Tonti alternator power generation.

[Stevex]

Electrickery has never been my strong point. I can follow a wiring diagram and fault diagnose with a volt meter, but that's about it.
I'm looking to gain some knowledge on my LM2's charging system which is totally standard and works very well. I went through the whole system
a few years back during the bikes refurb.
So, I get that the alternator produces a current which charges the battery via a regulator / rectifier and all the bike's services are run from the battery.
Does the alternator produce a set current independent of the load drawn from the battery? If so, where does the 'excess' current go...to the heat sink?
I've noticed my oem voltmeter indicates a good voltage when the lights are off, but with the lights on, the indicator arm drops a fair bit. Is this an indication of the batterys charge with and without lights on? Is it better to have a bigger draw on the battery, so the alternator is in effect being more efficient and loosing less of its generated power to heat dissipation?

[Kiwi_Roy]

I assume you are talking about lout Lemans II
The transistor regulator only lets enough current through to excite the rotor field, once the battery Voltage is high enough it throttles back the field current so it just balances the demand.
http://www.thisoldtractor.com/guzzi007/schematics/1978_LeMans_II.gif
Although the regulator doesn't measure the battery directly the 3 small diodes  are held to the same Voltage.
That and what Wayne says.

[Wayne Orwig]

Odds are, the reason that you see the voltage change with the lights on, is that the meter is wired into a circuit that also powers the lights. You are likely not looking at true battery voltage, but instead you are looking at the wiring harness loss. Most likely. Measure the battery voltage, at the battery, with a digital meter. Turn on the lights and measure it again. Compare that to the voltmeter reading. Let us know how much they change with the lights on.

[wirespokes]

You know - the charging system is pretty simple really with only four parts not including wires, but like all simple things, can get really complex especially when you look deeper. i never thought about the current aspect of the alternator, which I don't believe is regulated. It's the voltage, but regulating one, affects the other. The faster the alternator spins the higher the voltage, so it's cut off somewhere around 14+ volts. The regulator controls the strength of the rotor's magnetic field and in that way causes less electricity to be generated.

It's three phase, which gives a more steady voltage than single phase. That also means there's a positive phase and a negative phase requiring rectification and that's what the diode board is all about - getting rid of the negative and keeping the positive flow.

Like Wayne and Roy said, the voltmeter 'sees' the battery from a distance through wiring losses and is commonly a volt or so less. And then the total voltage in the system is divided between the lights and battery - so if you're reading just the battery it will be less by the amount the lights use.

The starter consumes the most electricity of anything on the bike and drains quite a bit from the battery. So when the bike first starts, voltage will read low for a while until the alternator gets it replaced. It can take 15 minutes at highway speed to replenish the battery from one start. Starting the bike a bunch of times over a short distance can leave the battery flat enough to barely restart. Because the rotor is attached to the crankshaft it spins only half as fast as autos where it's driven off the alternator.

Batteries do best when they drain the least and are kept charged. If the bike is kept in tune and starts immediately, the battery should last a long time.

[Groover]

In response to where does the excess go, Current is flow, so unless there is draw, there is no current therefore the excess you mention from the generator is just magnetic field and wire windings creating and holding voltage while spinning. The generator spinning will just keep the voltage until the demand is there to create the draw/current. Same as in a house; We all have voltage at our outlets that just sits there until we plug something in then there is current. So to wrap it up, in the house there is no waste so to speak by just having voltage at the outlets nor is there a buildup anywhere of current or heat. The heat is generated by flow/current not voltage.

At least that's my understanding of this in a nutshell.

[wirespokes]

Don't feel like the Lone Ranger, Steve - I don't think anyone has a complete grasp of electricity. I think it's one of the last systems guys get comfortable with, if at all. I recall a thread on Adventure Rider concerning an airhead charging issue that went a good fifty or sixty pages before it resolved. In the end it was the battery. LOL

For something so simple it can get incredibly complex. I think it just takes time and a willingness to be confused. Things will eventually clear up and get easier. I've been around these Bosch charging systems for 30 years and have a pretty good grasp (I wouldn't say 'great') on them, but it's still a challenge sometimes.

[n3303j]

In response to where does the excess go, Current is flow, so unless there is draw, there is no current therefore the excess you mention from the generator is just magnetic field and wire windings creating and holding voltage while spinning. The generator spinning will just keep the voltage until the demand is there to create the draw/current. Same as in a house; We all have voltage at our outlets that just sits there until we plug something in then there is current. So to wrap it up, in the house there is no waste so to speak by just having voltage at the outlets nor is there a buildup anywhere of current or heat. The heat is generated by flow/current not voltage.

At least that's my understanding of this in a nutshell.

Actually the Bosch charging system regulator is constantly monitoring system voltage. When charging current is required the system feeds more current to the rotor to strengthen the magnetic field and increase the output voltage (and charge the battery). The charging system robs less power from the engine when it is not charging the battery.

Now my V11EV has a permanent magnet rotor. The regulator monitors system  current and the battery conditional regulates current flow to charge the battery. When the system is charged the EV regulator feeds the alternator output to frame ground (they short the extra current to earth). That's why the EV regulator has cooling fins and sits in the airstream. This system is always taking away a portion of engine power.