Topic: why do cb's even have field coils?

[BomberMann650]

The 70's stator and field coil setup is a bit of a contrast from the modern stator reg/rec charging systems.

So why is the field coil there?  Does it need to be there?

Modern reg rec's can make charging happen with their respective rotors , 3 yellow wires, a ground, and a battery lead.

How is the 70's system different from current tech?

[bryanj]

Any generator requires magnetism to create power by either spinning the wire through the magnetism or rotating the magnetism through fixed wire, the field coil makes the magnetism and the machined groove in the rotor makes it move over the stator windings

[craz1]

Yes on my last project I forgot the C550 had a field coil(well I didn't forget just forgot to make sure it had 12vdc). 20 miles later the bike started to act up and died as I had used all the battery power.

[Dunk]

These alternators are more like a modern car alternator,at least the early designs in the 60s-70s with separate and external components. The field coil creates a magnetic field which the voltage regulator varies how strong the magnetic field is to vary the output amps.

Most newer bikes now use permanent magnets instead of a field coil, voltage is regulated by shunting excess power to ground.

Field coil designs are more efficient so far as power to turn them, as the magnetic field is only strong enough to match current draw. Permanent magnet designs are typically more compact and there are fewer parts to fail (granted I've seen a fair number of modern bike permanent magnet flywheel/rotor with epoxy (that encases the magnets) failing. In any event, a permanent magnet alternator is always generating max output (and using max HP to turn).

[BomberMann650]

Yes on my last project I forgot the C550 had a field coil(well I didn't forget just forgot to make sure it had 12vdc). 20 miles later the bike started to act up and died as I had used all the battery power.

Been a while since i looked at the wiring diagram for the 550.

The two field coil wires.  Are they just 12v pos and neg? 

[bryanj]

Nope, regulated up to12v positive on white and ground on green

[Don R]

  Because Mr. Honda said so. That's why. Nyuk nyuk nyuk.

[BomberMann650]

  Because Mr. Honda said so. That's why. Nyuk nyuk nyuk.

Makes sense

Nope, regulated up to12v positive on white and ground on green

I gotta do some homework on this.

[dave500]

as dunk posted the permanant magnet field types are more or less running flat out and the regulator just dumps excess to earth,they also dont need a rectifier circuit,it works but the regulated electro magnetic field type is more precise on its regulation or should be and the stator isnt being worked so hard,in time the permanant magnet will lose strength but that seems to be no big deal,also youll find on more modern bikes with car like electronics the voltage must be a very clean stable voltage to not confuse or harm the computerised systems so they may have a variable electro magnetic field alternator with multi diode rectifiers,the term alternator i think was coined by chysler cars who were i think the first to use them over dc voltage generators?the alternator is in fact just an ac generator which needs a rectifier to convert to dc.

[Bodi]

Early Hondas (CB77 for example) had permanent magnet single phase alternators without any regulator. The headlight switch would connect extra alternator windings and make the extra power, but it was hit and miss... you hoped that the battery wouldn't go flat or "boil" dry. Getting a year out of a battery was a good year.
The SOHC4 3 phase alternator is a big improvement. The induced field system keeps the rotor quite light, the 4 cylinder engine doesn't need a heavy flywheel and lighter means quicker revving up on the engine and less stress on the gears when shifting. Electrical output is regulated to provide just enough power to charge to and maintain battery voltage at a full charge level. Hopefully, at least. Using high power headlights, driving lights, heated gloves or vests, modified ignition system... there's only so much power available and there isn't much "extra" above a factory fresh bike's load.
Most current bikes have permanent magnet alternators. Magnet metallurgy has come a long way since the 70's and very powerful magnets can be small and light. Most systems do just dump excess power into heat, true. On a 100+ HP engine, one or two HP being wasted doesn't really matter, for a 750 with 60 or so HP it may matter - for a 350-4 it probably would be missed. Some do have actual regulators controlling output without wasting the excess, but the cost more that the shunt type. These bikes are designed with extra power available to handle accessory load, but every 746W of alternator power wasted is one horsepower wasted.
Another alternative is a DC generator, really old cars had them and probably some bikes too. These requires sliprings or brushes that wear out and generate sparks and electrical noise. Rarely seen except on antique cars and industrial equipment.

[bryanj]

Dynamos still have a field coil and rerly on magnetism

[TwoTired]

Generators need a magnetic field to excite electrons inside the wires.  Either the wire must move inside the magnetic field, or the field itself must be in motion.

