A comparison on the Kubota D722 Diesel Engine (Kubota GL9000 GenSet)

RF2 7.5

The RF series Radial Flux Generators  a single stator, single rotor permanent magnet design. The combination of novel winding techniques with innovative rotor and stator design gives the RF series significant advantage over current commercially available technologies.

The RF series generators are designed specifically to be compact, lightweight whilst remaining highly efficient. All materials used in construction are conventional, so as to minimize manufacturing cost whilst still providing the specified performance.

The RFL RF2-132-115/135 Bi-Gen is a technologically advanced PM brushless alternator, offering highest energy efficiencies while maintaining minimal physical size. It  sets a new industry standard. Its PM design Brush-Less Internal Magnetic Voltage Regulation (No AVR  or electronics)  means that possible points of failure are kept to a minimum by eliminating traditional brushes and AVRs.

The Kubota GL9000  Alternator (Sawafuji Elec Co Ltd GL90 A0)  was chosen as a comparison point for a 1 Phase application where the generator is supplying into a circuit that can be split into 2 separate 1 phase circuits (20 Amp 240V each ) to demonstrate the advantages of the RFL Bi-Gen connection.  Tests results of fuel economy, motor starting and other physical factors were analysed and the RFL alternator was found to be superior in almost all  aspects.

Testing Procedure

The original Alternator Sawafuji Elec Co Ltd GL90 A0) was run through a series of load and fuel usage tests. With the load connected direct to the output side of the man switch .

It was replaced with the RFL RF2-132-115/135 Bi-Gen alternator . This required a new adaptor plate and a new mounting feet bracket. The original cooling fan mounted on the flywheel was removed. A taper shaft adaptor was bolted to the flywheel to take the RFL Alternator. As the RFL Alternator has its own in-built cooling fan, the original fan was not re-fitted.

As the RFL Alternator has no AVR and only requires 3 wires to the main board, the wiring harness to the original alternator was removed.  The main board was modified to take 2×25 Amp Earth leakage breakers. We then  replaced the 3 x 15 amp sockets  with 4 x 15 amp sockets  . These were arranged as 2 x 15 amp sockets to each breaker. This gives 2 circuits 1 to each of the 2 phases of the B-Gen Alternator. This arrangement will allow up to 25 amps on each circuit ( 12.25 amps on each of the 15 amp sockets ). The total load can be up to  45 amps.

Fuel Savings:

From the testing changing to the RFL Alternator improved the fuel efficiency both at no load and at full load. The savings were between 10% and 15%. When we convert this fuel saving to money we find that if the alternator is run for 8,760 Hours, the savings are a substantial. At full load it is $5,900.00 and at half load it is $3,800.00 as the normal run time of these unit is around 20,000 hours, or 2 years , then the fuel saving  alone could easily pay for the cost of purchasing the unit.

Extra Power:

By changing to the RFL alternator the gen-set can be rated at least 1000 watts higher. The GL9000 could be re-rated as a GL10000.

Both these gains are due solely to increased Alternator efficiency.  The other gains will be due to lower maintenance costs and higher reliability of the alternator.

Better Waveforms:

The THD at no load and at full load is better than the original alternator. No load the THD = 1.7%. Full load, 10 Kw the THD is 4.0%.


Comparison Specification Chart

Physical Comparisons

Physical Comparisons

Length Comparison When RFL Alt Is Fitted

Electronic Comparisons

Electronics Comparison

Fuel/Performance Results

Alternator – Sawafuji Elec Co Ltd – GL90 A0

Engine – Kubota D722 3000 Rpm

Table 1

Table 1

Alternator – Radial Flux Laboratories Pty Ltd – RF2-132-115/135

Engine – Kubota  D722 3000 Rpm

Table 2

Table 2

Running cost savings**

Table 3

Table 3

*Maximum power of RFL alternator is 1000 Watts extra

**Based on wholesale Diesel price of AU$1.47

Fuel Usage Test Comparison

Table 4 – Graphical representation of Table 1 & 2

Motor Starting Comparison

Motor Starting Comparison for RFL Alternators

It can be seen that with the gen-set  fitted with the RFL Alternator has a slightly Higher voltage drop on motor starting than the Kubota Alternator . This is only on the circuit that has the motor start on. The other circuit shows no effect even with large motor starts.

Waveform Comparison

Waveforms of RFL alternator and Kubota Alternator at no load and at full load

RFL waveform comparison