EV Digest 6195
Topics covered in this issue include:
1) Re: Regenerative Cruising
by "Peter Gabrielsson" <[EMAIL PROTECTED]>
2) Re: Regenerative Cruising
by "David Roden" <[EMAIL PROTECTED]>
3) Re: Regenerative Cruising
by "Peter VanDerWal" <[EMAIL PROTECTED]>
4) Re: Regenerative Cruising
by Jack Murray <[EMAIL PROTECTED]>
5) Re: Regenerative Cruising
by Joel Hacker <[EMAIL PROTECTED]>
6) Re: Regenerative Cruising/bouncing
by "Dave Wilker" <[EMAIL PROTECTED]>
7) Controller voltage maximums
by Kenneth Dove <[EMAIL PROTECTED]>
8) RE: Controller voltage maximums
by "damon henry" <[EMAIL PROTECTED]>
9) Re: Regenerative Cruising/bouncing
by Jordan Crane <[EMAIL PROTECTED]>
10) Re: Regenerative Cruising
by Jordan Crane <[EMAIL PROTECTED]>
11) Re: Controller voltage maximums
by Joel Hacker <[EMAIL PROTECTED]>
12) Re: Regenerative Cruising
by Joel Hacker <[EMAIL PROTECTED]>
13) Re: Regenerative Cruising/bouncing
by "Peter Gabrielsson" <[EMAIL PROTECTED]>
14) Re: Regen with ADC motors
by "Mark McCurdy" <[EMAIL PROTECTED]>
15) Re: Controller voltage maximums
by "Roland Wiench" <[EMAIL PROTECTED]>
16) RE: Regenerative Cruising
by Don Cameron <[EMAIL PROTECTED]>
17) Re: Regenerative Cruising/bouncing
by Jordan Crane <[EMAIL PROTECTED]>
18) Re: Controller voltage maximums
by Jack Murray <[EMAIL PROTECTED]>
19) RE: Controller voltage maximums
by "Roger Stockton" <[EMAIL PROTECTED]>
20) One versus two motors in parallel (was: Direct Drive)
by Bill Dube <[EMAIL PROTECTED]>
21) RE: Introduction
by "Chuck Hays" <[EMAIL PROTECTED]>
22) Re: Regenerative Cruising
by "Lawrence Rhodes" <[EMAIL PROTECTED]>
23) Re: Regen with ADC motors
by [EMAIL PROTECTED] (Dana Havranek)
24) no transmission or transmission
by "Tim Gamber" <[EMAIL PROTECTED]>
25) Rabbit EV available
by Steve Powers <[EMAIL PROTECTED]>
--- Begin Message ---
What you describe is regen breaking. Anytime you extract energy from
the momentum of the car you will be slowing it down, hence regen
breaking.
On 12/6/06, Jordan Crane <[EMAIL PROTECTED]> wrote:
This is probably a very dumb question. I'm sorry.
I was reading about power generating windmills, and it occured to me,
what about capturing the power from the wheels of the car when it is
just cruising. Which is to say, the power is not being applied via the
accelerator, and the brakes aren't being applied via the brake, but the
car has speed, and is coasting. The turning of the wheels will generate
a current on the motor, which can then be captured in the battery.
I haven't read anything about this, why is that? It seems that it'd be
pretty simple to build a switch that charges the batteries when the
accelerator isn't being pressed.. Perhaps the amount of energy would
be negligible, but then, it seems, so would the weight of the device
to capture the energy. And then, if you changed your driving habits
a bit, I bet you could maintain the charge on the batteries for a bit
longer. Not on the freeway for sure, but for around town driving,
this could be ideal, coupled with regen braking.
Thank you for your help..
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--
www.electric-lemon.com
--- End Message ---
--- Begin Message ---
On 6 Dec 2006 at 9:23, Jordan Crane wrote:
> what about capturing the power from the wheels of the car when it is
> just cruising. The turning of the wheels will generate a current
> on the motor, which can then be captured in the battery.
>
> I haven't read anything about this, why is that?
Because it doesn't work. As soon as you draw from the car's kinetic energy,
it slows down.
