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en:ev:bms [2019/11/05 17:34]
tomykalm created
en:ev:bms [2020/05/20 17:38] (current)
Ruudi s
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-====== Battery Management ======+====== Battery ====== 
 +As we all already now that batteries main problem is that they tend to discharge too fast. There'​s never not enough energy. But technology, electronics and machines tend to develop and use more and more power. Seems like batteries are just a little bit behind in development,​ but it makes all the difference.  
 +Battery changes electric energy into chemical energy and stores it until someone connects a load to it and then it starts to change stored chemical energy  
 +into electricity on its plus and minus terminals. 
 +Batteries use to be measured in amphours Ah it meant how many amperes in one hour you could get from the battery.  
 +Its ok to use it on a usual ICE car starter battery because they mainly are 12Volt batteries.  
 +On electric cars its not very often so, only BMW is using this unit at the moment (2020) on their only EV, BMW i3.  
 +Now they offer 120Ah battery for the car but when they started to sell this model (in 2013) it had half the capacity 60Ah in the same space.  
 +In a few years batteries have gone twice as good! i3-s 60Ah is 22kWh and 120Ah battery is 42kWh. 
 +To describe batteries on EV-s mainly is used unit kWh kilo Watt hour. This is unit for measuring electric energy and it fits much better with cars since they use a lot of energy. Kilo Watt hours is also used to measure home energy consumption. Only difference is that you multiply Volts with Ah and you get Watt hours if there are many of them then you will use prefix kilo. 
 +For example New 2020 Nissan Leaf you can buy with 40kWh or 62kWh battery. The biggest batteries on road cars are right now 100kWh Tesla Model X. But allready manufacturers claim that there will be EV pickup trucks with 200kWh batteries and so on. 
 +Nissan Leaf battery without box 
 +===== Safety ===== 
 +There'​s electrical safety and physical safety. Physical safety means keeping the battery in suitable temperature range. Lithium batteries are best at 20C but some heat them up to 40C to get better fast charging speed. Theoretically they say that lithium batteries do not like charging in cold under 0C. But older EV-s had these situations in winter and they worked fine. Nowadays (2020) batteries have liquid heating and cooling systems to keep them in the best temperature region. 
 +Theres also high voltage risks, for example big crash and high voltage orange wires will be revealed. In that case EV control system will switch high voltage system off. Also there is new danger in the car workshop where technicians need to be trained to service and fix these cars. 
 +Crash tests are performed to design and make safe case for the battery. Same as with petrol cars where is flammable liquid in the petrol tank. 
 +Main problem with battery safety is that you cannot momentarily switch off the battery cell. In case of situation that there is a problem outside of battery box then there is no problem EV battery has 3 means of switching possibilities:​ 
 +  - + contactor 
 +  - - contactor 
 +  - manual safety disconnect connector 
 +picture of contactor and safety disconnect on a car Leaf 
 +But when it comes to enter into the battery box then there is quite a big danger ofcourse untrained persons are not allowed to make any repairs on EV-s but it will happen sooner or later. Main problem is that batteries will always have their charge even when they are discharged they have minimum of 3V per cell this makes 96*3V=288V of DC! 
 +Batteries need to be taken care of not to overcharge and undercharge. Nowadays 400V EV batteries consist of 96 cells connected serially. Each serial cell voltages are monitored that is the job of BMS 
 +===== Battery Management ===== 
 +Battery monitoring system (BMS) for example Nissan names it LBC lithium battery controller. Takes care of battery "​health"​. EV battery has to last for 10 Years and to fulfill this expectation there is a bunch of electronics and clever software. 
 +Main parameters are battery voltage, state of charge SOC. Usually SOC is displayed in percentage %. BMS can be inegrated to measure battery current and to control contactors and transmit information to cars ECU-s for displaying or other managment. Also when diagnosing car battery then BMS has all the data about the battery state of health internal resistances and even cars VIN. BMS will take care of battery in case of discharging it sends data to ECU-s about cell voltages and battery current then computers can count how manu kilometres can be driven and let the driver now if he or she can make it and when to charge. Ten years ago EV-s already were capable calculating if driver could reach where they wanted to or suggested a charging stop if needed. Most dangeraus for lithium batteries is too deep discharging here BMS will monitor cell voltages and depending of the car stops the car when first cell hits 3Volts then battery is empty and computer will not let drive further. Usually there is two or three warnings before that situations but I have heard that people do not believe or want to test the limits. In that case flat bed truck is needed to get to the nearest charging place. 
 +Other dangerous situation for the battery is charging specially BMS has to avoid overcharging. There is also depending of the manufacturer,​ some charge to 4.1 volts some maybe little bit more. Some people have tested overcharging lithium batteries, have forgotten batteries charging without BMS and have caused serious battery fires.  
 +===== Charging ​===== 
 +EV-s are charged from electric grid. Usually at home in the night or at work when car is parked. There is a possibility to charge even on the road, then it is usually DC fast charging. In 2020 the most powerful chargers are 350kW but at the moment there are not many cars that can use that much power. Porche Taycan is but it has to have the battery warm and at right state of charge to get maximum power, even then this power level lasts for some minutes Porche has claimed that that car can charge 100km range in 5 min. 
 +When charging from the grid the car uses on board charger wich converts the AC to DC and to suitable voltage for the battery. There are some differencies in plugs and countries who use 110V and some 230V but cars chargers are universal they can take 110-230V. Older cars have on the car side J1772 standard plug and in europe they use type2 plug. 
 +There is also differencies in DC fast charging connectors. The first was Japanese ChaDeMo plug wich was rated at the beginning 500V 120A and 50kW, then there'​s Tesla fast charging connector wich differ in USA and EU cars and then there is German manufacturers standard CCS or Combo plug. The last one can take 350kW power at max 800V. 
en/ev/bms.1572968088.txt.gz · Last modified: 2019/11/05 17:34 by tomykalm
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