Battery Boxes Nearly Finished; PCBs, Components and Charger Arrived

I've done several things since last update. None of them are finished yet but the goal is getting closer and closer.
Metal works on battery boxes are finished. Boxes and their metal retainer parts are welded, grinded and sanded to the final look. Here is the photo of them stacked together as they would be placed under the car. Only plastic battery retainers and covers left to do before putting the batteries in.

I received manufactured PCBs of my battery modules. The quality is good and boards look nice.

I placed them on the batteries in one box to see how it would look just for fun.

I also received a package of ordered SMD components for my modules - almost 800 items. It would be interesting experience to manufacture 45 boards :) So far I had time just to solder essential components to start the module working. You can see the LED lit on the center of the board that is controlled by ATtiny25V microcontroller which is placed on the center of other side of PCB. It now just runs basic test controlling the shunting current running through two big white 5W resistors. It controls the current using PWM signal switching the big black MOSFET. With 4V voltage shunting current can reach up to 1,7A and resistors get so hot that it is just bearable to touch them with the finger. With this voltage they can dissipate up to 7W of power but I think I'll use about half of that and will have longer balancing stage when charging.

I also received the charger from China. I like the quality and the look. I like that it is sealed it does not have any fans - no worries about moisture and dust getting inside. It came with AC socket and European AC cable. It has couple of meters of thick cable that should go to the batteries on the other side. It also came with CAN bus interface adapter - small black box with white label. I asked for this model because my BCMS will be able to control the charging voltage and current through all charging stages and also receive the status from the charger - cool. Of course I'll have to implement the CAN interface electronics and software of my BCMS. But that is worth it as at the end I will have a well-integrated flexible BMS system.

I also started discussion with local transport inspection and transport experts company regarding registration of my EV to make it street legal. They said they don't have any paperwork prepared yet and I would be the first to do it in Lithuania. So I'll have to work with them to prepare the technical requirements for registration and then arrange my EV inspection according to these requirements. It means more paperwork for me and I would need to push the process forward but I will be able to influence the requirements to better suit my own needs and possibly make them good for other EV converters here. So I reckon it's not that bad.
There are many things waiting to be done but step by step I'm slowly doing them to get closer to the goal.

BCMS and Battery Boxes

I caught some nasty flu on Thursday and needed to sit at home during almost whole weekend. Luckily wife with baby were out during it - visiting parents, so they were safe. Once I was feeling better I resumed some works on electronics and programming. I sent an order for battery module 45 PCBs. I expect to have them on Friday.

I've started programming the PDA graphical user interface. I'll use IPAQ or similar PDA with PocketPC 2003 system which will be mounted in the dashboard and give all information about car, batteries, temperatures, etc. For starters I just made it read the serial output sentences which are generated by BCMS. The protocol is NMEA which is widely used in GPS devices. I've created some custom sentence names which are used in my BCMS. The idea is that I'll have all parameters information along with GPS position of the car which will help car performance analysis after. Below is PDA emulator's program's simple screen which reads the data from serial port and displays in simple text fields. The parameters displayed are actually measured by BCMS.

When I got better on Sunday afternoon I went to garage and made a short session working on battery boxes. I welded the top mounting flange with one hole for initial mounting of the box. I also welded a M8 bolt part at the botom of the box where the batteries are being put. This bolt will be used to secure and press the batteries with V-shaped frame shown below. This will prevent any possible swelling of the cells.

Next will be a lot of grinding of the boxes to remove excess metal from the welds and improve aesthetic view. Nasty part will be cleaning the welds in inner corners of the boxes as it is not yet done properly. Then I will put stainless steel sheet into the boxes walls and they will be almost finished. Almost... There will be plastic retainer bars inside to stop cells from bouncing in the box. And also some plastic or maybe metal sheet cover on top of the boxes with openings at both ends to allow access for boxes interconnections.

More progress on battery module

Battery module design is being finalized with additional details for final production which were not needed in prototypes. Added the parts such as optional pulldown resistors, optional shunt LED, optional optocouplers and connector for master. Few minor changes still remaining but it is almost there and PCB design is half-finished.
If someone's watching this blog I know they'll have questions about two serial connectors and optocouplers. So I'll explain it now.
Two serial connectors are designed in such a way that wiring the the boards should be easy with single short wire going from cell to cell. You'll get the idea when I finish and post PCB design.
Optocouplers are not needed on all cells except the lowest and the highert in the chain. The lowest cell (the one having minus terminal running to the controller) will have the board with U2 optocoupler and J2 connector for serial input. The highest cell (with plus to controller) will have U3 uptocoupler and J2 connector for serial output. This saves the cost by needing just one PCB design and fewer components on it and the area of the PCB as connector J2 is shared.

Motor arrived and works started, BMS prototype in progress

My Warp 9 motor arrived in November - heavy beast. I've taken the ICE out from Honda. The gearbox and Warp9 were taken to metal workshop to produce the adapter plate with perfect center alignment. Adapter plate will be produced from 12mm aluminum sheet with the 30mm spacer for the motor flange. No clutch. Shaft adapter will be done from original clutch disk part bolted on steel disk mounted on Warp9 shaft.

As told earlier I will make my own integrated Battery management and Car management system with instruments. So far made following progress on it:

• Battery Module prototype made and programmed.Tests ongoing on model Lithium Polymer batteries. It is nicely balancing the 3-cell pack controlled by PC software via serial link. One module schematic is shown here:It is derived from a nice project being developed by Peter Perkins at http://www.batteryvehiclesociety.org.uk/forums/viewtopic.php?t=1245 .
  
• Once I finish testing I'll design and order PCBs along with all electronic parts needed for them.

• Master module prototyping started with real-time OS launched. Comms and several sensors tested. The core system will be based on ATmega 640 microcontroller. Interface will be provided on Pocket PC display running the GUI software which communicates to master module and displays graphical result. The screen will be integrated in the dashboard to blend into interior design.
• Ordered more sensors chips to have various measurement inputs.

45 TS 90AH batteries were ordered and sailing to me.

Equipment arrived since last post:
Motor: NetGain Warp 9
BMS: various chips and sensors

Ordered:
Batteries: 45 Thundersky 90Ah LiFePO4s
Vacuum pump: Mes-Dea ( haven't arrive yet)
BCMS: various sensors

Need to decide and order:
Battery charger: haven't decided yet
BCMS: haven't decided which cheap Pocket PC to take as a basis for dashboard screen
Power steering: would like to find an electric steering actuator similar to used in MGs

Work done:
ICE taken out. Warp9 adapter plate started. BMS battery module schematics design and programming almost finished. BCMS design guidelines decided. BCMS master module prototype started. Simple PC software for managing batteries made.

To-Do list: (Long... but main things are generaly listed in no particular order. Later smaller subtasks would be put in detail)

• Install the gearbox and motor when adapter plate finished
  
• Make battery boxes once batteries arrive
• Design the platform for controller and electronics installation
• Decide about charger ( might design my own 2kW charger...)
  
• Finish BMS battery modules design and order PCBs and components, build the modules
  
• Make a BCMS master prototype to perform basic functions to make a first drive-test safe for me and for equipment
• Design and laydown all the power and signaling cabling in the car
• Make a dashboard design change to integrate the BCMS Pocket PC screen
• Develop a software for Pocket PC to indicate main parameters
• Build a cabin heater
• Build power brakes system
• Decide upon and build a power steering system