CB1100 Alternator

[postoak_imp]

Okay this question has no real-world relevance to any bike I own or have owned, but is just out of curiosity. I've been watching old youtube videos on motors and alternators (I had hand surgery and won't be able to ride for three weeks and have to do something!), and am almost more confused than before I started. Anyway, how does the CB1100 alternator work?

Does it use a field coil in the stator? And what the heck is the purpose of a field coil, anyway? Does it have permanent magnets in the rotor or electro magnets? I know that older Hondas, at least, had a sort of slip ring arrangement on the end of the rotor to feed electricity into the coils on the rotor but what was the source of the electricity that flowed into the rotor? Was it AC or DC?

 

[Lord Popgun]

Our alternator is 2 parts. The stator, which is wired in a Delta configuration (basically, 3 coils wired in a triangle shape) and a rotor that has permanent magnets. The output is 3 phase AC to the voltage regulator.

Here is a picture of it. The rotor has the magnets. The coil doesn’t move and is thus known as the stator.

Field coils are used in devices that don’t use magnets for the magnetic field. Instead an electromagnetic field is used. Field coil - Wikipedia

In all generators, a wire must move through a magnetic field, or vice versa. If you spin the magnet you can just get that the output from the coil easily like on our bikes. If you spin the coil, it harder and slip rings, are used. Then you have brushes, etc. You can also Google commutators for more info on them. In motors, etc.

 

[peterbaron]

As per google...

"In a so-called 'DC generator', this AC current is generated in the rotating armature, and then converted to DC by the commutator and brushes. In an 'alternator', the AC current is generated in the stationary stator, and then is converted to DC by the rectifiers (diodes)."

You have lot of time to self-educate through google while recovering
Good luck and heal quickly & permanently

 

[Lord Popgun]

Peter, next up: left hand rule for motors, right hand rule for generators.

Did you have to learn about ELI the ICEman who lives in SARL PARC?

(Nothing to do with this discussions though)

 

[the Ferret]

You are never going to pass me in mileage pulling tricks like that young man.

Hope the healing goes well.

 

[postoak_imp]

So, as per popgun, on the CB1100, magnets on the rotor move near the coils in the stator and that changing magnetic field creates an AC current in the stator coils.

Or, a field coil in the stator makes a magnetic field around it which then produces a current in a coil in the rotor, which makes it a magnet and this magnetic field rotating through the stator coils produces AC current in them.

Or a pair of slip rings on the end of the rotor is used to feed current into the coils on the rotor which magnetizes them and then works the same as above.

In the early CB750s, I know a field coil was used to produce current in the rotor coils which then produced a magnetic field in them.

SOHC CB750 Alternator Showing Field Coil (Skip to 22:44.)

But in other early CBs I know that current was fed into the rotor coils to create magnetic fields in them. The current into the rotor went through slip rings (not sure if that is the correct term). I know this from looking at videos of these older style rotors. Where was the current for this produced?

[url=http://]CB650 Alternator Showing Slip Rings on end of rotor.

Is all that correct?

 

[pekingduck]

Popgun and Postoak are right, our alternators are 2-part, with a crank-mounted rotating permanent-magnet-lined rotor spinning outside the stator bolted to the outer case cover. (They used to run a smaller rotor inside the stator ring, but it couldn't generate enough power).

The first CB500/550/750s had a 3-part alternator. The stator was bolted to the outer case cover, as was a smaller diameter field coil. Sandwiched in between was a crank-mounted spinning rotor that was not magnetized until the field coil was energized. The advantage here was that there was less HP loss when the battery didn't need charging.


In between (1979-1982), Honda eliminated the field coil, and relied on brushes contacting the face (slip rings) of a spinning electromagnet rotor with the stator on the outside. Same benefits, but brushes tended to wear quicker than expected. Basically, car alternators work like that, although brushes are located along the shaft instead and last forever.

 

[Houtman_imp]

Brushes on the CBX lasted between 10 and 15 thousand miles , always had a spare set with me and easy to change on the road.
Early CBX 's were often made redundant because owners were afraid of an expensive repair or new alternator .Brushes were very cheap.

