DE102008023291A1 - Electrical light vehicle i.e. bicycle, has secondary switches for parallel switching of secondary coils with accumulators, respectively where secondary switches are switchable independent of each other - Google Patents

Abstract

According to the invention, an electric light vehicle is provided. In this, a fuel cell for generating a first voltage is provided. At this first voltage, a series connection of accumulators with at least a first accumulator and a second accumulator is connected. A transformer has a magnetizable core, magnetizable being understood to mean that the magnetic field strength of this core can be changed. The transformer also has a primary coil, a first secondary coil and a second secondary coil. The first primary coil is switchably connectable to the first voltage. A first secondary switch is provided for the parallel connection of the first secondary coil to the first accumulator. The electric drive system further comprises a second secondary switch for connecting the second secondary coil in parallel with the second accumulator. The first secondary switch and the second secondary switch are independently switchable.

Description

The invention relates to a light electric vehicle with an electric power supply unit and to a method for charging and discharging batteries of an electric light vehicle. Electric light vehicle is understood to mean two- or four-wheeled vehicles which have an electric drive which has a maximum nominal power of not more than 4 kW. The vehicles have a gross mass of not more than 350 kg, without the mass of the batteries. These may be, for example, bicycles with auxiliary motor, wheelchairs, mopeds, mopeds or scooters, all of which have in common that they have an electric drive. An example of such a battery powered electric light vehicle is in the DE 20 2005 006 684 U1 shown.

There the energy for the electric motor of a light vehicle must be carried along when driving, is special care directed to an energy saving drive unit. For example The electric motors are often used with high voltages fed, so that the energy transfer to the engine with as possible little transmission losses occurs. Will the energy become Providing the high voltages stored in accumulators, so they are often connected in series, so that each one Accumulator only a part of the total voltage available provides.

It has been shown that the accumulators have different capacities with increasing age, so that they are charged to different degrees. As a result, on the one hand, the existing charging capacity is not fully utilized, on the other hand threaten individual accumulators overloaded and thus to be defective. It is for example from the US 2002/00047686 A1 a battery charger known to load multiple series-connected batteries via taps from a series of resistors. However, in such a charging device with frequent charging and discharging a high power loss, which increases the energy consumption of the vehicle and thus reduces the range of the vehicle.

It is therefore an object of the invention, an electric light vehicle to provide with an electrical power unit, prevents overcharging of individual batteries can be. It is a further object of the invention to provide corresponding Method for charging and discharging batteries of this electric To provide light vehicles. These tasks are performed by the Objects of the independent claims solved. Advantageous embodiments will be apparent from the Dependent claims.

According to the invention an electric light vehicle with an electric drive system provided. In this is a fuel cell for generating a first voltage provided. At this first tension is a Series connection of accumulators with at least a first accumulator and a second accumulator connected. A transformer has a magnetizable core, wherein under magnetizable understood that the magnetic field strength of this nucleus can be changed.

The transformer also has a primary coil, a first secondary coil and a second secondary coil. The first primary coil is switchable to the first voltage connectable. A first Secondary switch is for parallel connection of the first secondary coil provided with the first accumulator. The electric drive system also has a second secondary switch for paralleling the second secondary coil with the second accumulator. The first secondary switch and the second secondary switch are independently switchable.

The electrical power unit is set up so that the accumulators can be charged or discharged individually. In addition, it is possible to use all accumulators simultaneously to charge the energy stored in the first voltage. Thereby, that the primary coil can be connected to the first voltage That is, the energy of a single accumulator can affect the entire Series connection of accumulators are transmitted.

The electrical power unit also allows Energy from one of the secondary coils to another secondary coil to transfer and thus different states of charge directly compensate. If the secondary switches respectively MOS transistors, the power loss is reduced. This saves additional energy. The saved Energy allows the vehicle for a given battery capacity and for a given supply of fuel for the fuel cell increased his range.

