Replacement for the original HD Model 32E alternator
Installation options for the following motorcycles:
Harley Davidson
- WLA 749 ccm 1940 - 1952
- WL 749 ccm 1945 - 1952
- WLC 749 ccm 1941 - 1944
- Panhead 749 ccm 1948 - 1965
- Knucklehead 998 ccm - 1200 ccm 1936 - 1947
- Shovelhead 1206 ccm - 1338 ccm 1966 - 1984
- Ironhead 883 ccm - 998 ccm 1957 - 1985
The Dynamo HD Project is another item in our wide range of replacement generators for vintage motorcycles.
The 6V and 12V dynamos we offer have proven themselves in practice on many British motorcycle brands, resulting in
a complete line of Type L dynamos. Our dynamos also perform well in German motorcycles, Polish motorcycles
(Junak), as well as those produced in the USSR, successfully replacing the original generators.
Owners of Harley-Davidson motorcycles were also searching for a generator replacement. They contacted us,
providing samples of the original generator and the requirements that the future DYNAMO HD should meet. Based
on several years of experience, we accepted the challenge and began work on building a device that was expected to
meet the following
Criteria:
1. The device must match the dimensions of the original generator.
2. The device must closely resemble the original solution and visually fit the motorcycle.
3. The dynamo must provide appropriate electrical parameters (voltage and output), which the original generators
barely achieve at maximum RPM, while the Dynamo delivers them already during calm city riding.
The core we had previously developed with a ½-inch offset could not be used for this project. Work had to begin by
designing a completely new core and an overall structure that would meet the above requirements.
Based on the dimensions of the original generator and the practical operating RPM ranges, a rotor/core assembly was
designed and sent for testing on a test bench. As is often the case, the first prototypes did not fully meet our
expectations. However, they provided insight and data indicating the direction in which we needed to proceed to
achieve the required electrical parameters within the specified RPM ranges. After five redesigns, we achieved the final
device concept that met all the criteria.
Once we had a functioning electrical-generating unit, we gave it a shape and appearance consistent with the original
Harley generator.
Dynamo HD 12V/150W
Sizes:
• Length 6,90 inch
• Diameter Ø 3,75 inch
• Rear cover length: 2,32 inch
Technical data:
• Voltage 12V/150W
• 3 chagrining Generator
• Charging 14,4 V without load 1200 RPM
• Charging 14,4 V under load 80 W by 1500 RPM
• Mass minus ( - )
• Electronic controller is located under the cover
Technical requirements:
• Mass minus ( - )
• 12V battery from 10 Ah - gel, lead-acid or lithium battery
The housing has external dimensions corresponding to the original generator. It consists of a front section with two
threaded holes, 5/16" and ¼" (22 threads per inch), allowing installation in both older and newer engine versions.
The rotor has been designed to allow mounting of both early-type and later-type drive gears. It features a multi-spline
shaft compatible with the original design, with a hole for the locking pin used with early-type gears, or alternatively, a
thread that enables installation in newer engine versions.
The threaded section must be removed when installing the unit in an older engine version.
The rotor is made from high-grade steel and has undergone heat-chemical treatment. Neodymium magnets suitable
for operation at temperatures up to 150 °C are mounted on the rotor. During testing, we observed that the device
temperature does not exceed the engine block temperature, which averages around 50–60 °C. Assuming that on a hot
summer day, under heavy engine load, it may reach a maximum of around 80 °C, the magnets have a substantial
thermal safety margin.
To achieve the required power output, we used strong neodymium magnets, which generate noticeable resistance
when the rotor is turned by hand. To address anticipated questions: during rotation, the rotor “clicks” or “steps” in a
characteristic way, unlike a traditional generator whose rotor spins freely when not excited. An excited generator
producing similar output to our Dynamo would create the same level of resistance on the rotor.
The device contains no brushes, eliminating the common source of wear and failure found in traditional generators.
We assumed that an output of 150 W would more than sufficiently cover the power demand of all electrical consumers
on the motorcycle.
The electronic regulator is integrated into the unit and covered by a metal housing (rear cover) matching the original
dimensions. It is also possible to use the original generator’s metal rear cover, as we have designed the mounting hole
layout to be identical to that of the original unit.
Voltage Regulator
The voltage regulator we have developed operates on a different principle than most solutions available on the
market.
Conventional regulators short-circuit the stator windings when the charging threshold is exceeded, which creates
maximum resistance for the device and causes the windings to heat up significantly. Over time, this inevitably leads to
damage.
Our solution disconnects the windings when the generated power is not needed. The regulator automatically adjusts
itself to the current power demand. Put simply:
If the device is loaded with 10 W, it will produce only 10 W—without overheating the core windings. When power
demand increases, the regulator correspondingly increases the output produced by the dynamo.
Battery
The battery should be selected so that its capacity is matched to the maximum power output of the dynamo. The
generally accepted rule is to choose a capacity (measured in ampere-hours, Ah) equal to one-tenth of the device’s
power (for the 6V version, slightly higher is recommended):
• for the 12V version, a battery with a minimum capacity of 10 Ah is recommended
• for the 6V version, a battery with a capacity of 8 Ah is recommended
In practice, lithium-ion batteries or AGM (Absorbent Glass Mat) lead-acid batteries currently perform the best. Of
course, traditional high-quality lead-acid batteries can also be used. Based on our own experience, we can recommend
a lithium-ion Moretti battery, which has been tested by us over a period of more than three years.
From our observations, manufacturers of traditional lead-acid batteries seem to operate on a “one-year shelf-life”
principle. We have observed cases where a brand-new lead-acid battery used in a motorcycle functioned for about one
year under normal conditions, and a spare battery stored on a shelf and connected to a standard maintenance charger
also lasted about the same amount of time. Both failed after roughly a year. The conclusion was that whether these
batteries are used or stored, their lifespan is approximately the same—after a certain period, they fail suddenly and
become unusable. Several customers have reported similar experiences.
