motor torque question

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motor torque question

Mike Boyles
Hi all, first post

Can anyone tell me the maximum "installed" torque I should reasonably
expect from a WarP 9 motor? I need to know the maximum torque I should
consider when designing my taper lock motor/flywheel joint. The only
motor curve I have only shows torque values under about 80 ft-#'s. I
understand torque is a function of amps and that could be limited by
either my controller (Zilla Z1K LV) or my batteries (yet to be
determined). I was told by one source the maximum torque the motor
could produce could be as high as 450 ft-#'s. This doesn't seem
reasonable to me. Any thoughts?
thanks,

--
MikeB2


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Re: motor torque question

Ian Hooper-3
Hi Mike,

Torque is reasonably proportional to amps, so you can get an  
approximate figure at 1000A by extrapolating NetGain's graphs (https://www.zeva.com.au/store/images/large/32-WarP_9_Graph.jpg 
)

Subtracting ~50A for static drag and working with a torque coefficient  
of ~0.25 foot-pounds per amp for the Warp 9, it looks like you can  
expect something like 250 foot-pounds at 1000A?

(The 450ft-lbs suggested might be with a Z2K?)

-Ian

On 20/07/2008, at 10:37 PM, Mike Boyles wrote:

> Hi all, first post
>
> Can anyone tell me the maximum "installed" torque I should reasonably
> expect from a WarP 9 motor? I need to know the maximum torque I should
> consider when designing my taper lock motor/flywheel joint. The only
> motor curve I have only shows torque values under about 80 ft-#'s. I
> understand torque is a function of amps and that could be limited by
> either my controller (Zilla Z1K LV) or my batteries (yet to be
> determined). I was told by one source the maximum torque the motor
> could produce could be as high as 450 ft-#'s. This doesn't seem
> reasonable to me. Any thoughts?
> thanks,
>
> --
> MikeB2
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ 
> ev
>
>


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Re: motor torque question

Mike Boyles
Thanks Ian,

That number looks a lot more reasonable since the tires will slip at
about 90 ft-#'s in first gear. My taper loc is good to transmit about
750 ft-#'s so I think it will be ok.

On 7/20/08, Ian Hooper <[hidden email]> wrote:

> Hi Mike,
>
> Torque is reasonably proportional to amps, so you can get an
> approximate figure at 1000A by extrapolating NetGain's graphs (https://www.zeva.com.au/store/images/large/32-WarP_9_Graph.jpg
> )
>
> Subtracting ~50A for static drag and working with a torque coefficient
> of ~0.25 foot-pounds per amp for the Warp 9, it looks like you can
> expect something like 250 foot-pounds at 1000A?
>
> (The 450ft-lbs suggested might be with a Z2K?)
>
> -Ian
>
> On 20/07/2008, at 10:37 PM, Mike Boyles wrote:
>
> > Hi all, first post
> >
> > Can anyone tell me the maximum "installed" torque I should reasonably
> > expect from a WarP 9 motor? I need to know the maximum torque I should
> > consider when designing my taper lock motor/flywheel joint. The only
> > motor curve I have only shows torque values under about 80 ft-#'s. I
> > understand torque is a function of amps and that could be limited by
> > either my controller (Zilla Z1K LV) or my batteries (yet to be
> > determined). I was told by one source the maximum torque the motor
> > could produce could be as high as 450 ft-#'s. This doesn't seem
> > reasonable to me. Any thoughts?
> > thanks,
> >
> > --
> > MikeB2
> >
> >
> > _______________________________________________
> > For general EVDL support, see http://evdl.org/help/
> > For subscription options, see http://lists.sjsu.edu/mailman/listinfo/
> > ev
> >
> >
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
>
>


--
MikeB2


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Re: motor torque question

Roland Wiench
In reply to this post by Mike Boyles
Hello Mike,

I have now been running my EV now for 6 years that weighs 7000 lbs with a
Warp 9 , Zilla 1K and 180 V T-145 Trojan battery pack.  It uses a Electro
Auto taper lock coupling and adapter plate that is connected to a manual
Saganaw 3-speed transmission that has a 1st gear ratio of 3.5:1 and with a
5.57:1 differential gear, makes a overall ratio of 19.495:1 and in 2nd gear
it has a overall ratio of 13.925:1.

Otmar of Café Electric was scared that the Zilla 1K would not do the job and
I would need a Zilla 2k.  I said not to worry, I have the gears and I have
been running with a 900 amp controller for 27 years with no problem and the
maximum motor ampere I ever pull was 600 amps while going up a 7% hill every
day for the last 10 years.