Of course, friction is already taking its toll, so already a vehicle can't
maintain a given speed on level ground without some input of energy. Taking
more of its kinetic energy to convert back to electricity would increase the
energy input required. In a practical sense, you would be taking energy
from the vehicle's momentum only to put it back to maintain the speed - and
since the conversion to electricity is not 100% efficient, you'd have to put
back more energy than you recovered (unless you count the wasted heat ;-).
The result would be a net loss, not a gain.
This is basic physics. Nothing personal, but every high school graduate
should know this intuitively. That such a misunderstanding is common
demonstrates the pitiful condition of the educational system in our nation
(and probably in some others, too).
David Roden - Akron, Ohio, USA
EV List Assistant Administrator
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--- End Message ---
--- Begin Message ---
<sigh>
There is no free energy. If you connect a generator to the wheels it
needs to extract energy FROM the wheels in order to convert it to
electricity. The energy it extracts has to come from somewhere, in this
case it comes from the kenetic energy that is keeping the vehicle moving.
So what happens is that the generator slows the vehicle down. Thbis is
great if you need to slow down (hence the name regenerative braking).
However, you can NOT extract the energy from the moving vehicle (kenetic
energy) and keep moving at the same speed.
Think about it this way. If you put a car in neural while cruising down
the highway, what happens? The vehicle starts slowing down. This is
because the vehicles kenetic energy is being used up to overcome friction
from the wheels and aerodynamic drag. If you add another energy drain
(the generator) the vehicle simply slows down faster.
Now if you're not in neutral and want to keep going at a steady speed, the
motor has to provide enough energy to offset the friction and drag. If
you add the generator, then the motor has to provide additional energy to
provide power for the generator. Because of losses in the drive train and
generator, the motor has to provide MORE energy than the generator
provides so you actually loose energy faster with the generator than you
do without it.
When it comes to energy, there is no free lunch The energy has to come
from somewhere. It's one of the basic laws of physics.
>
> This is probably a very dumb question. I'm sorry.
>
> I was reading about power generating windmills, and it occured to me,
> what about capturing the power from the wheels of the car when it is
> just cruising. Which is to say, the power is not being applied via the
> accelerator, and the brakes aren't being applied via the brake, but the
> car has speed, and is coasting. The turning of the wheels will generate
> a current on the motor, which can then be captured in the battery.
>
> I haven't read anything about this, why is that? It seems that it'd be
> pretty simple to build a switch that charges the batteries when the
> accelerator isn't being pressed.. Perhaps the amount of energy would
> be negligible, but then, it seems, so would the weight of the device
> to capture the energy. And then, if you changed your driving habits
> a bit, I bet you could maintain the charge on the batteries for a bit
> longer. Not on the freeway for sure, but for around town driving,
> this could be ideal, coupled with regen braking.
>
> Thank you for your help..
>
>
>
> - - - - - - - - - - - - - - - - - - - - - - - - -
> r e d d i n g k
>
> 1668 west boulevard. los angeles, CA 90019
> (323) 857 . 5326 http://www.reddingk.com
> - - - - - - - - - - - - - - - - - - - - - - - -
> -
>
>
--
If you send email to me, or the EVDL, that has > 4 lines of legalistic
junk at the end; then you are specifically authorizing me to do whatever I
wish with the message. By posting the message you agree that your long
legalistic signature is void.
--- End Message ---
--- Begin Message ---
you can do that, but when you lift the go pedal and do regen, the car
will slow down. you can say the same thing for a gas car, why not use
the engine cylinders that are pumping air in the pistons to supercharge
the engine to make it go faster? Just lift the throttle, and the engine
will go faster. hope that helps.
Jack
Jordan Crane wrote:
This is probably a very dumb question. I'm sorry.
I was reading about power generating windmills, and it occured to me,
what about capturing the power from the wheels of the car when it is
just cruising. Which is to say, the power is not being applied via the
accelerator, and the brakes aren't being applied via the brake, but the
car has speed, and is coasting. The turning of the wheels will generate
a current on the motor, which can then be captured in the battery.
I haven't read anything about this, why is that? It seems that it'd be
pretty simple to build a switch that charges the batteries when the
accelerator isn't being pressed.. Perhaps the amount of energy would
be negligible, but then, it seems, so would the weight of the device
to capture the energy. And then, if you changed your driving habits
a bit, I bet you could maintain the charge on the batteries for a bit
longer. Not on the freeway for sure, but for around town driving,
this could be ideal, coupled with regen braking.
