Battery upgrade

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I'm upgrading (not converting since it is already an E.V) the Think PIV4 also known as the 'Think City' or the 'Think Classic'.

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These little 2 seater cars were build in Norway around 2001 and a lot of them went to the USA under the name ' Ford Think City'.. and they all came back in 2005 or 2006 when Ford decided that E.V's where (again) not the way to go...

https://www.youtube.com/watch?v=uJBlZzihc_M

A lot of these cars are scrapped in the past years so only a few are left (mainly in Norway).



Originally it's equiped with 19 Saft 6V Nicad cells, so nominal 114V/100Ah. Has a Siemens drivetrain, PTC heater and a lot of other common Peugeot/Citroen mechanical parts.

The batteries are inside a 87cm x 75cm centralized batterybox under/inside the floorpan.
I have removed the old Nicad cells and cleaned the batterybox from all unwanted metal to make room for a full 24kWh Nissan Leaf battery.
With 24 modules in one stack and some modified endplates each stack is 35cm x 86,5cm and two of these fit perfectly inside the box with some room left for relais etc.

Since the Siemens inverter can only handle upto 385V and the original DC/DC upto 290V I have decided to 'break' and parallel the Leaf pack into a 196V pack. So instead of 48 modules in series I will parallel each two modules to get 24 modules in series. (each module is allready 2S2P).

The original battery had a 'BMS' and a contactorbox with pre-charge and main relay and some other functionality like cabin pre-heater, delayed/timed charging etc. By keeping the voltage under 200V I can almost certainly re-use all this functionality and re-use all HV components.

Although the firmware/software of the Siemens inverter is locked with a code that Siemens has to provide I managed to crack the code and can now make modifications with Siadis, the Siemens MS-DOS software. This opens the possibility to change setings like max Amps, Volts, top speed etc.

Why upgrading to a bigger battery:

https://www.youtube.com/watch?v=JcuDCZMmCKg

[bbadmin]

Breaking up the Leaf battery.

Since I have decided to break and parallel the Leaf pack from 48S into a 24S pack I needed to create new/other module connectors/busbars. Made from 1mm copper strips that came from an electric building/powerplant, cut into smaller 20mm strips of 120mm each, punched 4 holes of 7mm in each so i can parallel and series connect 4 modules.

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Heres the first protoype build of one stack:

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For the monitoring I'm using Zevan BMS modules. Two modules on each stack for 24 cells.

And two of these fit perfectly inside to original battery box:

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Prototyping and testfitting a terminal cover made from 1mm plastic

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Terminal covers finished, made from 2mm Lexan:

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[bbadmin]

So after a few days of tinkering the new Nissan Leaf based battery pack is finally installed in the little Think. Its a perfect fit and after initial adjustments to the Simotion controller the car runs very well. Originally it runs at 114V and now with the 48 Leaf modules on 194V but still has about the same 'performance'...

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It's time to speedup/tune things..
After modifying the inverter's current parameter from 100A to 225A the power went up from 20kW to 48kW and there is room for more but my main fuse at 250A is the limiting factor.
At this time the tyres 'screem' when pulling out every corner which is rather funny.
Topspeed was originally set to 90km/h and is now around 150ish..

Next step is lowering the suspension a bit and changing brakes to a ventilated setup at the front and disks at the rear from a Peugeot 106 GTI.

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I have tucked two Brusa NLG511 chargers at the front where the original ConstantPower charger was. The rest is kept original.
The Zeva BMS is in the batterybox at the front. Modified the original batterybox loom so its just a plug-n-play install to the cars connectors.

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Did some 'long-range' testing yesterday, had a 120km trip on the highway, centre lane, overtaking and pushing the speed limit, only used about 65% of the packs capacity. So with some more decent driving I assume a 200km range would be possible. I'm happy about that.

The only annoying 'problem' now is that my pre-charge is playing up. On the initial key-start/sequence (key off-key on) it triggers an error in my Simotion controller saying pre-charge > 3 seconds.
After a second key sequence the error is gone so something must be adjusted to the pre-charge to behave well within 3 seconds. Not sure yet what is causing the problem..

Looking at the pre-charge circuit/schematic it appears as a MOSfet driving 4 PTC's in parallel. Each PTC is 120R so in total its 30R. The MOSfet is capable of 200V/3.5A.
My pack voltage is 196V => 196V/30R is 6.5A. more the the MOSfet could handle..
So whats is causing the problem: the MOSfet locking up on the first pre-charge and working on the second ?
OR are the PTC's playing up on limiting any current on the first pre-charge and allowing current to flow on the second go ?

Doing some math:
Original pack voltage is 114V.
My pack voltage 196V.
Max current in the pre-charge circuit: 3.5A.
So i need to 'waste' 196V-114V over 3.5A => 24R, P = 287W.
By adding a beefy resistor in series with the pre-charge PTC's it should work, in theory

I need to find an easy way to measure the process without taking everything out of the car...

[bbadmin]

Well it's been almost a year since my last post in this thread so time for a little update:


In the past 11 months I have driven over 11.000km with great fun and success. In fact I use it a lot as my daily driver to work, about 120km one-way.

Doing a quick recharge at the worklocation with the twin Brusa chargers at 6kW works good. Although sometimes the EVSE kicks me off for not respecting its lower output The Brusa's currently work on a fixed profile but will soon be changed to CANbus control. Unfortunally a few weeks ago one of the Brusa's (bulk) stopped working and generates an error on some out of range voltage. The main/second Brusa charger still works and I managed to buy another charger of the same type and model for easy replacement.


I have thought about replacing the Brusa's for a modified Tesla Gen2 charger but because i'm working on/under the 200V limit and the Tesla is not the perfect setup for that so I'll keep the Brusa's in this project. When the defective Brusa is repaired (if possible) I will add it as the third charger so I can charge at 3-fase/10kW.



During the winter time I hardly could make it for 120km with the heater on and had to hold back on the 'throttle'. But since the temparature is rising it is clearly noticable that the former range is getting back.



Although the Leaf pack is said as being 24kWh but in reality it is lower. I'm using the Zeva BMS system and had to adjust the Ah setting back to 110Ah (I have two 60Ah cells in parallel, so it should be 120Ah) to reflect the real usage/capacity. I'm currently recharging until 4.12V (198V for 48S)
but i'm not sure if this will cause the drop of 5Ah per cell.


Next project is install of a full Leaf pack at 96S/384V in the new model Think City A306 as drop-in replacement for the defective Zebra battery.