Tires are high pressure type set at 65 PSI, which has a rolling
circumference of 94 inches.

On very smooth dead level grade at 25 mphs at a gear ratio of 19.495:1, then
motor ampere is 100 amps while the battery amps is 20 amps.  When the grade
gets rough and bumper, the motor amps goes to 150 amps and the battery amps
to 50 amps.

If I shift to 2nd gear or 13.925:1 my motor amps go to 200 amps with a
battery amps of 75 amps at 30 to 35 mph where I normally drive.

You must be able to deride all this data and more to determine what the
torque will be at startup, at a given motor rpm and speed.

To find this data on the Warp motors it is best to contact:

George F. Hamstra at NetGain     [hidden email]

Tell him all what vehicle you want a motor to be install in. You need to
know the weight, weight with battery packs, what types of batteries, the
transmission gear ratio, differential gear ratio, size of tires, the
diameter of tires, type of tires, what type of controller you are using,
frontal area of the vehicle, and the average speed and top speed you want to
go and for how long.

George will make up a complete spread sheet for your vehicle and will E-mail
you the data.

If you want to see the formulas for calculating a EV performance see:
http://www.geocities.com/capecanaveral/lab/8679/equations.html

You must first solve the first formula so the results are then inputted into
the next and so on.

Roland


----- Original Message -----
From: "Mike Boyles" <[hidden email]>
To: <[hidden email]>
Sent: Sunday, July 20, 2008 8:37 AM
Subject: [EVDL] motor torque question


> Hi all, first post
>
> Can anyone tell me the maximum "installed" torque I should reasonably
> expect from a WarP 9 motor? I need to know the maximum torque I should
> consider when designing my taper lock motor/flywheel joint. The only
> motor curve I have only shows torque values under about 80 ft-#'s. I
> understand torque is a function of amps and that could be limited by
> either my controller (Zilla Z1K LV) or my batteries (yet to be
> determined). I was told by one source the maximum torque the motor
> could produce could be as high as 450 ft-#'s. This doesn't seem
> reasonable to me. Any thoughts?
> thanks,
>
> --
> MikeB2
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
>
>


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Re: motor torque question

Mike Boyles
Thanks Roland,

George is the one who told me the "maximum" torque from the motor
"could" be as high as 450 ft-#'s. Though he did not have the benefit
of all the other data. I have run through the calculations based on
what I know today and did not see anything like a requirement for a
torque that high.  Thanks for sharing your experience, that makes me
feel even better about what I am doing. I am a mechanical guy
(responsible for off highway vehicle design) more comfortable with
hydro-dynamic transmissions and diesel engines. I have a lot to learn
about things electrical.


On 7/20/08, Roland Wiench <[hidden email]> wrote:

> Hello Mike,
>
> I have now been running my EV now for 6 years that weighs 7000 lbs with a
> Warp 9 , Zilla 1K and 180 V T-145 Trojan battery pack.  It uses a Electro
> Auto taper lock coupling and adapter plate that is connected to a manual
> Saganaw 3-speed transmission that has a 1st gear ratio of 3.5:1 and with a
> 5.57:1 differential gear, makes a overall ratio of 19.495:1 and in 2nd gear
> it has a overall ratio of 13.925:1.
>
> Otmar of Café Electric was scared that the Zilla 1K would not do the job and
> I would need a Zilla 2k.  I said not to worry, I have the gears and I have
> been running with a 900 amp controller for 27 years with no problem and the
> maximum motor ampere I ever pull was 600 amps while going up a 7% hill every
> day for the last 10 years.
>
> Tires are high pressure type set at 65 PSI, which has a rolling
> circumference of 94 inches.
>
> On very smooth dead level grade at 25 mphs at a gear ratio of 19.495:1, then
> motor ampere is 100 amps while the battery amps is 20 amps.  When the grade
> gets rough and bumper, the motor amps goes to 150 amps and the battery amps
> to 50 amps.
>
> If I shift to 2nd gear or 13.925:1 my motor amps go to 200 amps with a
> battery amps of 75 amps at 30 to 35 mph where I normally drive.
>
> You must be able to deride all this data and more to determine what the
> torque will be at startup, at a given motor rpm and speed.
>
> To find this data on the Warp motors it is best to contact:
>
> George F. Hamstra at NetGain     [hidden email]
>
> Tell him all what vehicle you want a motor to be install in. You need to
> know the weight, weight with battery packs, what types of batteries, the
> transmission gear ratio, differential gear ratio, size of tires, the
> diameter of tires, type of tires, what type of controller you are using,
> frontal area of the vehicle, and the average speed and top speed you want to
> go and for how long.
>
> George will make up a complete spread sheet for your vehicle and will E-mail
> you the data.
>
> If you want to see the formulas for calculating a EV performance see:
> http://www.geocities.com/capecanaveral/lab/8679/equations.html
>
> You must first solve the first formula so the results are then inputted into
> the next and so on.
>
> Roland
>
>
> ----- Original Message -----
> From: "Mike Boyles" <[hidden email]>
> To: <[hidden email]>
> Sent: Sunday, July 20, 2008 8:37 AM
> Subject: [EVDL] motor torque question
>
>
> > Hi all, first post
> >
> > Can anyone tell me the maximum "installed" torque I should reasonably
> > expect from a WarP 9 motor? I need to know the maximum torque I should
> > consider when designing my taper lock motor/flywheel joint. The only
> > motor curve I have only shows torque values under about 80 ft-#'s. I
> > understand torque is a function of amps and that could be limited by
> > either my controller (Zilla Z1K LV) or my batteries (yet to be
> > determined). I was told by one source the maximum torque the motor
> > could produce could be as high as 450 ft-#'s. This doesn't seem
> > reasonable to me. Any thoughts?
> > thanks,
> >
> > --
> > MikeB2
> >
> >
> > _______________________________________________
> > For general EVDL support, see http://evdl.org/help/
> > For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
> >
> >
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
>
>


