easy way to generate an ac signal

Oct 24, 2012 244 Replies

But each of the windings will be producing a near sine wave voltage where the commutator makes contact at nominally the peak voltage.

No motor winding produces a perfect sine wave, and even when a sine wave is highly desirable it's difficult to achieve, as evidenced by cogging in 3-phase motors, and the noise they make when spinning up.

I'm more talking about what the windings on a DC motor see after the commutator switches the DC to provide the AC needed. Harry seems to think only a perfect sine wave would make that motor work.

Quite. It's actually quite tricky to produce a perfect sine wave by any means.

=A0 London SW

Sine waves from practical rotating generators are only approximate You would need a single loop coil rotating in a uniform magnetic field to get a proper sine wave. Neither occurs in practice. Smaller machines are worse than bigger ones.

:

The only thing that "smooths" ripple in DC is energy storing devices. ie capacitors (in parallel) or inductors (in series)

It would be neccesary to have one hell of a big capacitor in a low voltage, relatively high current device like an automotive alternator which is why they don't have them and have a highly modified alternator instead.

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wave form is independent of speed. It will be the same at all speeds subject to hysteresis of the iron components. Frequency is dependant on speed. The voltage is dependent on speed and the magnetic flux density (which is controlled by the excitation current.)

The rotating part of any electrical machine caries AC. Is that hard to remember? Generaior or motor. Cogging?????????

except this once.

I'd suspect the diode pack was marginal and wouldn't have taken much to blow it. S*it happens - I've been aware of the possibility of blowing the diode pack for decades, but it's never happened to me in those circumstances and as the years have passed and tech has got better and more reliable I suspect the likelihood of it happening is lower now than it was 40 years ago. Viz, the s***ty Lucas ACR range - which were actually good enough in their day, but were a bit prone to losing diodes - luckily, cheaply repaired.

What, even in warp generators?

Chreeeist. It must have caused some brow-furrowing and teeth-clenching to write that.

Oddly I don't have any emotional stake in whether harry is an antisocial spiv (he is) but does know a few things (he does).

Mostly he is wrong, by like any random monkey, occasionally he types a sequence of letters on the keyboard that resembles a fact.

I never realised you were a Trekkie.

+0100, The Natural Philos>

There's no-one here more anti-social than you.

OK so what does the rotor of a car alternator carry then harry?..

In article , Grimly Curmudgeon scribeth thus

Over here Grimly LUCAS used to be called "The prince of darkness"

+0100, The Natural Philos>>

Standard Spiv response.

Must try harder.

Load of c*ck - Lucas were immeasurably better than the awful French or Italian electrics and even Bosch, imo. Dreadful 1950s electrical systems were terrible all round.

Or indeed the style of brushless motor where the rotor is all magnets and no coils at all :-)

Harry reverts to type.

It's like dogging but it's the AC/DC form...

It seemed a mainly US term.

Worst car electrics I ever had were by Delco - a US maker.

Lucas simply made what they were asked for at a price the car makers would pay. Their stuff for Rolls was very nicely made. ;-)

In article , Grimly Curmudgeon scribeth thus

This is the UK here;)..

I thought you were over there .. in the Emerald Isle?..

I think we can agree on that last sentiment.

To also include the 60's and 70's and a bit of the 80's;(....

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