Project Overview

 The project plan so far 

I've covered quite a bit about the motors and batteries in my previous ramblings so here is a quick debrief on each of these items and the considerations needed. 

70kWh Battery pack

My 70kWh battery pack will comprise of 28 of these modules from Zero EV.
It will have cooling plates made into the pack as part of the structure. 

Safety considerations - Lid switch, there will be an access lid on the battery box, this will be switched to turn off all contactors and chargers if opened.
A 400A quick disconnect Fuse.
A separate safety disconnect that can be used for maintenance to quickly and safely isolate the pack. 

Electric motor and controller

From Swindon Powertrains the motor is 240Kw and output from a LSD directly to the rear wheels. 
The controller is a Cascadia CM200.
"Operating voltage range 50-480 VDC with a continuous motor current of 300 Arms, a peak motor current of 740 Arms and a peak electrical power output of 225 kW"

The motor and controller are both watercooled and CAN compatible, being CAN compatible is a must to the project, everything will be linked to the AIM PDM. the motor and controller combo will also be capable of regenerative braking, when the motor is not consuming power it can be used as a generator, this can be turned on and off to suit different driving styles, another reason why having CANbus is so important to ensure the car doesn't turn into a birdsnest of wiring. All of these signals are sent over 2 wires that form the CANbus.  

On board 7.5kw charger

There will be 2 methods of charging, the first is the onboard charger, this is mainly for home charging, the unit takes the AC power from the mains then this charger converts the AC to DC power for the battery pack. It's the onboard charger here that controls the current into the battery pack. Originally I thought it would be good to have this charge port in the petrol filler cap, however its unfortunately too large. 
Again the charger supports CANbus so can all be controlled and all information kept not lost. 

CCS Fast Charger

In addition to the onboard charger I have a CCS fast charger to fit. Whereas the 7.5kw onboard charger takes the incoming AC and converts to DC. The CCS charger is takes DC coming directly from the charging unit, you know the big things at the side of petrol stations. It is capable of 200A and my pack voltage of 400V will equal 80Kw charging, slightly more than the 7.5Kw onboard charger. My whole 70kw pack can be charged in under an hour and in practice you rarely drop the vehicle down to 0% and charge to 100%.

In short I can get 57% charge in 30 minutes. (57% charge would mean 142miles)

DC-DC Converter

As there is no alternator and 'most' of the ancillaries cannot run on 400V, the vehicle has a 12V battery and needs to be charged. The DC-DC charger is actually combined into the 7.5kw charger. One of the advantages of the it being combined is less wiring and communications needed, also only one device to cool not 2. This is fairly simple it takes the 400V pack voltage and keeps the little 12V charged up for the ancillaries.  

Orion BMS2 Battery Monitoring system

Although the charger, either the onboard or the external in the case of CCS do monitor the whole pack voltage the BMS plays a vital role, it has cell tap wires on all the cells (that are in series) for the module and does 2 things, firstly balance the voltage in all 112 cells in my pack ensuring that none are overcharged and all the cells in the pack are charging equally. Also the BMS is ensuring that no damage comes to the pack, via the cell tap wires and also thermistors connected to each module. The BMS dictates to the charger and also the motor the current that can be drawn or added to the pack. Imagine if the pack is at 100% bursting at the seams with all those electrons and the first drive is a long downhill stretch. The motor controller needs to know that it cannot add power via regenerative braking, getting the BMS set up right will be one of the key parts of the vehicle ensuring maximum range, efficiency and life of the pack.

AIM PDM (Power Distribution Module)

The car does not have an engine, therefore no ECU. So my AIM PDM is going to be the brains of the car in effect it will become a VCU (Vehicle control unit). In its simplest form a PDM can be used as a solid state relay and fuse board. Taking inputs via switches and then outputting higher currents and protecting them via a 'fuse'. The clever people at AIM will cry with that description but in its simplest form that's what it can do, however it can do so much more. Take the 'fuse' aspect of a power output, you set this via the software, so although there are 32 different outputs that have different max amperage draws, you can give each output a current draw limit exactly when you want it to trip. You can also set a retry here also, so imagine a fuel pump. Funny as that's one that I wont be needing ;) but you could set your trip in the fuel pump to 10A if the PDM senses a greater draw then it trips, then for the retry you program say 200 retries 10 seconds apart, this could be enough to let the pump cool down and get you out of trouble. Maybe not the best example but you get the idea. Next is how programmable these outputs are, I won't go into all the detail but you can make status variables that can change depending on physical switches, messages across the CANbus or other variables, the outputs can then be programmed to be true depending on other condition. For example fog lights, need the headlights to be on and also the fog light switch to be depressed. You can write logic that looks a bit like this. I might do a write up on how I've programmed bits of the AIM PDM if I get the time or enough people badger me. 