--
MikeB2


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Re: motor torque question

Roger Heuckeroth
In reply to this post by Mike Boyles
Sounds about right.  Lifebatt is doing a project in the UK using a  
WarP 9 with a LogiSystems 750A controller.  They quote 500 ft-lbs of  
torque.  See

http://www.lifebatt.co.uk/r2/index.html

Maximum torque for a DC motor is at 0 RPM.  The reality if the tires  
will probably break friction before you get to 500 ft lbs, so they  
will be your limiting factor.



On Jul 20, 2008, at 10:37 AM, Mike Boyles wrote:

> Hi all, first post
>
> Can anyone tell me the maximum "installed" torque I should reasonably
> expect from a WarP 9 motor? I need to know the maximum torque I should
> consider when designing my taper lock motor/flywheel joint. The only
> motor curve I have only shows torque values under about 80 ft-#'s. I
> understand torque is a function of amps and that could be limited by
> either my controller (Zilla Z1K LV) or my batteries (yet to be
> determined). I was told by one source the maximum torque the motor
> could produce could be as high as 450 ft-#'s. This doesn't seem
> reasonable to me. Any thoughts?
> thanks,
>
> --
> MikeB2
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ 
> ev


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Re: motor torque question

Peter VanDerWal
> Sounds about right.  Lifebatt is doing a project in the UK using a
> WarP 9 with a LogiSystems 750A controller.  They quote 500 ft-lbs of
> torque.  See
>
> http://www.lifebatt.co.uk/r2/index.html
>
> Maximum torque for a DC motor is at 0 RPM.  The reality if the tires
> will probably break friction before you get to 500 ft lbs, so they
> will be your limiting factor.

I'm pretty sure the 500ft-lbs they are talking about is /wheel/ torque not
motor torque.


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Re: motor torque question

Matt Lacey
In reply to this post by Ian Hooper-3
Ian,

That's odd, I always thought the torque equation for series wound motors was
T=c*I^2,
So 70ft-lb at 334.5A is 625ft-lb (less probably due to less than optimal
timing) at 1000A.
 
That's troubling because if im wrong then I need to redo a lot of the
calculations for my conversion.

Matt

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Ian Hooper
Sent: Sunday, 20 July 2008 10:58 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] motor torque question

Hi Mike,

Torque is reasonably proportional to amps, so you can get an approximate
figure at 1000A by extrapolating NetGain's graphs
(https://www.zeva.com.au/store/images/large/32-WarP_9_Graph.jpg
)

Subtracting ~50A for static drag and working with a torque coefficient of
~0.25 foot-pounds per amp for the Warp 9, it looks like you can expect
something like 250 foot-pounds at 1000A?

(The 450ft-lbs suggested might be with a Z2K?)

