Series and parallel switching

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Series and parallel switching

Drewcifer
Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something similar to set up series and parallel switching?  Could it be linked to a separate contractor to shit down the controller with out adversely affecting the motors? What else might one need to work with it? It Would be used in a 144v system with a Kelly 156vkdh 600a controller and two 9hp pm motors running separately off the single controller in a gear reduction system or through two 4-1ish differentials.

Hope this makes sense couldn't find archive post about this!

Stephen
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Re: Series and parallel switching

EVDL Administrator
On 5 Feb 2013 at 13:53, Drewcifer wrote:

> Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something
> similar to set up series and parallel switching?  Could it be linked to a
> separate contractor to [shut] down the controller [without] adversely
> affecting the motors?

What is it that you'd like to connect in parallel and series depending on
motor speed?  The two motors? What's the objective here?

David Roden
EVDL Administrator
http://www.evdl.org/


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Re: Series and parallel switching

Drewcifer
Ideally yes the two motors. The goal is a 2 speed elec transmission  
Without the Zilla and hairball. I'm running two pm motors with the following, in a front wheel drive Saturn sl1 using 4-1 differentials gear reduction on each motor vs the auto trans.

MOTOR SPEC DATA:
97V  9 HP WITH 5,700 RPM

72V  6  3/4 HP WITH 4,200 RPM

60V  5  3/4 HP WITH 3,500 RPM

48V  4 1/2 HP WITH 2,700 RPM

36V  3 HP WITH 2,000 RPM

24V  1 1/4 HP WITH 1,100 RPM

THIS CONTINUOUS DUTY MOTOR WAS MODIFIED FOR HIGHER POWER OUTPUT AND INCREASED EFFICIENCY AND TESTED. UP TO 21HP INTERMITTENT AND THIS MOTOR CAN BE USED AS A HIGH POWER DC GENERATOR FOR HIGH CURRENT APPLICATIONS


Sent from my iPhone

On Feb 5, 2013, at 7:49 PM, "EVDL Administrator" <[hidden email]> wrote:

On 5 Feb 2013 at 13:53, Drewcifer wrote:

> Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something
> similar to set up series and parallel switching?  Could it be linked to a
> separate contractor to [shut] down the controller [without] adversely
> affecting the motors?

What is it that you'd like to connect in parallel and series depending on
motor speed?  The two motors? What's the objective here?

David Roden
EVDL Administrator
http://www.evdl.org/


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Re: Series and parallel switching

Pestka, Dennis J
In reply to this post by Drewcifer
Shitting on your controller is probably better than pissing on it, but I would discourage either.

Thanks;
Dennis                                            
Elsberry, MO                              
http://www.evalbum.com/1366 
http://www.evalbum.com/3715                                               


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Drewcifer
Sent: Tuesday, February 05, 2013 3:54 PM
To: [hidden email]
Subject: [EVDL] Series and parallel switching

Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something similar
to set up series and parallel switching?  Could it be linked to a separate
contractor to shit down the controller with out adversely affecting the
motors? What else might one need to work with it? It Would be used in a 144v
system with a Kelly 156vkdh 600a controller and two 9hp pm motors running
separately off the single controller in a gear reduction system or through
two 4-1ish differentials.

Hope this makes sense couldn't find archive post about this!

Stephen



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View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Series-and-parallel-switching-tp4661043.html
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Re: Series and parallel switching

Drewcifer
I agree, LMAO!!! Love auto correct!!

Sent from my iPhone

On Feb 6, 2013, at 10:28 AM, "Pestka, Dennis J [via Electric Vehicle Discussion List]" <[hidden email]> wrote:

Shitting on your controller is probably better than pissing on it, but I would discourage either.

Thanks;
Dennis                                            
Elsberry, MO                              
http://www.evalbum.com/1366 
http://www.evalbum.com/3715                                               


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Drewcifer
Sent: Tuesday, February 05, 2013 3:54 PM
To: [hidden email]
Subject: [EVDL] Series and parallel switching

Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something similar
to set up series and parallel switching?  Could it be linked to a separate
contractor to shit down the controller with out adversely affecting the
motors? What else might one need to work with it? It Would be used in a 144v
system with a Kelly 156vkdh 600a controller and two 9hp pm motors running
separately off the single controller in a gear reduction system or through
two 4-1ish differentials.

