Hybrid cars and regenerative charging of batteries

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
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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.
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RQ schrieb:

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
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I would bet that "dynamic braking" could give a subjective feeling of 'medium braking" if not "hard" braking.
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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
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Dwayne schrieb:

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
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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 :-)
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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
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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
snipped-for-privacy@peeshaw.ca
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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 (DonKelly)
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
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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.
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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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

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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
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daestrom: Very tricky, those dc motors/generators. thanks for the crash class on them., i'll keep it in mind.
oy
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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
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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
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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.
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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You're quite right. Apart from a couple of constraints the only difference is efficiency.
Newsey

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I read somewhere "Chrstie Industries" was bringing an EV Production Line into the US but nothing there after >>>> any body know of it ?
oy
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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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