Thank you for your help..
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
Hi Jordan,
The problem is that even with the nifty switch idea,
the windmill would add additional weight and drag to
the body of the car...Aerodynamics play an EXTREMELY
(emphasis added) extremely big role in the efficiency
of the car...
This additional drag would reverse any positive gain
you windmill might produce while braking or "coasting"
Jordan Crane wrote:
This is probably a very dumb question. I'm sorry.
I was reading about power generating windmills, and it occured to me,
what about capturing the power from the wheels of the car when it is
just cruising. Which is to say, the power is not being applied via the
accelerator, and the brakes aren't being applied via the brake, but the
car has speed, and is coasting. The turning of the wheels will generate
a current on the motor, which can then be captured in the battery.
I haven't read anything about this, why is that? It seems that it'd be
pretty simple to build a switch that charges the batteries when the
accelerator isn't being pressed.. Perhaps the amount of energy would
be negligible, but then, it seems, so would the weight of the device
to capture the energy. And then, if you changed your driving habits
a bit, I bet you could maintain the charge on the batteries for a bit
longer. Not on the freeway for sure, but for around town driving,
this could be ideal, coupled with regen braking.
Thank you for your help..
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
It sounds like the same thing as the windmill on the hood, to me. The energy
recovered would come at the expense of momentum.
Something I was thinking about was an article a few months back about shock
absorbers that used coils to generate current when "bouncing". The field
generation could also be used to resist movement.
David C. Wilker Jr.
USAF (RET)
----- Original Message -----
From: "Jordan Crane" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, December 06, 2006 9:23 AM
Subject: Regenerative Cruising
This is probably a very dumb question. I'm sorry.
I was reading about power generating windmills, and it occured to me,
what about capturing the power from the wheels of the car when it is
just cruising. Which is to say, the power is not being applied via the
accelerator, and the brakes aren't being applied via the brake, but the
car has speed, and is coasting. The turning of the wheels will generate
a current on the motor, which can then be captured in the battery.
I haven't read anything about this, why is that? It seems that it'd be
pretty simple to build a switch that charges the batteries when the
accelerator isn't being pressed.. Perhaps the amount of energy would
be negligible, but then, it seems, so would the weight of the device
to capture the energy. And then, if you changed your driving habits
a bit, I bet you could maintain the charge on the batteries for a bit
longer. Not on the freeway for sure, but for around town driving,
this could be ideal, coupled with regen braking.
Thank you for your help..
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
I would like to ask the list what would happen if the voltage rating
were exceeded on a controller?
Specifically, if one were to supply 98 volts to an Alltrax 72xx (72
volt) controller, would it melt down or explode or perform incorrectly, etc?
The motor in this setup is listed at 72 volts as well, but from what I
have read on this forum, these DC motors can handle excess voltages.
Does anyone have any experience or even tested such a scenario? Maybe
this is something that should not even be attempted. Obviously, the
alternative is to purchase a Curtis 1221C or its equivalent as a
replacement.
Thanks y'all.
--- End Message ---
--- Begin Message ---
Most likely the controller would protect itself from the overvoltage
condition and refuse to turn on. I have a 48 volt Alltrax and the max
overvoltage limit on it is 60 volts. IIRC Altrax controller are built with
parts rated at approx. 150% of the controller rating, so they can take some
overvoltage, but they are also controlled by a microcontroller that tries to
protect the controller from a number of bad things including too high of
voltage. Also, when using any controller at the very top of it's ratings,
it is usually necessary to have it out of the circuit during charging.
Damon
From: Kenneth Dove <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
Subject: Controller voltage maximums
Date: Wed, 06 Dec 2006 13:48:48 -0500
I would like to ask the list what would happen if the voltage rating were
exceeded on a controller?
Specifically, if one were to supply 98 volts to an Alltrax 72xx (72 volt)
controller, would it melt down or explode or perform incorrectly, etc?
The motor in this setup is listed at 72 volts as well, but from what I have
read on this forum, these DC motors can handle excess voltages.
Does anyone have any experience or even tested such a scenario? Maybe this
is something that should not even be attempted. Obviously, the alternative
is to purchase a Curtis 1221C or its equivalent as a replacement.
