Why DC instead of AC?

No transfer switch, no frequency fluctuations, no dependence on engine speed controls, no power loss converting from AC to DC, and no problems with voltage fluctuations. The DC generator is small, lightweight, and fuel efficient. Repair is simple; it can be picked up by hand and replaced in the field.

Polar’s 3.5 KW DC alternator has been derived from its proven and tested 2.2 KW military generator model. The 3.5 KW operates within 2500 to 3600 RPM; a higher speed range than other Polar alternators, which operate in the 1200 to 3000 RPM range. The higher speed of the 3.5 KW reduces the weight, size, and cost of the alternator and engine.

The 3.5 KW DC generator uses Polar’s Permanent Magnet Hybred Homopolar (PMHH) technology. This unique technology eliminates all parts which typically wear or fail inside an alternator, including brushes, slip rings, rotating fields, excitors, and bearings. The unique design also allows us to operate the engine at viable speeds while maintaining precise voltage regulation. The six-phase stator design reduces voltage ripple on the output and reduces filtering requirements.

The voltage regulator is unique in its ability to regulate and limit the output current. In an over-current condition, most DC generators will either stall the engine, overheat the alternator or engine, or trip the output circuit breaker. The most common cause of an overcurrent load is a battery in low state of charge. Polar’s generator will stay on-line without overheating, stalling, or tripping a circuit breaker.

Engine

Polar selected the Kawasaki Model FE290 to drive its alternator because it is the best engine on the market for this application. Note the following features:

• Oil Pump - The most important criteria Polar used in the selection of Kawasaki’s Model 290 was the full pressure lubrication system using an oil pump. Unlike your automobile, most small engines do not use an oil pump. Instead, these engines splash lubricant with the spinning crankshaft. Unfortunately, it takes a while for oil to migrate to the bearings supporting the shaft. Using splash lubrication requires critical maintenance for the engine oil level.

The once-a-week automatic exercise of the generator, or long periods without operation create the need for a full pressure lubrication system.

• Large 286CC Displacement - Most generator manufacturers use a 286CC displacement engine to deliver 5 KW. Polar derated the 286CC engine to deliver a continuously rated 3.5 KW in order to extend engine life. Engine duration is important for sets operating on propane and natural gas, because these fuels burn at higher temperatures, and can burn the exhaust valves.

• Low Vibration - Kawasaki has incorporated a unique reciprocating balancer within its engine design. Typical single-cylinder engines will vibrate more than multi-cylinder engines. Vibration causes noise and can adversely affect electronic assemblies located near the generator. Kawasaki’s Model 290 produces amazingly little vibration and noise.