating units (for defrosting) drawing 6-KW. The electric plants also supply vital power for the electronic "brain" which controls the entire system. The Onan generators are designed to handle the heavy starting cycle overload of the motors, when from 5 to 6 times as much current is required as during running cycles." (Diesel Progress, November 1953, Volume 19, page 19)

By 1954, in the April 1954 issue of Popular Architecture, an Onan advertisement showed diesel power plants up to 25,000 and 50,000 Watts.

By 1959, an advertisement in Western Construction magazine showed that Onan was offering Diesel power plants in the range of 50,000 to 200,000 Watts.

The Onan story continues as the company went through several changes in ownership:

• 1960 -- Studebaker-Packard purchased the D. W. Onan & Sons company. At the time of the announced purchase on October 5, 1960, Onan employed approximately 700 persons in Minneapolis. The company built a line of gasoline and diesel power plants ranging from 500 watts to 130 kilowatts, for primary, emergency and marine electric service. E. Warren Onan, the son of the Minneapolis company's founder, was president of D. W. Onan and Sons. (Associated Press story, with numerous variations in nationwide newspapers)
• 1975 -- Hawker Siddeley of the UK purchased a significant interest in the company. At that time of the initial offer, in mid July 1975, Studebaker-Worthington owned 80 percent of Onan. The end result was a complicated combination of stock transactions that included the purchase of Onan's publicly held stock. The Hawker Siddeley offer to buy the publicly held stock expired on December 22, 1975. At the end of the stock transactions, Hawker Siddeley held 1.1 million shares and Studebaker held 1.9 million shares, with only 18,000 shares still in the hands of the public. The final announcement in February 1976 showed that Hawker Siddeley held 36 percent of Onan.
• 1979 -- McGraw Edison purchased the of the Studebaker-Worthington company, including Studebaker's interest in the Onan company. At the time of the announcement on July 26, 1979, both McGraw Edison and Studebaker-Worthington were reported as being large diversified manufacturers.
• 1985 -- Cooper Industries of Houston, Texas, bought and merged with the McGraw Edison company in May 1985. The reported sale was for $1.1 billion.
• 1986 -- In late January 1986, Cummins, Inc. of Columbus, Indiana, began acquisition of Onan, buying Cooper's 63 percent interest. Hawker Siddeley of UK still owned 37 percent of Onan.
• By 1990, Onan was Cummins' largest subsidiary, and already had a long-standing relationship with Kubota of Japan to build small gasoline and diesel engines for the Kubota company.
• 1992 -- In June 1992 Onan Corporation became a fully owned subsidiary of the Cummins Engine Company (now Cummins Inc.) after Cummins bought out Hawker Siddeley, for a reported $64 million.
• 2017 -- Cummins combined the Onan brand with its own brand.

The Onan name continues to be used for modern versions of their traditional engine-driven generators for RV, marine, commercial mobility, home standby, and portable use. All Onan products are still manufactured in Minneapolis as part of the Cummins Power Generation group.

(Read the 88-page Onan company history compiled by the founder's grandson in 2012, at Archive.org)

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