TOPGUN wrote:A bundle of thanks for Night Train. I guess we will be needing your expertise in the near future. Thanks for all the useful information you put forward. There is a lot of food for thought. Our college is very helpful in supporting us. In fact this project is being completely funded by college. Our marketing department is also doing its bit. So in terms of support, we are not short of that.
That is great to have the college support the project. Need to be careful with the £8k budget and try to offset it against in house labour and expertise. You will want to save as much of that as possible for batteries.
I would suggest getting a good fork truck motor and then servicing and adapting it in the college to save money.
Fork Truck Service near Chesterfield has a huge stock of assorted motors all at £300. Maybe you can find a similar place nearer your college.
Also have a look at the
Paul and Sabrina Open Revolt Controller. It is open source and well documented
here on EcoModder. It would be a good controller at a lot less money, especially if you just bought the boards and then get the discrete components locally (or at least in the UK) and then manufacture the bus bars, heat sinks and case in house. It would be a good addition to the project to build and test the controller and maybe make some modifications (open source) to it as some users have done.
TOPGUN wrote:The decision is tilting for DC motor. The only problem I have heard with them is inability to climb and do long distance runs. Warp9 seems to be a popular DC choice. I am sure it will be able to climb as it seems powerful enough. Dont know if you can run the motor at very high rpm for 2 hours continuous.
The constraints on the motor are really down to designing the project right for your needs.
The Warp9 is popular. You could also consider the
Kostov11. It is a more torquey motor then the Warp9 but also a little smaller in diameter then the Warp11 and so might fit.
The chaps in the States seem happy with a 9" motor run fast at higher voltage to cope with hills. Larger motors can't spin as fast. A Warp9 may run at 6-7000rpm or sometimes more. My 12" won't be risked at above 3600rpm.
The motor will be run over voltage to give it sufficient speed for the car, that makes it run hotter. To solve the heat issue you could:
Add forced ventillation in addition to the existing fan.
Raise the voltage to reduce current and so reduce I2R losses that cause the heat. This is one reason for looking for a fork truck motor at 72v or 80v rather then 48v.
Reduce the load by making the car as light as possible, fibre-glass wings, frunk lid, door skins, etc. and removing the spoiler and other unnecessary parts.
Also it is unlikely that the motor will be running at maximum power for two hours continuously. You batteries will be probably be dead long before that, maybe after half an hour at full motorway speed.
Even then, changing the driving style makes a big difference.
Pulse and glide:- driving by pulsing the pedal, when the car is moving at a good speed let it glide a while and then nudge the pedal again to bump the speed up a bit. It is very energy efficient and practiced by sparrows and EV drivers alike.
Sparrows and other small birds fly by flapping frantically very briefly and then folding their wings for a while before flapping frantically again.
Changing gears to keep to maximum rpm:- Series DC motors are different to an ICE. With an ICE you would want to keep the rpm low to run a cool and efficient engine. With series DC motors they run at their most efficient when they are at maximum rpm. This is because the back emf in the field coils prevent any more torque being developed and so very few amps are drawn. You maybe driving using only 2nd gear in urban runs and 3rd or 4th gear on the motorway. On hills you would select the gear that just provides enough torque to keep moving at the desired speed. You will then rest the motor on the down hills. Just don't over speed it on the over run or it will explode.
Useful links:
Agni motors: Efficient Axial flux motors.
NetGain motors: Suppliers of Warp motors.
Albright International: High voltage DC contactors.
Jim Husted: DC motor Guru.
Gav's EV videos: A series of YouTube videos documenting Gav converting his car to an EV.
MR2 mk1 conversion: A good read.
DIY Electric Car Forum: A very active and helpful international EV forum. Again, I am on there as Woodsmith.