Public EVSE design

classic Classic list List threaded Threaded
13 messages Options
Reply | Threaded
Open this post in threaded view
|

Public EVSE design

Mark F
This post has NOT been accepted by the mailing list yet.
I’m curious why public charging stations have their own cords and j1772 connectors. It seems it would be more economical for each EV to use its own cord and plug. The charger host would only have to install the J1772 inlet. Every EV has a cord for home charging already. Is there something I’m missing?
Reply | Threaded
Open this post in threaded view
|

Re: Public EVSE design

Mark F
This post has NOT been accepted by the mailing list yet.
test
Reply | Threaded
Open this post in threaded view
|

Re: Public EVSE design

Cruisin
In reply to this post by Mark F
Yes, the charging station must meet all existing local and state laws governing the products connected to the charger. Some EV's not so smart people use cable and connectors that are garbage and have no listing or approval. Most don't want to spend money on a J1772. Why would you want to carry around a cable in your car when it is not necessary.
Reply | Threaded
Open this post in threaded view
|

Re: Public EVSE design

Mark F
This post has NOT been accepted by the mailing list yet.
Hi Cruisin,

I do get the code compliance thing and the - to j1772 or not issue but what is the difference if the cord is connected to the EV or the EVSE? If the charging station only has a j1772 inlet you would still have to have the j1772 connector with pilot signal capabilities. When EV's are more plentiful and more charging ports are needed in more locations it seems that having a bank of 10 plus charging ports with twisted power cords is going to be a mess. As it is now I have used probably 10 different cords on public EVSE's, that's 10 j1772 connectors and a bunch of expensive wire. In my opinion that is money that could have gone to more - less expensive charging stations. If the desire is to have more charging opportunities I think it would help to keep costs to hosts as low as possible and the aesthetic impact should be addressed.
Reply | Threaded
Open this post in threaded view
|

Odd Acceleration Behavior

Tom Keenan
In reply to this post by Cruisin
My EV (a converted 1989 Ford Escort) does not accelerate the way I think it should.  http://evalbum.com/4331

From a dead stop in 2nd gear, it accelerates relatively quickly, but never really reaches the controller limit. The Curtis 1221B is supposed to put out 400 amps, but it might briefly see 350 amps in 2nd gear.  It gets to 350 amps after a couple of seconds, then (as expected) tapers off as the motor spins faster up to about 25 MPH, where I need to change gears to continue accelerating.

On the freeway, the controller will put out 350 to 400 amps when accelerating.

From a dead stop in 3rd gear, the acceleration curve is much different.  It takes three to five seconds to get to 350 amps.  It is generally at about 15 MPH before it gets there, accelerating at a leisurely 200 amps or so.  Once above 15 MPH, it accelerates at about 350+ amps.

At first, I thought that the acceleration curve in the Curtis controller might be holding things back.  However, if I am at 25 MPH or so, and let the Electricar coast for a few seconds (simulating a stop) and floor it, it will get to 350+ amps after a second or so.  This would seem to make the acceleration table capable of putting out full power within one second, not the three to five seconds as noted in 3rd gear.

With my Alltrax controller in my old Citicar, it would put out 450+ amps (controller max) within a second from a dead stop, or moving - didn't seem to matter.

Is there some sort of feedback method the Curtis controller uses to limit power on a 'stalled' rotor?  Or is there some sort of limitation on my GE 9" series motor?  It would seem to me that the controller would put out full power consistently based on the acceleration time schedule, regardless of motor RPM, as long as the motor wasn't producing to much back EMF.

Any thoughts?

Tom Keenan
_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

EVDL Administrator
If you're reading battery current, this is much like what I've seen from
similar controllers.  

The controller is limiting motor current.  Except for the few times that you
are completely out of current limit at full pedal, when battery and motor
current are roughly equal, battery current will always be less.

At low motor speeds, your controller works like a DC transformer, converting
high battery voltage and low battery current to low motor voltage and high
motor current.  This is the reason you're seeing lower current at breakaway
in higher gears - motor speed is really low.

The other factor probably at play is that very few controllers can produce
their rated current for more than a few seconds.  They quickly heat up and
throttle back.  Some are apparently more dramatic at this than others - I
hear that the Chinese-made Kelly controllers seldom even approach their
ratings in real world use, for example.