Hope this makes sense couldn't find archive post about this!

Stephen



--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Series-and-parallel-switching-tp4661043.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.
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Re: Series and parallel switching

Drewcifer
In reply to this post by EVDL Administrator
Could you use arduino programming with the zolox or similar sensor to archive what the Zilla hairball achieves??

Sent from my iPhone

On Feb 5, 2013, at 7:49 PM, "EVDL Administrator [via Electric Vehicle Discussion List]" <[hidden email]> wrote:

On 5 Feb 2013 at 13:53, Drewcifer wrote:

> Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something
> similar to set up series and parallel switching?  Could it be linked to a
> separate contractor to [shut] down the controller [without] adversely
> affecting the motors?

What is it that you'd like to connect in parallel and series depending on
motor speed?  The two motors? What's the objective here?

David Roden
EVDL Administrator
http://www.evdl.org/


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Re: Series and parallel switching

Drewcifer
In reply to this post by EVDL Administrator
Ok so I'm a 4yr old in this world so my Apologizes  if this is lame but perhaps it will spark some idea in someone that is more skilled......ok here goes....

If you used the speed sensor to feed Rpm data to an arduino duo programmed to a switching contactor that switches the voltages from series to parallel coupled with something like a precharge resistor to keep Amps the same but ramp up the voltage wouldn't you be able to accomplish what the hairball does but at a lower amperage and speed then one would need for drag racing?? Thus making it more cost effective and hobbyist friendly????

 I'm  sure there's about ten steps i'm not thinking of and i have no clue where this would go in the system but that being said id love to hear everyones thoughts!!

Drewcifer

Sent from my iPhone

On Feb 5, 2013, at 7:49 PM, "EVDL Administrator [via Electric Vehicle Discussion List]" <[hidden email]> wrote:

On 5 Feb 2013 at 13:53, Drewcifer wrote:

> Coul you use a  Zolox Motor Speed Sensor Kit DL9-2171s or something
> similar to set up series and parallel switching?  Could it be linked to a
> separate contractor to [shut] down the controller [without] adversely
> affecting the motors?

What is it that you'd like to connect in parallel and series depending on
motor speed?  The two motors? What's the objective here?

David Roden
EVDL Administrator
http://www.evdl.org/


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Re: Series and parallel switching

Lee Hart
In reply to this post by Drewcifer
On 2/5/2013 10:11 PM, Ds2inc wrote:

> Ideally yes the two motors. The goal is a 2 speed elec transmission
> Without the Zilla and hairball. I'm running two pm motors with the
> following, in a front wheel drive Saturn sl1 using 4-1 differentials
> gear reduction on each motor vs the auto trans.
>
> MOTOR SPEC DATA: 97V  9 HP WITH 5,700 RPM
> 72V  6 3/4 HP WITH 4,200 RPM
> 60V  5 3/4 HP WITH 3,500 RPM
> 48V  4 1/2 HP WITH 2,700 RPM
> 36V  3 HP WITH 2,000 RPM
> 24V  1 1/4 HP WITH 1,100 RPM
> UP TO 21HP INTERMITTENT...

Sounds like an interesting approach.

The Zilla uses contactors to switch the between series/parallel (and
forwqard/reverse). It has logic to watch the contactors, and decide when
to switch for you. You would have to provide the equivalent of this in
your controller. The manual is online; you can look at the contactor
setup and see how it's done.

Basically, you wire up a set of contactors (or big switches) to do the
series/parallel switching. You will also need reversing contactors,
since you don't have a transmission with your setup. Finally, you need a
main contactor, to shut it off in case the controller goes berserk.

Depending on your wiring, there may be circumstances where it is
dangerous to turn on one contactor before another one turns off. The
Zilla setup uses contactors with auxiliary switches, so the hairball
*knows* whether a contactor has switched or not. For your setup, you'll
want to include something similar.