In a preferred embodiment, the light electric vehicle has a measuring circuit for measuring the voltage at a terminal of the primary coil or for measuring the current in the primary coil. By switching one of the secondary switches, the voltage applied to the corresponding accumulator can be measured on the primary side. Thus, the voltages across all accumulators can be measured individually by this measuring circuit without having to make individual measuring circuits on the secondary side. In addition, the same measuring circuit can be used to adjust the height of the first Measure tension.

alternative or additionally, a measuring circuit for measuring the Voltage at a connection of a secondary coil or the Current can be provided in a secondary coil. The tensions, which abut the primary coils, and the voltages that abut on the secondary coils can, if appropriate Wiring the primary switch and secondary switch the voltage at the terminal connected to the measuring circuit is, change.

In Another embodiment is a selector switch for selecting at least one connection from the measuring circuit provided for connection of one of the secondary coils. In this variant, a voltage can be applied by the multiplexer a secondary coil are measured, wherein for the multitude of voltages requires only one measurement circuit becomes.

In an embodiment is a DC-DC converter between the fuel cell and the first voltage provided. This is recommended especially if the fuel cell used is a voltage provides that lower than those for the motor is the most suitable voltage. For example. represents a common one Methanol fuel cell a voltage of 24 V available. For the operation of the engine but higher voltages are preferred so that the energy transfer from the energy storage to Engine is carried out loss as possible. The DC-DC converter thereby allowing the voltage to the desired Adjust operating voltage of the electric motor.

If the first voltage is applied to a stack of a fuel cell, are usually provided in a fuel cell No need for pumps. A stack consists of a multitude of metal layers. At the two outer metal layers the generated voltage is provided. The generated voltage is usually very load-dependent, the presented transformer but allows direct control of the stack. Especially suitable is the circuit for hydrogen fuel cells.

In In one embodiment, a charging circuit is additionally provided for charging the batteries and / or for charging the fuel cell provided from an external electrical energy source. through The charging circuit can, for example, from a utility network efficiently generated energy for charging the accumulators or the fuel cell be used. If additional energy in the fuel cell transported and stored there, it must be a reversible fuel cell act.

If the accumulators each designed as lithium-ion batteries a lot of energy can be stored in a relatively small space. However, it must be paid special attention that no one the accumulators is overloaded. In one embodiment also includes a control circuit for switching the secondary switch.

Especially The invention is suitable for a pedal-operated vehicle with electrical assistance, especially bicycle. at one such is a human power driven propulsion system and an electric drive system, wherein a power output of the electric drive system in accordance with the changes the output of the human powered propulsion system is controlled. In such bicycles with auxiliary engine is the space for the fuel is particularly limited and an energy-efficient transmission of energy in the accumulator increases the range of the Vehicle significantly.

The The invention also provides a method for charging accumulators an electric light vehicle according to the invention ready. In this procedure, first the voltage measured at the first accumulator and the voltage at the second accumulator. Then the primary switch is closed and the secondary switch for that accumulator closed, whose voltage was rated as too low. In order to Can selectively select energy from the series connection of accumulators be transferred to a single accumulator.

In In one embodiment, the measurement is performed in such a way that that the voltage at the first accumulator by measuring the voltage at a terminal of the primary coil or by measuring the current measured in the primary coil. Thereby can All voltages to the accumulator with a single Measuring circuit are measured. Opposite devices with several ren measuring circuits has the advantage that no Production differences between the different measuring circuits Can cause measurement errors.

In Another embodiment includes the power supply system at least one further series connection of accumulators. Another Coil is provided, which is connected to the voltage at the first Series connection of accumulators is applied, connectable is. Thus, the voltage in addition of a Accumulator transferred to a single one of several series circuits if only the voltage applied to this series connection, is too low.