Thanks y'all.
_________________________________________________________________
WIN up to $10,000 in cash or prizes enter the Microsoft Office Live
Sweepstakes http://clk..atdmt.com/MRT/go/aub0050001581mrt/direct/01/
--- End Message ---
--- Begin Message ---
To clarify: I was *reading* about windmillls, but I'm not proposing
to use windmills on the car. I know that would slow the momentum
and waste energy, and *that* is like trying to lift yourself up by your
own belt.
If I understand correctly, regenerative braking is when the polarity
on the motor is switched in order to slow the car down. Then the
energy is captured in a battery. I'm saying that I'd like to convert
the forward motion of the wheels into electricity via the spinning
of the motor.
Look at it like this then: barring wind resistance and friction, you
ought to get the same amount of generated energy from stopping
the car quickly in 10 feet or, removing your foot from the accelerator,
cruising slowly to a stop in 200 feet. This is correct reasoning, no?
--- End Message ---
--- Begin Message ---
Yes sir, I understand the perpetual motion impossibility. I know
the car will slow down when you remove your foot from the
accelerator, and I actually do understand the physics. That's
not what I'm asking. Please let me rephrase my question then.
I'm interested in capturing all energy that is not being used. So.
Here's a scenario. You're driving in town. You see up ahead
about a block and a half that the light is red, so you take your
foot from the accellerator. The car then begins to slow because
of wind and friction. However, you've put in energy to get the
weight of the car moving that fast, so there's some potential
there. The state that the car is in: It is slowing down, but the
brakes are not being applied. The motor is spinning. A current
is being generated. This is collectable, correct?
Another scenario, if you'll bear with me. Imagine that your car
is just a generator on wheels. You push it to the top of a hill,
and let it roll down. It generates some electricity. That's the
electricity I'm talking about capturing.
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
Is the controller still going to have appropriately rated
snubbing circuits to handle any inductive spikes from the
switching and pwm into the motor?
Kenneth Dove wrote:
I would like to ask the list what would happen if the voltage rating
were exceeded on a controller?
Specifically, if one were to supply 98 volts to an Alltrax 72xx (72
volt) controller, would it melt down or explode or perform incorrectly,
etc?
The motor in this setup is listed at 72 volts as well, but from what I
have read on this forum, these DC motors can handle excess voltages.
Does anyone have any experience or even tested such a scenario? Maybe
this is something that should not even be attempted. Obviously, the
alternative is to purchase a Curtis 1221C or its equivalent as a
replacement.
Thanks y'all.
--- End Message ---
--- Begin Message ---
yes, that is called regenerative braking and comes with many
AC installations, and can be applied if carefully engineered
into a DC system (energizing the field winding of the motor)
while recapturing the energy from the armature.
Jordan Crane wrote:
Yes sir, I understand the perpetual motion impossibility. I know
the car will slow down when you remove your foot from the
accelerator, and I actually do understand the physics. That's
not what I'm asking. Please let me rephrase my question then.
I'm interested in capturing all energy that is not being used. So.
Here's a scenario. You're driving in town. You see up ahead
about a block and a half that the light is red, so you take your
foot from the accellerator. The car then begins to slow because
of wind and friction. However, you've put in energy to get the
weight of the car moving that fast, so there's some potential
there. The state that the car is in: It is slowing down, but the
brakes are not being applied. The motor is spinning. A current
is being generated. This is collectable, correct?
Another scenario, if you'll bear with me. Imagine that your car
is just a generator on wheels. You push it to the top of a hill,
and let it roll down. It generates some electricity. That's the
electricity I'm talking about capturing.
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
This is still regen braking, just very mild regen braking. Several EV
manufacturers have this as a feature. For an example; read about AC
propulsions Ebox on their website.
It seems it's your understanding of regen braking that's lacking, you
don't reverse the polarity of the motor to get regen, you drop the
input voltage below the back emf voltage of the motor. This causes the
current to flow from the motor to the battery, you can control the
amount of regen braking by controlling said voltage differential.
On 12/6/06, Jordan Crane <[EMAIL PROTECTED]> wrote:
Look at it like this then: barring wind resistance and friction, you
ought to get the same amount of generated energy from stopping
the car quickly in 10 feet or, removing your foot from the accelerator,
cruising slowly to a stop in 200 feet. This is correct reasoning, no?
