How does a Zilla HV control high pack voltage to the motor?

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How does a Zilla HV control high pack voltage to the motor?

AMPhibian
I've seen a number of EV's in the album that show a 240 volt or higher pack voltage running through a Zilla to an 8,9, or 11 inch motor that I thought was rated at 156-192 max.  How does this not destroy the motor?  Does the Zilla step down the pack voltage, or is the PWM average setting enough to protect the motor at the higher voltages?
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Re: How does a Zilla HV control high pack voltage to the motor?

Ian Hooper-3
On 13/01/2009, at 9:53 PM, AMPhibian wrote:

> I've seen a number of EV's in the album that show a 240 volt or  
> higher pack
> voltage running through a Zilla to an 8,9, or 11 inch motor that I  
> thought
> was rated at 156-192 max.  How does this not destroy the motor?  
> Does the
> Zilla step down the pack voltage

Yep.

> or is the PWM average setting enough to
> protect the motor at the higher voltages?

To be precise, you certainly can damage a 144-192V rated series DC  
motor if you have a 240V pack. You can program the Zilla to limit  
motor side voltage to whatever your motor is rated to, and the  
controller will then restrict maximum PWM duty so as to never exceed  
this voltage.

Ian Hooper
--
"Never doubt that the work of a small group of thoughtful, committed  
citizens can change the world." - Margaret Mead
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Re: How does a Zilla HV control high pack voltage to the motor?

AMPhibian

Ian Hooper-3 wrote
To be precise, you certainly can damage a 144-192V rated series DC  
motor if you have a 240V pack. You can program the Zilla to limit  
motor side voltage to whatever your motor is rated to, and the  
controller will then restrict maximum PWM duty so as to never exceed  
this voltage.
So the Zilla is restricting the PWM which sends an average voltage to the motor, doesn't the motor still see full voltage for a microsecond?  Basically a controller sends full voltage then shuts it off.  The averaged PWM voltage "looks" like the proper voltage to the motor components and even if it's higher than the motor is rated for, say 240, if you average it to 144 everything is OK?
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Re: How does a Zilla HV control high pack voltage to the motor?

Dennis at e v school
In reply to this post by AMPhibian
The Insulation in the windings is likely 4 to 10 times the rated max  
voltage. So, we are concerned about max. voltage to limit commutator arcing  and
excessive brush wear. With a PWM controller, arcing is limited by the  controller.
 
 
In a message dated 1/13/2009 9:08:59 A.M. Eastern Standard Time,  
[hidden email] writes:




Ian Hooper-3 wrote:

>
>
> To be  precise, you certainly can damage a 144-192V rated series DC  
>  motor if you have a 240V pack. You can program the Zilla to limit  
> motor side voltage to whatever your motor is rated to, and the  
> controller will then restrict maximum PWM duty so as to never  exceed  
> this voltage.
>
>
>
So the Zilla  is restricting the PWM which sends an average voltage to the
motor, doesn't  the motor still see full voltage for a microsecond?
Basically a controller  sends full voltage then shuts it off.  The averaged
PWM voltage  "looks" like the proper voltage to the motor components and even
if it's  higher than the motor is rated for, say 240, if you average it to
144  everything is OK?
--
View this message in context:  
http://www.nabble.com/How-does-a-Zilla-HV-control-high-pack-voltage-to-the-motor--tp21435183p21436381.html
Sent  from the Electric Vehicle Discussion List mailing list archive at  
Nabble.com.

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Re: How does a Zilla HV control high pack voltage to themotor?

Bob Rice-2

----- Original Message -----
From: <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, January 13, 2009 9:21 AM
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage to
themotor?