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


_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

Tom Keenan
I'm still puzzled by this.  I don't have a meter for motor current, but was
under the impression that the controller would be able to handle either 400
battery amps, or 400 motor amps, whichever is greater (given that heating
and other limits exist).  I understand that below controller limits, the
battery current may be lower than the output (motor) current.  But power to
the motor is power to the motor, it is not?  If the controller is putting
out 400 amps to the motor (disregarding input at this point), shouldn't the
motor should deliver a relatively fixed amount of power/torque?  

From a purely subjective standpoint, the acceleration feels like this (using
each word as approximately one second) with 'poor' being the worst, and
'max' being the quickest for this setup:

poor - poor - poor - leisurely - leisurely - leisurely - leisurely - OK - OK
- OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a 16
second time period from a standing start in 3rd gear - about 4.89:1 overall
reduction).  The fall off after it hits MAX is due to back EMF effects from
increasing RPM, and is expected.  In second gear, the acceleration feel is
about the same, but the time scale is compressed to about eight seconds,
vice 16.

Poor (in battery amps) is about 100 to 150 amps.  Leisurely is about 200
amps, OK about 250 amps, and max is about 350 amps or so.

I would expect it to feel more like this, with the first second or so being
the acceleration table limits:

poor - OK - MAX - MAX - MAX - MAX - MAX - MAX - MAX - OK - OK - leisurely -
leisurely.

The poor acceleration seems to be caused by a very low amount of torque
available at low motor RPM, no matter which gear I happen to use.  Based on
the other EV I've driven extensively (my old Citicar) and other series DC
motor EVs I've seen, a series DC motor should have buckets of torque
available right from the start- torque that doesn't fall off until a certain
RPM is reached.

If the controller were putting out 350+ amps to the motor, even when the
battery amps were low, I would expect that acceleration would feel like the
'max' setting once the acceleration table allows max power.  

On the freeway, it will go to the max value in about a second when floored,
and hold max (350+ amps) for a significant amount of time, so it does not
seem to be a slow acceleration table or a controller overheating issue.

Tom Keenan

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of EVDL Administrator
Sent: Wednesday, December 05, 2012 7:30 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Odd Acceleration Behavior

If you're reading battery current, this is much like what I've seen from
similar controllers.  

The controller is limiting motor current.  Except for the few times that you
are completely out of current limit at full pedal, when battery and motor
current are roughly equal, battery current will always be less.

At low motor speeds, your controller works like a DC transformer, converting
high battery voltage and low battery current to low motor voltage and high
motor current.  This is the reason you're seeing lower current at breakaway
in higher gears - motor speed is really low.

The other factor probably at play is that very few controllers can produce
their rated current for more than a few seconds.  They quickly heat up and
throttle back.  Some are apparently more dramatic at this than others - I
hear that the Chinese-made Kelly controllers seldom even approach their
ratings in real world use, for example.

David Roden
EVDL Administrator

_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

Cor van de Water
Tom,
Series DC motor has lots of torque *if* you can pour enough motor amps
on it. Since your controller has only 400A max motor current, it will
draw very low power at low RPM because the low back EMF causes the
current limit to be reached at very low voltage to the motor, the result
is that very low power is drawn from the battery. An example:
Say at 500 RPM the back EMF is 10V and the resistance of the motor is 25
milliOhm, so 400A results in another 10V across the motor, then the
power in the motor is only 20V x 400A = 8kW.
Once you are up to speed and the motor has revved up to for example 3500
RPM
then the back EMF is for example 70V so 400A into the motor is reached
at 80V and the power into the motor is 80V x 400A = 32kW.
Note that 400A is the max, normally you will see lower values due to the
current limit throttling back at higher temp and another effect is the
pulse-shape behavior of the current so it is important to limit the max
instantaneous peak current, not only the average current. This can also
lead to a substantial lower average current limit, to avoid transistors
and diodes blowing from the current spikes.

I am guessing that if you would install a motor amp meter shunt (or move
the battery shunt to after the controller) then you would see the max
current from 1 sec after pressing the pedal until it starts tapering due
to back emf or due to battery current limit.

