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Starter/Generators vs. Alternators

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A little discussion has been going on over at the "big" Yahoo! group about which is "better" on Kohler engines (or any other small engine, for that matter): Starter/Generators or Alternators.

I, of course, :P voiced my "theory" (opinion? :D ) and have now decided to investigate and discuss this subject here at Redsquare. :thumbs:

After the initial question of "which is better?" by another member, I responded as follows:

A starter/generator was a good set-up in its day. It's a little more

complicated to explain, and definitely has more upkeep/maintenance and

more moving/wearing parts. (drive belt, generator bearings, brushes,

regulator contacts, etc.) A belt-driven generator "robs" power from the

engine to operate WHEN CHARGING and also requires electrical power to

produce electrical power. The amperage draw through the switch is not

as great as you might think, but you still have the ability to install

a seperate solenoid and use the correct 5 terminal ignition switch if

the original goes bad.

An alternator like used on Kohlers is considered "free power". A ring

of permanent magnets mounted within the already-rotating flywheel

revolve around a multi-pole stator and generate roughly 25 to 28 volts

of 2 phase A.C. electricity at full governed speed. This two phase A.C.

voltage is converted to D.C. by a "solid-state" (diode-type) rectifier

with a built-in "solid-state" regulator to produce a maximum ouput of

+/- 13 volts (and normally 15 AMPS max) to maintain battery charge

level.

It's entirely up to you as to what you use. Both systems can offer

years of trouble-free service with only minor maintenance. If

originality is what you're after, install the S/G. If you use the

tractor for very short periods of time, you can always hook up a jumper

wire from the "F" (field) terminal directly to ground, which

will "force" the S/G to produce full power - constantly -- to rapidly

recharge the battery.

Am I off base for thinking a flywheel that has to turn anytime the engine is running -- with no contact with other parts, or attachments to belt driven generators is not producing "free power" ? (Meaning no parasitical loss.)

I know there is a magnetic field produced by the magnets revolving around the stator, but wouldn't inertia overcome that resistance? The cooling fins on the flywheel would produce far more drag than the magnetic field! :thumbs:

Help me out here. :D

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Terry I agree with your thought process here. The spinning movement odf the flywheel should be hindered very little by the magnetic field produced by the stator. Now it has been many years since I've taken physics, so don't ask me to figure out the exact resistence even remotely :thumbs: , but I do agree with your thoughts on the systems.

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My basis is that any flywheel, regardless of whether it has magnets or a stator under it or not, requires a percentage of horsepower to turn it, but once it is spinning, its own mass actually helps to keep it spinning (inertia) as does the explosions in the cylinder of the engine to which said flywheel is attached. :thumbs:

If that spinning motion is also utilized for the production of electrical power from a source that does not put a physical "drag" on the engine, then I say it's "free power". (I associate this with a water wheel -- the water is going to flow downstream regardless if someone diverts it over a "paddle wheel" and uses it to turn another object, or if that same person stands on the stream bank drinking a beer and just watches the water pass by. :thumbs: )

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I agree. I've always considered anything belt driven off the engine as a HP robber. Thus the reason water pumps are electric driven and alternators are non existent on a full blown drag car. Every belt driven piece robs just a few more HP. I would think it would be the same for the starter generator. Like you said the flywheel has to rotate wether its producing power or not.

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Well........ kind of but... When the spinning fixed magnet is rotating around the coils a magnetic field will be generated in the coils which will resist the motion of the permanent magnet, the flywheel. The energy required to keep the flywheel with the magnet moving is exactly equal to the electrical energy generated (friction aside). So as they mentioned on Yahoo energy is neither created nor lost. It will require energy to overcome this magnetic resistance (the generation of electricity), and the rotational inertia will need to increase as the electrical energy increases to overcome this magnetic resistance. The bigger the loops (greater amp circuit) the higher the resistance, the more rotational energy required overcome the magnetic resistance.

We know this since this is how electrical generation takes place. The bigger generators require larger engines because of this magnetic resistance, otherwise we would have large flywheels with 3.5HP briggs engines powering our homes.