-Ian

On 20/07/2008, at 10:37 PM, Mike Boyles wrote:

> Hi all, first post
>
> Can anyone tell me the maximum "installed" torque I should reasonably
> expect from a WarP 9 motor? I need to know the maximum torque I should
> consider when designing my taper lock motor/flywheel joint. The only
> motor curve I have only shows torque values under about 80 ft-#'s. I
> understand torque is a function of amps and that could be limited by
> either my controller (Zilla Z1K LV) or my batteries (yet to be
> determined). I was told by one source the maximum torque the motor
> could produce could be as high as 450 ft-#'s. This doesn't seem
> reasonable to me. Any thoughts?
> thanks,
>
> --
> MikeB2
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/ For subscription
> options, see http://lists.sjsu.edu/mailman/listinfo/
> ev
>
>


_______________________________________________
For general EVDL support, see http://evdl.org/help/ For subscription
options, see http://lists.sjsu.edu/mailman/listinfo/ev


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Re: motor torque question

Steve West-6
Matt,

I'm no expert, but my understanding is that coils have a point where they
saturate. At low currents (below saturation) you would expect to see a
square relation, transitioning to a linear one as one of the coils
saturates.

Steve

On 21/07/08 5:01 PM, "matt" <[hidden email]> wrote:

> Ian,
>
> That's odd, I always thought the torque equation for series wound motors was
> T=c*I^2,
> So 70ft-lb at 334.5A is 625ft-lb (less probably due to less than optimal
> timing) at 1000A.
>  
> That's troubling because if im wrong then I need to redo a lot of the
> calculations for my conversion.
>
> Matt
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On Behalf
> Of Ian Hooper
> Sent: Sunday, 20 July 2008 10:58 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] motor torque question
>
> Hi Mike,
>
> Torque is reasonably proportional to amps, so you can get an approximate
> figure at 1000A by extrapolating NetGain's graphs
> (https://www.zeva.com.au/store/images/large/32-WarP_9_Graph.jpg
> )
>
> Subtracting ~50A for static drag and working with a torque coefficient of
> ~0.25 foot-pounds per amp for the Warp 9, it looks like you can expect
> something like 250 foot-pounds at 1000A?
>
> (The 450ft-lbs suggested might be with a Z2K?)
>
> -Ian



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Re: motor torque question

Lee Hart
In reply to this post by Matt Lacey
matt wrote:
> That's odd, I always thought the torque equation for series wound
> motors was T=c*I^2. So 70ft-lb at 334.5A is 625ft-lb (less probably
> due to less than optimal timing) at 1000A.

The T=c1*I^2 equation works for low currents (below nameplate current).
But as you go higher, it gradually changes to simply T=c2*I as the iron
moves into saturation. (c1 and c2 are different constants).

--
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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Kill A Watt for 240Vac

rodhower
I have a couple of Kill A Watt meters,
http://www.p3international.com/products/special/P4400/P4400-CE.html
These work great for such a low cost device.

A few have mentioned a similar 240Vac version, but I
could not find which one they were talking about.
Was it this
http://www.pat-training.co.uk/230V_electricity_meter.htm

Are there any other brands that people have used?
Thanks,
Rod


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Re: motor torque question

Matt Lacey
In reply to this post by Lee Hart
Ah ok, that makes sense.
Any ideas as to what current a warp 9 would go into saturation?
Does anyone know at what current density iron goes into saturation?

Matt

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Lee Hart
Sent: Monday, 21 July 2008 10:26 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] motor torque question

matt wrote:
> That's odd, I always thought the torque equation for series wound
> motors was T=c*I^2. So 70ft-lb at 334.5A is 625ft-lb (less probably
> due to less than optimal timing) at 1000A.

The T=c1*I^2 equation works for low currents (below nameplate current).
But as you go higher, it gradually changes to simply T=c2*I as the iron
moves into saturation. (c1 and c2 are different constants).

--
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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Re: Kill A Watt for 240Vac

Matt Lacey
In reply to this post by rodhower
 hi Rod,
What are you using it to measure?
Here in Australia were stuck with a ms-6115 from electus distribution, which
doesn't have any harmonic distortion correction (though its power factor
correction is fairly accurate).
Basically it was useless for measuring power draw from a switch mode power
supply (or just about any good battery charger).

If you are intending to use a low cost power meter for measuring your Evs
energy requirement from the grid, make sure you compare it to a known
accurate meter first.


Matt
-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Rod Hower
Sent: Monday, 21 July 2008 10:33 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] Kill A Watt for 240Vac

I have a couple of Kill A Watt meters,
http://www.p3international.com/products/special/P4400/P4400-CE.html
These work great for such a low cost device.

