KEV on Wheels

The Department of Electromechanics and Power Electronics (KEV) has prepared, in cooperation with MS Kart, a prototype of an electric kart with LiFeYPO4 batteries, MOSFET converter, sensors and electronic control system. The prototype has output power comparable with classic karts for rent in the market. The topology of the kart is very modular adopted for supplementing by future student's projects.

Karts are divided into two categories - racing karts and karts for rent. Karts for rent have lower power than racing karts, their power lies within 10 HP (7 kW). Racing karts are more powerful, up to 60 HP (42 kW) and a special category of superkarts has engine with 100 HP (74 kW) output power.

The concept of electric kart is supposed to have similar output power as normally available kart for rent. The topology of the prototype is shown in photo gallery below the article. The components of the kart include LiFeYPO4 batteries, MOSFET converter, direct current machine with permanent magnets, logging unit, display, thermal sensors, speed sensors, accelerometer etc. The topology itself is ready for further supplementation.

The LiFeYPO4 batteries are widly used kind of Li-ion batteries in electric traction with higher safety and longer lifetime than other available Li-ion batteries. LiFeYPO4 batteries are replacement of traditional LiFePO4 batteries with particularly replaced iron by yttrium. Usage of yttrium reduces batteries' weight, increases lifetime, input and output current of the battery. The kart utilizes 4 LiFeYPO4 batteries in series for obtaining 48 V DC and nominal capacity 80 Ah.

The chosen Thunder-Sky LP12V80AH battery composes of four cells with electrochemical balancing, therefore they do not have any electronic balance unit. Balancing of complete battery pack will be provided by a balancing unit on each battery.

The buck/boost DC converter for the DC motor is made of four parallel coupled IRFP4568 MOSFET transistors and it is designed for nominal current 300 A with possibility of overload to 400 A for one minute. Motor's low inductance requires usage of 16 kHz switching frequency. Maximal input voltage of the converter may be up to 100 V and it is cooled by two axial fans.

The drive of the kart is an electronically commuted DC machine MARS Electric LLC ME 0708 with nominal output power 4.8 kW, nominal voltage 48 V and 13.1 Nm torque at 3200 rpm. Temporarily it may be overloaded to 14.6 kW. The motor utilizes its own cooling from the manufacturer but as a part of the kart it is cooled by an auxiliary fan, which ensures better cooling condition of the machine at lower speeds. The weight of the motor is 13 kg.

The kart is equipped by a set of sensors monitoring almost all single components, but there are also sensors for monitoring kart's speed etc. The current flowing to the motor is detected by a LEM HTFS 400-P current sensor, which utilizes Hall effect. There are two such sensors, one for reading current from batteries and one for reading current into the motor.

Further sensors detect battery voltage to keep it within given range even within acceleration or recuperative deceleration. In fact, they ensure fully working battery management system (BMS).

The kart is furthermore equipped with eight thermal sensors Dallas DS18S20, where two of them are monitoring the temperature of the motor (temperature of output air and machine's case), four of them are placed on batteries and two remaining detect temperature on the converter and ambient temperature. A digital accelerometer Analog Devices ADXL345 integrates detection of kart's acceleration, additionally it senses centrifugal forces and vibrations of chassis. The kart is also equipped with AS5040 speed sensor, which gives information about speed of the DC motor.

From topological point of view the kart integrates more control unit, such as MOSFET converter control unit, battery management unit, logging unit and instrument board with LCD display. All of them are interconnected via CAN bus.

Acknowledgements

Special thanks belong to MS Kart company which lent the INDOOR 08 chassis, which is the main part of the kart. Further to colleagues from  Department of Applied Electronics and Telecommunications (KAE), whose advices have accelerated the development of electronic part of the kart a lot.

  • Floor projection of the kart
  • Control units
  • Instrument plane
  • Driver
  • Buck/boost DC converter
  • Universal board
  • Chassis of the kart
  • Electroinstallation
  • Electroinstallation
  • Electric kart is also cash-friendly

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