> The Insulation in the windings is likely 4 to 10 times the rated max
> voltage. So, we are concerned about max. voltage to limit commutator
> arcing  and
> excessive brush wear. With a PWM controller, arcing is limited by the
> controller.
>
    Well, think of it in Gas Rig frame of mind; You may HAVE hundreds of HP
on tap, but do you USE all of it?IF you TRY to run yur EV at battery voltage
alot, unless yur drag racing? And you shut it off in 8-12 seconds, so you
don't fireball the motor!Of course the DC motors willing to take hy voltage
surges is legendery! Not to mention yur gunna suck the battery voltage down,
anyhow?Age old EV issue! NO rock solid, like catenery, voltage that you can
bring with ya!Sigh!

   But you get into uncharted territory, like Berube, Wayland and Dube, our
household names here.WHO Ever thought of running HUNDREDS of volts through
workaday forklift motors. WHO EVer played with brush timing, before, or
built racing motors, joyful works of art! Like Jim Husted's examples? The
World built motors to pull trains, trolleys, golf carts, etc.etc, NEVER
thinking of overvoltaging them like OUR racing guyz!I mean you could pick up
Zombie's Siamese motor and set it on the bench, and NOT be a guy my size!
Hundreds of HP in yur arms! Pick up an equilivent V-8! Better get some help!
I think Dennis said HIS motor was a 36 volt forklift motor in Smoke Screen?"
He's running her , a tad,on the high side?

  What are the "limits?" Stay tuned! And I'm talking DC motors woth the
brushs being the limiting thing? AC? ! YEAH! NO brushes! Bring on lavish
amounts of voltage? Let's go after those laws of physics defying Top fool,
er, FUEL guyz! All it takes is volt an' AMPS!

    Seeya

    Bob......... Drag Racing is MUCH more fun than Wars to promote (Invent)
technology! Nobodies haveng any fun in Gaza!

> In a message dated 1/13/2009 9:08:59 A.M. Eastern Standard Time,
> [hidden email] writes:
>
>
>
>
> Ian Hooper-3 wrote:
>>
>>
>> To be  precise, you certainly can damage a 144-192V rated series DC
>>  motor if you have a 240V pack. You can program the Zilla to limit
>> motor side voltage to whatever your motor is rated to, and the
>> controller will then restrict maximum PWM duty so as to never  exceed
>> this voltage.
>>
>>
>>
> So the Zilla  is restricting the PWM which sends an average voltage to the
> motor, doesn't  the motor still see full voltage for a microsecond?
> Basically a controller  sends full voltage then shuts it off.  The
> averaged
> PWM voltage  "looks" like the proper voltage to the motor components and
> even
> if it's  higher than the motor is rated for, say 240, if you average it to
> 144  everything is OK?
> --
> View this message in context:
> http://www.nabble.com/How-does-a-Zilla-HV-control-high-pack-voltage-to-the-motor--tp21435183p21436381.html
> Sent  from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
> _______________________________________________
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>
>
>
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Re: How does a Zilla HV control high pack voltage to the motor?

Harris, Lawrence
In reply to this post by AMPhibian
The motor does not actually see the maximum.  The inductance ensures
that voltage does not rise instantly to the max available but rises
slowly and the nature of the circuit means the average is really what it
sees.  Besides that the motors insulation is good for 1000's of volts
(typically) and the actual voltage is infact the voltage applied minus
the back EMF.  You may be applying 200 volts but the motors spinning is
generating 100 volts so the motor only sees 100 volts and the power is
then 100v * available amps.  It's the amps that cause the heating and
ultimatly limit the motors maximum power and run time.

Lawrence

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of AMPhibian
Sent: Tuesday, January 13, 2009 6:06 AM
To: [hidden email]
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage to the
motor?




Ian Hooper-3 wrote:

>
>
> To be precise, you certainly can damage a 144-192V rated series DC  
> motor if you have a 240V pack. You can program the Zilla to limit  
> motor side voltage to whatever your motor is rated to, and the  
> controller will then restrict maximum PWM duty so as to never exceed  
> this voltage.
>
>
>
So the Zilla is restricting the PWM which sends an average voltage to
the
motor, doesn't the motor still see full voltage for a microsecond?
Basically a controller sends full voltage then shuts it off.  The
averaged
PWM voltage "looks" like the proper voltage to the motor components and
even
if it's higher than the motor is rated for, say 240, if you average it
to
144 everything is OK?
--
View this message in context:
http://www.nabble.com/How-does-a-Zilla-HV-control-high-pack-voltage-to-t
he-motor--tp21435183p21436381.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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Re: How does a Zilla HV control high pack voltage to themotor?