A few have mentioned a similar 240Vac version, but I could not find which
one they were talking about.
Was it this
http://www.pat-training.co.uk/230V_electricity_meter.htm

Are there any other brands that people have used?
Thanks,
Rod


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options, see http://lists.sjsu.edu/mailman/listinfo/ev


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Re: motor torque question

Jeff Major
In reply to this post by Matt Lacey

--- On Mon, 7/21/08, matt <[hidden email]> wrote:


> Any ideas as to what current a warp 9 would go into
> saturation?
> Does anyone know at what current density iron goes into
> saturation?
>
> Matt
>
Hi Matt,

It is not current density, but flux density.  So it all depends on the particular magnetic circuit design and turns per coil on the field for the particular motor in question.  For sheet steel used for motor laminations, saturation starts about 1.0 tesla(T) and knees over to heavy saturation at about 1.3 T.  Without having the design specs for the motor, or running a no-load magnetization curve, I can't give you an exact figure for current.  However, it was Lee I think, gave some good advice.  Above the motor's one hour rated current, chances are you're getting into saturation.  Another 100 amps and you're well into it.  So at current limits, like 400 amps or above on a series motor of that size, no doubt you're saturated and torque per amp in nearly linear.

Regards,

Jeff M


     


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Re: motor torque question

Matt Lacey
Thanks for the help guys, much appreciated.

Sounds like I have yet more researching to do.

Cheers,
Matt

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Jeff Major
Sent: Monday, 21 July 2008 11:46 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] motor torque question


--- On Mon, 7/21/08, matt <[hidden email]> wrote:


> Any ideas as to what current a warp 9 would go into saturation?
> Does anyone know at what current density iron goes into saturation?
>
> Matt
>
Hi Matt,

It is not current density, but flux density.  So it all depends on the
particular magnetic circuit design and turns per coil on the field for the
particular motor in question.  For sheet steel used for motor laminations,
saturation starts about 1.0 tesla(T) and knees over to heavy saturation at
about 1.3 T.  Without having the design specs for the motor, or running a
no-load magnetization curve, I can't give you an exact figure for current.
However, it was Lee I think, gave some good advice.  Above the motor's one
hour rated current, chances are you're getting into saturation.  Another 100
amps and you're well into it.  So at current limits, like 400 amps or above
on a series motor of that size, no doubt you're saturated and torque per amp
in nearly linear.

Regards,

Jeff M


     


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Re: motor torque question

Roger Heuckeroth
In reply to this post by Matt Lacey
This is interesting.  The toque is proportional to the strength of the  
magnetic field... correct?  So, are we saying that the strength of the  
magnetic field starts out as a squared function of current, and then  
transitions to a linear function of current... and this is because of  
what?  Eddy currents in the iron?  Saturation?

I'm just trying to understand this?  There was another thread on how  
to improve the old tried and true series wound DC motor.  Sounds like  
different material to avoid saturation would be a good idea.


On Jul 21, 2008, at 10:52 AM, matt wrote:

> Ah ok, that makes sense.
> Any ideas as to what current a warp 9 would go into saturation?
> Does anyone know at what current density iron goes into saturation?
>
> Matt
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]]  
> On Behalf
> Of Lee Hart
> Sent: Monday, 21 July 2008 10:26 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] motor torque question
>
> matt wrote:
>> That's odd, I always thought the torque equation for series wound
>> motors was T=c*I^2. So 70ft-lb at 334.5A is 625ft-lb (less probably
>> due to less than optimal timing) at 1000A.
>
> The T=c1*I^2 equation works for low currents (below nameplate  
> current).
> But as you go higher, it gradually changes to simply T=c2*I as the  
> iron
> moves into saturation. (c1 and c2 are different constants).
>
> --
> 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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>
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> No virus found in this incoming message.
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> 19/07/2008
> 2:01 PM
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Re: motor torque question

David Dymaxion
In reply to this post by Mike Boyles
My first post was firing from the hip, now for some back-of-the-envelope. Working backwards from the Amps, Volts, voltage sag, an assumption that the motor drops out of current limit at mid rpm, etc. At mid rpm, I estimate the motor makes about 180 ft*lbs of torque with no current multiplication (nice to see that is close to your estimate). So Peter you are right, it does look like that are quoting wheel torque (unless they have a whole lotta current multiplication going on).


----- Original Message ----
From: Peter VanDerWal <[hidden email]>
...


     

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Re: motor torque question

Jeff Major
In reply to this post by Roger Heuckeroth
Hi Roger,

A few comments inserted......

