I would like to decrease the load on my alternator by switching to LED bulbs wherever possible, I already replaced the H4 halogen 55/65wheadlight bulb with a 17 watt unit, but a thought occurred to me - will that actually do anything? Does an alternator charge full all the time [rpm related] and the regulator sheds the the excess in the form of heat? Or does the alternator somehow produce less with a lesser load?
I should mention, 91 Ultra, tons of lighting ...
Thanks, Frank

 

The alternator in a Harley is a permanent magnet alternator, it puts out power depending on the RPM.

The output is converted to Direct Current, and controlled by the Voltage Regulator dumping the power to the heat sink.

The load on the alternator will not decrease by using LED bulbs, the regulator will just dump that extra power to the heat sink.

 

not exactly.
the pmg is fixed and cannot be excited like the old shovels.
the regulator is like a very fast switch so it is in a constant state of switching. when off, it is off.
if you look at the schematic, you will find it ahead of the battery and runs the system directly. the battery will supply the short fall if needed.
there is a protection circuit that will bleed current to ground when voltage gets too high, but it bleeds ac not dc. as long as the system load keeps voltage in check, the protection circuit is off.
hd designed them to just do the job and nothing more due to $$$$ considerations. it is most efficient in the mid rpm range where most riding is done.
if you reduce system load, the regulator will adjust. it is plumb stupid to run a system under full load when not needed, even the old electro-mechanical regulators did not do so. instead of a semi-conductor, it used a mechanical points contact. it was a balance system.

 

What exactly did I say wrong?

It is a Permanent Magnet Alternator, it produces alternating current, not DC.

The rotor/stator produces max power output all the time, voltage regulator dumping excess to the heat sink.

If you reduce the power required by the system (turning a light off, turning a radio off etc), the VR will just dump more power to the head sink, it does not reduce the load on the rotor/stator.

 

The benefit will be reduced electrical load through the switches and wiring connections if you have eleventy jillion lights.

 

Thanks fellas, but reading both answers I'm feeling there were two answers there. Will reducing the lighting/load requirements reduce the work that the alt needs
to do? Or will it work just as hard?

 

The alternator will work just as hard, but as Ed said, using LED lights will reduce the electrical load in the wiring.

 

ok, two diff tangets.
pmg
regulator
the pmg open ended cannot flow any current. it is also not grounded if so, it would not work.
the regulator can be thought as a grounding regulator as it controls the current going to ground through the system loads. if you reduce 10 amps to 1 amp, ohm's law dictates there is less wattage to be dissipated.
the regulator levels are usually controlled by a zener diode since they are cheap and very accurate and long lived. there are many switching technologies as SCR, MOSFET, and TRANSISTORS. there is a new animal on the market, the SMPS but more $$$$.
these semi-conductors must be biased on or they cannot conduct, hence zero current flow except maybe some small leakage current. the old single transistor regulators were huge, produced a lot of heat and were short lived. most regulators use a flip-flop between two semi-conductors and produce less heat as the load is shared, more stable and longer lived(could use smaller units). they also take advantage of producing power from both sides of the wave form.
there is a protection circuit on the ac side and usually set via a zener also and a typical of 50 volts (variances). if you are tooling down the road and the system load keeps the ac output below 50 volts, that protection circuit is idle, but suppose you kick it up and the ac voltage rises, that circuit bleeds the ac to ground. there is less current value and heating compared to the dc side.
the dc side of the regulator just keeps switching on/off according to demand.
the mechanical regulator was also a on/off via balance between mechanical and electrical forces. there was a bleed current via a resistor used in the field forcing of the generator which was a AC machine.
if the points were open, no current could flow, same as no bias to turn on the semi-conductor.
look at a light dimmer using triac, you control at what point in the sine wave it conducts, the rest of the wave does not go to ground.
put an inline amp meter on the system, does it not go up when more demand is called for and the reverse??? if it was fully loaded, the meter would be steady state. the bias just keeps the semi-conductors on longer or shorter to suit.

 

There seems to be a little mystique about the little black boxes known as the regulator and a couple of old wives tales on how they work so this I hope will clear some things up. If we can understand something better, we are more apt to diagnose and repair it. The generator adjusts itself to the load and no excess current is sent to ground.

