Can anyone explain how the sudden and large jolts of electrical power from
braking can be stored in a battery.
In order for meaningful amounts of energy to be converted to actually
stopping a heavy car the electrical jolt must be pretty big.
I have visions of boiling batteries and smoke wires, but of course that
doesn't happen so how does the system handle it.
rq
Dynamic breaking, or what I know it about does not produce large amounts of
current and voltage. The motor poles are reversed and the motor acts like a
generator. Since it requires power to drive a generator it is pretty
effective breaking. A small amount of generated power is put back into the
batteries. Sustained breaking, (minutes) might deliver a charge big enough
to boil the batteries. Not sure where you going to find a hill like that or
how your going to get the electric car up there.
Hello,
a good brake is able to stop a car much faster than the motor would need
to accelerate to the same speed before braking. In other words, the
brake is able to consume much more power than the motor is able to generate.
But it is impossible to store the energy from an emergency braking back
to the battery, the battery and the electrical brake ( in fact, an
electrical generator ) should be too big, heavy and expensive.
An electrical and a mechanical brake must be combined, if you brake
soft, the energy can be stored in the battery, if you have to brake
hard, the mechanical brake is used and the energy is lost.
The trick is to avoid hard braking and to brake early and soft instead.
But if you can avoid braking, the energy conservation is even better.
Every loading and unloading of the battery is causing a loss of energy.
Bye
The electric motor(s) is(are) used as a generator(s). The forward momentum
of the vehicle powers the generator(s), and then in turn charge the battery.
Braking power is limited to the generating capacity, just like acceleration
is limited to motor power. In other words, you can use the regenerative
braking to slow down gradually. Also you can't accelerate from 0-60mph
instantaneously, therefore you cannot brake instantaneously. In order to
panic stop you will need friction brakes. If I recall correctly, the
theoretical efficiency of regenerative braking is 33%.
Dwayne
Hello,
if we assume an efficiency of 75 % each for the electric motor, the
generator, the charged battery, the discharged battery, we get a total
efficiency from kinetic energy before braking back to kinetic energy
after acclerating again of 0.75*0.75*0.75*0.75 which is 0.31 or 31 %.
Very close to the 33 % you recalled.
Bye
LISTEN: You guys are in a nightmarish cycle on breaking an electrical
vehicle.,
Somehow feeding it a back current or reversing the voltage is not a good
braking method even if the motor is designed for reversing.
what someone seems to recommend is like switching a standard motor into
reverse to slow it down or hard brake it., though the motor won't drop
off as a transmission would I seriously doubt that it is the best method
to brake an electric motor.#1 the strain is not something you'd be
comfortable in a vehicle. #2 there has to be an outside mechanical
influence on the drive system to brake the motor #3 precision braking of
en electrical motor using electrical or electronic signaling is probably
more of a dream than it is a reality for EV's. [yet possible]
you're better off just designing a power transfer/cut off to the motor &
diverting the transit power to the batteries recharge circuitry as
suggested, while employing conventional braking., if you want to get
fancy to boost your specs & prices; then fine, mess around with motors &
generators and see if you can build one that would screech to a halt on
a digital fed reverse voltage/power application, (consider variable ev
weight) would you need a clutch ? A State of the Art Clutch? I think it
would be too dynamic for current performance needs and it'd heat up &
consume too much of the sparse energy in the vehicle.The Energy being
the Issue.
Clutch/Transfer + Generated Power to Batteries ~ Dynamic Braking = all
power disconnect not too good., besides what good would an idle
generator do connected to a battery pack.
nevertheless a few seconds or minutes of generated power backfed into
your system is better than none, even if a minor consideration., one
could coast on a downhill strip and recharge };-) could be the
difference in a fun ride or pushing it to an outlet.
®oy
give me a few more years :-)
Regenerative braking does not involve an energy input from the batteries or
power supply. Rather it uses the forward momentum of the vehicle to
generate electricity from the electric motor(s). Regenerative braking is
well know and currently in use on some production electric & hybrid
vehicles.