The The invention also relates to a method for discharging a rechargeable battery an electric light vehicle with the following steps: It will the voltage at the first accumulator and the voltage at the second Accumulator is applied, measured. If the voltage on the first Accumulator is too high, becomes the first secondary switch closed and then the primary switch closed. This can efficiently take the energy of a single one Accumulator transferred to the series connection of accumulators become.

at a method for charging an accumulator of an electric Drive unit is the voltage at the first accumulator and the Voltage applied to the second accumulator, also measured. If the voltage at the first accumulator falls below a threshold value, the primary switch is closed and then the secondary switch is closed. This can be targeted energy be transferred to a single accumulator.

In In one embodiment, the threshold value is based on The voltages applied to the accumulators of the series circuit are with which the accumulators are charged evenly.

embodiments The invention will be described below with reference to the attached Figures explained in more detail. It shows

1 a pedal-driven vehicle;

2 an electric drive system of the vehicle 1 ;

3 the discharge of a battery of the electric drive system;

4 the waveform for discharging the accumulator;

5 the charging of an accumulator of the electric drive system;

6 the waveforms for charging the accumulator;

7 a schematic diagram for measuring the charge states of the accumulators;

8th another embodiment of an electric drive system;

9 the power consumption for charging and discharging the accumulators.

10 shows a performance comparison between a conventional and a charging method according to the invention.

11 shows a section of the electric drive system according to another embodiment.

1 shows a side view of the basic structure of a bicycle according to the invention 1 with pedals operated by human power and with an electric drive unit 3 , The pedals 2 and the electric drive unit 3 both cause the movement of a chain 4 and thus the rear wheel 5 , The pedal-powered vehicle is an example of an electric light vehicle, but it may also be, for example, a wheelchair or a scooter.

2 shows a schematic diagram of the electric drive system 3 , The electric drive system 3 has an AC / DC converter 9 , a transformer 12 , a microprocessor 13 , a DC-DC converter 14 , a fuel cell 10 , a voltage measuring circuit 15 , a current measuring circuit 16 and a motor 17 on. The fuel cell 10 , which is designed, for example, as a methanol fuel cell, generates a voltage U _B of 24 V. The DC-DC converter 14 generates from this voltage, the so-called first voltage U1 of 40 V, which is between a node K and the ground 36 is applied. This first voltage U1 is also due to the motor 17 so that he drives the vehicle in a torque request.

Also to the first voltage U1 is the voltage measuring circuit 15 , which also contains circuits for energy management, connected. This voltage measuring circuit 15 measures the first voltage U1 and receives information about the expected consumption. The voltage measuring circuit controls in accordance with the magnitude of the first voltage U1 and the level of the expected consumption 15 the fuel cell 10 to increase the voltage U1.

The fuel cell 10 Provided energy is stored in the series connection of the accumulators C1 to Cn. In this case, a first connection of the accumulator C1 to the ground 36 while its second terminal is connected to the first terminal of the second accumulator C2. A second terminal of the second accumulator C2 is connected to the first terminal of the accumulator C3, followed by the series of remaining accumulators. In a selected embodiment, the number of accumulators n = 10, so that each of the accumulators C1 to Cn stores the electric charge at a voltage of 4V each.

For some types of rechargeable batteries, such as lithium-ion batteries, special care must be taken not to allow a single cell is overloaded. If too high a voltage is applied to one of the accumulators, the accumulator is defective, so that no energy is stored in the entire series of accumulators.

In order to ensure that the accumulators C1 to Cn are evenly charged, the transformer is 12 intended. The transformer 12 has a magnetizable core 11 on. To this core 11 a primary coil Np is wound, which has 90 windings in the embodiment. A first terminal A1 of the primary coil Np is connected to the node K, while a second terminal A2 of the primary coil is connected to a first terminal of a primary switch Sp1, whose second terminal is connected to ground 36 connected is. The primary switch Sp1 also has a switching input. Depending on this switching input, a connection between the first connection and the second connection is closed or opened.

The transformer 12 also has n secondary coils. In the 2 the first secondary coil N1, the second secondary coil N2, the third secondary coil N3, and the nth secondary coils N _{n are} explicitly drawn. These secondary coils N1 to Nn each have three windings around the core 11 are laid. The core 11 is magnetizable and is used to transfer energy from the primary coil Np to a secondary coil or to a plurality of secondary coils N1 to Nn. Each of the secondary coils can be connected in parallel with one of the accumulators C1 to Cn.