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 Tom Keenan
Sent: Friday, December 07, 2012 3:20 PM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Odd Acceleration Behavior

I'm still puzzled by this.  I don't have a meter for motor current, but
was
under the impression that the controller would be able to handle either
400
battery amps, or 400 motor amps, whichever is greater (given that
heating
and other limits exist).  I understand that below controller limits, the
battery current may be lower than the output (motor) current.  But power
to
the motor is power to the motor, it is not?  If the controller is
putting
out 400 amps to the motor (disregarding input at this point), shouldn't
the
motor should deliver a relatively fixed amount of power/torque?  

From a purely subjective standpoint, the acceleration feels like this
(using
each word as approximately one second) with 'poor' being the worst, and
'max' being the quickest for this setup:

poor - poor - poor - leisurely - leisurely - leisurely - leisurely - OK
- OK
- OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a
16
second time period from a standing start in 3rd gear - about 4.89:1
overall
reduction).  The fall off after it hits MAX is due to back EMF effects
from
increasing RPM, and is expected.  In second gear, the acceleration feel
is
about the same, but the time scale is compressed to about eight seconds,
vice 16.

Poor (in battery amps) is about 100 to 150 amps.  Leisurely is about 200
amps, OK about 250 amps, and max is about 350 amps or so.

I would expect it to feel more like this, with the first second or so
being
the acceleration table limits:

poor - OK - MAX - MAX - MAX - MAX - MAX - MAX - MAX - OK - OK -
leisurely -
leisurely.

The poor acceleration seems to be caused by a very low amount of torque
available at low motor RPM, no matter which gear I happen to use.  Based
on
the other EV I've driven extensively (my old Citicar) and other series
DC
motor EVs I've seen, a series DC motor should have buckets of torque
available right from the start- torque that doesn't fall off until a
certain
RPM is reached.

If the controller were putting out 350+ amps to the motor, even when the
battery amps were low, I would expect that acceleration would feel like
the
'max' setting once the acceleration table allows max power.  

On the freeway, it will go to the max value in about a second when
floored,
and hold max (350+ amps) for a significant amount of time, so it does
not
seem to be a slow acceleration table or a controller overheating issue.

Tom Keenan

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf
Of EVDL Administrator
Sent: Wednesday, December 05, 2012 7:30 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Odd Acceleration Behavior

If you're reading battery current, this is much like what I've seen from
similar controllers.  

The controller is limiting motor current.  Except for the few times that
you
are completely out of current limit at full pedal, when battery and
motor
current are roughly equal, battery current will always be less.

At low motor speeds, your controller works like a DC transformer,
converting
high battery voltage and low battery current to low motor voltage and
high
motor current.  This is the reason you're seeing lower current at
breakaway
in higher gears - motor speed is really low.

The other factor probably at play is that very few controllers can
produce
their rated current for more than a few seconds.  They quickly heat up
and
throttle back.  Some are apparently more dramatic at this than others -
I
hear that the Chinese-made Kelly controllers seldom even approach their
ratings in real world use, for example.

David Roden
EVDL Administrator

_______________________________________________
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)

_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

EVDL Administrator
In reply to this post by Tom Keenan
On 7 Dec 2012 at 15:19, Tom Keenan wrote:

> the acceleration feels like this (using each word as approximately one
> second) with 'poor' being the worst, and 'max' being the quickest for
> this setup:
>
> poor - poor - poor - leisurely - leisurely - leisurely - leisurely - OK - OK -
> OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a 16
> second time period from a standing start in 3rd gear - about 4.89:1 overall
> reduction).

This matches my experience with similar Curtis controllers.  This is about
the performance I'd expect for a 400 amp controller in a 1989 Escort.  

Your evalbum entry ( http://www.evalbum.com/4331 ) says you have a 108v
system with golf car batteries.  Your car weighs about 3400lb.  

At 108v, 400a is about 43kW.  So you have about the power of a 1961 VW
Beetle - which was no barnstormer, believe me, my father owned one  - in a
car weighing ~80% more than the VW did.  This is not a recipe for fast
acceleration.

> Based on the other EV I've driven extensively (my old Citicar) and
> other series DC motor EVs I've seen, a series DC motor should have
> buckets of torque available right from the start- torque that doesn't
> fall off until a certain RPM is reached.

