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Discussion Starter #1
Jeff Major,

I think you are just getting fouled up in termnology. Hp stays the same
4 large poles or 8 1/2 size poles. the same pole area, same power in
same power out. But for a given total pole area it can be configured in
multiple torque/rpm configurations.

Now either I configure the motor for less torque and higher rpm and gear
it down more or I configure for twice that torque at 1/2 the rpm @ the
same frequency.

There is a range of frequency that is reasonable for the materials and
the cost. frequency costs. On the other end, torque costs. So each
manufacturer achieves their own tripple point of best freq range,
gearing, and pole count.

think of it like the siamese 8 setup the poles run their current in
series so for a given amperage output you get twice the torque that the
same size inverter could otherwise give. You could switch from 8 pole to
4 pole on the fly just like the siamese 8 with a zilla does.

There is also slow rpm smoothness to consider. Skewing the rotor bars
helps but you will find low rpm "torque " motors like wheel motors are
usually about 12 pole.

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Discussion Starter #2
Jeff Shanab wrote:

> If someone can get there hands on a wound rotor slip ring AC motor in
> the size we need for drag racing, well the race would be on!

What inverter?

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Discussion Starter #3
> In that case, I can't explain the difference. Electric motors have a
> certain horsepower per pound. It isn't really affected by AC vs. DC, but
> rather the basic physics involved. Assuming you're using the same copper
> wire, iron laminations, bearings, magnets, etc. then either an AC or DC
> motor will have the same performance characteristics

Hold on, that isn't true, at least not as you've expressed it. I've seen
10hp motors that weight less than 10 lbs and others that weigh over 200
lbs.

Increasing the RPM of a motor allows it to produce more power for the same
weight.

I can see a relationship between torque and weight, but I don't see it
between power and weight.

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Discussion Starter #4
Peter VanDerWal wrote:

> Increasing the RPM of a motor allows it to produce more power for the same
> weight.

Yes, but at some point it no longer will be be *continuous*
power we're debating. Only large mass (more thermal reserve)
motors will allow to increase *and sustain* higher power by
spinning faster. Light motors only allow high(er) peak power.

Victor

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Discussion Starter #5
Ryan asks What inverter?

Good question! But it would need same or less peak amps than
corresponding ACIM inverter (no 2-5x starting current for the torque at
launch)
you would get more torque per amp at launch.

I wonder if a crude drag race only could actually be fixed frequency
that you turn on at the first yellow to get the magnetic field rotating
then and a rotor resistance control that you go from open to high
resistance for the launch then to low resistance for the 1/8 then
adjusts to short ass you run.

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Discussion Starter #6
>> Electric motors have a certain horsepower per pound. It isn't
>> really affected by AC vs. DC, but rather the basic physics
>> involved. Assuming you're using the same copper wire, iron
>> laminations, bearings, magnets, etc. then either an AC or DC motor
>> will have the same performance characteristics

Peter VanDerWal wrote:
> Hold on, that isn't true, at least not as you've expressed it. I've
> seen 10hp motors that weight less than 10 lbs and others that weigh
> over 200 lbs.
>
> Increasing the RPM of a motor allows it to produce more power for the
> same weight.
>
> I can see a relationship between torque and weight, but I don't see
> it between power and weight.

My answer assumed the usual "all things being equal..." proviso. Sorry;
I should have stated that explicitly.

A motor is basically a transformer. Instead of electrical power in,
electrical power out; it is electrical power in, mechanical power out.
The more power you cram in, the more power you get out. The only real
limits are thermal -- how *long* can you get a given amount of power
before it overheats. So, to compare motors, you need to also specify for
how *long* they can develop that power level. "Continuous duty" ratings
are common. EV-duty motors are often rated at the 1-hour rating. Extreme
cooling measures, or extremely short on-times will allow extremely high
power-to-weight ratios on any motor.

The next issue is materials. At some magnetic flux density, the iron
saturates and little useful increases in torque will be produced above
that point. You can change the magnetic material to improve performance;
but any material can be used in any motor to get the same ultimate limit.

Likewise, you can change the electrical conductors. Copper is almost
universally used. Aluminum appears in some cheap motors. Silver is the
better, but very rarely used due to cost. Superconducting coils are
possible, but now you're *really* getting exotic.

Finally, transformers only work on AC. The same is true for motors; all
practical designs are AC motors. The power-to-weight ratio for a
transformer or motor is directly related to frequency -- the higher the
frequency (RPM), the higher the power. In motors, this becomes a
strength of materials issue; is your extremely good magnetic material
also extremely strong mechanically?