The Secondary coils N1 to Nn each have a first and a second port, each at one end of the Whole turns are located. The first connection of a secondary coil is connected to the second terminal of an accumulator while the second terminal of the secondary coil with a first Connection of a secondary switch is connected, whose second terminal connected to the first terminal of the accumulator is. A switching input of the secondary switch controls whether the electrical connection of the first terminal to the second Connection of the secondary switch is closed.

The second terminal of the first accumulator C1 is connected to the first terminal of the first coil N1, whose second terminal is connected to the first terminal of the first switch S1. The second terminal of the switch S1 is connected to the first terminal of the accumulator C1. Similarly, the second terminal of the second accumulator C2 is connected to the first terminal of the second secondary coil N2. The first terminal of the second switch S2 is connected to the second terminal of the second secondary coil N2 and its second terminal is connected to the first terminal of the second accumulator C2. The connections between the accumulators, secondary coils and switches takes place in the same way for the remaining accumulators C3 to Cn. The microcontroller 13 controls the switches Sp1 and S1 to Sn of the transformer 12 each on. By closing one of the secondary switches S1 to Sn, a secondary coil is connected in parallel with an accumulator.

The accumulators can alternatively also by the charging circuit 9 , which is connected with a plug with an external AC power supply, for example, 110 or 230 V can be charged. For this purpose, the charging switch SL1 is closed, whereby the series circuit of charging switch SL1 and charging circuit 11 is connected to the series circuit of accumulators C1 to Cn which are thereby charged. At the same time the fuel cell becomes 10 switched off. This charging is useful when power from the outlet is cheaper than the energy from the fuel cell.

If it is the fuel cell 10 is about a reversible fuel cell, it is also possible excess electrical energy in the fuel cell 10 in chemical energy in the fuel cell 10 to convert them there to save them.

3 illustrates the discharge process of one of the accumulators in two phases. To the right of the accumulators C1 to C6, respectively, the states of charge of the accumulators are shown. The accumulators C1, C3, C4 and C6 are each 90% charged, the second accumulator C2 is charged to 70%, while the fifth accumulator C5 is charged to 100%. The fifth accumulator C5 threatens to become defective when the 100% is exceeded.

At first were from the microprocessor 13 the charge states of the individual accumulators C1 to C6 measured by a secondary switch S1 to Sn is closed in each case. Subsequently, the voltage at the second terminal A2 of the primary coil is measured, from which it is concluded that the charge states of the individual accumulators C1 to C6.

During the measurement it is determined that the fifth accumulator C5 has to be discharged. In a first phase, which is shown on the left in the figure, the fifth secondary switch S5 is closed, whereby the current in the fifth secondary coil N5 increases. This will do that in the core 11 existing magnetic field changes, with energy from the fifth secondary coil N5 on the core 11 is transmitted.

In a second phase, the right in Fi gur is shown, the fifth secondary switch S5 is first opened again before the primary switch Sp1 is closed. The magnetic field in the core 11 induces a voltage in the primary coil Np which increases the first voltage U1 applied across the series connection of the accumulators C1 to C6. Since only one of the accumulators C1 to C6 is discharged, relatively little charge is reloaded, so that the increase of the first voltage U1 is not so great that this is a danger for the electric drive system 3 would mean.

4 shows selected waveforms of the voltages and currents 3 , The signal curves are shown for a period t _cycle of 40 μs. The period is divided into a secondary phase PS, a primary phase PP and a break.