The motor isn't the limiting factor here, the controller is (and to some
extent the batteries are).  

That controller will never deliver more than 400 amps at either battery or
motor, and as it warms up, its maximum current will fall.  

With fixed current, the usable motor power (voltage * current) available
will ramp up as motor speed (and effective motor voltage) increases.  Power
will peak just as the controller comes out of current limiting.  From there
motor back-EMF will rise and reduce effective motor voltage, again reducing
motor power.  

This exactly matches your acceleration curve above.

To get more acceleration, you need to increase power at the wheels, lighten
the car, or both.

You can get more high-end acceleration by going to a higher system voltage,
if your controller supports it.  This will broaden the maximum power motor
bandwidth (just above current limiting) by overcoming motor back-EMF for
longer.  Switching to 8 volt batteries is an easy way to do this, but
they'll have a somewhat shorter life.  You could also add more 6v batteries,
but the extra weight would hurt acceleration somewhat, and probably wouldn't
be practical in this car.  

If you want more breakaway acceleration, you'll have to buy a bigger
controller with a higher current limit.  Or, you could go to a crude 2- or 3-
step contactor controller, like the original Citicar had.  That would have
>no< current limit except the resistance of the car's wiring.

I've seen golf car batteries produce 1000-1200 amps.  That's probably not
the theoretical top, but I don't like to live any more dangerously than
that.

However, golf car batteries are not made for that kind of current.  They're
born to produce 75-100 amps driving a little light car round a golf course
at 5-10mph.  They will not be happy little guys producing 700-1000-1200
amps, and will let you know of their displeasure by having relatively
shorter lives.  

For high power, you need AGM lead batteries.  

Switching to lithium batteries would lighten the car, improving matters.  I
think that some lithium batteries would also be abke to produce more power
without damage, if you had the controller to use it, but I don't know enough
about lithium to say what types or brands.  I don't get the impression that
the cheap Chinese LiFePO4 batteries are capable of really high power,
however.

Bottom line here is that your car isn't a street racer.  It doesn't even
have family-car performance, by 2012 standards.  A 0-60 time of 25-30
seconds isn't atypical for a conversion of this type.  

You have the wrong EV components for going fast - even by 1961 standards,
let alone 2012 standards.

Or you could say you have OK components, but the wrong car.  If you could
somehow reduce the vehicle weight to, say, half what you have now (1700lb,
which with 1200lb of batteries leaves you only 500lb for the glider) you'd
have better-than-1961-VW-Beetle performance.  Maybe a fiberglas kit car?

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me.  To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

gtyler54
You, and many others on this list, have much more experience than me of
this, but the way I see it is like this:
        Acceleration = force/mass.
        Force can be calculated from motor torque and gear ration, tire dia.
        You know the mass.
        Motor torque relates to current in a particular motor and can be
looked up, but it is maximum at zero RPM, when output power is zero.

If motor current is constant from zero up until the controller comes out of
current limit, then the torque (and acceleration) should be constant too
apart from tapering off due to wind drag, friction, etc.  so acceleration
should be highest at zero speed?

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of EVDL Administrator
Sent: Saturday, 8 December 2012 5:53 p.m.
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Odd Acceleration Behavior

On 7 Dec 2012 at 15:19, Tom Keenan wrote:

> the acceleration feels like this (using each word as approximately one
> second) with 'poor' being the worst, and 'max' being the quickest for
> this setup:
>
> poor - poor - poor - leisurely - leisurely - leisurely - leisurely - OK -
OK -
> OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a 16
> second time period from a standing start in 3rd gear - about 4.89:1
overall
> reduction).

This matches my experience with similar Curtis controllers.  This is about
the performance I'd expect for a 400 amp controller in a 1989 Escort.  

Your evalbum entry ( http://www.evalbum.com/4331 ) says you have a 108v
system with golf car batteries.  Your car weighs about 3400lb.  

At 108v, 400a is about 43kW.  So you have about the power of a 1961 VW
Beetle - which was no barnstormer, believe me, my father owned one  - in a
car weighing ~80% more than the VW did.  This is not a recipe for fast
acceleration.