"Know where all that braking energy goes when you stop in a normal car?
Nowhere, it's wasted. So when Toyota created the Prius, they came up with a
better idea.A regenerative braking system operates the electric motor as a
generator. So when you put your foot on the brakes, the kinetic energy is
converted into electrical energy and stored in the battery.The system is
particularly effective in recovering energy during city driving where
patterns of repeated acceleration and deceleration are common.What's the
point?
This system increases overall efficiency, and thus fuel economy."
http://www.toyota.com.au/Prius03/Portal/Article/0,1225,191-266-6223,00.html
Other Links (google regenerative braking):
http://www.hybridcarguide.com/regenerative-braking.html
http://www.insightcentral.net/encyclopedia/enregenerativebraking.html
Dwayne
LISTEN: You guys are in a nightmarish cycle on breaking an electrical
vehicle.,
Somehow feeding it a back current or reversing the voltage is not a good
braking method even if the motor is designed for reversing.
what someone seems to recommend is like switching a standard motor into
reverse to slow it down or hard brake it., though the motor won't drop
off as a transmission would I seriously doubt that it is the best method
to brake an electric motor.#1 the strain is not something you'd be
comfortable in a vehicle. #2 there has to be an outside mechanical
influence on the drive system to brake the motor #3 precision braking of
en electrical motor using electrical or electronic signaling is probably
more of a dream than it is a reality for EV's. [yet possible]
you're better off just designing a power transfer/cut off to the motor &
diverting the transit power to the batteries recharge circuitry as
suggested, while employing conventional braking., if you want to get
fancy to boost your specs & prices; then fine, mess around with motors &
generators and see if you can build one that would screech to a halt on
a digital fed reverse voltage/power application, (consider variable ev
weight) would you need a clutch ? A State of the Art Clutch? I think it
would be too dynamic for current performance needs and it'd heat up &
consume too much of the sparse energy in the vehicle.The Energy being
the Issue.
Clutch/Transfer + Generated Power to Batteries ~ Dynamic Braking = all
power disconnect not too good., besides what good would an idle
generator do connected to a battery pack.
nevertheless a few seconds or minutes of generated power backfed into
your system is better than none, even if a minor consideration., one
could coast on a downhill strip and recharge };-) could be the
difference in a fun ride or pushing it to an outlet.
®oy
give me a few more years :-)
---------
Regenerative braking is a tried and true method of braking - It has been
used succesfully in many applications. Motor switching or reversal is not
involved. When the motor generated voltage (so-called back emf) is greater
than the supply voltage, the current and energy flow reverse, not the
voltage so the motor acts as a generator. No separate generator is involved
and no mechanical switching is needed.
A hybrid car doesn't have a separate generator- the electric drive motor is
expected to do this, whether driven by the gasoline engine or by the wheels
on the road, and the control circuitry is designed for this.
However the main drawback of regenerative braking is that it cannot bring
the vehicle to a stop as its effectiveness decreases with speed.
Conventional braking is needed to actually stop or get effective braking at
low speed. . For most braking applications, i.e. reducing speed, say from 60
to 30, it is practical and beneficial.
Re: Hybrid cars and regenerative charging of batteries
Group: alt.engineering.electrical Date: Thu, Apr 14, 2005, 4:34am
(EDT+4) From: snipped-for-privacy@peeshaw.ca (Don Kelly)
LISTEN: You guys
are in a nightmarish cycle on breaking an electrical vehicle.,
Somehow feeding it a back current or reversing the voltage is not a good
braking method even if the motor is designed for reversing.
what someone seems to recommend is like switching a standard motor into
reverse to slow it down or hard brake it., though the motor won't drop
off as a transmission would I seriously doubt that it is the best method
to brake an electric motor.#1 the strain is not something you'd be
comfortable in a vehicle. #2 there has to be an outside mechanical
influence on the drive system to brake the motor #3 precision braking of
en electrical motor using electrical or electronic signaling is probably
more of a dream than it is a reality for EV's. [yet possible]
you're better off just designing a power transfer/cut off to the motor &
diverting the transit power to the batteries recharge circuitry as
suggested, while employing conventional braking., if you want to get
fancy to boost your specs & prices; then fine, mess around with motors &
generators and see if you can build one that would screech to a halt on
a digital fed reverse voltage/power application, (consider variable ev
weight) would you need a clutch ? A State of the Art Clutch? I think it
would be too dynamic for current performance needs and it'd heat up &
consume too much of the sparse energy in the vehicle.The Energy being
the Issue.