PM motors run at a speed controlled by the voltage. If you run them in
series, the current (torque) in each motor is the same, and the voltage
(speed) will self-adjust; they act like a standard differential.

If you run PM motors in parallel, their voltage is the same, and they
both run at the same speed. They behave like a limited-slip or locking
differential. Nice in snow or on a drag strip; but it leads to extra
losses in normal driving. Going around a curve, the outside motor is
forced to turn faster, so it becomes a generator, and is actually
dragging the wheel backward (negative torque). The current it generates
drives the inside motor harder, trying to make it turn faster.
--
A truly excellent politician will tell you everything you want to hear.
A truly excellent engineer will tell you the truth. -- D.C. Weber
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Drewcifer
Lee thank you for all this info extremely helpful!

In regard to the drag during turning will this apply and/or be as detrimental if using a motor/4-1 diff/cv/axel/wheel set up??

"They behave like a limited-slip or locking differential. Nice in snow or on a drag strip; but it leads to extra losses in normal driving. Going around a curve, the outside motor is forced to turn faster, so it becomes a generator, and is actually dragging the wheel backward (negative torque). The current it generates drives the inside motor harder, trying to make it turn faster."

Thanks again

Stephen

Sent from my iPhone

On Feb 7, 2013, at 10:53 AM, Lee Hart <[hidden email]> wrote:

> They behave like a limited-slip or locking differential. Nice in snow or on a drag strip; but it leads to extra losses in normal driving. Going around a curve, the outside motor is forced to turn faster, so it becomes a generator, and is actually dragging the wheel backward (negative torque). The current it generates drives the inside motor harder, trying to make it turn faster.
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Re: Series and parallel switching

Drewcifer
In reply to this post by Lee Hart
Also if I read this correctly with pm motors there is no need to run them in parallel to achieve higher hp I just need more voltage in each parallel?? Am I missing then concept here??

Hmmmmm great for a lifePo traction pack perhaps not for a flooded pack tho I suppose?

Stephen

Sent from my iPhone

On Feb 7, 2013, at 10:53 AM, Lee Hart <[hidden email]> wrote:

On 2/5/2013 10:11 PM, Ds2inc wrote:

> Ideally yes the two motors. The goal is a 2 speed elec transmission
> Without the Zilla and hairball. I'm running two pm motors with the
> following, in a front wheel drive Saturn sl1 using 4-1 differentials
> gear reduction on each motor vs the auto trans.
>
> MOTOR SPEC DATA: 97V  9 HP WITH 5,700 RPM
> 72V  6 3/4 HP WITH 4,200 RPM
> 60V  5 3/4 HP WITH 3,500 RPM
> 48V  4 1/2 HP WITH 2,700 RPM
> 36V  3 HP WITH 2,000 RPM
> 24V  1 1/4 HP WITH 1,100 RPM
> UP TO 21HP INTERMITTENT...

Sounds like an interesting approach.

The Zilla uses contactors to switch the between series/parallel (and forwqard/reverse). It has logic to watch the contactors, and decide when to switch for you. You would have to provide the equivalent of this in your controller. The manual is online; you can look at the contactor setup and see how it's done.

Basically, you wire up a set of contactors (or big switches) to do the series/parallel switching. You will also need reversing contactors, since you don't have a transmission with your setup. Finally, you need a main contactor, to shut it off in case the controller goes berserk.

Depending on your wiring, there may be circumstances where it is dangerous to turn on one contactor before another one turns off. The Zilla setup uses contactors with auxiliary switches, so the hairball *knows* whether a contactor has switched or not. For your setup, you'll want to include something similar.

PM motors run at a speed controlled by the voltage. If you run them in series, the current (torque) in each motor is the same, and the voltage (speed) will self-adjust; they act like a standard differential.