The primary switch SP1 and the fifth secondary switch S5 are each formed as NMOS transistors. Their respective connection is closed when the voltage at their control input exceeds 2V. During the secondary pulse PS, the fifth secondary switch S5 is closed by applying a voltage of 5 V at the gate of the fifth secondary switch S5. As a result, the current IDS through the fifth secondary coil N5 increases from 0 A to about 18 A. As a result, energy is applied to the core 11 transfer. At the beginning of the primary phase following the secondary phase, the voltage at the gate of the fifth switch S5 is reduced to 0V. In addition, the voltage at the gate of the primary switch SP1 is increased from 0 to 5 V, so that the primary switch SP1 is closed.

In the primary coil NP is now induced voltage, so a current of initially 5 A, then linear on 0 A falls, is generated. This one increases the first Voltage U1. At the end of the primary pulse is also the voltage at the gate of the primary switch SP1 lowered to 0V, so during the break, none of the switches SP, S1 to S6 open is.

To the break closes again a secondary phase if any of the accumulators C1 to C6 are discharged should.

5 illustrates the charging of one of the accumulators in two phases. The accumulators C1 to C6 are charged in the same way in the first phase as during the first phase in 3 , The control circuit has recognized that the second accumulator C2 has not been charged enough. For this reason, the method for selectively charging the secondary battery C2 is started. During the first phase, the first primary switch SP1 is closed, resulting in a voltage drop across the primary coil NP. The current generated thereby causes a change in the magnetic field in the core 11 , which puts energy in the nucleus 11 is transmitted.

In the, in 5 shown on the right side, second phase, the primary switch SP1 is first opened before the second secondary switch S2 is closed. As a result, the second secondary coil N2 is connected in parallel to the second accumulator C2. In the second secondary coil N2 now a voltage is built up, which is then reduced by a discharge current. This discharge current I2 causes the second secondary battery C2 to be charged to a value of 70% + x of the charge capacity.

6 shows the waveforms at selected nodes during the two in 5 illustrated phases. The period t _cycle is divided into a primary phase, a secondary phase and a pause, which follow one after the other.

While the primary phase becomes the gate of the primary switch SP1 is driven with a voltage of 5 V, so the primary switch SP1 closes. This increases the current in the primary coil Np from 0 A to about 4 A At the beginning of the secondary phase is the voltage at the gate of the secondary switch SP1 to zero lowered and then the voltage at the gate of the second Secondary switch S2 increased to 5V. Which resulting current from the beginning 15 A decreases within 12 μs to 0A.

7 shows the circuit for measuring the charge capacities of the accumulators C1 to Cn. The microcontroller 13 selectively sequentially controls the secondary switches S1, S2, S3 to Sn to turn them on one by one for a short time each. By turning on a voltage in one of the secondary coils N1 to Nn is generated, which causes a change in the voltage at the second terminal A2 of the primary coil Np. The voltage is at the input of the low pass filter 22 whose output is connected to the input ADCin of the microcontroller 13 connected is. This input is the input of an analog-to-digital converter, with the aid of which the filtered voltage is first converted analogously and then further processed digitally.

ever after what is the voltage on the accumulator is the voltage at the second terminal A2 of the primary coil NP bigger or smaller. By means of the described Devices become the voltages across the accumulators C1 to Cn measured and compared. Is one of the voltages greater as 5% of the mean of all tensions, then the corresponding Unload accumulator. If, on the other hand, the voltage at one of the accumulators is smaller as 5% of the mean of all over the accumulators Voltages, this accumulator is charged.

Thereby will be during all loading and unloading operations made sure that the accumulators are each about the same are much charged, causing overcharging a battery is prevented and the accumulators evenly getting charged.

It is also possible, in addition to the individual Charges all accumulators C1 to Cn at the same time to charge or discharge by all secondary switches S1 to Sn are closed simultaneously. This is in the chosen one Embodiment only for short periods intended. After these short periods will be back the voltages measured and the accumulators selectively as needed charged or discharged.

An in 2 shown block of ten accumulators has a capacity of 10 to 20 Ah. The transformer is about 4 cm × 4 cm × 1 cm in size and able to transmit about 10 A. The efficiency is 98%, ie only 2% of the power is converted into heat loss.

