Sine-ish wave?

J

Jordan

Guest
I don't know much about permanent magnet alternators, but am surprised
at the very un- "sine" like shape of the output waveform, on a single
phase motorbike type I'm working on. It's very "peaky", with first
gently sloping excursions but that then become steep spikes, like
nothing in the text books. Is this normal, or am I doing something silly
with the CRO? By comparison, a 240V-18V transformer I tried has the
classic sinewave shape.
 
"Jordan"
I don't know much about permanent magnet alternators, but am surprised at
the very un- "sine" like shape of the output waveform, on a single phase
motorbike type I'm working on. It's very "peaky", with first gently sloping
excursions but that then become steep spikes, like nothing in the text
books. Is this normal, or am I doing something silly with the CRO? By
comparison, a 240V-18V transformer I tried has the classic sinewave shape.
Click to expand...
** Simple alternators do not produce a sine wave emf - more often it looks
like a flattened off sine wave with a wiggle near each zero crossing.

Where the wave is used to produce DC, this flattened shape is an advantage.

Imagine if it were a good square wave, then rectification would give you
pure DC.


..... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:ac9ridF2fnrU1@mid.individual.net...
"Jordan"

I don't know much about permanent magnet alternators, but am surprised at
the very un- "sine" like shape of the output waveform, on a single phase
motorbike type I'm working on. It's very "peaky", with first gently
sloping excursions but that then become steep spikes, like nothing in the
text books. Is this normal, or am I doing something silly with the CRO? By
comparison, a 240V-18V transformer I tried has the classic sinewave shape.


** Simple alternators do not produce a sine wave emf - more often it
looks like a flattened off sine wave with a wiggle near each zero
crossing.

Where the wave is used to produce DC, this flattened shape is an
advantage.

Imagine if it were a good square wave, then rectification would give you
pure DC.


.... Phil
Yes, in fact alternators don't 'naturally' generate sinewaves, you have to
Click to expand...
work hard at the design of the machine geometry in order to get a reasonable
one. With large power station machines, the shaping and alignment of the
pole pieces is very precise, on littlies like auto gensets it's not so
important.
 
On 24/09/12 12:30, Bruce Varley wrote:
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:ac9ridF2fnrU1@mid.individual.net...

"Jordan"

I don't know much about permanent magnet alternators, but am surprised at
the very un- "sine" like shape of the output waveform, on a single phase
motorbike type I'm working on. It's very "peaky", with first gently
sloping excursions but that then become steep spikes, like nothing in the
text books. Is this normal, or am I doing something silly with the CRO? By
comparison, a 240V-18V transformer I tried has the classic sinewave shape.


** Simple alternators do not produce a sine wave emf - more often it
looks like a flattened off sine wave with a wiggle near each zero
crossing.

Where the wave is used to produce DC, this flattened shape is an
advantage.

Imagine if it were a good square wave, then rectification would give you
pure DC.


.... Phil
Yes, in fact alternators don't 'naturally' generate sinewaves, you have to
work hard at the design of the machine geometry in order to get a reasonable
one. With large power station machines, the shaping and alignment of the
pole pieces is very precise, on littlies like auto gensets it's not so
important.
Click to expand...
Mine seems to have the opposite extreme, with relatively little "area
under the curve". Could be it's just not a high quality design.
Interesting to hear about sinewaves not happening naturally.
Thanks.
 
"Jordan"

Mine seems to have the opposite extreme, with relatively little "area
under the curve".
Click to expand...

** Sure you got that scope DC coupled ?



.... Phil
 
On 24/09/12 17:06, Phil Allison wrote:
"Jordan"

Mine seems to have the opposite extreme, with relatively little "area
under the curve".


** Sure you got that scope DC coupled ?



... Phil
Click to expand...
I tried every possible setting on the CRO, not knowing much about them!
I'll confirm DC coupling, thanks.
 
On 2012-09-24, Jordan <jordan@koora.com> wrote:
I don't know much about permanent magnet alternators, but am surprised
at the very un- "sine" like shape of the output waveform, on a single
phase motorbike type I'm working on. It's very "peaky", with first
gently sloping excursions but that then become steep spikes,
Click to expand...
That waveform is not unprecidented, I've seen similar waveforms
discussed for bicycyle PM generators.

--
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