If you run PM motors in parallel, their voltage is the same, and they both run at the same speed. They behave like a limited-slip or locking differential. Nice in snow or on a drag strip; but it leads to extra losses in normal driving. Going around a curve, the outside motor is forced to turn faster, so it becomes a generator, and is actually dragging the wheel backward (negative torque). The current it generates drives the inside motor harder, trying to make it turn faster.
--
A truly excellent politician will tell you everything you want to hear.
A truly excellent engineer will tell you the truth. -- D.C. Weber
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Lee Hart
In reply to this post by Drewcifer
Drewcifer wrote:
> Could you use arduino programming with the zolox or similar sensor to
> archive what the Zilla hairball achieves??

Possibly; but it's not really a "computer" kind of problem.

Fundamentally, you have to decide *when* you want to shift between
series and parallel. That can be a human decision (when you flip a
switch), or an automatic one (based on some criteria you have to define;
like "above 40 mph" or "when I floor the accelerator pedal and the
controller is not in current limit").

When you want to shift, the sequence of events is something like:

1. Release the accelerator pedal, so the motors drop to zero current.
2. Switch the contactors from series to parallel (or parallel to
    series).
3. Re-apply the accelerator pedal.

Safeguards should also be included, so all h*ll won't break loose if
some contactor is stuck on or off. Improper operation can result in
unstoppable full-power acceleration, going into reverse when you are at
a high forward speed, shorting the motor (which would essentially lock
the tires), etc.
--
If we knew what we were doing, it wouldn't be called research, would it?
        -- Albert Einstein
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Lee Hart
In reply to this post by Drewcifer
Drewcifer wrote:
> If you used the speed sensor to feed Rpm data to an arduino duo
> programmed to a switching contactor that switches the voltages from
> series to parallel coupled with something like a precharge resistor
> to keep Amps the same but ramp up the voltage wouldn't you be able to
> accomplish what the hairball does but at a lower amperage and speed
> then one would need for drag racing?? Thus making it more cost
> effective and hobbyist friendly????

You don't want to switch an inductive load (like a motor) when current
is flowing. If you do, you get hellish amounts of arcing. So to switch
between series/parallel, you first have to take your foot off the
accelerator pedal so the controller is at (about) zero motor current.

Then after the series/parallel switch, you can step on the accelerator
again. It doesn't require a computer to do this, though you can use one
anyway if you wish.
--
*BE* the change that you wish to see in the world. -- Mahatma Gandhi
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Lee Hart
In reply to this post by Drewcifer
On 2/7/2013 1:31 PM, Ds2inc wrote:
> In regard to the drag during turning will this apply and/or be as
> detrimental if using a motor/4-1 diff/cv/axel/wheel set up??

Yes. Get yourself two PC DC motors. Wire them in parallel. Turning the
shaft of one makes it act as a generator, which causes the shaft of the
other one to turn as well.

If these are really crappy motors, they are so lossy that the second
motor might only turn at half the speed of the first one. But if you do
this with really good, high efficiency motors, they behave almost like
there is a shaft coupling them together.

--
Anyone can make the simple complicated. Creativity is making the
complicated simple. -- Charles Mingus
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Cor van de Water
Great way to make an electric LSD (Limited Slip Diff)

Practically, I fail to see any significant issues.
When the vehicle is at speed, there is hardly ever a
significant difference in speed between wheels
(you can't turn a 90 deg corner at freeway speeds)
and if there is a large speed difference it is likely to be
the case of a one-wheel traction loss (hitting a patch of
sand or an oil leak or aquaplaning or a wet metal surface)
so the built-in traction control characteristic of two
parallel motors will avoid that one wheel spins freely and the
other has no traction at all, as is the case in a normal diff
and the reason that when it matters, performance cars have
relied on LSD to solve that problem.

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Lee Hart
Sent: Thursday, February 07, 2013 4:56 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Series and parallel switching

On 2/7/2013 1:31 PM, Ds2inc wrote:
> In regard to the drag during turning will this apply and/or be as
> detrimental if using a motor/4-1 diff/cv/axel/wheel set up??

Yes. Get yourself two PC DC motors. Wire them in parallel. Turning the
shaft of one makes it act as a generator, which causes the shaft of the
other one to turn as well.

