Renault Twingo Battery Box

Now after all the battery talk let's have a closer took at the battery box in the Renault Twingo. The battery box is located on the rear of the car, just behind the rear axle, where on a petrol version the fuel tank and the spare wheel would sit.

The box has been located in a cutout of the floorpan in a way that half of the box is below the floorpan and half of the box is above. The total height of the box is about 30 cm.

In the first picture you can see the boot of the car:

In a petrol powered Twingo, the boot floor would be about 15 cm lower, here we are pretty level with the door sill. So let's have a look what's under the carpet:

So here we have a protection cover over the actual battery box. And in the picutre, you can also see the only disadvantage of the battery box location: On a normal Twingo, the rear bench can be moved forward and backwards to either gain more space in the boot or backwards to allow for more legroom. This was actually one of the iconic features of the first series Twingo, when sliding the rear bench completely back the rear passengers would have more legroom than in the Renault 25! If you look at the picture here above and below you will see that the bench cannot be moved backwards as the battery box is protruding from the floor, so the seat is stuck in a middle position, which offers a good compromise between boot space and legroom. Here you can see the cover removed: That's the shiny enclosure of the actual battery box.

In the next picture you can see the lower part of the same battery box from below the car. As you can see, the car doesn't loose any ground clearance and the box is well protected by the rear axle and the chassis frame.

In the lower part of the picture, we can see the high voltage cabling running towards the front of the car, where the motor and power electronics are located.

CALB 6s2P Battery Modules

The CALB 6s2p modules are another good battery option for tight spaces and higher voltages.

These modules were actually my number one choice for the Renault Twingo as I would be able to perfectly fit 12 modules of these with cooling plates into the original battery box in two layers separated by a cooling plate. Here's a quick drawing I made just to see how they would fit:

Let's go into some technical details of these:

One module is 22.2V nominal and 100Ah, which translates into 2.2 kWh per module. To do the same calcualtions as with the other batteries, here's what we would get for the Twingo:

Voltage: 12 x 22.2V=266.4V which would be absolutely perfect as we have a target voltage of 270V.

Engergy: 12 x 2.2kWh = 26.4kWh total capacity (very good!), density 26.4kWh/116 Litres = 0.227 kWh/Litre of space in the battery box. This is slightly higher than the Samsung SDI modules which come in at 0.214 kWh/Litre but still lower than the Tesla modules that come in at 0.274 kWh/Litre.

There is a very good source in Europe for these modules: Zero EV in the UK are doing a brilliant job in configuring whole battery packs with cooling plates, piping, busbars and everything. Check out their Mazda MX-5 Miata Conversion with these very same battery modules on Youtube where you see how these packs are assembled:

They use 10 modules in the Video, two less than I would have put in my Twingo.

So why didn't I go ahead with these modules in the end? Reading the technical sheets of these batteries I noticed that these modules are meant to be used in a normal position or flipped to their side by 90 degrees, but NOT mounted upside down (flipped by 180 degrees)! Not exactly sure where the problem would be, but I am not a huge fan of shortcuts when it comes to battery safety. In my setup, I would have mounted 4 battery modules per cooling plate, and put the cooling plates into the box in a horizontal way. So the lower 2 modules would of course be upside down.

Zero EV cooling plates for CALB modules, taken from the Zero EV Webiste.

If I wouldn't have identified a different, equally good solution in terms of size and voltage, I would probably have gone ahead with these CALB modules, as they are fitting so perfectly both in terms of size and voltage!

Renault 4CV Handbrake Mechanism ¦ EV Conversion

Handbrake Mechanism Renault 4CV

Let's have a look at a detail of a technical solution in the EV conversion process of the Renault 4CV. The handbrake mechanism which spreads the force of the handbrake lever to the two rear drum brakes is mounted on the bottom of the old engine, on the cover under the flywheel (same cover as the Oil pan).

Of course this supporting part needed to go with the ICE engine, so we had to find a new solution in order to attach the handbrake mechanism at the same location.

If you followed my previous posts you might know that we built a custom clutch bell housing between the new motor and the gearbox. So this would be the location where the hand brake mechanism would need to go:

The challenge now was to draw and produce the fitting mounting brackets and parts in order to mount the mechanism onto the new clutch bell housing.

I was very lucky and got everything right in the first attempt. And this is how the mechanism now sits on its new location - which is exactly at the same place as on the combustion engine:

This is an important achievement as all changes regarding brakes etc. would potentially cause a problem with homologation if the modification would be substantial. I have to say that I am really pleased with the result, as the new mechanism sits exactly at the same place as before with the same attachments. Also, it follows my approach to keep things as original as possible!

Samsung SDI LX86 Ford PHEV modules

So after we discovered in the last post that the total Voltage of 6 Tesla modules would only be half of the required value for the Renault Twingo, let's have a quick look at a different option just for the fun of it:

I have been offered a set of brand new Samsung SDI LX86 modules. These are Li-Ion modules configured in 12s1p with a nominal voltage of 43.2V (so double the value of the Tesla modules, as these here are in 12s whereas the Tesla modules are 6s). The Total capacity of a module is 2.07 kWh, 12 kg each. These modules are used in Ford hybrid vehicles (PHEV) such as the Ford Kuga PHEV.

Picture courtesy of Eco Lithium BV

The module measurements are 355 x 151 x 108 mm. So again if we have a quick look at the battery box measurements (800 x 520 x 280 mm) we can see that it would be possible to fit 12 modules into the box.

If we make the same calculation like for the Tesla modules, we would put 12 of these modules in series, which would result in 12 x 43.2V=518.4V. As you can easily see, this is much too high, as we were looking for about 270V. So if with the Tesla modules we were only half the value, here we have nearly double the value! So we will need to find something in between.

Let's do a quick calculation on density and capacity: 12 x 2.07kWh=24.84 kWh total capacity, 24.84/116 Litres = 0.214 kWh/Litre of energy density in the battery box. The Tesla solution would have had a density of 0.274 kWh/Litre in this box, so these Samsung SDI modules are nearly 20% less dense than the Tesla modules in this configuration.

But of course our main problem is the voltage here. If it would be possible to create two strings of 6 modules (2p6s), we would be pretty perfect (6 x 43.2=259.2V). Unfortunately, splitting packs into parallel strings creates a whole lot of complexity on the BMS and safety side. So unfortunately I had to abandon this route, even though I would have got these modules at a very convenient price.

Maybe you are interested how cooling of these modules would work. As you might have learned on the previous post, the Tesla modules have an integrated cooling circuit. These modules here don't have any plumbing for cooling included, so here we would work with cooling plates. The modules would be "glued" to the cooling plate with a heat transfer film. Other modules such as e.g. CALB-modules work in a very similar way.

Picture courtesy of Eco Lithium BV

So again, today we learned a lot about a specific battery technology, without finding a solution for our problem.

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!