Except for the 650, The SOHC4 rotor is made of ferrous metal which is magnetized by a stationary field coil.  The rotor becomes the core of the electromagnet when current flows through the field coil.  Varying the voltage and current flowing though the field coil varies the strength of the rotating magnetic field that passes though the windings of the stator, and thus the power output of the alternator.  This system has no spinning insulated wires that can be stressed by centrifugal forces or shock impulses from firing cylinders.  It is very robust as long as the wire insulation and connections remain healthy.  It is sized to only provides enough power to run stock electrical devices and maintain a stock sized lead acid battery.  It is self limiting and self protecting, and cannot provide more power (watts) than designed. If more current is is demanded, the voltage will fall, preventing any internal destructive overheat.  It’s only moving part is not subject to any operational wear or routine maintenance or replacement of components.

It’s a pity that connection components aren’t matched in robustness, especially with corrosion factors.

There are varying schemes for PM generators, for a comparison to SOHC4, pick one to compare against and supply a schematic diagram.

Cheers,

[BomberMann650]

Thanks TwoTired - a well of knowledge as always.

I suppose there haven't been any successful attempts to adapt the 650 stator to the 550 (?)

Though as bodi described, the field coil setup is more efficient in terms of parasitic HP loss.

[TwoTired]

Thanks TwoTired - a well of knowledge as always.

I suppose there haven't been any successful attempts to adapt the 650 stator to the 550 (?)

I don't know of any without a whole engine unit swap.  But, I'd be leary.  There have been lots of posts on 650s with bad rotors.  The windings short due to wire insulation separation, likely due to centrifugal force, cylinder firing pulses, or simple insulation breakdown.  It's rather an expensive repair that often takes out the Vreg, as well.

Cheers,

[PeWe]

A friend have an Aprilia Falco with charging system on full speed burning power to stabilize.
He said that using lower wattage bulbs can cause issues making the charging system to run hotter. The bulbs are part of the system.

A charging system with a throttling device as CB's have must be better. It could produce more to cover for heated devices, fuel injection etc.
All that power burnt away must affect fuelage. There is no free power here.

[dave500]

i think we should all have propellers on our helmets to recharge the batteries?

[bryanj]

At my age the batteries take a lot of charging!

[dave500]

at my age i need a propeller to get me out of bed!

[bryanj]

Got a wife for that, plus 3 cats and a dawg!

[BomberMann650]

Honda already patented the bike battery charging propeller.
Cb4 interceptor concept.

[Don R]

 I feel like I understand the charging system a little better. Thanks to all.

[BomberMann650]

I feel like I understand the charging system a little better. Thanks to all.

Hear hear

[MRieck]

Honda already patented the bike battery charging propeller.
Cb4 interceptor concept.

Smokey Yunick created one for Nascar to get rid of the belt which was a source of failure. That was probably over 50 years ago.

[BomberMann650]

Honda already patented the bike battery charging propeller.
Cb4 interceptor concept.

Smokey Yunick created one for Nascar to get rid of the belt which was a source of failure. That was probably over 50 years ago.

I feel like some old studebakers would make good candidates for wind impeller generator conversion

[HondaMan]

These alternators have a 3-level output, not counting the K0 early ones with a different regulator.

The Diecast K0 and later 750 regulator has 3 positions. The "OFF" position is when the moving arm's contact relaxes and touches the top contact: this applies full battery voltage to the field coil, making the most power come out of the phase coils (it makes the most magnetic flux happen in the electromagnet that is the field coil). When the 'windows' in the steel rotor cut across those lines of magnetic flux, it induces an on-off-on-off pulse in the outer stator's coils, making a sort of AC electrical current. It's not very 'clean' by today's standards, but the battery is the filter for it, so it works OK.

When the battery voltage reaches 13.2 volts the coil in the regulator pulls the little relay arm in between the upper and lower contacts. This inserts the resistor on the voltage regulator into the circuit to the field coil, dropping the field current about 30%. This then reduces the amount of magnetic flux in the field coil, so the on-off-on-off pulses from the stator coils are lower in current. This is the normal running situation, usually around 3000 RPM and up.

When the battery voltage rises too high, the relay contact pulls all the way down to the bottom regulator contact, which grounds the field coil completely. This stops all battery charge, even more than simply unplugging the regulator would, because if just unplugged, the Earth's magnetic lines of flux will still generate about 8 watts of power from this alternator (guess how I know that? ).

In the very first K0 bikes the regulators were a 'chattering' type. They constantly turned full ON, then OFF, then ON again, at the rate of about 3 to 10 times per second. These were noisy and they damaged the silver contacts (which all have, and are quite soft) in short order, plus they made the headlights 'strobe' visibly at night when the battery was getting old enough that it didn't act like a filter anymore.

So, they are very simple gadgets, really. This is why you can test the stator and field coils by just jumping +12 volts to the field (ground one lead, tie the other to battery) and fire up the engine: if the alternator windings are then putting out current above 3 amps then they are at least working.