Cor van de Water
Ahem, it may be best to consult a simple schematic of a
(series) motor controller to see that the controller is
essentially only 3 components:
- switch to connect the battery pack to the motor
- freewheel diode that carries the motor current
  when the switch is "off"
- capacitor that supplies the motor current peaks
  so the battery sees a low continuous current.

The switch (typically a FET or IGBT) repeatedly
connects the motor directly to the battery pack, so
the motor *does* see the full battery pack voltage,
all controllers do this and only by using a series
inductor can you remove part of these voltage peaks.

Then why does the commutator not turn into a fireball
when a 36V or 72V motor is attached to a controller
that sends 300+V peaks to this motor?

Simple, because the controller is programmed
to never be continuous on, by setting a lower
motor output voltage, the controller is forced
to create this average voltage by switching
between ON (full pack voltage) and OFF (zero volts)
at the frequency of the controller, typically this
happens several times per millisecond.
So, any start of arcing is stopped as soon as the
controller voltage suddenly goes to zero, so even
while the peak voltage is higher than the comm
should be able to handle, the continuous on/off
switching will prevent if from burning up.

Hope this clarifies,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Harris, Lawrence
Sent: Tuesday, January 13, 2009 11:43 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage to
themotor?

The motor does not actually see the maximum.  The inductance ensures
that voltage does not rise instantly to the max available but rises
slowly and the nature of the circuit means the average is really what it
sees.  Besides that the motors insulation is good for 1000's of volts
(typically) and the actual voltage is infact the voltage applied minus
the back EMF.  You may be applying 200 volts but the motors spinning is
generating 100 volts so the motor only sees 100 volts and the power is
then 100v * available amps.  It's the amps that cause the heating and
ultimatly limit the motors maximum power and run time.

Lawrence

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of AMPhibian
Sent: Tuesday, January 13, 2009 6:06 AM
To: [hidden email]
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage to the
motor?




Ian Hooper-3 wrote:

>
>
> To be precise, you certainly can damage a 144-192V rated series DC  
> motor if you have a 240V pack. You can program the Zilla to limit  
> motor side voltage to whatever your motor is rated to, and the  
> controller will then restrict maximum PWM duty so as to never exceed  
> this voltage.
>
>
>
So the Zilla is restricting the PWM which sends an average voltage to
the
motor, doesn't the motor still see full voltage for a microsecond?
Basically a controller sends full voltage then shuts it off.  The
averaged
PWM voltage "looks" like the proper voltage to the motor components and
even
if it's higher than the motor is rated for, say 240, if you average it
to
144 everything is OK?
--
View this message in context:
http://www.nabble.com/How-does-a-Zilla-HV-control-high-pack-voltage-to-t
he-motor--tp21435183p21436381.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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Re: How does a Zilla HV control high pack voltage to themotor?

Peter Gabrielsson
On Tue, Jan 13, 2009 at 10:57 AM, Cor van de Water <[hidden email]> wrote:
>
> So, any start of arcing is stopped as soon as the
> controller voltage suddenly goes to zero, so even
> while the peak voltage is higher than the comm
> should be able to handle, the continuous on/off
> switching will prevent if from burning up.
>
> Hope this clarifies,
>

This is not quite correct. The commutator does NOT see the full pack
voltage due to the series inductance of the field coils, it sees the
average. The motor (series inductance plus armature) does see full
pack voltage every time the switch turns on.


--
www.electric-lemon.com

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Re: How does a Zilla HV control high pack voltage tothemotor?

Cor van de Water
Did you measure the brush voltage?

