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'[EE]: a question about stators'
2011\08\25@105510
by
Electron
Hi,
talking about a stator mounted on a engine's flywheel:
if at 2000 RPM it outputs (say) 30VAC, and at 4000 RPM twice as many volts,
how does the max output current vary instead? Is it constant or it ~doubles,
just like the voltage?
In other words, how do output watts vary with varying rotational speed,
assuming no losses, saturation, etc..?
Thanks!
Mario
2011\08\25@110613
by
RussellMc
> talking about a stator mounted on a engine's flywheel:
> In other words, how do output watts vary with varying rotational speed,
> assuming no losses, saturation, etc..?
Current will increase approximately linearly with speed up until
saturation and then be relatively constant. Voltage will tend to keep
increasing ~linearly with speed throughout
2011\08\25@140916
by
Electron
At 17.05 2011.08.25, you wrote:
>> talking about a stator mounted on a engine's flywheel:
>> In other words, how do output watts vary with varying rotational speed,
>> assuming no losses, saturation, etc..?
>
>
>Current will increase approximately linearly with speed up until
>saturation and then be relatively constant. Voltage will tend to keep
>increasing ~linearly with speed throughout.
Thanks. May we assume the max current from inductance (67 mH) and
resistance (18 Ohm) of the stator, and RPM? Of course it will be
an estimate, as we know nothing about the magnets in the flywheel.
But I can assume it was designed decently (it's a motorbike's CDI
generator).
Of course at this current the voltage will be zero, so to get max
possible power from stator I have to use a lower current (70.7%?).
Cheers,
Mario
2011\08\25@173840
by
Fred Langley
But won't the impedance of the inductor not increase with frequency until
the inductive reactance becomes so large that no additional power is created
with additional speed?
{Original Message removed}
2011\08\25@224407
by
RussellMc
> >> talking about a stator mounted on a engine's flywheel:
> >> In other words, how do output watts vary with varying rotational speed,
> >> assuming no losses, saturation, etc..?
> >
> >
> >Current will increase approximately linearly with speed up until
> >saturation and then be relatively constant. Voltage will tend to keep
> >increasing ~linearly with speed throughout.
>
> Thanks. May we assume the max current from inductance (67 mH) and
> resistance (18 Ohm) of the stator, and RPM? Of course it will be
> an estimate, as we know nothing about the magnets in the flywheel.
> But I can assume it was designed decently (it's a motorbike's CDI
> generator).
Maximum current is saturation limited ans is usually less than the
system would produce if it did not saturate, so, no, you can't
determine maximum current it will produce. You can determine the
maximum it won't produce :)  from I = V/R. It will be saturation
limited before that point.
Russell
2011\08\25@230415
by
Richard Prosser

On 26 August 2011 14:43, RussellMc <spam_OUTapptechnzTakeThisOuTgmail.com> wrote:
{Quote hidden}>> >> talking about a stator mounted on a engine's flywheel:
>> >> In other words, how do output watts vary with varying rotational speed,
>> >> assuming no losses, saturation, etc..?
>> >
>> >
>> >Current will increase approximately linearly with speed up until
>> >saturation and then be relatively constant. Voltage will tend to keep
>> >increasing ~linearly with speed throughout.
>>
>> Thanks. May we assume the max current from inductance (67 mH) and
>> resistance (18 Ohm) of the stator, and RPM? Of course it will be
>> an estimate, as we know nothing about the magnets in the flywheel.
>> But I can assume it was designed decently (it's a motorbike's CDI
>> generator).
>
> Maximum current is saturation limited ans is usually less than the
> system would produce if it did not saturate, so, no, you can't
> determine maximum current it will produce. You can determine the
> maximum it won't produce :)  from I = V/R. It will be saturation
> limited before that point.
>
>
> Russell.
> 
I think that pert of the problem is that once the current starts to
saturate the magnetic material, the inductance will drop, so any
limitation imposed by the inductance and frequency (speed) will also
reduce. So the whole thing is somewhat interrelated and will depend on
the mechanical design and material proerties as much as any outright
electrical limitations.
RP
'[EE]: a question about stators'
2011\09\06@034939
by
Electron
I just found this, it looks very interesting thus I'd like to share it:
http://www.advrider.com/forums/showthread.php?t=189734
{Quote hidden}>Hi,
>talking about a stator mounted on a engine's flywheel:
>
>if at 2000 RPM it outputs (say) 30VAC, and at 4000 RPM twice as many volts,
>how does the max output current vary instead? Is it constant or it ~doubles,
>just like the voltage?
>
>In other words, how do output watts vary with varying rotational speed,
>assuming no losses, saturation, etc..?
>
>Thanks!
>
>Mario
2011\09\06@045425
by
RussellMc
> I just found this, it looks very interesting thus I'd like to share it:
> http://www.advrider.com/forums/showthread.php?t=189734
The page is interesting but says very little unexpected.
Saturation is "soft" but if you plot V & I without suppressed zeros on
both axes it's not as soft as it appears here. Th Honda and KTM curves
are close enough to identical
eg he gets about 13A at 3000 RPM and under 15A at 9000 RPM. ie for
practical purposes saturation is about 13A.
(4th box down labelled "Estimated stator parameters based on DC output".)
The XR having 10 stator poles equipped but only 4 wound is the "magic
bullet" for the Honda. This just means that the designers purposefully
chose to limit the power to about 40% of what is sensibly available
and he has increased the available power by using all the steel.
Russel
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