If these are really crappy motors, they are so lossy that the second
motor might only turn at half the speed of the first one. But if you do
this with really good, high efficiency motors, they behave almost like
there is a shaft coupling them together.

--
Anyone can make the simple complicated. Creativity is making the
complicated simple. -- Charles Mingus
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
For EV drag racing discussion, please use NEDRA
(http://groups.yahoo.com/group/NEDRA)

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Re: Series and parallel switching

Peter C.
In reply to this post by Lee Hart
Sounds to me like what was actually used on the 1995 Tropica?  


Peter Crisitello
[hidden email]




-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Lee Hart
Sent: Thursday, February 07, 2013 1:54 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Series and parallel switching

On 2/5/2013 10:11 PM, Ds2inc wrote:
> Ideally yes the two motors. The goal is a 2 speed elec transmission
> Without the Zilla and hairball. I'm running two pm motors with the
> following, in a front wheel drive Saturn sl1 using 4-1 differentials
> gear reduction on each motor vs the auto trans.
>
> MOTOR SPEC DATA: 97V  9 HP WITH 5,700 RPM 72V  6 3/4 HP WITH 4,200 RPM
> 60V  5 3/4 HP WITH 3,500 RPM 48V  4 1/2 HP WITH 2,700 RPM 36V  3 HP
> WITH 2,000 RPM 24V  1 1/4 HP WITH 1,100 RPM UP TO 21HP INTERMITTENT...

Sounds like an interesting approach.

The Zilla uses contactors to switch the between series/parallel (and
forwqard/reverse). It has logic to watch the contactors, and decide when to
switch for you. You would have to provide the equivalent of this in your
controller. The manual is online; you can look at the contactor setup and
see how it's done.

Basically, you wire up a set of contactors (or big switches) to do the
series/parallel switching. You will also need reversing contactors, since
you don't have a transmission with your setup. Finally, you need a main
contactor, to shut it off in case the controller goes berserk.

Depending on your wiring, there may be circumstances where it is dangerous
to turn on one contactor before another one turns off. The Zilla setup uses
contactors with auxiliary switches, so the hairball
*knows* whether a contactor has switched or not. For your setup, you'll want
to include something similar.

PM motors run at a speed controlled by the voltage. If you run them in
series, the current (torque) in each motor is the same, and the voltage
(speed) will self-adjust; they act like a standard differential.

If you run PM motors in parallel, their voltage is the same, and they both
run at the same speed. They behave like a limited-slip or locking
differential. Nice in snow or on a drag strip; but it leads to extra losses
in normal driving. Going around a curve, the outside motor is forced to turn
faster, so it becomes a generator, and is actually dragging the wheel
backward (negative torque). The current it generates drives the inside motor
harder, trying to make it turn faster.
--
A truly excellent politician will tell you everything you want to hear.
A truly excellent engineer will tell you the truth. -- D.C. Weber
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Lee Hart
In reply to this post by Drewcifer
On 2/7/2013 1:44 PM, Ds2inc wrote:
> Also if I read this correctly with pm motors there is no need to run
> them in parallel to achieve higher hp I just need more voltage in
> each parallel? Am I missing then concept here?

Mechanical power (horsepower) is torque x RPM. Electrical power (watts)
is volts x amps. With a PM DC motor, volts = RPM, and amps = torque. The
relationships aren't perfect (they assume the motor is 100% efficient).
But in practice, a motor can easily be 90% efficient, so this
relationship is accurate within about 10%.

A PM motor tries as hard as it can to run at the RPM demanded by the
voltage. With the numbers you gave (72V 6.75HP 4200 RPM), you can expect
something like:

no load: 72v, 10 amps, 0hp, 4300rpm
full load: 72v, 80 amps, 6.75hp, 4200rpm
double load: 72v, 160amps, 13.5hp, 4100rpm

If you increased the load, the motor would just keep trying. The RPM
would barely fall, but the current would go up to supply the horsepower
demanded, until the motor burned up from excessive current.