> Based on the other EV I've driven extensively (my old Citicar) and
> other series DC motor EVs I've seen, a series DC motor should have
> buckets of torque available right from the start- torque that doesn't
> fall off until a certain RPM is reached.

The motor isn't the limiting factor here, the controller is (and to some
extent the batteries are).  

That controller will never deliver more than 400 amps at either battery or
motor, and as it warms up, its maximum current will fall.  

With fixed current, the usable motor power (voltage * current) available
will ramp up as motor speed (and effective motor voltage) increases.  Power
will peak just as the controller comes out of current limiting.  From there
motor back-EMF will rise and reduce effective motor voltage, again reducing
motor power.  

This exactly matches your acceleration curve above.

To get more acceleration, you need to increase power at the wheels, lighten
the car, or both.

You can get more high-end acceleration by going to a higher system voltage,
if your controller supports it.  This will broaden the maximum power motor
bandwidth (just above current limiting) by overcoming motor back-EMF for
longer.  Switching to 8 volt batteries is an easy way to do this, but
they'll have a somewhat shorter life.  You could also add more 6v batteries,

but the extra weight would hurt acceleration somewhat, and probably wouldn't

be practical in this car.  

If you want more breakaway acceleration, you'll have to buy a bigger
controller with a higher current limit.  Or, you could go to a crude 2- or
3-
step contactor controller, like the original Citicar had.  That would have
>no< current limit except the resistance of the car's wiring.

I've seen golf car batteries produce 1000-1200 amps.  That's probably not
the theoretical top, but I don't like to live any more dangerously than
that.

However, golf car batteries are not made for that kind of current.  They're
born to produce 75-100 amps driving a little light car round a golf course
at 5-10mph.  They will not be happy little guys producing 700-1000-1200
amps, and will let you know of their displeasure by having relatively
shorter lives.  

For high power, you need AGM lead batteries.  

Switching to lithium batteries would lighten the car, improving matters.  I
think that some lithium batteries would also be abke to produce more power
without damage, if you had the controller to use it, but I don't know enough

about lithium to say what types or brands.  I don't get the impression that
the cheap Chinese LiFePO4 batteries are capable of really high power,
however.

Bottom line here is that your car isn't a street racer.  It doesn't even
have family-car performance, by 2012 standards.  A 0-60 time of 25-30
seconds isn't atypical for a conversion of this type.  

You have the wrong EV components for going fast - even by 1961 standards,
let alone 2012 standards.

Or you could say you have OK components, but the wrong car.  If you could
somehow reduce the vehicle weight to, say, half what you have now (1700lb,
which with 1200lb of batteries leaves you only 500lb for the glider) you'd
have better-than-1961-VW-Beetle performance.  Maybe a fiberglas kit car?

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me.  To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


_______________________________________________
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)


No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.930 / Virus Database: 2634.1.1/5442 - Release Date: 12/08/12
12:19:00

_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

Tom Keenan
In reply to this post by EVDL Administrator
This explanation (and Cor's more mathematical answer) make sense - Thanks to
you both!

> With fixed current, the usable motor power (voltage * current) available
will ramp up as motor speed (and effective motor voltage) increases.  Power
will peak just as the controller comes out of current limiting.  From there
motor back-EMF will rise and reduce effective motor voltage, again reducing
motor power.  

Interesting that the setup in my Electricar (converted by US Solar/US
Electricar in 1992 before they went to the Dolphin setup) has a very
ICE-like power output, with a somewhat narrow power band centered around
1,500 to 2,500 rpm.  Not at all like the 'instant power' most EV advertisers
speak of.

To its credit, it has been a very reliable car, transporting people from
point A to point B for over 20 years - albeit slowly!

