48Amp single phase VS 50 Amp three phase

As many of you who ride 1997 to 2005 FLH/FLT models have discovered, they do not seem to get the stator life you may expect. For those of you that do not know what a stator is, it is part for the charging system. Its job is to supply electrical current to charge the battery and run electrical devices. 


 In 1995 Harley Davidson introduced its first production fuel injected motorcycle. A larger charging system was needed to run the electric fuel pump. A 38-amp single-phase system was developed. It was a dependable system that delivers 16 amps at 1000 rpm and 38 amps at 2500 RPM. The full dressed fuel injected models still needed more electrical power. Instead of developing a completely new system Harley bumped up the output of the 38-amp system by increasing the strength of the magnets on the rotor. This is where the problems began. To make an analogy it is kind of like taking a stock motor, boing and stroking it to the max, then adding the most radical cam you can find. Man it really puts out but when it hits it hits hard. All this extra power puts more stress on down stream components. This extra stress can shorten the life span of some parts that are not designed to handle it.

With the addition of the stronger rare earth magnets on the rotor the system was called a 45-amp system. In 1999 with the introduction of the twin cam motor they started calling it a 48-amp system. The 45 and 48 amp systems are basically the same systems. This is the first system Harley made that can produce more amperage then it is rated for. This system puts out 30 amps at 1000 RPM and about 54 amps maximum. When drawing over 45 amps out of this system, the stator will produce heat faster than it can get rid of it. The temperature of the stator will rise until it gets hot enough to melt the insulation. Once the insulation burns up the stator shorts out and will no longer work.


We spent years upgrading our stators to increase the durability of this system. As luck will have it all of our other stators have received the benefits from this quest.

 The plastic over molding insulation used on other stators melts at 4250 F. By 4500 they are toast. We have developed a stator that can withstand peaks of 6000F. But Continuous operation at this temperature will shorten the stators life span. Drawing full power out of the 48-amp system (54 amps) can result in temperatures this high.


Another draw back to using the stronger rare earth magnets is they produce an AC waveform that results in harsh power delivery. Alternators produce alternating current commonly refers to as AC. If you made a graph plotting AC voltage agenst time it would make a reciprocating wave. Ideally it would make what is known as a sine wave. A sine wave has a rounded almost semi circle shape to it. The more commonly used ceramic magnet rotors produce a wave that rise and drop of more gradually. The stronger magnets used on the 48-amp rotor produce a square output wave. This square waveform indicate a vary fast change in voltage which leads to vary high instantaneous current. These high instantaneous current spikes produce a lot of heat and go hard on the regulator and battery. This is what I mean when say the 48 amp system hits hard.


Until recently there where on other charging systems available with enough output to replace the 48 amp single phase system. The introduction of the 50 amp three-phase system gives another option. There are many benefits to the 50-amp system. The three main advantages are better durability; smother power delivery and lower cost.

 The larger three-phase stator used in the 50-amp system has18 polls to do the same work of the 12 polls on the single-phase stator. This spreads the load out over a larger area. On top of that each poll has only two layers of wire compared to four layers on the old stator. This will lead to better heat dissipation and lower operating temperature.


The 50 amp three-phase system delivers a smother power delivery for two reasons. First of all, the rotor in this system uses the ceramic magnets. As I mentioned before they make a smother out put wave. The second reason is the three-phase system has three sets of charging coils. These coils produce waves that are offset 120 degrees from each other. This is kind of like having a motor with three smaller cylinders instead of one big one.

The smaller smother more frequent waves produced by this system delivers a smother charge.


The rare earth magnets used in the 48 amp three-phase system are dreadfully expensive. The ceramic magnets used in the 50-amp system are fairly inexpensive. So basically for a little more then the cost of the 48-amp rotor you can buy the entire 50-amp system.


Due to the benefits of the three phases 50 amp system Cycle Electric Inc. will no longer sell the 45/48 amp single-phase systems in kits. We will continue to sell replacement parts. We do offer 50 amp upgrade kits to fit 1998 and later.


 If all you need is a regulator or stator it is more economical to just replace that part. If you have had chronic stator problem I would recommend upgrading to the 50-amp system. If you need a rotor you should go with the upgrade. All things considered, compared to the 48-amp system, the complete 50-amp kit is the way to go.

Let the road you choose to ride bring you happiness.

Karl Fahringer


Cycle Electric Inc.