8th shows a further embodiment of a transformer. About the core 11 In addition, a tertiary coil Nhv is wound. It is thus possible to transfer the energy also to a further series connection of accumulators. A series connection of accumulators is also referred to below as a block.

So can transfer energy from the primary coil Np to the tertiary coil Nhv or vice versa. Alternatively, energy also from the secondary coils N1 to Nn on the tertiary coil Nhv be switched.

9 shows an embodiment with two blocks 120 and 121 , each a series circuit of accumulators C1 to Cn, as well as parallel connected transformer 12 exhibit. The block 120 is with its negative pole to the mass 36 connected and with its positive pole to the negative pole of the block 121 connected, whose positive pole is connected to the node K. It is also possible to add more blocks in series with the blocks 120 and 121 to switch.

The block 120 provides a voltage U120 while the block 121 provides a voltage U121. The two voltages U120 and U121 add up to the first voltage U1. The primary coils Np are for transferring energy from an accumulator to an entire block 120 respectively. 121 , The block 121 includes a tertiary switch St1, a secondary coil Nt1, and a diode D1. The first connection of the tertiary switch St1 is with the ground 36 while its second terminal is connected to a first terminal of the tertiary coil Nt1 whose second terminal is connected to the anode of the diode D1. The cathode of the diode is connected to the node K.

Also connected in series are the tertiary switch St2, the tertiary coil Nt2, and the diode D2 interconnected. A first connection of the switch St2 is connected to ground, its second terminal is connected to a first terminal of the tertiary coils Nt2. The second terminal of the tertiary coil Nt2 is connected to the anode connected to the diode D2, whose cathode is at the potential of the voltage U1 is located.

By means of the tertiary coils Nt1 and Nt2, energy provided by the first voltage U1 can be divided into individual accumulators C1 to Cn of the blocks 120 and 121 getting charged.

10 shows a comparison of the power consumption of a known from the prior art charging circuit with the presented active charging circuit. The individual accumulators have a target voltage of 3.6 V. The charging circuit marked with I has a series connection of resistors whose connection nodes are selectively connected to a terminal of a rechargeable battery. The power loss for charging and discharging the accumulators is correspondingly large, so that a power consumption of 18.5 W was simulated, wherein 18 W are due to the actual recharging and 0.5 W are consumed by the control circuit. The charging circuit shown with II corresponds to one of the above-presented active charging circuit of an electric drive system.

The Power consumption for the active charging circuit is 2W, again 0.5W to the control circuit, which is essentially realized in the microcontroller is eliminated.

11 shows a section of the electric drive system according to another embodiment. In the figure, the series connection of accumulators C1 to Cn, the secondary coils S1 to Sn and the secondary coils N1 to Nn are shown, as shown for example 2 are known. There is a difference with regard to the measuring circuit 13 , An n: 1 multiplexer is provided, which switches one of the intermediate nodes between the capacitors C1 to Cn to the input of the low-pass filter, the output of which is connected to the input ADCin of the microprocessor 13 connected is. The measurement takes place in the microprocessor 13 analogous as in the embodiment according to 7 ,

1

bicycle

2

pedals

3

electrical drive unit

9

core

10

fuel cell

11

AC / DC converter

12

exchangers

13

microcontroller

14

DC converter

15

Voltage measuring circuit

16

Current measurement circuit

17

engine

22

Low Pass Filter

C1

first accumulator

C2

second accumulator

C3

third accumulator

S1

first switch

S2

second switch

S3

third switch

N1

first secondary coil

N2

second secondary coil

N3

third secondary coil

np

primary coil

Sp1

primary switch

U1

first tension

U120

first Supply voltage

U121

second Supply voltage

UB

fuel cell voltage

SL1

Charging circuit switch

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 202005006684 U1 [0001]
• US 2002/00047686 A1 [0003]

Claims (17)