Tom Keenan

_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

Cor van de Water
In reply to this post by gtyler54
If you want to know how long your vehicle will take
before reaching a certain speed, then you can easily
find a minimum time and power from realizing that a
vehicle at speed has a certain amount of energy more
than the same vehicle at rest. This Kinetic energy is
supplied by the motor from the batteries and causes
the increase of speed and thereby energy.
For example, my truck with me (driver) included weighs
4000 lbs or 1800 kg.
To reach a speed of 65 MPH (= 29 m/s) with this mass,
it needs an amount of energy added of 0.211 kWh.
(the kinetic energy is 1/2 * mass * velocity squared, so
in my case 900 (kg) * square (29 m/s) which is 760kJ or Ws)
If the motor can develop an amount of power that results
in 40kW of mechanical power (meaning that it will take
more than 50kW of electrical power before losses) then
it takes at minimum 19 seconds continuously feeding 40kW
into the vehicle mass in acceleration, to achieve the
65 MPH (ignoring losses for now).
If the motor cannot develop the 40kW because of limitation
in the controller (current limit and low voltage due to
low back EMF) and say the motor develops only 8kW then it
is adding energy at a five times slower pace, even if the
torque itself might be constant over the whole acceleration.

BTW, my truck has an even lower current limit of approx 320A
but the automatic transmission allows the motor to spin higher,
especially if I keep it in kick-down. But I also have a
golfcart pack so I actually happy for the pack that it is
protected by the low current controller - it will have a long
life. The drawback is that acceleration is "glacial" as the
120V pack never develops more than about 35kW of power.
For me, speed really requires an "investment" of energy in
my truck and it takes a while to build up that investment.
That is why I am not happy when someone suddenly merges right
in front of me and immediately starts braking or when someone
in front of me first brakes hard and then moves to the exit or
turn lane, instead of first getting out of the way of through
traffic and then braking. Oh well, I presume that other traffic
is equally annoyed with me if I am driving away on an incline
and it takes forever to go from 25 to 30 MPH (after stopping
before an overpass or a merge onto an elevated freeway)

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 George Tyler
Sent: Saturday, December 08, 2012 3:16 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Odd Acceleration Behavior

You, and many others on this list, have much more experience than me of
this, but the way I see it is like this:
        Acceleration = force/mass.
        Force can be calculated from motor torque and gear ration, tire
dia.
        You know the mass.
        Motor torque relates to current in a particular motor and can be
looked up, but it is maximum at zero RPM, when output power is zero.

If motor current is constant from zero up until the controller comes out
of
current limit, then the torque (and acceleration) should be constant too
apart from tapering off due to wind drag, friction, etc.  so
acceleration
should be highest at zero speed?

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf
Of EVDL Administrator
Sent: Saturday, 8 December 2012 5:53 p.m.
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Odd Acceleration Behavior

On 7 Dec 2012 at 15:19, Tom Keenan wrote:

> the acceleration feels like this (using each word as approximately one
> second) with 'poor' being the worst, and 'max' being the quickest for
> this setup:
>
> poor - poor - poor - leisurely - leisurely - leisurely - leisurely -
OK -
OK -
> OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a
16
> second time period from a standing start in 3rd gear - about 4.89:1
overall
> reduction).

This matches my experience with similar Curtis controllers.  This is
about
the performance I'd expect for a 400 amp controller in a 1989 Escort.  

Your evalbum entry ( http://www.evalbum.com/4331 ) says you have a 108v
system with golf car batteries.  Your car weighs about 3400lb.  

At 108v, 400a is about 43kW.  So you have about the power of a 1961 VW
Beetle - which was no barnstormer, believe me, my father owned one  - in
a
car weighing ~80% more than the VW did.  This is not a recipe for fast
acceleration.

> Based on the other EV I've driven extensively (my old Citicar) and
> other series DC motor EVs I've seen, a series DC motor should have
> buckets of torque available right from the start- torque that doesn't
> fall off until a certain RPM is reached.

The motor isn't the limiting factor here, the controller is (and to some

extent the batteries are).  

That controller will never deliver more than 400 amps at either battery
or
motor, and as it warms up, its maximum current will fall.  

With fixed current, the usable motor power (voltage * current) available

will ramp up as motor speed (and effective motor voltage) increases.
Power
will peak just as the controller comes out of current limiting.  From
there
motor back-EMF will rise and reduce effective motor voltage, again
reducing
motor power.  

This exactly matches your acceleration curve above.

To get more acceleration, you need to increase power at the wheels,
lighten
the car, or both.

You can get more high-end acceleration by going to a higher system
voltage,
if your controller supports it.  This will broaden the maximum power
motor
bandwidth (just above current limiting) by overcoming motor back-EMF for

longer.  Switching to 8 volt batteries is an easy way to do this, but
they'll have a somewhat shorter life.  You could also add more 6v
batteries,

but the extra weight would hurt acceleration somewhat, and probably
wouldn't

be practical in this car.  