Two motors in parallel would supply exactly the same RPM. But each motor
draws half the current and supplies half the torque (thus half the power
in, and power out). The main advantage of two motors is that they can
supply power for twice as long before burning up.

With PM motors, RPM is *directly* controlled by voltage. Double the
voltage, double the RPM, etc. It doesn't matter how many motors you
parallel; they *all* run at the same RPM.

You said your motors produce 4200 RPM at 72v, and your gear ratio is
4:1. That lets us precisely calculate your maximum speed. Your wheel
will be turning at 4200/4 = 1050 RPM. A 24" diameter tire moves 3.14 x
24" = 75.36" per revolution. 75.36"/rev x 1050 RPM = 79128"/minute =
6594 feet/minute = 1.249 miles/minute = 75 miles an hour. If your motors
were connected straight to a 72v pack, the car would go 75 mph, uphill
or downhill, drawing as much current from the batteries, or regenerating
as much current into the batteries as it could to stay at this speed, as
if you had a "cruise control" engaged.

--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
  -- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Drewcifer
Lee thank you again so very much for the clarification on the two wiring effects and on you confirming my math re: speed at rpm! As a newbie I am not always sure I'm applying the data and formulas correctly!!



Sent from my iPhone

On Feb 7, 2013, at 5:24 PM, Lee Hart <[hidden email]> wrote:

On 2/7/2013 1:44 PM, Ds2inc wrote:
> Also if I read this correctly with pm motors there is no need to run
> them in parallel to achieve higher hp I just need more voltage in
> each parallel? Am I missing then concept here?

Mechanical power (horsepower) is torque x RPM. Electrical power (watts) is volts x amps. With a PM DC motor, volts = RPM, and amps = torque. The relationships aren't perfect (they assume the motor is 100% efficient). But in practice, a motor can easily be 90% efficient, so this relationship is accurate within about 10%.

A PM motor tries as hard as it can to run at the RPM demanded by the voltage. With the numbers you gave (72V 6.75HP 4200 RPM), you can expect something like:

no load: 72v, 10 amps, 0hp, 4300rpm
full load: 72v, 80 amps, 6.75hp, 4200rpm
double load: 72v, 160amps, 13.5hp, 4100rpm

If you increased the load, the motor would just keep trying. The RPM would barely fall, but the current would go up to supply the horsepower
demanded, until the motor burned up from excessive current.

Two motors in parallel would supply exactly the same RPM. But each motor draws half the current and supplies half the torque (thus half the power in, and power out). The main advantage of two motors is that they can supply power for twice as long before burning up.

With PM motors, RPM is *directly* controlled by voltage. Double the
voltage, double the RPM, etc. It doesn't matter how many motors you
parallel; they *all* run at the same RPM.

You said your motors produce 4200 RPM at 72v, and your gear ratio is
4:1. That lets us precisely calculate your maximum speed. Your wheel
will be turning at 4200/4 = 1050 RPM. A 24" diameter tire moves 3.14 x
24" = 75.36" per revolution. 75.36"/rev x 1050 RPM = 79128"/minute =
6594 feet/minute = 1.249 miles/minute = 75 miles an hour. If your motors
were connected straight to a 72v pack, the car would go 75 mph, uphill
or downhill, drawing as much current from the batteries, or regenerating
as much current into the batteries as it could to stay at this speed, as
if you had a "cruise control" engaged.

--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Series and parallel switching

Roger Stockton
In reply to this post by Peter C.
Peter Crisitello wrote:

> Sounds to me like what was actually used on the 1995 Tropica?

I don't know if the drivetrain configurations varied for different years, but my understanding is that the Tropica used a pair of smaller ADC series-DC motors, each independently driving a rear wheel through a fixed reduction belt drive, and each powered via its own Curtis controller.

It is possible that both were connected to a single Curtis, but in either case there was no series-parallel switching, and series motors don't behave quite the same as PMDC.

Cheers,

Roger.