 

[postoak_imp]

Thanks, why did the field coil type reduce HP loss when the battery didn't need charging? Was power to the field coil cut (using some sort of feedback mechanism)?

Brushes on the CBX lasted between 10 and 15 thousand miles , always had a spare set with me and easy to change on the road.
Early CBX 's were often made redundant because owners were afraid of an expensive repair or new alternator .Brushes were very cheap.

What do you mean they were made redundant?
The CB1100 type, with its permanent magnets is so simple compared to the other two types that I think there must be some downside to it or why would they have gone to so much trouble to use electromagnets on the rotor?

 

[max]

"The CB1100 type, with its permanent magnets is so simple compared to the other two types that I think there must be some downside to it or why would they have gone to so much trouble to use electromagnets on the rotor?"

We've now come to the voltage regulator part of the electrical charging system, the task of this system is to provide 14 volts to the electrical system and the battery.
Once the bike is started the alternator starts charging the battery and supply energy to the on-board electrics like ecu, lights, injectors, fuel pump etc.
Initially the charging system needs to replenish the battery's energy used by starting the engine with the starter motor, so the alternator delivers more current until the battery is charged back up.

This is all controlled by the voltage regulator/rectifier and works in a similar way than a toilet cistern, it maintains ( regulates ) a constant level of water pressure ( electrical voltage ) whatever the usage ( current ) requires.

The technology has changed over the years and so have the alternators.
There were no powerful mosfet transistors in 1970, the technology used was a coil with a set of contacts (cb550) and a spring that was set to maintain 14 volts dc. and six diodes.
Later it became possible to use transistors instead of the coil and spring to regulate the 1 ampere or so to control the field wiring.
The last step happened when there were powerful mosfet transistors available that were capable of handling 40 amperes in a very efficient way called "pulse width modulation", in effect the same as the old coil and spring in the way it switched on and off but now in a very high frequency so it looked like dc.

So rather than control a field coil to behave like a magnet that can be controlled with variable current we could now control the output efficiently, no need for a complex field coil, it was replaced by more reliable and cheaper permanent magnets.

And so all the regulation and dc rectifiers are housed in one unit with three yellow wires going in and constant 14 volts dc from the two red and black wires leaving the small very efficient waterproof unit at up to 40 amps, simple.

 

[postoak_imp]

Thanks Max, that sheds some light on it but this sentences confuses me:

Quote:There were no powerful mosfet transistors in 1970, the technology used was a coil with a set of contacts (cb550) and a spring that was set to maintain 14 volts dc. and six diodes.
Which coil are you referring to (stator, field, rotor, or ignition) and what is the spring you are referring to?

 

[max]

Thanks Max, that sheds some light on it but this sentences confuses me:

Quote:There were no powerful mosfet transistors in 1970, the technology used was a coil with a set of contacts (cb550) and a spring that was set to maintain 14 volts dc. and six diodes.
Which coil are you referring to (stator, field, rotor, or ignition) and what is the spring you are referring to?

Which coil are you referring to (stator, field, rotor, or ignition) and what is the spring you are referring to?
This small coil was inside the regulator and maintained the 14 volts against the( adjustable ) spring tension.
It was the most common regulator system used on all vehicles at the time, it's mechanical/electrical, the more tension on the spring the higher the regulated voltage, the spring is the equivalent to the float height in the cistern.

The spring would pull against the magnetic field, if the magnetic force was getting stronger ( higher voltage ) it would overcome the strength of the spring, open the contact and break the supply to the field coil, voltage would lower, contact would close again etc.
so it would be vibrating in it's own rhythm and maintain 14 volts

 

[Lord Popgun]

And thankfully those things are over and gone! Here is a pic schematic of one. Google Search:

And here is one that is like ours: Google Search:

It uses SCR’s, not MOSFET’s though.

 

[SportsterDoc]

Great responses from Popgun and Max, with helpful info from pekingduck.

Max, does the CB regulator draw full current at all times and waste unused or only draw what is required?

The latter is a benefit of Cycle Electric regulators over stock H-D regulators. I do not know as much about Honda as Harley.

 

[pekingduck]

Thanks, why did the field coil type reduce HP loss when the battery didn't need charging? Was power to the field coil cut (using some sort of feedback mechanism)?