If I am not mistaken, in a series motor the
field windings have very low impedance, whereas
the armature sees almost all of the applied motor
voltage, so consequently the commutator is seeing
the larger part of this motor voltage, divided
down only a little bit between the low impedance
field and the much higher impedance armature, two
inductors in series.
I am guesstimating that the brushes will see about
95% of the applied motor voltage (square wave).

Please share if you have any brush voltage
measurements that show otherwise, so I can learn.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Peter Gabrielsson
Sent: Wednesday, January 14, 2009 12:47 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage
tothemotor?

On Tue, Jan 13, 2009 at 10:57 AM, Cor van de Water <[hidden email]>
wrote:
>
> So, any start of arcing is stopped as soon as the
> controller voltage suddenly goes to zero, so even
> while the peak voltage is higher than the comm
> should be able to handle, the continuous on/off
> switching will prevent if from burning up.
>
> Hope this clarifies,
>

This is not quite correct. The commutator does NOT see the full pack
voltage due to the series inductance of the field coils, it sees the
average. The motor (series inductance plus armature) does see full
pack voltage every time the switch turns on.


--
www.electric-lemon.com

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Re: How does a Zilla HV control high pack voltage to the motor?

James Massey
In reply to this post by Peter Gabrielsson
G'day Cor, All

At 06:54 AM 14/01/09, Cor van de Water wrote:
>Did you measure the brush voltage?

I haven't measured this on a motor, but I have measured on an analogue
(simulation). Big inductor, strip of stainless steel in a water bath
(running at about 10kW from 36V). Across the inductor is a square (actually
rectangular) wave, across the armature (strip of steel in my simulation, so
not a *perfect* simulation, but near enough) is pretty smooth DC. This was
testing a Curtis 1205 controller, so I was really looking at the
*controller* not the load, but for interest I did poke at the load side.

B+===M+----|
   _|_     [A]
   /_\      |
    |      [F]
    |-------|
  |-  M-
  |-
    |
    B-

the strip of stainless takes the place of [A] armature, big inductor takes
the place of [F] field (I also had a 1000A/75mV meter shunt in the loop but
I'm not certain where).

The inductor (Field) has a square wave (not actually square as I was
running about 75% on-time, so a 25%/75% rectangular wave), the controller
side going (IIRC) 1V/32V (measured to B-) at M-. The [A] to [F] join was at
about 10V measured with respect to B-, lots of induced noise but very
little of the waveform. In a real motor there will probably be more of the
waveform than I saw, as my inductor is probably bigger than the inductance
of a motor. I can jig this up with a motor field in place of the inductor
if you really want to have a definitive answer (I have more 1205s to test).

So, the approximate answer is that the motor overall sees the B+/B-
switching, but the armature sees the duty cycle voltage. At standstill the
full voltage will appear across the field (peak to peak) as a low on-time
pulsing DC voltage. As the armature spins up, the armature end of the field
becomes equivalent to the PWM duty cycle. So at 50% duty cycle, the field
will have a square wave across it of 50% of the battery voltage (peak to
peak). As the duty cycle approaches 100% the peak-to-peak voltage again
rises due to the armature end of the fields approaching battery voltage
whilst the controller side is still going B+/B-.

When a Zilla is controlling the motor voltage, all it is doing is limiting
the pulse-width modulation so that the average motor voltage is whatever
the setting is (the PWM % is a dynamic number as the battery voltage
varies). The M+ to M- is still seeing full battery volts (peak to peak),
but the inductance of the field reduces the armature voltage to the average.

Hope this helps.

Regards

[Technik] James

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Re: How does a Zilla HV control high pack voltage tothemotor?

Morgan LaMoore
In reply to this post by Cor van de Water
> If I am not mistaken, in a series motor the
> field windings have very low impedance, whereas
> the armature sees almost all of the applied motor
> voltage

You have to consider the impedance at the given frequency. At DC, the
field windings have very low impedance.

However, at the PWM switching frequency, the field has many more turns
of wire than the armature, so it has significantly higher inductance.

Thus, most of the AC voltage appears across the field, even though
most of the DC voltage appears across the armature.