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Re: Series and parallel switching

Cor van de Water
In reply to this post by Drewcifer
Of course,
with the two motors in series the expected max speed is half (37 MPH)
so this sounds like an interesting city/freeway drive setup where
the City setting allows the full current through both motors, giving
twice the max torque at lower speeds, while the freeway setting gives
higher voltage (higher speed) at the cost of lower torque (current
divided between the two motors if the wheels turn at the same speed)

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Ds2inc
Sent: Thursday, February 07, 2013 5:37 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Series and parallel switching

Lee thank you again so very much for the clarification on the two wiring
effects and on you confirming my math re: speed at rpm! As a newbie I am
not always sure I'm applying the data and formulas correctly!!



Sent from my iPhone

On Feb 7, 2013, at 5:24 PM, Lee Hart <[hidden email]> wrote:

On 2/7/2013 1:44 PM, Ds2inc wrote:
> Also if I read this correctly with pm motors there is no need to run
> them in parallel to achieve higher hp I just need more voltage in
> each parallel? Am I missing then concept here?

Mechanical power (horsepower) is torque x RPM. Electrical power (watts)
is volts x amps. With a PM DC motor, volts = RPM, and amps = torque. The
relationships aren't perfect (they assume the motor is 100% efficient).
But in practice, a motor can easily be 90% efficient, so this
relationship is accurate within about 10%.

A PM motor tries as hard as it can to run at the RPM demanded by the
voltage. With the numbers you gave (72V 6.75HP 4200 RPM), you can expect
something like:

no load: 72v, 10 amps, 0hp, 4300rpm
full load: 72v, 80 amps, 6.75hp, 4200rpm
double load: 72v, 160amps, 13.5hp, 4100rpm

If you increased the load, the motor would just keep trying. The RPM
would barely fall, but the current would go up to supply the horsepower
demanded, until the motor burned up from excessive current.

Two motors in parallel would supply exactly the same RPM. But each motor
draws half the current and supplies half the torque (thus half the power
in, and power out). The main advantage of two motors is that they can
supply power for twice as long before burning up.

With PM motors, RPM is *directly* controlled by voltage. Double the
voltage, double the RPM, etc. It doesn't matter how many motors you
parallel; they *all* run at the same RPM.

You said your motors produce 4200 RPM at 72v, and your gear ratio is
4:1. That lets us precisely calculate your maximum speed. Your wheel
will be turning at 4200/4 = 1050 RPM. A 24" diameter tire moves 3.14 x
24" = 75.36" per revolution. 75.36"/rev x 1050 RPM = 79128"/minute =
6594 feet/minute = 1.249 miles/minute = 75 miles an hour. If your motors
were connected straight to a 72v pack, the car would go 75 mph, uphill
or downhill, drawing as much current from the batteries, or regenerating
as much current into the batteries as it could to stay at this speed, as
if you had a "cruise control" engaged.

--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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For EV drag racing discussion, please use NEDRA
(http://groups.yahoo.com/group/NEDRA)

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Re: Series and parallel switching

Lee Hart
In reply to this post by Cor van de Water
On 2/7/2013 7:09 PM, Cor van de Water wrote:
> Great way to make an electric LSD (Limited Slip Diff)
> Practically, I fail to see any significant issues.

The only issue is when turning a corner on normal dry pavement. The
outside wheel has to rotate faster than the inner wheel. The inner wheel
has to produce all the "motoring" torque, and the outer wheel becomes a
brake, trying to hold the vehicle back.

The sharper you turn, and the faster you go, the worse this effect
becomes. As for how "bad" the extra loss is, that will depend on how
efficient the motors are. This is a case where the worse the motor's
efficiency is, the less of a problem this will be.

If a car's wheels are 5 feet apart, and it has a 30-foot turning circle,
then the inner wheel has a 27.5-foot circle and the outer wheel a
32.5-foot circle. That's a 18% difference in wheel speeds. This is
probably tolerable with 80% efficient motors, whose speed difference
could be 20% between full load and no load. But it could make 90%
efficient motors really fight!

If this turned out to be a problem, you could simply force the motors to
be in series during sharp turns. Save parallel operation for high speeds
where you should never be turning sharp anyway.

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
         -- Antoine de Saint Exupery
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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