I do agree that the actual loss is less because of friction. Remember that energy is not created, and friction uses energy as well.

Not sure if this makes any sense or not :thumbs:

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I totally understand, Karl. But like I said at the Yahoo group -- I wasn't talking about "free energy", I was talking about making the electricity to recharge the battery with the parts that are already on the engine (more or less) -- not an additional external "parasitical" device requiring constant horsepower to turn it. (even if it is a tiny amount.)

I had a K-91 here with a S/G and if it was running at 1/4 throttle and I grounded the field terminal it would actually stall the engine! I don't ever recall of hearing an alternator-equipped engine "pull down" when a load was placed on the battery. :thumbs:

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You're right, and that's because the electrical current generated increases and decreases with engine speed. It is part of Faraday's laws of induction. The faster the engine turns the more electric current generate and the more resistance. It is a fixed (variable with engine speed) amount and the excess is more or less wasted. The more coils you have the more electrical current is generated. This is so much easier with napkins and peanuts.

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I guess I would like to put my two cents in here. Terry You said "I don't ever recall of hearing an alternator-equipped engine "pull down" when a load was placed on the battery." now I know I'm talking about a car but, hook jumper cables up to a car with a dead batt. and listen to the engine labor to help keep up with the demand on it. But I do agree with the alt/ stator on these little engine is probably better and uses less power to run, but the electrical demand is so minamal, start hooking some big lights up to it and see what happens. as the demand goes up so does the magnetic drag. But you know what I still think the S/G motors look cool. That's my 2 cents or maybe 5 cents

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I guess I would like to put my two cents in here. Terry You said "I don't ever recall of hearing an alternator-equipped engine "pull down" when a load was placed on the battery." now I know I'm talking about a car but, hook jumper cables up to a car with a dead batt. and listen to the engine labor to help keep up with the demand on it. But I do agree with the alt/ stator on these little engine is probably better and uses less power to run, but the electrical demand is so minamal, start hooking some big lights up to it and see what happens. as the demand goes up so does the magnetic drag. But you know what I still think the S/G motors look cool. That's my 2 cents or maybe 5 cents

I did mean the small engines, Kelly. My pick-up truck would damn near stall when I would hook the jumper cables up to the Mack! :D

I too like the look of the S/G engines -- especially in the long frame tractors. (like my 1056) I have a full service repair shop for them about 7 miles away and have also gotten pretty good at troubleshooting that system, but the alternator system is still very compact and simple -- compared to the S/G.

As far as extra lighting goes, that's another 20 page discussion. :P

Guys will always start adding up the wattage of the lights, and the amperage draw -- and then you have to get in to calculus and astro-psysics, etc. (that's when it gets confusing :thumbs: )

95% of my tractors don't even have headlights, and I have yet to outrun the original 4411's on my 416. :thumbs:

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The generator on the 55 Chevy has never worked as well as an alternator. One things about factories and production is that they always find a cheaper, sometimes better way to make products. I'll bet it was a whole lot cheaper to add a few coils, diodes and a small starter than to make that giant generator, regulator, belt and guard.

All that aside I'll take the quite slow chugging sound of the smooth old S/G over the high-pitched whining grind of a starter any day. Somehow the old generator seems to sing just a little bit about how things used to be.

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And it didn't take long before they started using permanent-magnet gear-drive starter motors instead of the electrical wire-wound field type either. (magnets are cheaper than copper wire)

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No such thing as "free' energy. The alternator will have less frictional drag, and might be more efficient at changing the mechanical motion of the flywheel into energy, but bottom line, any time energy is "created" something had to create it. Ever heard of E=MC squared? The generator or alternator is converting mechanical motion into electricity, not creating it.

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As a last clarification (on my behalf) on this subject....

At no time did I use the term "free energy". I know it takes power to make power -- but it takes less engine power to make ELECTRICITY using a flywheel that it already HAS to turn than it does to spin a generator that's turned by a belt hooked to the engine. (parasitical loss)

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