Brushes on the CBX lasted between 10 and 15 thousand miles , always had a spare set with me and easy to change on the road.
Early CBX 's were often made redundant because owners were afraid of an expensive repair or new alternator .Brushes were very cheap.

What do you mean they were made redundant?
The CB1100 type, with its permanent magnets is so simple compared to the other two types that I think there must be some downside to it or why would they have gone to so much trouble to use electromagnets on the rotor?

Yes, as Max said, the mechanical regulator had a set of points that an electromagnet would close when battery voltage dropped enough to weaken the electromagnet. When it was charging, it added some frictional drag from the magnetism. Some production road racers used to have a toggle switch to interrupt the power to the exciter coil. Maybe one or two horsepower more, maybe it was all in their heads.

 

[max]

Great responses from Popgun and Max, with helpful info from pekingduck.

Max, does the CB regulator draw full current at all times and waste unused or only draw what is required?

The latter is a benefit of Cycle Electric regulators over stock H-D regulators. I do not know as much about Honda as Harley.

Doc, the regulator is small and efficient ( not much heat to dissipate ) it somehow ( thanks popgun ) switches the output devices average current very fast to maintain regulated output.

It works by switching the output devices hard on and off in the same way the old school regulator did but at a much faster rate, so the device does not dissipate a lot of power, it only dissipates the amps times the volt drop across the device, let say 20 amp across 0.02 volts = 0.4 watts multiplied by 3 or six devices is 1.2 watts plus control circuitry and diodes if any.

The trick is how long to switch it on for in relation to the off period, the "width" of the "on" pulse,
This "time on" is the variable that determines how much energy is released in the electrical system to maintain 14 volts, which is done by the electronic regulator drivers inside the device.
This ratio is called the "duty cycle" and is anywhere between 0% and 100% depending of the load at the time

Nothing or very little is wasted and no ballast ( old way of dumping unwanted energy ) is used, it is simply not generated.

The output of an alternator such as ours generates as much as 50 volts ac unloaded, we just nibble enough of it ( regulate ) off to supply the electrics of the bike.

Just used practical values to explain, the actual values will be different but in the ballpark.

 

[postoak_imp]

I see Max, I missed the sentence where you said you were now talking about the voltage regulator.

Since there is no field coil or rotor coils voltage to control, how do our regulators work? Do they send excessive current to ground?

 

[pekingduck]

I see Max, I missed the sentence where you said you were now talking about the voltage regulator.

Since there is no field coil or rotor coils voltage to control, how do our regulators work? Do they send excessive current to ground?

Yes.

 

[SportsterDoc]

Interesting thread

Pre 04 EVO Sportsters have only a single phase stator and output 24 VAC per 1,000 RPMs. Thus, at 6,000 RPMs, the regulator/rectifier is seeing 144 VAC. Unlike Honda, the regulator is mounted in front of the frame for cooling.

http://www.cycleelectricinc.com/Diegnosing Alternators.htm

 

[Houtman_imp]

Thanks, why did the field coil type reduce HP loss when the battery didn't need charging? Was power to the field coil cut (using some sort of feedback mechanism)?

Brushes on the CBX lasted between 10 and 15 thousand miles , always had a spare set with me and easy to change on the road.
Early CBX 's were often made redundant because owners were afraid of an expensive repair or new alternator .Brushes were very cheap.

What do you mean they were made redundant?
The CB1100 type, with its permanent magnets is so simple compared to the other two types that I think there must be some downside to it or why would they have gone to so much trouble to use electromagnets on the rotor?

What do you mean they were made redundant?
The CB1100 type, with its permanent magnets is so simple compared to the other two types that I think there must be some downside to it or why would they have gone to so much trouble to use electromagnets on the rotor? With redundant I meant that often the owner did not repair the bike and just let it sit in his garage/shed and after a while tried to sell it.
Once I bought a 79 CBX with only 14000 miles on it for $ 600 in Upstate NY and the only thing it needed was a new set of brushes. The bike would not charge/run and owner afraid of repair bill

After some years later the cheap and easy repair became well known and than the bikes were not that cheap any longer !