-Morgan LaMoore

On Tue, Jan 13, 2009 at 1:54 PM, Cor van de Water <[hidden email]> wrote:

> Did you measure the brush voltage?
>
> If I am not mistaken, in a series motor the
> field windings have very low impedance, whereas
> the armature sees almost all of the applied motor
> voltage, so consequently the commutator is seeing
> the larger part of this motor voltage, divided
> down only a little bit between the low impedance
> field and the much higher impedance armature, two
> inductors in series.
> I am guesstimating that the brushes will see about
> 95% of the applied motor voltage (square wave).
>
> Please share if you have any brush voltage
> measurements that show otherwise, so I can learn.
>
> Regards,
>
> Cor van de Water
> Director HW & Systems Architecture Group
> Proxim Wireless Corporation http://www.proxim.com
> Email: [hidden email]    Private: http://www.cvandewater.com
> Skype: cor_van_de_water     IM: [hidden email]
> Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
> Tel: +91 (040)23117400 x203 XoIP: +31877841130
>
> Please consider the environment before printing this e-mail.
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Peter Gabrielsson
> Sent: Wednesday, January 14, 2009 12:47 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] How does a Zilla HV control high pack voltage
> tothemotor?
>
> On Tue, Jan 13, 2009 at 10:57 AM, Cor van de Water <[hidden email]>
> wrote:
>>
>> So, any start of arcing is stopped as soon as the
>> controller voltage suddenly goes to zero, so even
>> while the peak voltage is higher than the comm
>> should be able to handle, the continuous on/off
>> switching will prevent if from burning up.
>>
>> Hope this clarifies,
>>
>
> This is not quite correct. The commutator does NOT see the full pack
> voltage due to the series inductance of the field coils, it sees the
> average. The motor (series inductance plus armature) does see full
> pack voltage every time the switch turns on.
>
>
> --
> www.electric-lemon.com
>
> _______________________________________________
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>
>
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>

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Mid Atlantic Shows or displays?

Mark Cobb
In reply to this post by AMPhibian
Hi, long time no hear. Got the vw 90 fox and 99 geo metro. I was wondering if there was a show or something on a Saturday, Friday or this holiday this Monday I could go to surrounding the Richmond,va area to see an ev and get more ideas.

Thanks.

Cobb


     

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Re: How does a Zilla HV control high pack voltage to the motor?

Cor van de Water
In reply to this post by James Massey
Hi James,

Your simulation of a motor may be deceiving.
While I agree that a running motor may have
properties (such as back-EMF) beyond the
normal inductor, for simplicity it may be
best to consider the "stalled" situation as
a worst case and simple to reason through case.

BOTH field and armature are inductors, in fact
if I am not mistaken it is the field that has
very little windings of thick wire, I have even seen
flattened (strip-shaped) coils windings while the
armature has the many windings and carries most
of the voltage, so it would be wrong to simulate
that with a piece of resistance only.

Please add to this discussion if you have more info,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
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-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of James Massey
Sent: Wednesday, January 14, 2009 7:49 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How does a Zilla HV control high pack voltage to the
motor?

G'day Cor, All

At 06:54 AM 14/01/09, Cor van de Water wrote:
>Did you measure the brush voltage?

I haven't measured this on a motor, but I have measured on an analogue
(simulation). Big inductor, strip of stainless steel in a water bath
(running at about 10kW from 36V). Across the inductor is a square
(actually
rectangular) wave, across the armature (strip of steel in my simulation,
so
not a *perfect* simulation, but near enough) is pretty smooth DC. This
was
testing a Curtis 1205 controller, so I was really looking at the
*controller* not the load, but for interest I did poke at the load side.

B+===M+----|
   _|_     [A]
   /_\      |
    |      [F]
    |-------|
  |-  M-
  |-
    |
    B-

the strip of stainless takes the place of [A] armature, big inductor
takes
the place of [F] field (I also had a 1000A/75mV meter shunt in the loop
but
I'm not certain where).