Clutch/Transfer + Generated Power to Batteries ~ Dynamic Braking = all
power disconnect not too good., besides what good would an idle
generator do connected to a battery pack.
nevertheless a few seconds or minutes of generated power backfed into
your system is better than none, even if a minor consideration., one
could coast on a downhill strip and recharge };-) could be the
difference in a fun ride or pushing it to an outlet.
®oy
give me a few more years :-)
---------
Regenerative braking is a tried and true method of braking - It has been
used succesfully in many applications. Motor switching or reversal is
not involved. When the motor generated voltage (so-called back emf) is
greater than the supply voltage, the current and energy flow reverse,
not the voltage so the motor acts as a generator. No separate generator
is involved and no mechanical switching is needed.
A hybrid car doesn't have a separate generator- the electric drive motor
is expected to do this, whether driven by the gasoline engine or by the
wheels on the road, and the control circuitry is designed for this.
However the main drawback of regenerative braking is that it cannot
bring the vehicle to a stop as its effectiveness decreases with speed.
Conventional braking is needed to actually stop or get effective braking
at low speed. . For most braking applications, i.e. reducing speed, say
from 60 to 30, it is practical and beneficial.
-- Don Kelly --
Except for the part of the Motor/Generation ~>
[which needs to be made optimal by design, the nature of an electrical
motor in itself isn't cause for much plus on the energy of the batteries
to engine cycles]
maybe should have a seperate eff generator on the axles or somewhere,
like dynamos that could be engaged with a lever or switch., then a push
could get you a long way};-)
®oy
LISTEN: You guys
are in a nightmarish cycle on breaking an electrical vehicle.,
Somehow feeding it a back current or reversing the voltage is not a good
braking method even if the motor is designed for reversing.
what someone seems to recommend is like switching a standard motor into
reverse to slow it down or hard brake it., though the motor won't drop
off as a transmission would I seriously doubt that it is the best method
to brake an electric motor.#1 the strain is not something you'd be
comfortable in a vehicle. #2 there has to be an outside mechanical
influence on the drive system to brake the motor #3 precision braking of
en electrical motor using electrical or electronic signaling is probably
more of a dream than it is a reality for EV's. [yet possible]
you're better off just designing a power transfer/cut off to the motor &
diverting the transit power to the batteries recharge circuitry as
suggested, while employing conventional braking., if you want to get
fancy to boost your specs & prices; then fine, mess around with motors &
generators and see if you can build one that would screech to a halt on
a digital fed reverse voltage/power application, (consider variable ev
weight) would you need a clutch ? A State of the Art Clutch? I think it
would be too dynamic for current performance needs and it'd heat up &
consume too much of the sparse energy in the vehicle.The Energy being
the Issue.
Clutch/Transfer + Generated Power to Batteries ~ Dynamic Braking = all
power disconnect not too good., besides what good would an idle
generator do connected to a battery pack.
nevertheless a few seconds or minutes of generated power backfed into
your system is better than none, even if a minor consideration., one
could coast on a downhill strip and recharge };-) could be the
difference in a fun ride or pushing it to an outlet.
®oy
give me a few more years :-)
---------
Regenerative braking is a tried and true method of braking - It has been
used succesfully in many applications. Motor switching or reversal is
not involved. When the motor generated voltage (so-called back emf) is
greater than the supply voltage, the current and energy flow reverse,
not the voltage so the motor acts as a generator. No separate generator
is involved and no mechanical switching is needed.
