Polar Power, Inc. first tested its DC Alternator using its PMHH technology in 1992. Since then numerous organizations have performed extensive testing on Polar’s generators, including the US Army. Polar’s DC generator sets (genset) meets both Military and Belcore power applications. Test reports are available. Polar has designed its Model 6250 and 3500 DC alternators incorporating state-of-the-art technologies and all new tooling to meet the increased performance demand for:

• No Maintenance
• No Mechanical Adjustments
• Very High Quality Electrical Output
• Light Weight
• High Efficiency
• High and Low Ambient Operation (-40° to 125° F)
• Adjustable Power Outputs via Engine RPM

Polar Power selected and optimized the alternator using the Permanent Magnet Hybrid Homopolar (PMHH) technology. This technology does dot require brushes, slip rings, rotating fields, neither exciters nor field flashing. Its small compact design allows use of a bearing less pancake design.

The PMHH technology is two alternators built into a single simple package. The permanent magnet alternator being the simplest, most efficient and reliable of all the technologies has one drawback in not being able to regulate the voltage output in response to load transients. The homopolar alternator provides the fastest response to load transients among the brush less alternator technologies. The permanent magnetic portion produces the majority of the output power, the homopolar portion boosts the power produced by the permanent magnet and provides excellent voltage regulation in response to the load transients.  

The PMHH technology uses a solid rotor with magnets revolving around a stationary stator and field coil. The construction is extremely simple and requires no maintenance or replacement parts.

To reduce ripple and improve output harmonics, we incorporated a 6 phase stator with each phase rotated 60°. To further improve ripple and output harmonics, we used a 12-pole configuration.

The voltage regulator incorporates pulse width modulation (PWM) circuitry to provide a true proportional output to the field coil. Most other voltage regulators simply turn the field on/off at lower frequencies, which creates ripple on the generator output.

The 6-phase bridge rectifier assembly has been custom designed to our specifications using the most efficient schottky diodes. The power loss through our 6 phase bridge is less than half that of competitor products.

Engine performance under electrical load is greatly improved due to the 12 poles, 6 phases, and proportional output from the voltage regulator. The engine under these favorable conditions has a smooth and even torque requirement over the 360° flywheel (or shaft) rotation.

Low Maintenance and High Reliability

1. The unique alternator design allows us to turn the engine at low speeds, thereby extending engine life.

2. The Model 710 Voltage Regulator has automatic two-step engine speed control. At high electrical load demands the regulator, through an external solenoid, automatically increases engine RPM; at low loads the engine speed is automatically decreased.

3. Polar Power’s PMHH alternator has no bearings, couplings, brushes, slip rings, nor rotating fields. There are no alternator parts to wear out.

4. The entire stator assembly is vacuum dipped and baked with a polyester coating. This seals off the metal surfaces from corrosion. Resistance to salt fog is extremely high. The coatings also protect the stator from abrasion and vibration.

5. There are no electronic parts (diodes, etc.) nor electrical connections inside the alternator. There is nothing to short or vibrate loose inside the alternator.

6. The alternator is almost impossible to damage electrically. The outputs can be shorted for minutes without damage.

7. The alternator is thermally protected; a sensor on the yoke can alert the operator of a high temperature condition. If no action is taken, the regulator automatically reduces the output current so the alternator can run cooler.

8. The voltage regulator through an external current transducer monitors the output current. The voltage regulator has an adjustable current limit on the output. It is virtually impossible to overload the alternator.

9. Polar Power’s PMHH alternator should have an MTBF exceeding 100,000 hours, as there are no parts which rub, wear, or overheat under normal operating conditions.

10. The Diode Bridge set is remote from the alternator and mounted on a large heat sink to keep cool.

11. The Model 710 Voltage Regulator has lightning and surge protection on both the input and output.

12. All the electronic components within the voltage regulator are operated at less than 50% of their rated values.

13. The alternator’s rotor is dynamically balanced to improve the engine’s bearing life.

Very High Quality Electrical Output

Low EMI emissions are designed into the system. There are no brushes or slip rings. Field coil is isolated from the buss through fast diodes and capacitance. The voltage regulator does not strobe the field coil on and off. Proportional control reduces the back EMF produced by the field coil.

1. The 6-phase stator, with each phase placed 60° apart, reduces the amplitude of the current waveform. The 12-pole design also reduces the amplitude of the voltage and current waveforms. The combination of alternator frequency and multi-phasing reduces ripple and improves output harmonics.

2. The relatively large iron and copper mass in conjunction with a fast responding voltage regulator reduces the load transient response time to under 200 milliseconds from no load to full load and vise-versa.

3. The voltage regulator maintains the voltage drift too less than 1.5% during a change in ambient temperatures of 60° F over 8 hours.

4. Output ripple is less than 300 millivolts without external capacitors.

5. Distortion factor is less than .01.

6. Voltage regulation from no load to full load is less than 1.5%.

7. There is a load dump built into the voltage regulator to limit the voltage rise transient after a sudden change from full load to no load to under 6 Vdc of set point. The 6 Vdc voltage transient does not last longer than 200 milliseconds. If required, the load dump can be increased to maintain voltage to within 1 Vdc.

8. Voltage adjustment range is 24 to 32 Vdc or 48 to 64 Vdc.

Model 6250 Alternator weighs 83 lbs., and the Model 3500 weights 23 lbs., including voltage regulator. This is a weight savings of over 160 lbs. over other brushless direct drive alternators. The lightweight can be attributed to the high-energy Neodymium-Iron-Boron magnets and the "pancake" design of the assembly.

Low Fuel Consumption for the selected engine

The PMHH alternator has an efficiency of between 75 to 85% versus 45 to 70% for other DC alternators.

Low Acoustic Noise

Improving alternator efficiency reduces the horsepower demand on the engine, which reduces the engine noise.