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Paul, I finally finished reading this thread. You have accomplished so far more than some of the experts in the EV conversion field. While others just talk a good game you actually got off you A$$ and made it happen. Congrats on your accomplishment to date.
I have a few things that you may want to consider as you go forward. I'm not sure how much room you have available on the ATMEGA8, but some of these features may make a more complete controller.
1. As we discussed on the EVtech DL, motor overspeed failure is something that has happened to too many people, especially EV newbies. I think you are already working on this. The one thing to make sure of is that whatever sensor you use, it needs to stay isolated from the chassis ground for safety.
2. Pre-charge. I noticed in the video that you had a separate pre-charge switch. Do you plan to have this feature automated? IMO it definitely should be something that is automatic. For example, you get in the vehicle and turn the key to on. This closes a relay that feeds 12V power to the controller, then you turn the key to the start position and this engages another relay that pre-charges the caps, 2-3 second delay, and then the main contactor engages the traction pack. Good to go.
3. If you have the speed sensor feeding in the RPM information into the controller you may want to have the program multiply that signal by X times and then output it so that it can run a tachometer. Tachometers normally translate pulses to RPM the X depends upon the number of cylinders and the specific type of speed sensor the OEM used. However, having that output would be a nice feature. That may be tricky as you will need an optocoupler make sure the signal stays isolated from the chassis ground.
4. Failsafe is something to always keep in mind. There has been talk about what if the mosfets fail shorted. That is unfortunately not unheard of. It happens. If your controller sends the signals to the precharge relay and the main contactor (as suggested above), it can also turn off the main contactor if it finds that the current has surpassed the hardware current limiter. In the scheme of things I think its very unlikely that the hall effect current sensor it going to fail at the same time the mosfets fail.
5. If the current sensor does fail it will probably register 0 current, it should be easy enough to program the controller to be able to tell that something it wrong it the duty cycle is anything more than 0 there should be some current flowing.
6. Many controllers allow you to set the maximum battery current. This prevents you or someone you let drive your car from damaging the batteries. If you want your batteries to last you don't want to over amp them. This becomes more true for Lithium batteries than it is for lead, but there have been some EVers that have gotten almost 10 years out of their golf cart type batteries by babying them.
7. Don't know if you want to get this elaborate, but you can also monitor the pack voltage with a simple voltage divider and allow for a soft low voltage limit. Its really bad for batteries to over discharge them. You could have the controller lower the current limit when pack voltage starts to get too low. This way you will feel like your running out of power before you actually run out and murder a battery.
Anyway, just food for thought. Maybe things to implement down the line. You set out to make a cheaper controller, but you could end up making a cheaper, better controller than Curtis, Kelly, Logisystems, etc.
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