If you want more breakaway acceleration, you'll have to buy a bigger
controller with a higher current limit.  Or, you could go to a crude 2-
or
3-
step contactor controller, like the original Citicar had.  That would
have
>no< current limit except the resistance of the car's wiring.

I've seen golf car batteries produce 1000-1200 amps.  That's probably
not
the theoretical top, but I don't like to live any more dangerously than
that.

However, golf car batteries are not made for that kind of current.
They're
born to produce 75-100 amps driving a little light car round a golf
course
at 5-10mph.  They will not be happy little guys producing 700-1000-1200
amps, and will let you know of their displeasure by having relatively
shorter lives.  

For high power, you need AGM lead batteries.  

Switching to lithium batteries would lighten the car, improving matters.
I
think that some lithium batteries would also be abke to produce more
power
without damage, if you had the controller to use it, but I don't know
enough

about lithium to say what types or brands.  I don't get the impression
that
the cheap Chinese LiFePO4 batteries are capable of really high power,
however.

Bottom line here is that your car isn't a street racer.  It doesn't even

have family-car performance, by 2012 standards.  A 0-60 time of 25-30
seconds isn't atypical for a conversion of this type.  

You have the wrong EV components for going fast - even by 1961
standards,
let alone 2012 standards.

Or you could say you have OK components, but the wrong car.  If you
could
somehow reduce the vehicle weight to, say, half what you have now
(1700lb,
which with 1200lb of batteries leaves you only 500lb for the glider)
you'd
have better-than-1961-VW-Beetle performance.  Maybe a fiberglas kit car?

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me.  To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =


_______________________________________________
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)


No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.930 / Virus Database: 2634.1.1/5442 - Release Date:
12/08/12
12:19:00

_______________________________________________
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)

_______________________________________________
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)

Reply | Threaded
Open this post in threaded view
|

Re: Odd Acceleration Behavior

matt lacey-3
In reply to this post by gtyler54
> If motor current is constant from zero up until the controller comes out
> of
> current limit, then the torque (and acceleration) should be constant too
> apart from tapering off due to wind drag, friction, etc.  so acceleration
> should be highest at zero speed?

Hi George,

Current output from a motor controller isn't really constant

Torque is only highest at 0 rpm when the motor is powered directly from the
battery (no motor controller)

With a motor controller, torque will be highest when back-emf = battery
voltage (assuming battery and motor current limits are the same)

This is because most controllers will (or at least attempt to) limit peak
motor current to near the controllers rated current.
This means at 0 rpm, a "400A" controller will limit peak current to 400A,
but average motor current may be closer to 200A at worst case (0 - 400A - 0A
on each cycle, with a small controller driving a large low resistance low
inductance motor)

as rpm increases the average current gets closer to the peak current, and
torque increases.
the reason the average current increases is because the at higher rpm the
additional back-emf reduces the voltage actingon the inductance, which slows
the current ramp up rate.

It's the average motor current that determines motor torque.
interestingly, its the RMS motor current that determines the resistive
(copper) losses in the motor

Matt
----- Original Message -----
From: "George Tyler" <[hidden email]>
To: "'Electric Vehicle Discussion List'" <[hidden email]>
Sent: Saturday, December 08, 2012 7:16 PM
Subject: Re: [EVDL] Odd Acceleration Behavior