Correct.
--
www.electric-lemon.com
--- End Message ---
--- Begin Message ---
when you google something and the link is dead, go back to google search
results and click on the cached link toward the bottom of the listing, that
will at least give you the text of the webpage and give clues on how to find
a full version of the page if the pictures don't load
----- Original Message -----
From: "Jack Murray" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, December 06, 2006 10:24 AM
Subject: Re: Regen with ADC motors
thanks Roland, but the link that comes up in google is dead.
I did find a paper written by Dean Thompson which is excellent,
http://eprints.usq.edu.au/archive/00000501/01/DeanTHOMPSON-2005.pdf
It looks like all I need is to add a high-side switch to my existing
controller. That's what I thought, but I recall something about the field
needing to be seperately excited. The Thompson paper doesn't do that.
Jack
Roland Wiench wrote:
Hello Jack,
The following is a technical paper by Paul Hills on the theory of DC
motor speed control, circuit diagrams, the math and includes
regeneration.
Just type in your search engine, Paul Hills Speed Controller, and it
will go right to the WEB address. I can't type his WEB address because I
do not have my keyboard set up to print a wavy line.
Roland
----- Original Message -----
From: "Jack Murray" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, December 05, 2006 10:48 PM
Subject: Regen with ADC motors
I'd like to build a controller for the ADC motors that does regen
braking.
Where would I find more info on what that involves?
Jack
--- End Message ---
--- Begin Message ---
No problem, I ran a 144 v controller that was mod for a 180 volts and even
withstand 210 volts charge battery volts. See what the power components are
rated for, which my was at or above 300 volts. A voltage divider circuit
was added which was made from a series of heat sinking power resistors in
the range of 50 to 100 watts at 100 to 4700 ohms This drop the control
voltage to the 144 V level for the control circuits.
Roland
----- Original Message -----
From: "Joel Hacker" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, December 06, 2006 12:14 PM
Subject: Re: Controller voltage maximums
> Is the controller still going to have appropriately rated
> snubbing circuits to handle any inductive spikes from the
> switching and pwm into the motor?
>
> Kenneth Dove wrote:
>
> > I would like to ask the list what would happen if the voltage rating
> > were exceeded on a controller?
> >
> > Specifically, if one were to supply 98 volts to an Alltrax 72xx (72
> > volt) controller, would it melt down or explode or perform incorrectly,
> > etc?
> >
> > The motor in this setup is listed at 72 volts as well, but from what I
> > have read on this forum, these DC motors can handle excess voltages.
> >
> > Does anyone have any experience or even tested such a scenario? Maybe
> > this is something that should not even be attempted. Obviously, the
> > alternative is to purchase a Curtis 1221C or its equivalent as a
> > replacement.
> >
> > Thanks y'all.
> >
> >
>
>
--- End Message ---
--- Begin Message ---
Hi Jordan,
When a car coasts to a stop, there are there major forces that slow the car
down:
- air friction
- tire to road friction
- mechanical friction in the drive line
Is there a way to capture the energy from these? Not in a practical manner.
There would have to be a device to capture the heat dissipated from the
friction - this device might be unwieldy because it would have to capture
heat from the road, the air and various places throughout the driveline.
When coasting down a hill - yes you can capture this energy. It is called
regenerative braking, that is common in lots of EVs. For example, when I
coast down a hill, I lightly press my brake pedal which activate the
generator (but no brakes) - this charges the battery. I also do the same
when coasting to a stop. Only when I actually have to stop the car do I use
the friction brakes. (Usually at the end of a stop or in an emergency)
Note that it is not free energy, as it takes force to turn the generator.
This energy would then come from the moving vehicle and it slows the vehicle
down. There is no way to turn a generator without force.