The inductor (Field) has a square wave (not actually square as I was
running about 75% on-time, so a 25%/75% rectangular wave), the
controller
side going (IIRC) 1V/32V (measured to B-) at M-. The [A] to [F] join was
at
about 10V measured with respect to B-, lots of induced noise but very
little of the waveform. In a real motor there will probably be more of
the
waveform than I saw, as my inductor is probably bigger than the
inductance
of a motor. I can jig this up with a motor field in place of the
inductor
if you really want to have a definitive answer (I have more 1205s to
test).

So, the approximate answer is that the motor overall sees the B+/B-
switching, but the armature sees the duty cycle voltage. At standstill
the
full voltage will appear across the field (peak to peak) as a low
on-time
pulsing DC voltage. As the armature spins up, the armature end of the
field
becomes equivalent to the PWM duty cycle. So at 50% duty cycle, the
field
will have a square wave across it of 50% of the battery voltage (peak to

peak). As the duty cycle approaches 100% the peak-to-peak voltage again
rises due to the armature end of the fields approaching battery voltage
whilst the controller side is still going B+/B-.

When a Zilla is controlling the motor voltage, all it is doing is
limiting
the pulse-width modulation so that the average motor voltage is whatever

the setting is (the PWM % is a dynamic number as the battery voltage
varies). The M+ to M- is still seeing full battery volts (peak to peak),

but the inductance of the field reduces the armature voltage to the
average.

Hope this helps.

Regards

[Technik] James

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Re: How does a Zilla HV control high pack voltage to the motor?

James Massey
In reply to this post by James Massey
G'day Cor, All

At 09:05 PM 14/01/09, Cor wrote:
>Hi James,
><snip>
>BOTH field and armature are inductors, in fact
>if I am not mistaken it is the field that has
>very little windings of thick wire, I have even seen
>flattened (strip-shaped) coils windings while the
>armature has the many windings <snip>

The fields contain many windings, between 10 and 24 turns per pole:
http://jcmassey.gallery.netspace.net.au/Daihatsu-and-motor/Image_529
The fields are then two or four in series. I have yet to see a field with
less than 10 turns.

Wheras the armature has one turn between one brush and the next:
http://jcmassey.gallery.netspace.net.au/Hitachi_11_inch/Hitachi_comm_damage_2
I have yet to see a series DC brush motor with more than one turn
brush-to-brush in the armature, although my sample of motors is somewhat
small (only about a dozen or so).

If I'd thought about it I could have had a look when the Australian
Maritime College - Vessel Propulsion Lab motor:
http://jcmassey.gallery.netspace.net.au/album02
was on their dyno a couple of months ago.

My belief is that the armature inductance is only 5 to 10% of the total
motor inductance, the rest being from the fields.

Regards

[Technik] James

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Re: How does a Zilla HV control high pack voltage to the motor?

Jeff Major
In reply to this post by James Massey

--- On Wed, 1/14/09, James Massey <[hidden email]> wrote:

> I have yet to see a series DC brush motor with more than
> one turn brush-to-brush in the armature,

Hi James,

Yeah, but that is the armature coil which is out of the picture.  It is all the armature coils inbetween which are in fact in the circuit.  Here is a description I did a while back....

All the coils in
the DC armature are connected in a closed circuit, at
the comm bar risers.  Most DC motor armatures used by
you and other EVers are 4 pole, wave wound, with
hairpin type coils giving one turn per coil, two coil
sides per slot.  This requires a odd number of comm
bars.  Each armature coil end is connected to an
adjacent coil end where it is brazed or welded to the
comm bar.  This follows around for, let's say, all 37
coils, forming a closed loop on itself.  It is only
when the brushes are contacting the comm that this
closed loop of coils gives rise to two current paths.

If the brushes were very narrow and just had a point
contact with the comm, then current (Ia/2) would flow
thru each and every armature coil.  Effectively 18.5
coils in series and 2 parallel paths.  Now the brushes
are wide enough to cover 2, maybe 3 comm bars.  So the
coils connected to the comm bars which are shorted by
the brushes are taken out of the mix.  Those coils are
shorted turns, not open.  The coil has current flowing
in one direction as its comm bar encounters the brush,
is shorted by the brush and then has current flowing
in the opposite direction as its comm bar departs the
brush.