> You, and many others on this list, have much more experience than me of
> this, but the way I see it is like this:
> Acceleration = force/mass.
> Force can be calculated from motor torque and gear ration, tire dia.
> You know the mass.
> Motor torque relates to current in a particular motor and can be
> looked up, but it is maximum at zero RPM, when output power is zero.
>
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf
> Of EVDL Administrator
> Sent: Saturday, 8 December 2012 5:53 p.m.
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Odd Acceleration Behavior
>
> On 7 Dec 2012 at 15:19, Tom Keenan wrote:
>
>> the acceleration feels like this (using each word as approximately one
>> second) with 'poor' being the worst, and 'max' being the quickest for
>> this setup:
>>
>> poor - poor - poor - leisurely - leisurely - leisurely - leisurely - OK -
> OK -
>> OK - MAX - MAX - OK - leisurely - leisurely - leisurely (represents a 16
>> second time period from a standing start in 3rd gear - about 4.89:1
> overall
>> reduction).
>
> This matches my experience with similar Curtis controllers.  This is about
> the performance I'd expect for a 400 amp controller in a 1989 Escort.
>
> Your evalbum entry ( http://www.evalbum.com/4331 ) says you have a 108v
> system with golf car batteries.  Your car weighs about 3400lb.
>
> At 108v, 400a is about 43kW.  So you have about the power of a 1961 VW
> Beetle - which was no barnstormer, believe me, my father owned one  - in a
> car weighing ~80% more than the VW did.  This is not a recipe for fast
> acceleration.
>
>> Based on the other EV I've driven extensively (my old Citicar) and
>> other series DC motor EVs I've seen, a series DC motor should have
>> buckets of torque available right from the start- torque that doesn't
>> fall off until a certain RPM is reached.
>
> The motor isn't the limiting factor here, the controller is (and to some
> extent the batteries are).
>
> That controller will never deliver more than 400 amps at either battery or
> motor, and as it warms up, its maximum current will fall.
>
> With fixed current, the usable motor power (voltage * current) available
> will ramp up as motor speed (and effective motor voltage) increases.
> Power
> will peak just as the controller comes out of current limiting.  From
> there
> motor back-EMF will rise and reduce effective motor voltage, again
> reducing
> motor power.
>
> This exactly matches your acceleration curve above.
>
> To get more acceleration, you need to increase power at the wheels,
> lighten
> the car, or both.
>
> You can get more high-end acceleration by going to a higher system
> voltage,
> if your controller supports it.  This will broaden the maximum power motor
> bandwidth (just above current limiting) by overcoming motor back-EMF for
> longer.  Switching to 8 volt batteries is an easy way to do this, but
> they'll have a somewhat shorter life.  You could also add more 6v
> batteries,
>
> but the extra weight would hurt acceleration somewhat, and probably
> wouldn't
>
> be practical in this car.
>
> If you want more breakaway acceleration, you'll have to buy a bigger
> controller with a higher current limit.  Or, you could go to a crude 2- or
> 3-
> step contactor controller, like the original Citicar had.  That would have
>>no< current limit except the resistance of the car's wiring.
>
> I've seen golf car batteries produce 1000-1200 amps.  That's probably not
> the theoretical top, but I don't like to live any more dangerously than
> that.
>
> However, golf car batteries are not made for that kind of current.
> They're
> born to produce 75-100 amps driving a little light car round a golf course
> at 5-10mph.  They will not be happy little guys producing 700-1000-1200
> amps, and will let you know of their displeasure by having relatively
> shorter lives.
>
> For high power, you need AGM lead batteries.
>
> Switching to lithium batteries would lighten the car, improving matters.
> I
> think that some lithium batteries would also be abke to produce more power
> without damage, if you had the controller to use it, but I don't know
> enough
>
> about lithium to say what types or brands.  I don't get the impression
> that
> the cheap Chinese LiFePO4 batteries are capable of really high power,
> however.
>
> Bottom line here is that your car isn't a street racer.  It doesn't even
> have family-car performance, by 2012 standards.  A 0-60 time of 25-30
> seconds isn't atypical for a conversion of this type.
>
> You have the wrong EV components for going fast - even by 1961 standards,
> let alone 2012 standards.
>
> Or you could say you have OK components, but the wrong car.  If you could
> somehow reduce the vehicle weight to, say, half what you have now (1700lb,
> which with 1200lb of batteries leaves you only 500lb for the glider) you'd
> have better-than-1961-VW-Beetle performance.  Maybe a fiberglas kit car?
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> EVDL Information: http://www.evdl.org/help/
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Note: mail sent to "evpost" and "etpost" addresses will not
> reach me.  To send a private message, please obtain my
> email address from the webpage http://www.evdl.org/help/ .
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
> _______________________________________________
> 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)
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.930 / Virus Database: 2634.1.1/5442 - Release Date: 12/08/12
> 12:19:00
>
> _______________________________________________
> 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)
>

_______________________________________________
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)