--- On Mon, 7/21/08, Roger Heuckeroth <[hidden email]> wrote:

> This is interesting.  The toque is proportional to the
> strength of the  
> magnetic field... correct?

The torque is the product of armature current and flux.

> So, are we saying that the
> strength of the  
> magnetic field starts out as a squared function of current,
> and then  
> transitions to a linear function of current... and this is
> because of  
> what?  Eddy currents in the iron?  Saturation?

Saturation.  Flux no longer increases but armature current can.

> I'm just trying to understand this?  There was another
> thread on how  
> to improve the old tried and true series wound DC motor.
> Sounds like  
> different material to avoid saturation would be a good
> idea.

There are only a few ferromagnetic materials, like iron.  All other materials have basically the permeability of a vacuum.  So use wood or plastic to avoid saturation.  The excitation would kill you, but you won't saturate without iron.  But iron is like tens of thousands of times a better magnetic "conductor" than just about everything else.  Mankind is lucky to have iron.  You come up with something better, you'll be a rich man.

Regards,

Jeff M


     


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Re: motor torque question

Roger Stockton
In reply to this post by Roger Heuckeroth
Roger Heuckeroth wrote:

> This is interesting.  The toque is proportional to the
> strength of the magnetic field... correct?  So, are we saying
> that the strength of the magnetic field starts out as a
> squared function of current, and then transitions to a linear
> function of current... and this is because of what?  Eddy
> currents in the iron?  Saturation?

Right.

The field strength is proportional to the field current in a wound field machine.

Torque is proportional to armature current times field strength, so torque is proportional to the product of armature current and field current.  In a series wound machine, the armature and field current are the same, so torque is proportional to the square of the current.

As the field saturates, its strength stops increasing with additional current, so eventually the current will increase only linearly since increasing armature current continues to increase torque.

In theory. ;^>

If you look at the published data for typical motors used in EVs, you will find that the torque never really increases as the square of the current, even at low currents (e.g. 100A or less).  This may be partly due to the fact that the theoretical relationship doesn't take into account that some of the torque is consumed internally (bearings, fan/windage, brush drag) and so the measured shaft torque will be somewhat to much less than expected (since at low currents the shaft speed is high and the losses due to the internal fan will be high).

Typically, the available torque seems to increase as a low 1.xth power (i.e. better than linearly, but less than squared) of the current.  Most motor data goes out to about 500A, so if you take a couple of points near the upper end of the curve and extrapolate linearly you will have a conservative estimate of the torque available at higher currents.

Cheers,

Roger.


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Re: motor torque question

Bob Rice-2
In reply to this post by Jeff Major

----- Original Message -----
From: "Jeff Major" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Monday, July 21, 2008 4:55 PM
Subject: Re: [EVDL] motor torque question


> Hi Roger,
>
> A few comments inserted......
>
> --- On Mon, 7/21/08, Roger Heuckeroth <[hidden email]> wrote:
>
>> This is interesting.  The toque is proportional to the
>> strength of the
>> magnetic field... correct?
>
> The torque is the product of armature current and flux.
>
>> So, are we saying that the
>> strength of the
>> magnetic field starts out as a squared function of current,
>> and then
>> transitions to a linear function of current... and this is
>> because of
>> what?  Eddy currents in the iron?  Saturation?
>
> Saturation.  Flux no longer increases but armature current can.
>
>> I'm just trying to understand this?  There was another
>> thread on how
>> to improve the old tried and true series wound DC motor.
>> Sounds like
>> different material to avoid saturation would be a good
>> idea.
>
> There are only a few ferromagnetic materials, like iron.  All other
> materials have basically the permeability of a vacuum.  So use wood or
> plastic to avoid saturation.  The excitation would kill you, but you won't
> saturate without iron.  But iron is like tens of thousands of times a
> better magnetic "conductor" than just about everything else.  Mankind is
> lucky to have iron.  You come up with something better, you'll be a rich
> man.
>
> Regards,
>
> Jeff M
   You bet! This is WHY the godamn motors are so heavy!I TRIED super thin
iron field housing on a old forklift motor in Taiwan, 40 years ago.Wasn't
worth a damn! NO torque or Power! An E.E.(Chinese guy) told me that AFTER we
machined up a new field!Well, ya live and learn, I guess?All physics laws
transcend national boundries, anyhow

   Bob
>
>
>
>
> _______________________________________________
> For general EVDL support, see http://evdl.org/help/
> For subscription options, see http://lists.sjsu.edu/mailman/listinfo/ev
>


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