That would give us 16 coils in series carrying half of
the total armature current and the other 16 coils in
series carrying the other half of the current.  That
would mean that there are 32 out of the 37 coils doing
their full job.  The 5 coils that are shorted by the
brushes are positioned in the interpolar region anyway
and would contribute no torque even if they had
current flow........

Actually the equivalent series turns for the armature and field in this type of motor is nearly equal.  Or at least in a range of 1.5 to 1, depending on the particular design.  In other words, the field has about the same number of amp-turns as the armature in a series wound motor.

It is the fact that the armature is in quadrature with the field that gives rise to the fact that armature inductance is substantially less than the field inductance.  In other words, the field magnetic circuit is nice and tight.  The magnetic circuit for the armature points inbetween the field poles and therefore represents a poor path for the flux which would be produced by the armature MMF.

Peter is correct when he said......

The commutator does NOT see the full pack
voltage due to the series inductance of the field coils, it sees the
average. The motor (series inductance plus armature) does see full
pack voltage every time the switch turns on..........

The series field inductance is much greater than the armature inductance.

Regards,

Jeff M








     

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Re: How does a Zilla HV control high pack voltage to the motor?

Otmar
In reply to this post by AMPhibian
Hello All,

Remember those stories about how many IRC users it takes to change a light bulb? Well this thread has me chuckling in similar vein :-) Lot's of replies full of speculation, some even with authority, but not one of you has actually measured what is happening! Sorry, I don't mean to rib you all so much, but you must admit it's pretty funny. But now on to actually being helpful:

Back in the mid 1990's, when I determined the voltage limits on the ADC motors using a camera on the commutator and meters in view of the camera, I also wondered about the balance of voltage stress on the motor and what effects it may have. From my measurements I found that first off, the inductance of a typical 9" motor measured with a LCR meter at 120hz and 1khz is approximately equally split between the armature and field. Additionally if you scope the waveforms of a fast switching 15 kHz controller you will see that the windings share pulse voltage stress approximately equally. Putting a small capacitor on either the armature or field will shift the pulse voltage stress to the other winding. The capacitor seems to make no difference in the threshold of arcing in both drive and regen modes. (A few of you remember that I spent a couple years trying to get ADC motors to survive at reasonable levels of regen on a 144V pack voltage and that I was not successful.)

From my tests I determined that average voltage affects commutator arcing the same as DC voltage. Why exactly this is I don't know, and how much inductance, capacitance and EMF it would take to accurately model a DC motor I also don't know, but until we can model the cause of brush arcing I don't see how it would help to know.

Have fun!
-Otmar
-Otmar-

914 EV, California Poppy, Zilla research vehicle.
http://evcl.com/914/

The Zilla factory is at:
http://manzanitamicro.com/

Zilla Support is still at:
http://cafeelectric.com/Ssupport.php
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Re: How does a Zilla HV control high pack voltage to the motor?

Jeff Major

--- On Wed, 1/14/09, Otmar <[hidden email]> wrote:

> Additionally
> if you scope the waveforms of a fast switching 15 kHz
> controller you will
> see that the windings share pulse voltage stress
> approximately equally.

Hi Otmar,

Did this.  It was before 1990.  Back when 5 kHz was thought to be fast.  I don't have any pictures, but remember the field doing almost all the voltage averaging.  Looked like pretty much average DC to the armature.  This was while the motor was under load on a dynamometer.

Can't say why your meter showed equal inductance between the armature and field.  Were they physically separated?

Regards,

Jeff M


     

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Re: How does a Zilla HV control high pack voltage to the motor?

Otmar
Jeff Major wrote
Hi Otmar,

Did this.  It was before 1990.  Back when 5 kHz was thought to be fast.  I don't have any pictures, but remember the field doing almost all the voltage averaging.  Looked like pretty much average DC to the armature.  This was while the motor was under load on a dynamometer.

