I have a 2003 model year EVT4000e scooter with a USA spec governed controller. On looking at the output of this controller, it was only running at 80% duty cycle on the PWM. After investigating different ways of getting around this (dumping voltage into the motor directly, fooling the controller to turn itself on for 100% duty cycle etc.) I decided the best path might be to build a new controller. Since I only pretend to be an electrical engineer, this was an interesting challenge.
I built the new controller based on a New Micro's isopod microcomputer. This was a really big overkill since in reality all I needed was something to read an analog signal (the throttle) and to generate the PWM signal. This microcontroller had eight PWM outputs, eight analog inputs and about 20 digital channels. Oh well, it did work but is a bit more expensive than I needed ($99.00)
The rest of the circuit was based loosely on the original EVT controller (at least for the high current part). I was amazed at how few parts that I needed to really make it go. If you look at the original controller, it's got a whole bunch of stuff. The total for my new controller only had about 15 or 20 components (I did not bother driving the dash LED's). It was all just hand soldered up on a prototyping board.
Programming was done in a language called Forth -- it is a bit hard to learn but easy once you know how (like any programming language)
Now for the exciting part -- how does it work? I was pleasantly surprised it worked on my first attempt. I put it together into the case assuming I would just try it out and have to go make some modifications. However, it worked so well it stayed there for the next four or five days until I finally tore myself away to take it apart to finalize some of the wiring.
The stock controller would do 47 km an hour on the speedo (this seems to be actually quite accurate compared to my GPS). With the new controller, it'll do about 61 kph on the flat with no wind. Wow, this is way more than I expected. I thought I might get about 5 kph. I can go on almost any road in the city (barring the freeways) and easily keep up with traffic.
It seems to run a lot cooler than the old one -- I guess because at full throttle it's not doing any switching -- the fet's are just turned on all the time. As well, there seems to be a bit more range (about 33 km hard city driving measured last night)
Thanks for listening, I'm so excited I had to tell somebody who might be interested.
If anybody is interested, I can post a picture and a schematic.