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Discussion Starter #1
This might sound crazy, but is sorta in response to the "no cheap AC
motor" thread, how hard would it be to sync an AC and a DC motors? I
know, the immediate question is "why??". Well, doing so would add
some desirable features to both systems; my idea would be to use a
cheaper AC controller and motor (primarily for regen, low speed
movement and high speed augmentation) and combine it with a more high
performance DC system (for the get up and go moments requiring more
torque and speed).

I know there would be some weight considerations, but what other
complications would there be?

Thanks,

Ralph.






--
Victory belongs to the most persevering.
--Napoleon Bonaparte--

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Discussion Starter #2
as I mentioned before I think it's worth looking into getting the motors
used in all the current hybrids. I think there is something like 5 SUV
hybrid models in USA right now which should have fairly powerful AC
motors that can't cost 15000$.

but if you wanted to hack something then why not take a normal DC motor
and make the controller do the commutation...

Dan


R Patterson wrote:
> This might sound crazy, but is sorta in response to the "no cheap AC
> motor" thread, how hard would it be to sync an AC and a DC motors? I
> know, the immediate question is "why??". Well, doing so would add
> some desirable features to both systems; my idea would be to use a
> cheaper AC controller and motor (primarily for regen, low speed
> movement and high speed augmentation) and combine it with a more high
> performance DC system (for the get up and go moments requiring more
> torque and speed).
>
> I know there would be some weight considerations, but what other
> complications would there be?
>
> Thanks,
>
> Ralph.
>
>
>
>
>
>
>

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Discussion Starter #3
R Patterson wrote:
> This might sound crazy, but is sorta in response to the "no cheap AC
> motor" thread, how hard would it be to sync an AC and a DC motors? I
> know, the immediate question is "why??". Well, doing so would add
> some desirable features to both systems

Since electric motors have been around over 100 years, and some of the
greatest engineering minds of the century have applied themselves to it,
it should come as no surprise that this has been done.

The Ward-Leonard system is a prime example that has been widely used. It
has three motors; an AC motor and a DC generator directly connected by
their shafts, and a third DC motor that drives the load. The
fixed-frequency fixed-voltage AC mains drives the AC motor directly. It
spins the DC generator, whose output is varied by its field winding.
This variable-voltage DC drives the third motor to drive the load.
Though it requires three motors, speed control only uses low-power
circuits and the system is very reliable and versatile.

Another common approach is to use a DC motor coupled to a wound-rotor AC
motor. Its stator windings are driven by the AC mains. Its rotor
windings are brought out by slip rings, rectified, and drive the DC
motor. In this way, slip power isn't burned up as heat in the rotor, but
instead gets converted to mechanical power by the DC motor. Again, the
goal is to get smooth stepless efficient speed control over a wide range
with a fixed-frequency fixed-voltage AC source.

I've used yet another old system. Use a wound-rotor AC alternator as a
motor. It is fairly easy to build a variable-frequency fixed-voltage
inverter; it's just a square-wave inverter with a variable frequency.
Use a small DC PWM to drive the rotor winding. Rather than halving the
AC voltage at half the frequency; you apply full voltage at half the
frequency, and double the field current. This has the added advantage
that field current adjust power factor; I deliberately over-excited the
field to get a leading power factor. This allowd the inverter to use
inexpensive SCRs, which automatically commutate off with a capacitive load.

Finally, there is the obvious approach -- use a small AC drive for
cruising power and regen, plus a large series motor and simple PWM or
contactor controller for rapid acceleration.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #4
Dan Frederiksen wrote:
> as I mentioned before I think it's worth looking into getting the motors
> used in all the current hybrids. I think there is something like 5 SUV
> hybrid models in USA right now which should have fairly powerful AC
> motors that can't cost 15000$.

The existing hybrids have PM AC (a.k.a. brushless DC) motors of around
40 KW peak power capability. However, they are built very lightly with
poor cooling, for very low duty cycle operation. They could be use, but
you'd need to substantially improve their cooling systems.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #5
you have looked into all of them?

the tesla roadster motor is also "built very lightly with poor cooling"
isn't it?

Dan

Lee Hart wrote:
> Dan Frederiksen wrote:
>
>> as I mentioned before I think it's worth looking into getting the motors
>> used in all the current hybrids. I think there is something like 5 SUV
>> hybrid models in USA right now which should have fairly powerful AC
>> motors that can't cost 15000$.
>>
>
> The existing hybrids have PM AC (a.k.a. brushless DC) motors of around
> 40 KW peak power capability. However, they are built very lightly with
> poor cooling, for very low duty cycle operation. They could be use, but
> you'd need to substantially improve their cooling systems.
>

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Discussion Starter #6
Lee Hart wrote:
>> The existing hybrids have PM AC (a.k.a. brushless DC) motors of around
>> 40 KW peak power capability. However, they are built very lightly with
>> poor cooling, for very low duty cycle operation. They could be use, but
>> you'd need to substantially improve their cooling systems.

From: Dan Frederiksen
> you have looked into all of them?

No; but I have the motors out of a Toyota Prius in my garage right now. Compared to continuous-duty EV motors, they have comparatively small sized wire in the windings, and relatively little cooling.

In comparison, the GM EV1 motor is twice the size of both Prius motors put together, and has many times more cooling capacity.

> the tesla roadster motor is also "built very lightly with poor
> cooling" isn't it?

I don't know what kind of cooling they have for their motor.

--
"Excellence does not require perfection." -- Henry James
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Discussion Starter #7
Lee Hart wrote:
> No; but I have the motors out of a Toyota Prius in my garage right now. Compared to continuous-duty EV motors, they have comparatively small sized wire in the windings, and relatively little cooling.
>
when you haven't even looked at the SUV hybrid motors I talked about
then don't pretend you have by generalizing from a prius.
maybe visit a dealer and ask to have a look. might be the perfect motor
there. I don't think the 350HP SUV people will use a 10HP electric motor

Dan

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Discussion Starter #8
Dan,

You launched the idea of using a hybrid SUV motor.
Why don't *you* go to a dealer to have a look at the motor
out of a SUV? (I doubt they will have one on display, but
hey, I am just giving you back your own suggestions.)

Anyway, if the SUV is simply a scaled-up version of the
Prius' THS (Toyota Hybrid System) which only has an oil
splash-lubrication (with a very tiny oil pump) then you
know that the power that is extracted from the motor is
very limited and designed to be just enough for this
specific application, one of the reasons Toyota frowns
on plug-in conversions and warranty is void as soon as
you do this conversion.

You are free to take a Hybrid transaxle (which usually
can be had for a mere $1000, sometimes including the
AC motor controllers and DC/DC) and improve on the
cooling of the motors to make them heavier duty.

Success,

Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Dan Frederiksen
Sent: Saturday, October 27, 2007 10:55 PM
To: Lee Hart; Electric Vehicle Discussion List
Subject: Re: [EVDL] syncing an AC and DC motor

Lee Hart wrote:
> No; but I have the motors out of a Toyota Prius in my garage right now. Compared to continuous-duty EV motors, they have comparatively small sized wire in the windings, and relatively little cooling.
>
when you haven't even looked at the SUV hybrid motors I talked about then don't pretend you have by generalizing from a prius.
maybe visit a dealer and ask to have a look. might be the perfect motor there. I don't think the 350HP SUV people will use a 10HP electric motor

Dan

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