Can't say why your meter showed equal inductance between the armature and field.  Were they physically separated?

Regards,

Jeff M
Good thing! Glad someone is actually measuring things.

Looking up my data from then I see the measurements that I took on a stock motor (fully assembled) were not what I had remembered. Here are the actual notes:
7/11/96 - 10:19 AM
Measured stock 9" motor resistance here in shop. at 3.44 A
Field = 12.32 mv  for 3.5g8 milliohms
Armature 250 mv for 72.7 milliohms.
108.5 milliohms total.
Inductance Measured with Wavetek DM27XT
50 µH Field alone
166 µH Armature alone
189 µH S1-A1 Series
246 µH S1-A2 Series

Clearly there is coupling between the armature and field, and I wonder if that coupling is what brings about the sharing of the pulse waveform?

When I measured the 9" ADC motor waveforms it was installed in a car in the usual configuration.
I do specifically remember being able to shift all the pulse waveform from one winding to the other with a small disc capacitor (probably only 0.01uF or so, I don't remember what I used). I remember testing it at stall, but IIRC the pulses are added to the BEMF when at speed. This was many years ago and I did not document that so I could be off a bit.

As for why you saw all the effect on the field, I don't know what caused that. Many motors come with small noise caps on the armature to limit EMI from brush arcing. If your motor had those then it would explain your results.

-Otmar-

914 EV, California Poppy, Zilla research vehicle.
http://evcl.com/914/

The Zilla factory is at:
http://manzanitamicro.com/

Zilla Support is still at:
http://cafeelectric.com/Ssupport.php
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Re: How does a Zilla HV control high pack voltage to the motor?

Stephen Chapman
Good information!  I just ordered an LC meter and will post the results of measurements from my 11" GE series wound motor when it arrives.
Stephen Chapman


Good thing! Glad someone is actually measuring things.

Looking up my data from then I see the measurements that I took on a stock motor (fully assembled) were not what I had remembered. Here are the actual notes:
7/11/96 - 10:19 AM
Measured stock 9" motor resistance here in shop. at 3.44 A
Field = 12.32 mv  for 3.5g8 milliohms
Armature 250 mv for 72.7 milliohms.
108.5 milliohms total.
Inductance Measured with Wavetek DM27XT
50 µH Field alone
166 µH Armature alone
189 µH S1-A1 Series
246 µH S1-A2 Series

Clearly there is coupling between the armature and field, and I wonder if that coupling is what brings about the sharing of the pulse waveform?

When I measured the 9" ADC motor waveforms it was installed in a car in the usual configuration.
I do specifically remember being able to shift all the pulse waveform from one winding to the other with a small disc capacitor (probably only 0.01uF or so, I don't remember what I used). I remember testing it at stall, but IIRC the pulses are added to the BEMF when at speed. This was many years ago and I did not document that so I could be off a bit.

As for why you saw all the effect on the field, I don't know what caused that. Many motors come with small noise caps on the armature to limit EMI from brush arcing. If your motor had those then it would explain your results.

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Re: How does a Zilla HV control high pack voltage to the motor?

Jeff Major
In reply to this post by Otmar

--- On Wed, 1/14/09, Otmar <[hidden email]> wrote:

> at 3.44 A
> Field = 12.32 mv  for 3.5g8 milliohms
> Armature 250 mv for 72.7 milliohms.

>If your motor had those then it would
> explain your
> results.

Hi Otmar,

That is an awfully high armature resistance.  Must have included the brushes (?).  Typically, field and armature resistance are close.  Armature resistance needs to be measured at comm bars 90 degrees apart for a 4 pole motor, wave wound, which I pretty sure is the case, without the brushes in the circuit.  Was the inductance meter used with the brushes in the circuit?

And no, motor for my test had no caps.

I wish I still had my notes from back then, or the equipment to run those tests again.

Regards,

Jeff M


     

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