The PDM also controls the display, honestly I have been nerding out so much on the possibilities. When the vehicle is charging the display swaps to something with the relevant info, I just love tinkering with all the possibilities. Again the key here is the CANbus control for all the modules in the car. Everything will pass through the PDM and can be controlled from here. 

You can see the PDM does a lot more than just replace the relay and Fuses. It's the brain of the car and will hopefully simplify the wiring massively. It's easy to change a few lines of code, harder to rewire a relay or switch once the car is complete.

Electric cabin heater and Air conditioning

Although I will have cooling from battery packs and the motor, this wouldn't be suitable for a demist, an IVA requirement, although I've always found it interesting there is no time requirement on the IVA demist. I don't have explosions making heat, but I do have 400V to play with. There are a few companies out there doing PTC heater matrixes these will be nice and heat up instantaneously, of course draining the main battery therefore the range, but you don't get anything for free. Now my thought on every aspect of this car is 'I want it to be like driving a brand new car' now as GD's are new cars they do this mechanically, but I mean creature comforts. So I am keen on looking at fitting air conditioning, I have enough power to run a electric compressor like this. I plan on having a hardtop, my ideal would be to actually use this as my daily for commuting, and living in England a hardtop is non optional if you want more than summer use. I'm tempted to look at electric heated windscreens too, this might be more efficient than using the blower to demist, this could save me a few miles on range. 

Dual ally radiator

The car will need cooling, although not to the level of a combustion engine. Items like the controller actually need cooling to constantly flow though the device or certain components will burn out very quickly. Because of this there will be a pump from the flow end of the circuit and then a flow meter at the return side so I can verify there is flow before powering up the controller. See again a need for logic on the PDM, 'wait for a flow of greater than xx for 5 seconds before controller start up' or something to that effect anyway. The cooling system actually needs to be split into 2, you can cool the batteries and the motor under the same circuit however as they have different needs it's ideal to have a split system. One for the batteries and one for the motor & controller. To get the highest charging current to the batteries you actually need to heat them in cold conditions, so having this split would allow this in the future, not a plan I have currently but good to know I'm building provisions for this. From what I can see this early on it adds little expense and allows more thermal control so in for a penny in for a pound. 

Electronic Handbrake

I've added this into the list, it's a fairly small in comparison but one that I need to consider. After researching EPB's its the controllers that are the difficult bit but I think I can use the PDM to do this, or maybe make my own from a microcontroller. They are very simple systems, a motor that uses 2 wires, power one way and you apply the handbrake, power the other way and it releases. Again I won't keep banging on about how amazing the PDM is but it allows you to monitor the current from an output, the EPB controllers apply the motor until a current is reached, this is effectively measuring the pressure being applied by the motor. Having this feedback will allow me to stop the motor once the designated load is reached for x seconds. Then releasing the handbrake will just spin the motor in reverse for x seconds. This needs more research, but I'm confident that it will work. This also lets me do checks like, Handbrake must be on while charging. 

Alarm / Immobiliser & electronic doors

I didn't like the door handles on my last cobra so I fitted solenoids on the door release latches, very simple and effective, especially as I'm thinking about a hard top. I'd like to be able to open the doors from the outside, hopefully small things like this loose the kitcar compromises that we all make. Also security is non existent on most kit cars. I'm going to fit an immobiliser and lock to combat this. The lock will be more electronic than mechanical, the doors cannot be opened till the alarm is disarmed. I have bought this motorcycle alarm to see if I can work out an easy way of connecting it all in the way I would like it to work. 



So that concludes my plan so far, there is a lot to get working on and I'm sure more than I haven't considered.