This is a big project for me, and it will always be something I will remember.
I have tried my best to get it up to the point where I can hand in my document for marking, but I will be continuing to work on the electric car to get it up and running as it is something I am really passionate about.
With all the knowledge I have gained from this project I am sure to find to useful in future, whatever that may be. I am thankful for the support I have had from my parents, teachers and peers as it has been really inspiring and hope to continue on with my renewable sustainability work in future, particularly with the drive to battle climate change for future generations on Earth!
This week, I have been updating all my blog posts, document and planning to mount batteries in the car. In mechanical engineering class, I have been making spacers for the stators to mount together properly, plus assembling it with all the M16 nuts and washers I bought from bunnings.
This week was mock exams week, so I didn't get as much work done as normal.
Last weekend, I began to wire up the BMS to 9 of the battery modules as a test. (This BMS supports between 8 to 32 modules in series).
It took me a while to figure it all out, but after hooking up balancing wires, positive and negative, the LCD and ON/OFF switch, and downloading the app, I managed to get it all going!
This is the BMS I am using, which I paid just under $200 for from Aliexpress:
Wiring the BMS up to the modules:
I really like the display, it shows a lot of data from the batteries which is crucial for a rebuilt recycled battery setup from old laptop batteries!
It has 2 internal temperature sensors (1 on power mosfets and 1 on balance circuitry) + 4 optional external sensors, which I will probably use for 3 stator temp sensors in the electric motor, and an outside temp.
The phone app allows you to configure many parameters, such as cell count in series, max current, high and low voltage cut off, etc. which is just awesome for this setup.\
Another thing I did over the weekend was buy over 100kg more 18650 cells, as an investment for future projects and to possibly complete the battery modules for the electric car battery.
This is an estimate of over 2000 cells!
I was having a lot of trouble with the array coding in the Arduino and it was causing me lots of issues with the LCD display, so I have left the idea.
Over the week, I came into school and worked on getting the whole setup working with a button to toggle display modes.
This is how it is looking now:
So each Arduino UNO can monitor 6 temperatures and display 3 at a time, which the button toggles between the 2.
In future, if I get the time, I plan to integrate cooling fans if needed and LED indicators for high and low temp warnings, etc.
Over the next week, I worked hard at getting all the battery modules wired together.
This proved to be rather tedious task with all my DIY setups, but I managed to get it all done in the end after maybe 20 hours of hard work.
My process included cutting 63cm segments of 6mm2 2C + E wire; stripping each individual wire; removing 2 strands of the thicker wire; doubling over the wire; twisting wire; cable-tying to modules; stapling other end; cutting 1/4W resistor legs; spot welding to cells over copper bus wires; soldering to wire; repeating last couple steps for each module.
And doing this 27 times! The repitition is hard, but should be well worth it.
Anyway here are the photos from wiring up the batteries!
My next step will be to make the copper lug terminals for the end of each module from the scrap copper I got from McCauley metals Whakatane!
After cleaning them up, I got to making the terminals on the weekend.
After coming up with a copper lug terminal design I was happy with, I got to making 58 of these (couple extra just in case).
Steps I took in making these:
cutting 4.5cm bits of pipe;
cleaning inner tube;
flatten 2cm in vice;
drill 8mm hole;
round edges, deburr;
final clean;
This took me a 2 or 3 minutes to make each one, so I was finished in just under 5 hours.
So yeah, another lot of work!
After fabricating all these lug terminals, I crimped them on to each battery module, by bending the wire end of each module to fit the terminals and squishing them on tight!
I am happy with how these are turning out, and after another hour or so, all 27 battery modules were now kind of complete!
My next step would be to test wire the modules together with the BMS to see how it is all looking.. and finally insulate the modules and install them into the car!
I also fixed up the rotor wobble as best I could by welding strategically to contract areas and 'pull' them into position. This worked OK, but the rotor is likely unsuitable for an electric car at present. I want to get it remade properly, and use the idea to manufacture a much better version that can push lots more power!
Here is how it is looking running on my DIY electric lawnmower brushless controller:
This week I managed to get all the battery modules cut out. I had to buy another 1200 x 1200 9mm sheet of plywood which I only used half of. I managed to cut out 56 plywood holders (2 spare), which I then finished up with the belt sander to remove rough edges for painting.
I got a couple cans of black spray paint to make the modules look neater and be more weather proof. I had a lot of trouble with the spray cans not working so got nice and dirty after puncturing one of the cans that had clogged up lol trying to figure out why it no work :)
I then spent a sleepless night on Thursday sorting through every single cell and doing what is known as repacking, which capacity matches every parallel group of 18650's. In my case this meant each 'module' had to have the same total capacities. As all the cells are recycled in my build from old laptop batteries, this means they are all different ages and capacities which have to be matched up for the pack to perform well.
An online program known as www.repackr.com/ helps rearrange cells into equally sized capacity modules. It took me roughly 7 hours to get this done and I was glad by the time I finished!
I then inserted all the cells into the plywood module holders and assembled them so they are ready to wire together now!
This is the wiring plan for each module. I need to reduce the amount of copper used for each module so I don't go through like 30m of house wiring. The copper bus wires do have to be rather large though to carry up to 250A current at full capacity.
I then grabbed as many scrap resistors from our Mechatronics class which I will be using the resistor legs to fuse each cell when I spot weld them. These fuses will then be soldered to the main copper shunts making for a more efficient and safer wiring process. I went to a couple electrical stores seeing if they have any scrap copper wiring I could use for this but it is quite difficult to use as a very fine strand copper will become messy and hard to remove insulation and bundle together, and a solid core it much harder to solder to. I would like to use with the house wiring as it is a several stranded copper core which is easier to bend and wire in as well as solder. The only problem is removing all the insulation as there is quite a bit of time and waste from it. But it will all be worth it hopefully!
Another week!
I have mainly been setting up the CNC machine every avaliable time to cut out 3 plywood battery modules at a time. I have been able to cut out 3 plywood holders in just under 30 minutes, which should make for a total CNC time of 9 hours!
While I let the CNC router cut out all the battery modules, I worked on trying to get the rotor running straighter. Currently it has a fairly large wobble to it which will be causing rubbing of the stator and rotor.
The physics of how a weld bead contracts as it cools, pulling the 2 metals it is joining slightly closer together is what caused the warping to begin with. To correct this, opposing weld areas to the offset should help pull the rotor back into straightness. I welded the top joining piece of the rotor housing and tried to correct the balance then, but it may have only made it worse.
This is what the whole assembly is looking like at the moment.
You can see the wobble in the rotor in the lathe running at a slow speed:
This week I have been trying to crack on with getting the temperature monitoring circuitry together.
I have decided to use standard 20 x 4 LCD displays with each Arduino, which should be able to display all cell data nicely. However I have been having trouble getting data to print onto the LCD screen. I think this might have something to do with the contrast pin not being tuned correctly. I will try wiring in a potentiometer next week.
This is the proper wiring diagram which I will follow.
I have had success with the 10K thermistors getting accurate temperature measurements using the equations provided online for the temperature resistance curve of the thermistors.