Don Cameron, Victoria, BC, Canada
see the New Beetle EV project www.cameronsoftware.com/ev
---------------------------------------------------
"It is not the critic who counts: not the man who points out how the strong
man stumbles or where the doer of deeds could have done better. The credit
belongs to the man who is actually in the arena, whose face is marred by
dust and sweat and blood, who strives valiantly, who errs and comes up short
again and again, because there is no effort without error or shortcoming,
but who knows the great enthusiasms, the great devotions, who spends himself
for a worthy cause; who, at the best, knows, in the end, the triumph of high
achievement, and who, at the worst, if he fails, at least he fails while
daring greatly, so that his place shall never be with those cold and timid
souls who knew neither victory nor defeat." - Teddy Roosevelt
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Jordan Crane
Sent: December 6, 2006 10:44 AM
To: [email protected]
Subject: Re: Regenerative Cruising
Yes sir, I understand the perpetual motion impossibility. I know the car
will slow down when you remove your foot from the accelerator, and I
actually do understand the physics. That's not what I'm asking. Please let
me rephrase my question then.
I'm interested in capturing all energy that is not being used. So.
Here's a scenario. You're driving in town. You see up ahead about a block
and a half that the light is red, so you take your foot from the
accellerator. The car then begins to slow because of wind and friction.
However, you've put in energy to get the weight of the car moving that fast,
so there's some potential there. The state that the car is in: It is
slowing down, but the brakes are not being applied. The motor is spinning.
A current is being generated. This is collectable, correct?
Another scenario, if you'll bear with me. Imagine that your car
is just a generator on wheels. You push it to the top of a hill, and let it
roll down. It generates some electricity. That's the electricity I'm
talking about capturing.
- - - - - - - - - - - - - - - - - - - - - - - - -
r e d d i n g k
1668 west boulevard. los angeles, CA 90019
(323) 857 . 5326 http://www.reddingk.com
- - - - - - - - - - - - - - - - - - - - - - - - -
--- End Message ---
--- Begin Message ---
Ah yes! Thank you. It is indeed my understanding of regen braking
that is lacking. Your explanation is perfect and clear. I was beginning
to suspect that what I was describing must be a form of regenerative
braking, but was unable to find a clear description of regen braking that
discussed it in any terms other than the act of braking.. many thanks
for the clarification.
>This is still regen braking, just very mild regen braking. Several EV
>manufacturers have this as a feature. For an example; read about AC
>propulsions Ebox on their website.
>
>It seems it's your understanding of regen braking that's lacking, you
>don't reverse the polarity of the motor to get regen, you drop the
>input voltage below the back emf voltage of the motor. This causes the
>current to flow from the motor to the battery, you can control the
>amount of regen braking by controlling said voltage differential.
>
>
>
>
>On 12/6/06, Jordan Crane <[EMAIL PROTECTED]> wrote:
>
>>
>>Look at it like this then: barring wind resistance and friction, you
>>ought to get the same amount of generated energy from stopping
>>the car quickly in 10 feet or, removing your foot from the accelerator,
>>cruising slowly to a stop in 200 feet. This is correct reasoning, no?
>>
>Correct.
>
>
>--
>www.electric-lemon.com
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Why do you need to use higher voltage?
Can the Alltrax handle more amps?
I've been meaning to ask the list, why couldn't you use a transmission
to get a higher top speed from a lower voltage pack?
Jack
I would like to ask the list what would happen if the voltage rating
were exceeded on a controller?
Specifically, if one were to supply 98 volts to an Alltrax 72xx (72
volt) controller, would it melt down or explode or perform incorrectly,
etc?
The motor in this setup is listed at 72 volts as well, but from what I
have read on this forum, these DC motors can handle excess voltages.
Does anyone have any experience or even tested such a scenario? Maybe
this is something that should not even be attempted. Obviously, the
alternative is to purchase a Curtis 1221C or its equivalent as a
replacement.
Thanks y'all.
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Jack Murray wrote:
> I've been meaning to ask the list, why couldn't you use a
> transmission to get a higher top speed from a lower voltage
> pack?
Yes, provided you have enough power. The transmission will allow the
wheels to spin faster for a given motor RPM, but you need to have enough
motor power to overcome the various sources of drag at the higher speed
you wish to reach (plus have some extra to allow acceleration to the
target speed).
Vehicles with lower voltage packs require higher current levels to allow
the same power level as vehicles with higher voltage packs.
Hope this helps,
Roger.
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There are a couple of reasons why it is better to use two motors in
parallel dividing the current than just one with all the available current.