First of all, the generator is actually an alternating current devise (ac). Since silicon rectifiers were not invented yet, the ac was changed to dc by the commutator and brushes. As the commutator is rotated in the magnetic field, a current is induced into the armature windings and is sent to the commutator segments and brushes to the output. The current and voltage will peak as the magnetic field peaks and starts to decay to a negative value on the ac wave form, but just before the it transitions to a negative direction, the brushes switch the ends of the armature coil where the current and voltage is now rising to a peak positive value. These peak values from the armature windings are combined to create a high steady value instead of a series of high/low pulses.

THE BALANCING ACT



The regulator consists of three sections: cut out relay, current regulator and voltage regulator.

1. CUT OUT RELAY: Generator at high speed is equal to exceeds battery voltage, charging takes place, but at low speeds, generator output is below battery voltage and will discharge the battery through the generator so the cut out relay opens to prevent this from occurring.
2. CURRENT REGULATOR: Limits the generator out put amperage to prevent the armature winding from burning out.
3. VOLTAGE REGULATOR: Maintains the voltage to a set level to charge the battery with out damaging it.

The cut out relay has two coils, one for the battery and one for the generator that perform a balancing act of two magnetic fields. The coil on the battery holds the contact open so no current can back flow to the generator and its ground brush. When the generator out put exceeds the battery voltage, the magnetic field on its coil over comes the coil on the battery and closes the contact allowing current to flow. When the generator out put goes below battery voltage, the magnetic field on the battery coil over comes the generator coil and the contact opens to prevent back flow.

The voltage regulator has a shunt winding of fine wire connected across the generator and an accelerator or series winding that speeds up the action of the vibrating contacts. A flat steel armature attached by a hinge is above the coil core and has a set of contacts. When the voltage regulator is not operating, the tension of s spiral spring holds the armature away from the core so the contacts connect the generator field coils to ground. When the generator voltage reaches a set value, the magnetic field over comes the armature spring tension and pulls the armature down and the contacts open which inserts a resistance into the generator field circuit and the field current is reduced. The reduction of generator voltage reduces the magnetic field of the regulator shunt winding and the magnetic field is weak enough to allow the spring to pull the armature away from the core and close the contacts. When the contacts are closed, the field coils are grounded and cause the generator out put to increase. Remember in the generator the field coils are fed from the output of the armature current. This cycle is repeated many times a second and keeps the voltage at the desired level.

The current regulator has a few heavy turns of wire, which carries the full generator output amperage. A flat armature with a hinge is over a coil core and has a set of contacts. When the regulator is not operating, a spring holds the armature away from the coil core and the contacts are closed. The generator field circuit is completed through the contacts in series with the voltage regulator contacts. When the generator current reaches its set value, the magnetic field of the coil pulls the armature down over coming spring tension. This action inserts a resistance in the generator field circuit and the generator output is reduced. The reduction in current from the generator reduces the magnetic field of the current regulator coil and the weak field is overcome by the spring tension and the contacts are closed. This grounds the generator field coils and the generator output increases. This cycle is repeated several time a second and keeps the amperage at a set level. This also prevents the generator from burn out due to high current through the armature windings.



All mechanical adjustments and contact cleaning must be done with the battery disconnected. “ The cut out relay must never be closed by hand with power connected or it will over current the regulator and damage it. This is what smokes the resistors on the back of the regulator.”

Very slight adjustments can be made to the voltage regulator point gaps to change the settings. The same is true for the current regulator. However, you must use a calibrated current source to correctly set it or you could over max the generator and burn the armature windings.

There are ways to test the regulator on the machine. Do not over look the battery! A high battery temperature will reduce its resistance and the regulator will over charge it. Shorted plates will also affect the regulator but not effect the rest of the electrical system until the battery output is too low.

Remember, the machine will primarily run off the generator output and only draw power from the battery if the generator cannot keep up.



What’s up next, possibly a 101 on the electronic version. Yes they can be repaired if you want to take the time and effort!!

 

I`m confused...
The discussion is about the charging system in a modern Harley.
There is no commutator, just a permanent magnet and a stator.