Re: Hey do you know your car's alternator only outputs 7-10% while it's running?

He is NOT wrong. At curb idle the average alternator is not capable of producing nameplate power. Curb idle of 750RPM spins most alternators at roughly 2100 RPM due to the pulley ratio. The BIG advantage of alternators is that belted at 3:1, at 6000 rmp engine speed (18000 rpm alternator speed) the rotor does not unwind itself - there is no catastrophic separation of the commutator, and all the other nasty stuff that happened to generators at high speeds.

And most definitely not all wind turbines gear up the alternator. Most of the BIG commercial units do have a gearbox - in many cases incorporating a governor.

Something like that - yes.

No shit. Did you spend your entire life coming to that conclusion, or did someone just hit you upside da haed with a common sense stick?

It certainly does not require 2000 rpms either.

Wrong. ALL wind turbines gear up the rotational ratio to the driven shaft. ALL of them. The governor is for the blades, NOT the alternator.

Got a small wind turbine here... with a straight shaft, blades to armature, no gearing/belting. Nelson

Apparently you have never heard of direct drive wind turbines ?

When building variable speed wind turbines, you are going to need some power electronics to convert the variable frequency power from the generator to the fixed 50/60 Hz mains frequency. When the power electronic is needed, why not let the generator operate at a low RPM, generate very low frequency electricity for the inverter and skip the failure prone gearbox.

In practice, direct drive wind turbines use permanent magnet generators, which tend to have a large diameter, often requiring a large nacelle.

For instance Enercon makes direct drive wind turbines in the 2 MW category.

Paul

Home hobbyist retard projects do not count.

Permanent magnet. Would that not then be a generator, not an alternator?

Anyway, the show I saw had shots of some pretty big gearbox hardware. I figured that everyone followed that. Just shows that no matter what gets invented, the rest of the world improves on it.

I think we should us elevated water reservoirs and use the turbines to pump water up from the water table, and up into the reservoir to be used with water driven turbines that are much more efficient.

It would be like going back to the old days with the lever on the back of the shaft, drawing water up from the well.

As others have pointed out to you, you got it wrong.

In order to get a useful voltage out of an old DC generator, you had to rev up the engine slightly. This was simply because they were belted to run at a slower RPM. This was necessary because when the engine was turning at 3k-4k, you couldn't have the generator spinning much faster than 4k itself or it would disintegrate from the centrifugal forces. (unless you want to spend the $ on a variable-ratio belt drive for just the DC generator).

Alternators are connected to the engine with a belt drive that steps-up the RPM so that when the engine is idling, the alternator is spinning much faster. Thus, it is able to produce a usable voltage even with the engine idling. The mechanical design of the alternator uses two strong metal pieces with interlocking 'fingers' to hold the winding and can withstand much higher speeds than a conventional DC generator rotor.

Another gross generalization based on thin air.

daestrom

Really, to function at all. Even so, at idling speed, output was effectively zero, since the voltage at maximum excitation was lower than system voltage, and the cutout operated. Imagine that in today's stop-start city driving conditions.

A DC generator is limited by how fast it can be run without the armature disintegrating. Automotive alternators' rotors are wound coaxially to the shaft with shaped "wrap around" pole pieces and can inherently be run faster.

DC generators were usually run at not much more than engine RPM (if even that), alternators much faster, witnessed by the respective ratios of pulley diameters, alternators having much smaller driven pulleys.

One of the selling points was their still giving useful output at idling speed.

In fact, alternators are run much faster than 2000RPM. A 6" pulley on the crankshaft and a 2" pulley on the alternator with an engine that redlines at over 6000 RPM says it all. He should take a look under the hood (if he can find it ;-)).

I plonked him ages ago. Patience exhausted.

Still *some* power, though.

Take a look at:

That document also describes the use of switched mode rectification to optimize output power, and postulates an expression for output power which is a reasonable fit to experimental data.

No. Permanent magnet rotor, windings on the stator. Still an alternator.

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

There are no cars that incorporate variable ratio belt drives in America. It is too expensive, and there is no need.

The belt drive on generators was NOT 1:1 or anywhere near it.

Cars topped out at 5500 rpm back then from the factory. It was not until the muscle car era that rpms crept up, and that was still not for offline production. The drive hub on the harmonic balancer and the hub on the generator were about 2:1 up. I was building engines at the time, and I also used a generator as a motor on one of my go-carts, so I remember the hub sizes.

I do not need a primer from a dope that doesn't even know how generators were driven.

NOT true. They were nearly double engine speed.

Alternators are at about 4 to 1.

I doubt that there are ANY driven devices on cars that have a mere two inch hub. It makes the belts arc at a smaller than recommended rate, which would wear the belts out far too soon.

You will find that there is a pulley size minimum that makers will typically not fall below. A toothed belt can turn tighter, but V-belts had specs that are well above two inches.

That minimum will define the main crank pulley size, based on the ratios required by the driven hubs in the pulley system. Those driven hubs will all have to be normalized to their desired rotational rates to each other from the drive hub on the crank.

Google "ungeared wind turbine" and confirm that you are always, always AlwaysWrong.

Hey, catching your mistakes is both fun and educational.

John

Does anybody still use vee belts for alternator drive on vehicles these days? Everything I've seen recently uses flat poly-vee ("serpentine") belts.

I've got some power transmission catalogs somewhere at work. I'll have a look tomorrow for minimum radii on vee and poly-vee and get back to you with some figures.

Depends on the implementation. And the alternator. And whether you mean engine RPM or alternator RPM.

A Piggott wind turbine is direct drive - and since a Piggott wind turbine most definitely exists, by deduction it is clear that NOT ALL wind turbines gear up the rotation ratio. There are many other "plans built" wind turbines out there that are also direct drive (and I am certain also at least several commercial units in the low - mid power range)

And if the governor limits blade speed, what does that do to alternator speed??? Are you aware of any wind turbine employing a CVT??? (contantly variable transmission)