>>>> Commutation limitations <<<<
The biggest reason is commutator survival. If you attempt to
dump twice the current in a commutator that is already on the edge of
failure, you are not going to get the vehicle to go any faster. :-)
The plasma severity is caused by the combination of current
in the armature and the RPM of the armature. (Voltage is dependant on
these two. You can choose to use voltage and current to explain it,
but if you stick with RPM and current, it is easier to understand.)
As the comm bar comes out from under the brush, the current
attempts to drop to zero. An arc forms to dump the stored magnetic
energy and let the current ramp down to zero in that armature
winding. As you increase the current, the arc gets worse. As you
increase the RPM, you attempt to cut off the current more quickly, so
the arc gets worse (and longer.) Also, the arc has less time to blow
out between bars.
There is also the problem of overheating the brushes with
too much current. Twice the current will make them four times as hot.
>>> Back EMF <<<
At the end of the drag strip, you are generally running out
of voltage to push in the amps. Thus, you are typically voltage
limited, rather than current limited.
In a series-wound motor, (at modest current) the back EMF is
proportional to the current times the RPM. There is always some
dependance on current, even at high currents. Even if you could get a
bit more torque-per-amp by halving the current, you also get more
back EMF per amp, so you are at the same place (when in voltage
limit), not even considering ohmic resistance.
Dividing the current between two motors allows you to cram
in more amps with a given voltage, since there is indeed ohmic
resistance and perhaps some degree of dependance of back EMF on
current. Cramming in more amps at a given voltage results in more HP
to the ground.
>>> Efficiency <<<<
The motors are more efficient at lower currents. By dividing
the current between two motors, more of the input wattage results in
output HP.
>>>> Square law at big amps <<
It all depends on how you do the math. If you calculate
torque/amp using the total torque divided by the total amps, you
always get an exponent greater than one. If instead, you calculate
the change in torque over the change in amps, you get close to one as
an exponent.
Indeed, there are always chunks of iron here and there that
are not seeing the full H field, and saturate at higher currents, but
it isn't a big factor.
Bill Dube'
At 03:40 PM 12/4/2006, you wrote:
Jeff Shanab wrote:
> The two DC motors on the same controller you would of had
> before on just 1 motor (and a decent enough pack voltage
> to do this for a few thousand RPM) You will still get twice
> the torque off the line as with one motor.
So far so good...
> Obviously this goes to sleep pretty fast as the rpm's climb
> and a switch from series to parallel is called for. Where
> again you get twice the torque per amp you would of had with
> only one motor Up to the limit of the controller.
Nope; I believe you are being too optimistic here.
The switch to parallel is made so that more voltage may be applied to
each motor; otherwise the motors can see no more than 1/2 pack voltage.
There is *no* torque advantage to operating the motors in parallel vs
running a single motor, and indeed, there is actually a *loss*.
Problem is that unless you have so much current on tap that you can
saturate the motor(s) even at 1/2 the controller output (since in
parallel each motor sees 1/2 the total motor loop amps), then the torque
is proportional to current raised to a power somewhere between 1 and 2.
I think Rich Rudman has posted data showing a better than linear torque
to current relationship even out to currents in excess of 1000A.
Consider that if torque is proportional to amps^1.2 (which I believe is
right in the ballpark for 8" and 9" ADC motors) and you put 1000A
through each of a pair of paralleled motors, then your total torque is
proportional to 2*(1000^1.2) = 7962. If you put the same 2000A total
through *one* of the motors, the torque would be proportional to
2000^1.2 = 9146.
Counter-intuitively enough, this means the single motor would deliver
13% more torque than the parallel combination! (John are you listening?
I just found the 'Zombie 13% more HP for the last 1/2 of the run! ;^)
If the motors are stout enough and/or the demand brief enough (e.g. drag
racing), it might just be that the better arangement would be to start
in series mode and switch to a single motor rather than paralleled
motors.
Cheers,
Roger.
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Thanks Don, my understanding they did about 40mph.
Maybe if you were going downhill with the thottle WFO.
Remembering these from younger days, 30 mph was
about the absolute max on the flat. Cool little vehicles,
though. Going up a hill with just one person and no
load they were usually on the floor in first gear at 10
mph. They had a governor, but even a busted gov
didn't get you much above 35.