A hybrid car doesn't have a separate generator- the electric drive motor
is expected to do this, whether driven by the gasoline engine or by the
wheels on the road, and the control circuitry is designed for this.
However the main drawback of regenerative braking is that it cannot
bring the vehicle to a stop as its effectiveness decreases with speed.
Conventional braking is needed to actually stop or get effective braking
at low speed. . For most braking applications, i.e. reducing speed, say
from 60 to 30, it is practical and beneficial.
-- Don Kelly --
Except for the part of the Motor/Generation ~>
----------
such as? Please explain your contention. There is no inherent difference
between a motor and a generator so a motor can function quite well as a
generator.
----------------
[which needs to be made optimal by design, the nature of an electrical
motor in itself isn't cause for much plus on the energy of the batteries
to engine cycles]
-----------------
If so, try it again in English- as is the statement is meaningless.
Motors are what ! Just like Generators ?
then lets put a voltage across a generator and see how many rpms we get
from it.
Please Mr. Kelly you are standing too close to the Rift
®
If you knew a bit more about DC motors and generators, you would see that
Don is absolutely correct. Mechanically, and electrically, a shunt-wound DC
motor *IS* a shunt-wound DC generator. There is no difference at all,
except one you hook up to a DC power supply to turn a load, and the other
you hook up to a spinning shaft to generate electricity.
Old-style UPS systems used an AC induction motor to drive a synchronous AC
generator and a DC generator to charge batteries. Upon a loss of AC power
to the induction motor, the current in the DC machine would simply reverse
direction and draw power from the battery. The DC generator would instantly
become a DC motor, spinning in the same direction, just drawing power from
the battery instead of supplying power to the battery. The AC synchronous
generator output is used to supply the load at all times. It can't even
tell whether the shaft is being driven by the AC induction motor or the DC
machine acting as a motor.
If built with a substantial flywheel, these units can supply uninterruptable
power where voltage sine wave is hardly perturbed at all during the loss of
power to the AC induction motor.
Maybe you should learn there are more kinds of electrical machinery than the
blender you use to mix your drinks with. Although not very 'main stream',
DC machinery is quite flexible as a motor/generator.
daestrom
what i know about motors & generators is that the magnetic flux in
motors is induced mostly or all by electricity, with generators it is
imposed on the metallurgy or you'd get no excitement or hysterisis
curve.Not that they are all that harmonic, duhhh.....
you must think I'ma dolt......
®oy
so I don't know it all, who does, but, still the drive mechanism
employed must shift the power off the motor, and transfer the (any)
output generated, back into the batteries through a controled charge
circuit, (whatchu macall it) and the best charges should still be durng
coasting or motor free axle spins.
how they do it I haven't seen..
Anyone have a website with specs or do I need to activate my IEEE
student membership to dig around files?
®oy
Motors are what ! Just like Generators ?
then lets put a voltage across a generator and see how many rpms we get
from it.
Please Mr. Kelly you are standing too close to the Rift
-----------
And you are trying to look up from the bottom.
I've run (many times) motors as generators and generators as motors-- no
problem. The only real difference is the direction of power flow. Direction
of rotation is unchanged. polarity of voltage is unchanged. (note: IF a DC
machine has a series field, then it is necessary to reverse the field to
avoid voltage reversal.- this is not necessary with a PM, shunt or
separately excited machine).
For AC machines, there is also no problem. In fact there are many places
where ordinary induction motors are used as generators. In some locations
they are connected to small water wheels and are started from the grid, run
up to speed as a motor, then the water valve is opened so they are driven
above synchronous speed and generate. AC synchronous generators can be and
are used as motors.
I can suggest some references for you, if you wish.
stop and consider, the braking can approximate the accelerating current.
that may also be controlled.
they usually use a pulse-width modulator and it controls the current when
it's
regenerating (charging) just like as when i's trying to accelerate the auto.
it does, however, take a bit more charging to restore an amount of power
when regenerating than it delivers when powering the auto.(discharging)
NIMH cells take about 1.5 times charging power for the amount of delivered
power.
sammmm
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