Blog: twingo1

Electric Renault Twingo: Tesla Modules ¦ EV Conversion

The TESLA model S battery is always the first choice in conversions for many reasons: Excellent energy density, good availability, integrated liquid cooling system and easy BMS options (recommended BMS system: SimpBMS, see documentation here. Here's how simple this BMS looks like:

The main disadvantage of the Tesla module is its packaging. It needs a watertight outer battery box, and needs to be mounted on rails.

One Module measures 690 x 315 x 80 mm. So if you have a quick look at the battery box measurements (800 x 520 x 280 mm), you will see that if we would pack the modules in a horizontal way, we would only have space for 3 modules (280/80), but if we would be able to mount them in a vertical way on the long side, we could theoretically fit 6 of them (520/80). But as you can easily see, this is not possible in practice, as we would have 35mm missing in height.

Although there would probably be a solution to that by modifying the battery box itself in height, we would face another problem: The nominal voltage of a Tesla moudle is 22.8 V. Putting 6 of them in series means that we can add the voltages of the 6 modules, so 6x22.8V=136.8V. So we only are at half of the target voltage of 270V, which of course isn't any good. Some people went ahead to modify the Tesla modules with some surgery on the internal configuration of the pack (making it 12s instead of 6s) to double the voltage in order to meet the target voltage (would be perfect in my example), but this isn't something for the faint-hearted, and there are some other implications such as different currents and some other risks. I wouldn't recommend doing it, and I only know very few projects in automotive settings that effectively went ahead with 12s Tesla modules.

One Tesla module has a capacity of 5.3 kWh, so 6 modules would be 31.8 kWh. If we calculate the energy density in our specific battery box in the Renault Twingo, we get 31.8/116=0.274 kWh/Litre. So let's keep this in mind when comparing it with other battery systems!

So unfortunately we have to rule out the normal Tesla module at this point - let's look at other options!

Electric Renault Twingo: Battery considerations ¦ EV Conversion

Choosing the right battery is dependent from many factors. The most obvious one is of course the desired range, which translates into a target kWh value of energy.

But in practice it is very hard if you start off from a specific target range, as the main restricting factor is usually the available space, and then also the target Voltage of the system.

So these three factors (space, capacity and voltage) create a magic triangle with sometimes conflicting goals. Now we need to solve the dependencies in the right order.

In conversion projects, the space is usually the most important factor that dictates. The second factor is usually the target voltage, and the capacity (=range) is therefore the last and dependent variable.

So let's go through these factors step by step:

Our goal is to get the most kWh into the space available. The measurement here is kWh/Litre of space.

The existing battery box in the back of the Twingo is 800 x 520 x 280 mm and was designed to hold the ZEBRA Molten-Salt Battery. The total volume of the battery is therefore 116 Litres. We would now need to pack this space as densely as possible to get the most energy in, not forgetting about cooling etc. in the process.

The target Voltage in our system is 270V. This is the original nominal Voltage of the Molten-Salt-Battery, and we need to stay in that region because of all the other components in the drivetrain such as Inverter, Converter, Motor, Charger, Heating etc.

The target capacity would ideally be equal or higher than 20 kWh, as this is the capacity of the existing Molten-Salt Battery and also the capacity of the first series Renault Zoe, which proved to be a very capable car that brought my family of five all the way from the Swiss Alps to Barcelona on holidays back in 2016 without any problem - so that is about the behavior that I would need!

See the next articles for different battery options.

Renault Twingo Electric Charger Inlet ¦ EV Conversion

Let's have a look at the charging inlet on the Renault Twingo - and there's a surprise by opening the flat that usually would hide the fuel filler: You would have expected a Type 2 inlet, wouldn't you? Instead, we can see a male CEE16/3 plug. Very surprising to me. As the Renault Twingo was equipped with a Molten-Salt temperature battery which had to be kept at an operating temperature of about 300 degrees celsius, the car would have been mostly plugged into one of these camping plug outlets at a home or at a workplace when standing still. It wouldn't draw a lot of energy, but it needed to keep those batteries warm.

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If we are going ahead in installing a different battery system, we want to have at least Type 2 charging (if not Chademo or CCS). So this will be something that will be changed. I might be choosing a two-step-approach: First Type 2 limited to about 3.7 kW with the existing charger, in a second step maybe DC charging ability. This means that we need to keep this in mind when selecting the BMS for the new battery system. Of the two shortlisted BMS systems, only one actually supports DC charging! More on that to follow.

Renault Twingo: First look into the motor bay

So let's open up that bonnet on the Renault Twingo to see the different components of the conversion. I am very happy that the motor has been coupled to a fixed reduction gearbox like in a modern EV such a Renault Zoe or a Tesla. This setup would be very difficult to homologate in a new conversion today, so I am delighted that this car is already road-legal with this setup. But more on that later. For the moment, we look at the electrical components in the motor bay:

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On the bottom, we can easily see the 12 V battery, then on top the Inverter (TIM 400, 80-400 Vdc, max Output current 280 A). Underneath the Inverter we can see the onboard-charger for the traction battery, and further up the white HV junction box. On the top right side we can barely see the DC-DC converter, and on the left side we can notice that the radiator and cooling fan is still there and connected to a cooling circuit which serves the Inverter and other components, and could hopefully also be used to cool a battery system.