People like to say that the commutator in a DC motor limits its maximum
RPM. That is true for traditional commutators that are built for low-RPM
motors. But there are also designs for 10,000 RPM and even 100,000 RPM
commutators. They just aren't normally used in cheap motors.

The key point is not to look at the limitations of a particular motor,
and assume that they apply to *all* versions of that motor.

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Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
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Discussion Starter #7
Now here victor I too have to disagree

hp = (rpm * torque)/5252 both are 90% eff and convert the 6.6kwh input
into 4.75 shaft hp

one at [email protected] torque and the other at 100 rpm and 250 lb.ft
Which motor weights more?

Unless you are saying that they both can't be the same effiency?


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Discussion Starter #9
--- Jeff Shanab <[email protected]> wrote:

> Jeff Major,
>
> I think you are just getting fouled up in
> termnology. Hp stays the same
> 4 large poles or 8 1/2 size poles. the same pole
> area, same power in
> same power out. But for a given total pole area it
> can be configured in
> multiple torque/rpm configurations.
>
> Now either I configure the motor for less torque and
> higher rpm and gear
> it down more or I configure for twice that torque at
> 1/2 the rpm @ the
> same frequency.
>
Hi Jeff S,

I don't disagree with your above statements, except
for the first sentence :) But where we appear to
part is back to your original post: "Now take the
traditional 4 pole motor and turn it into a 12 pole
motor, same amount of windings and iron and the torque
triples".

I been trying to think of a wheelbarrow analogy, but
no luck. So let's use the mechanical translational
analogy. Where you have force instead of torque.

You have a horseshoe magnet one inch thick. It is
able to lift a 10 lb piece of steel, maximum. It has
two poles, one N and one S. Now, cut the magnet in
half. So you have two horseshoe magnets, each 1/2
inch thick. Assume the flux density has remained
unchanged. Now you have 4 poles. Can the two 1/2
inch thick horseshoe magnets together lift 20 lbs of
steel? I think not.

So, after you change your 4 pole motor to 12 poles,
nothing will be gained. Yes, you will have altered
the speed frequency relationship. But your premise,
as I understood it, was that the exercise would result
in a higher power for a given motor mass. This is not
the case.

Regards,

Jeff M






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Discussion Starter #10
It sounds like you're both saying the same thing!

Jeff Shanab <[email protected]> wrote:
> > Now either I configure the motor for less torque and
> > higher rpm and gear
> > it down more or I configure for twice that torque at
> > 1/2 the rpm @ the
> > same frequency.

Jeff Major <[email protected]> wrote:
> So, after you change your 4 pole motor to 12 poles,
> nothing will be gained. Yes, you will have altered
> the speed frequency relationship. But your premise,
> as I understood it, was that the exercise would result
> in a higher power for a given motor mass. This is not
> the case.

The number of poles/windings is just a tradeoff between speed and
torque; it seems like you're both saying that. For the same size, you
get the same power, whether with low torque at high RPMs or high
torque at low RPMs.

-Morgan LaMoore

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Discussion Starter #12
>
> The number of poles/windings is just a tradeoff between speed and
> torque; it seems like you're both saying that. For the same size, you
> get the same power, whether with low torque at high RPMs or high
> torque at low RPMs.
>
> -Morgan LaMoore

Yes, up to the point where we add one more dimension, time or frequency.

Now we take a motor that would otherwise not have enough torque to do
the job and we spin it fast by applying a higher frequency to a higher
polecount smaller motor. That motor is smaller because 10,000 rpm @
100lb'ft is 190hp but it is un-useable in that form.

We have two choices to make it useable, transform it down
electro-magnetically or mechanically

I have seen 72pole permanaent magnet motors that can put out really high
torque but at a low rpm that are only a few inches thick and less than a
foot in diameter.
I can't


http://www.emoteq.com/

look at the motors here, there are 24,40,48 pole motors the 72 pole was
a french company Here is their site but I can't find that motor today

http://www.alxion.com/bin/e_moteur-kit-stk.html

look at these

300 STK 4M

12"od 8" length

1nm = .737 lb ft

air cooled
max continuous = 230lbft
peak 1050lbft

water cooled the peak becomes continous.

but rpm is low

Since we started talking about an existing motor, raising the frequency
and gearing it down is our only viable option.


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