The plan

The overall plan of this project is to get rid the ICE (Internal Combustion Engine), the fuel and exhaust systems and istead put in an electric motor, a bunch of lithium ion batteries, a controller for the motor and lots of other stuff thats needed to get the car working. I have a pretty detailed plan right now, but the actual components might change depending on what prices I can obtain.

Brakes

I have already mentioned the brake system in earlier posts, and this is only to circumvent (follow?) the Swedish regulations for converting cars. It has nothing to do with the electric conversion.
There is one more thing to the brakes though. Most modern cars have vacuum assisted brake servo and so does my A2. However, when the ICE is removed there is no source for vacuum so I will need a separate electric vacuum pump.

Motor and controller

The motor I plan to use is a Kostov K9" 220V. Kostov is a Bulgarian company who manufacture motors for fork lifts and now for DIY (Do It Yourself) electric cars. The motor develops 32 kW sustained and 78 kW peak. The peak power is only available during short accelerations for  couple of seconds, but this is usually what you want power to. If you use the max power for much longer the motor and/or controller will overheat and shut down. The motor is rated for a voltage of 220V DC and at peak power the current will be 500A! It is not very big, only 22cm diameter, 46cm long and weighs 45kg!
To control the speed of the motor I need a motor controller. The controller applies voltage in shorts bursts thereby limiting the average voltage and the speed. I am planning to use an Evnetics Soliton Jr which can handle up to 340V battery voltage and up to 600A motor current. This will be just right for the motor. I nice feature with the Soliton is that it is configurable via a standard Ethernet connection and a web browser.

Transmission

Transmision? Do you really need a transmission in an electric car? Well, it seems that the easiest way to convert a car to electric is actually to keep the transmission and the clutch. The available (affordable) electric motors have a torque curve that is usually flat up to around 3000rpm and then torque decreases down to the max rpm which is usually around 6000rpm. This means that if you go only one gear you either have to use a high gear to obtain a decent top speed. This means sluggish acceleration and high currents at low speed. Or you chose a low gear that gives you good low speed acceleration, but low top speed. An easier way is to keep the transmission and use two gears; second gear for city driving and fourth gear for highway, for example.

Battery and charger

The most important part of the conversion (and the most expensive) is the battery pack. I am planning to use Lithiun Iron Phosfate (LiFePO4) cells which have a good combination of good energy density, life time, and security (they don't go in flames if you overcharge them which I have heard some other LiIon chemistrys do). The newer cells also work pretty well at low temperature which is important if you live in northern Sweden. Each cell has a nominal (the voltage changes during discharge) voltage of 3.2V and the battery pack voltage I am aiming for is 230V nominal. This means I will be using 72 cells. Each cell will hold a charge of 70 or 100Ah. I will decide which when I know the available space for batteries in the car. If I go for the 100Ah cells some math tells us that 72 x 3.2V x 100Ah = 23kWh of energy. The weight of the cells will be around 250kg so the car will probably become around 100-150 kg heavier than before the conversion. The cells I would like to use are manufactured in China by China Aviation Lithium Battery (CALB), but I haven't found a decent price on them yet.
To charge the batteries I obviously need a charger. The standard Swedish power outlet is 230V,10A and a standard three phase outlet is 230V or 400V,16A. I have not decided on charger yet, but I would like it to be able to utilise both of these outlets. It will probably be a 3kW charger (230V,16A) since I haven't seen any reasonably priced 400V chargers.

Battery management and monitoring

Basicly the idea about battery monitoring and management is that you should not overcharge nor overdischarge the individual cells in your battery since this will decrease their life time. So, in order to prevent over discharge and overcharge a battery monitoring system can be used to detect potential over discharges (low cell voltage)  and potential over charge (high cell voltage). Battery management systems then either disconnect a cell from charging using a shunt or shuts down the whole vehicle during discharge. The act of disconnecting a cell from charge results in a more even charge among the cells in the battery. This is called balancing the cells and specifically this is called top-balancing since the balancing is done near the maximum allowed charge of the cells.
There is an ongoing debate in the DIY community about battery management and monitoring (BMS). The agument for not using a BMS is that the most damage to a cell is done when over discharging, not when over charging it. In order to prevent unbalance near the minimum allowed charge bottom balancing can be used onstead of a BMS. This is probably the route I will go and I will likely spend an upcoming post on the topic.

Heating

Heating of the passenger compartment is important in northern Sweden. Without the ICE there is no heat source. I believe I will need at least 3kW and preferably 4kW of heat power. Many DIYers use ceramic air heaters which they put in instead of the heater core that is heated by the cooling fluod from the  engine. Since my A2 has a ACC my idea is to keep the water heater core and put in a thermostat controlled water heater and a water pump instead. I figure the output from the ACC to the temperature flap can be used to control on/off of the water heater and pump so that the heater will no be on in the summer. The battery voltage of 230V means I can use European standard heaters. Still, I haven't decided on which to use. Maybe one or two Calix engine heater. Or a MES DEA heater with bulit-in pump.

Performance

My simulations of the car ends up in a top speed of 140km/h, acceleration 0-100 km/h in 10s and an energy consumption of 16 kWh/100km using the EU drive cycle. The theoretical range would then be  23/16 x 100 = 144km when driving the same speeds and inclinations as the EU cycle. A more realistic computation ends up in a range of 130km when driving 100km/h and discharging the battery to 80%. Since my commute is around 60km/day I believe that a range of 100km is sufficient. That will give me some margin for error and heat in the winter.

Steering

Many modern cars have power assisted steering powered by the ICE. The A2 has hydro electric power steering (powered by an electric motor) so it will hopefully work even without the ICE.

Instrumentation

Some new things will be nice to monitor in the electric car. For example, the charge of the battery,  battery voltage,  motor current, energy consumption. Some new instrumentation will be needed to show all this and I will also try to retain the original instruments as far as possible. For example using the existing tachometer and the fuel gauge to show battery charge. Most of this is controlled via a CAN bus in modern cars so hacking into the CAN will be one fun challange.

Budget

Well, I have already spent SEK 55 000 (EUR 6 100) on the car and my total budget is SEK 200 000 (EUR 22 200). More than half of the 145 000 for the conversion budget is for the Lithium cells. Then comes the motor controller, the motor and the charger as the next most expensive parts in the conversion.