It should also be mentioned that the battery installed in a Harley is subjected to significant vibrations. Lower-quality
batteries may not withstand these vibrations. The internal cells can break or become detached, causing immediate
battery failure. Lithium-ion and AGM lead-acid batteries, due to their construction, are much more resistant.
Cable Harness Connections
The HD Dynamo has a built-in electronic voltage regulator:
• Connect the system by disconnecting the positive A (+) wire from the original regulator, marked as number 32 in the
diagram, and then connecting this wire to the output on the dynamo marked A (+).
• The ground wire for the charging indicator light should be connected to the output marked F, which serves as the
negative (–) terminal for the charging indicator bulb.
• The HD Dynamo has its negative (–) terminal connected to the housing body, which must be properly connected to
the motorcycle’s ground.
The connection is made as follows:
First, the positive cable (+) is disconnected from the original regulator (shown as component No. 32 in the diagram).
This cable is then connected to the A (+) output of the Dynamo HD.
The ground connection of the charging indicator light is connected to the F output, which serves as the negative (–)
pole for the indicator lamp.
Installation of the Dynamo
(1) Carefully read the warranty card.
(2) Carefully follow the installation diagram supplied with the device and verify that it matches the motorcycle’s
wiring diagram.
In case of discrepancies, determine whether any previous modifications conflict with the changes required
for installing the dynamo.
(3) Use a battery suitable for operation with the dynamo: minimum 10 Ah for the 12 V version (8 Ah for the 6 V
version). Under no circumstances should gel batteries—such as those used in home alarm systems—be used.
If a traditional lead-acid battery is used, a vent tube must be installed to discharge electrolyte fumes below the edge of
the rear fender.
(4) The device operates with negative (-) ground. The battery terminal marked as negative (-) must be connected to
the motorcycle frame using a wire of at least 1.5 mm². The wire should be fitted with copper or brass terminals,
preferably additionally soldered to the conductor.
(5) The HD Dynamo has its negative (-) terminal connected to the housing. Ensure that the housing has a stable and
reliable ground connection to the motorcycle frame.
(6) The positive (+) wire marked A (+) can be connected to terminal number 4 on the ignition switch. This ensures
that the voltage regulator is not powered while the motorcycle is parked. Terminal number 3 will also work correctly
in standard configurations.
(7) The wire marked F is the negative (-) terminal for the charging indicator light.
When wired correctly, the charging indicator—supplied with (+) power from the opposite side—should illuminate.
WARNING:
The indicator light will function correctly
only when the battery is connected and the negative (-) is
properly grounded (see point 4). If the battery polarity is reversed (positive grounded instead of negative), the voltage
regulator may be permanently damaged, and such damage is not covered by the warranty.
The charging indicator will not illuminate if:
• the voltage regulator is not connected to the battery (positive and negative wires disconnected)
• the battery’s positive terminal is not connected to the motorcycle frame (misfiring of ground)
• the indicator light socket is damaged, the bulb is improperly seated, or the bulb is burned out
• voltage is applied to the wire marked F (negative output from the regulator to the indicator).
This may permanently damage the indicator control circuit. In such cases, charging will still work, but the indicator
light may stay permanently on or remain off.
This often occurs when replacing a bulb under power, or during service work in the headlamp where poor access can
cause accidental short circuits.
The circuit can be tested by touching the end of wire F to the housing of the HD Dynamo.
The neutral indicator light circuit can be checked by touching the wire to the motorcycle frame; the indicator should
illuminate.
If it does not, the fault must be sought in the indicator socket or the wiring inside the headlamp.
If the indicator light does not work, troubleshooting should begin with checking the bulb installed in the neutral
indicator.
(8) Mechanical assembly
The dynamo is a replacement for the original generator and is installed exactly according to the proper mounting
principles of the original unit.
For correct installation, it is recommended to remove the engine’s side cover to ensure unobstructed access to the
gears.
The gear backlash must be adjusted using shims, following the original instructions, so that the backlash is
neither too large nor too small. For a new gear set, the correct backlash is 0.05–0.1 mm.
WARNING:
The gear backlash must be checked after the unit is fully tightened, as it may change during tightening.
Before installation, verify that the idler gear does not have excessive play between the bushing and the shaft.
If excessive play is present, the gears may “lock up” during operation and damage the dynamo shaft (including
breaking it), or cause very rapid wear of the interacting gear teeth.
Additionally, using a worn idler gear or an old gear with a new dynamo gear will in most cases produce significant
noise.
We recommend that if the original gear train is retained, at least the idler gear and shaft should be replaced, as they
will mesh with the new HD Dynamo gear.
Failure to remove excessive play, or setting the gears too tightly, may result in very rapid bearing wear, which is not
covered by the warranty.
The device uses new FAG bearings with C3 clearance. Their wear at mileage below 25,000 km is practically
impossible.
Note:
Many customers ask whether it is normal to feel sequential “clicking” when rotating the gear attached to the
dynamo rotor by hand.
This is completely normal—the device contains permanent magnets that generate this effect during rotation.
It is not a sign of bearing damage.
An original generator, when excited, also produces a comparable resistance on the gear train depending on the power
it generates
On delivery include:
- Dynamo HD
- Warranty card
- Operating Instructions
- Packaging
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INFO !
Outside EU without 19% VAT, will be deducted from the price in the invoice!
Prices including 19% VAT
Dynamo HD
Part number: 00 25767 HD 12 - Dynamo HD- 12V/150W - 650,00 €
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