Electric light vehicle with an electrical power unit ( 3 ), comprising: - a fuel cell ( 10 ) for generating a first voltage (U1), - connected to the first voltage (U1) series circuit of accumulators (C1, C2, C3, Cn) with at least a first accumulator (C1) and a second accumulator (C2), - a Transformer ( 12 ), which has a magnetizable core ( 11 ), a primary coil (Np), a first secondary coil (N1) and a second secondary coil (N1), wherein the primary coil (Np) is switchably connected to the first voltage (U1), - a first secondary switch (S1) for the parallel connection of first secondary coil (N1) to the first accumulator (C1) and a second secondary switch (S2) for parallel connection of the second secondary coil (N2) with the second accumulator (C2), wherein the first secondary switch (S1) and the second secondary switch (S2) independently are switchable from each other. Electric light vehicle according to claim 1, characterized characterized in that the secondary switches each as MOS transistors are formed. Electric light vehicle according to claim 1 or 2, characterized by a measuring circuit for measuring the voltage at a terminal (A2) of the primary coil (Np) or the current in the primary coil (Np). Electric light vehicle according to claim 1 or 2, characterized by a measuring circuit for measuring the voltage at a terminal of a secondary coil (N1, N2) or the Current into a secondary coil (N1, N2). Light electric vehicle according to claim 4, characterized by a selector switch ( 110 ) for selecting a connection from the measuring circuit to a terminal of one of the secondary coils (N1, N2). Light electric vehicle according to one of claims 1 to 5, characterized in that a DC-DC converter ( 14 ) between the fuel cell ( 10 ) and the first voltage (U1) is provided. Electric light vehicle according to one of claims 1 to 6, characterized in that a charging circuit ( 9 ) for charging the accumulators (C1, C2, C3, Cn) and / or the fuel cell ( 10 ) is provided from an external electrical energy source. Electric light vehicle according to one of the claims 1 to 7, characterized in that the accumulators (C1, C2, C3, Cn) are each designed as lithium ion accumulators are. Electric light vehicle according to one of Claims 1 to 8, a control circuit ( 13 ) for switching the secondary switches (S1, S2, S3, Sn). Electric light vehicle according to one of Claims 1 to 9, characterized by a voltage measuring circuit ( 15 ) for measuring the first voltage (U1). Light electric vehicle according to one of claims 1 to 10, characterized in that at least one further series circuit ( 121 ) of accumulators is provided and a further coil (Np1) is provided, which is connectable to the partial voltage (U120), which is applied to the first series circuit of accumulators. Electric light vehicle according to one of the claims 1 to 11, characterized in that the first voltage (U1) to abuts a stack of a fuel cell. Electric light vehicle according to one of the claims 1 to 12, characterized in that it is a pedalbetätigter Vehicle with electrical assistance, especially bicycle, with a human powered power system and an electric drive system, wherein a power output of the electric drive system in accordance with the changes of the output of the human power operated drive system is controlled. Method of operating a vehicle, with the following steps: - Provide a light electric vehicle after one of claims 1 to 13, - To open the primary switch (Sp1) and the secondary switch (S1, S2) - Measuring the voltage applied to the first accumulator (C1) Voltage, and measuring the voltage applied to the second accumulator (C2) Tension, - If the voltage applied to the first accumulator voltage less than a threshold is closing the primary switch (Sp1) and closing the first secondary switch. Method according to claim 14, characterized in that that the measurement of the voltage applied to the first accumulator by measuring a voltage or current at a terminal (A1, A2) of the primary coil (Np) takes place. Method of operating an electrical Light vehicle, comprising the following steps: - Providing a light electric vehicle according to one of claims 1 to 13, - Opening the primary switch (Sp1) and the secondary switch (S1, S2) - Measuring the voltage applied to the first accumulator (C1), and measuring the am second accumulator (C2) voltage applied - if the voltage applied to the first accumulator voltage is greater than a threshold: closing the primary switch (Sp1) and closing the first secondary switch. Method according to one of claims 14 to 16, characterized in that the threshold value of the plurality of voltages, which are applied to the accumulators, is calculated.