Harley-Davidson Charging Systems

Posted on 24. Oct, 2011 by in Open Road, Panman's Garage

Without a good working charging system on your bike, you are not likely to go far. But don’t confuse your Harley-Davidson charging system with the charging system of an automobile.

Most automobiles use a battery to operate electrical components when the engine is not running and to start the engine. After the engine is started the electrical components and systems operate using power from the charging system or alternator. Therefore, if you disconnect a battery cable from an automobile while the engine is running, the engine and electrical systems will continue to operate.

Harley-Davidson’s operate completely off of the battery and the charging system simply replaces the voltage at the battery as it is used. If you disconnect a battery cable while a Harley is running – everything stops!

For a quick check to see if your charging system is working correctly, simply connect a volt meter to the positive and negative posts on the battery. With the engine running at 2000RPM you should read more than 14 VDC and not more than 14.7 VDC.

In General, a Harley-Davidson’s charging system is made up of only three components (not counting wires). The Stator, Regulator/Rectifier and the Battery.

Several windings of copper wire coiled around an iron core mounted to the engine case (left side) with a magnetic ‘Rotor’ splined to the sprocket shaft. The plug exits at the left front of the engine case.

Test the stator for continuity, check to be sure it’s not grounded, test A/C voltage and amperage output. Inspect the rotor for signs of rubbing on the engine case or stator wiring and for any loose, cracked or broken magnets. When replacing the stator, the four mounting bolts should always be replaced. If that is not possible be sure to clean and loctite the four bolts holding it to the engine case.

The regulator is a solid state unit (mid 1970s and later) with cooling fins on the top. It is usually mounted near the front of the frame or engine.

The regulator is grounded to the frame or engine, plugged in to the stator plug at the left front of the engine case with a long wire to the Main fuse or the battery.

There is no true way of testing the regulator other than replacement. Plugging or unplugging the regulator while the motor is running can cause an electrical spike and short out the regulator. By testing for proper voltage at the battery, and then testing for proper voltage coming from the stator, you can determine the general condition of the regulator by the process of elimination.

Regulators are easy to damage. Just a little too much amperage and that’s all she wrote.

Harley-Davidson AGM (Absorption Glass Mat) Battery
Sealed battery technology was originally developed in 1985 for military aircraft where power, weight, safety, and reliability were paramount considerations.

AGM battery technology has continued to develop and offer improvements over other sealed battery technologies. AGM technology has become the next step in the evolution of both starting and deep cycle sealed batteries for motorcycle, marine, RV, and aviation applications. This “next generation” technology delivers increased safety, performance, and service life over all other existing sealed battery types, including gel technology.

In AGM sealed batteries, the acid is absorbed between the plates and immobilized by a very fine fiberglass mat. No silica gel is necessary. This glass mat absorbs and immobilizes the acid while still keeping the acid available to the plates. This allows a fast reaction between acid and plate material.
The AGM battery has an extremely low internal electrical resistance. This, combined with faster acid migration, allows the AGM batteries to deliver and absorb higher rates of amperage than other sealed batteries during discharging and charging. In addition, AGM technology batteries can be charged at normal lead-acid regulated charging voltages, therefore, it is not necessary to recalibrate charging systems or purchase special chargers.

A battery will most often fail in three different ways, won’t take a charge, won’t hold a charge, and won’t release the charge under load (lights and electrical work but it won’t crank the motor over).

Have the battery tested if you suspect it may be bad (insist on a “load test”).

Charging System Operation

Using the rotation of the engine, the magnetic stator rotor rotates around the stator windings turning magnetism into AC voltage. Electrons flow to the regulator/rectifier which converts the AC voltage to DC voltage and regulates it to approximately 14.5vdc, routing the excess voltage to ground. The 14.5vdc is routed to the battery (usually by way of the main breaker), recharging the battery.

Charging System Tips

Never “jump” a motorcycle that has a low or dead battery. Motorcycle batteries should be charged at a 2 amp per hour or “trickle charge” rate.

Never jump a bike battery from an automobile or anything with a higher amperage than your bike. Never charge the battery in the bike at any greater rate than 2 amp/hrs (you could damage the regulator).

Remember that this is not an automotive system and it does not work the same as automotive systems, if you disconnect the battery the engine will not stay running.

Often when your regulator goes bad, the stator cannot release it’s power and will damage itself. The catch 22 is that often if you install a good regulator to a stator that has gone bad, the malfunctioning stator may fry the new regulator and if you install a new stator with a bad regulator, again it’s possible to damage the new stator.

Harley-Davidson made great improvements to the stators in their bikes in 2008. Although a newer stator may still go bad, it is not uncommon to find stators going bad in the years prior to 2008. Fortunately, there are a lot of excellent aftermarket motorcycle parts, including stators and regulators that meet and even exceed manufacturer’s requirements. Companies like Accel have excellent replacement stators.

Another common problem that may also lead to the replacement of your Harley-Davidson Stator is a damaged or leaking stator plug.

The stator plug is used where the wires from the stator pass through the left inner case to the regulator. Once this plug becomes worn or damaged, there is little you can do to prevent the leaking of your oil through the hole. The recommended repair is once again the replacement of your stator, either with a quality OEM motorcycle stator, or an aftermarket stator.

You can find quality OEM motorcycle parts and aftermarket motorcycle replacement parts for your Harley-Davidson at https://www.cycle-parts.com at prices you can afford. And although we have been discussing Harley-Davidson charging systems, you will find that most motorcycle charging systems are the same. Look for quality Honda motorcycle parts, Kawasaki motorcycle parts, Suzuki motorcycle parts, and Yamaha motorcycle parts as well. Cycle-parts.com can provide you with all the parts you will need to keep your motorcycle charging system in full operation.

There are a number of videos on you-tube that show you step by step how to replace your Harley-Davidson stator. Also, look for additional articles in Panman’s Garage at http://www.hdopenroad.com on maintaining your Harley-Davidson.

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One Response to “Harley-Davidson Charging Systems”

  1. Todd Kryway

    23. Jun, 2012

    thank u for the tips , my system is really givin a @#*&^%[email protected] headache.

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