I like the Cushman design better -- the front suspension
is a little beefier and the body is a lot less tippy in
corners. Our garbage guys used to run these little
Cushmans with dump boxes. They'd scream around
the neighbourhood collecting trash while the Mother
Ship cruised down the middle of the street and
waited for the little guys to come dump.
Whatever you do, keep the weight as low as you can.
That fibreglass body has a higher center of gravity than
the old steel body with aluminum top works.
Fun to drive, as I know from experience. You'll get
some looks.
How far you gotta go to get to work?
Chuck Hays
Kamloops BC
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The turning of the wheels will generate
a current on the motor, which can then be captured in the battery.
The resulting drag will negate any gain. In fact regen is used to slow
electric vehicles down. I rarely use my brakes on my Lepton Scooter.
Lawrence Rhodes....
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Nice article by Otmar, circa 1998:
http://cafeelectric.com/curtis/regen/index.html
Dana
-------------- Original message ----------------------
From: Jack Murray <[EMAIL PROTECTED]>
> I'd like to build a controller for the ADC motors that does regen braking.
> Where would I find more info on what that involves?
> Jack
>
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Hi i was wondering what people think about direct drives as compared to
leaving the transmission in. Is the reduction in weight worth taking the
transmission out? Can you take the transmission out and keep the clutch for
saftey in case anything goes wrong?Will i get more performance out of a
direct drive or a transmission (if i had a direct drive i would gear it for
about 80mp/h max)?
_________________________________________________________________
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There is a Rabbit EV on E-bay right now, ending Saturday night that I was
planning to buy.
1979 Other Makes : Volkswagen Rabbit Electric Car Item number: 140060416080
So, if I was planning to buy it, why and I tipping all of you off to it?
Well, I've been talking to the guy who owns it for the past several days trying
to get an idea of its condition etc. He has been trying to get it into a
working order to get some more money for it. But, it seems after all that the
controller is not working, and the car will not go.
It is a DC shunt wound, 108 V system. No replacement controller is available
anywhere. So, the options are to fix what it has, build a custom controller,
or changeover to a series motor and a series controller. The last option
basically consists of using it as a chasis and starting from scratch.
Benefits of the car:
1979 Rabbit with ultra low miles.
Stored many years inside (in a museum) - super clean
Supposedly worked when parked (but batteries removed). When batteries were
put back in, it did not work. Several attempts were made, but it just plain
will not go.
Has beefed up suspension.
The bad:
controller is in-op, no way to just go out and buy a replacement
it has been sitting for a very long time
it may need work from sitting - brakes, etc.
the charger is 108 V, old technology
the battery box looks like a poor design, but I've not see it in person.
The car is only 105 miles from my house, so I was going to look at it, but
when we couldn't get it running by talking over the phone, I realized it may be
more of a project than I want right now. I am not a fan of shunt wound motors
or 30 years old museum cars (been there, done that, got the T-shirt, and "lost
my shirt" $$$ in the process. I don't have time to do another project like
that. It could be relatively easy, but don't bank on it firing right up.
He tried different voltage packs between 72 and 120. The car now has 10 x 12
V batteries out of an electric bus. It still does not run. It also may not
have any fluids (i.e. brake fluid). That may require a complete brake system
rebuild, or maybe not.
He also has an AC motor and controller that he is willing to sell seperately.
I think his plan was to convert the car to AC. He said he would let the parts
go relatively cheap.
So, given all this, and the risk associated with that old of a car and no way
to get an appropriate controller without custom building it, I am going to pass
on the deal. I hope it ends up going to a good home. Maybe someone on the
list.
Just FYI, this is not the same car that my friend Jim asked for help with.
That one is a 74 EVA Metro, which also just happens to have the same problem -
odd ball shunt wound motor with inop controller and no way to get an off the
shelf replacement. Things are going slow getting that car to work, so I am
cautious about starting another one with the same issues.
On a high point, the Rabbit does still have parts available for the chasis,
and may be very similar to Mr. Sharkey's very well documented car. But, who
can be sure and that is a lot of money to chance on a maybe.
http://www.mrsharkey.com/rabbit.htm
http://www.mrsharkey.com/SCT/index.html
I'm open to any comments or suggestions.
Also, BTW, the car has no title because it is here in GA and more than 20
years old, we don't title them. That could be a big issue for someone.
Steve
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