Kermit comes home

Kermit left his home of the past 15 months at TechShop, and made the 10 mile trip back to my house in Mountain View this evening. It was a little bit nervewracking setting out on the open road for the first time, but we made it without assistance from AAA. I set the maximum current to the motor at 30 amps, and limited the maximum RPM to about 3600, so I definitely didn't set any speed records. It was a trick accelerating from a stop through certain traffic lights before they turned yellow again, and I'm sure I irritated more than one other driver. Accelerating from 0-5 mph was very difficult, with torque not picking up until the car got going a bit. Once rolling, though, it felt peppy, at least compared with the stodgy original acceleration.

I need to fiddle with the voltage, current and frequency parameters a bit until I get acceptable performance. Mostly, I wanted to be assured of getting home without overheating my motor, which was no problem. I could hold my hand on the motor once I got home.

It feels really good to have come this far. Even though the car is by no means done, it is a usable means of transport at this point, and I will be driving it to work and dragging groceries home.

I'll keep updating this space with further news as Kermit rolls on.

We don't need no stinkin' capacitors

One solution for the inrush shenanigans described in the last post is to construct an inrush limiting circuit with a large resistor and a contactor- the capacitor is charged through the resistor until the operating voltage is reached, when the contactor is closed, bypassing the resistor. The other way is to yank out the capacitor. The purpose of the capacitor is to filter the rectified AC mains supply so that it is a smooth DC source for the inverter. A battery is already a nice smooth DC source, so the capacitor isn't really needed. I already ditched the 20-plus pound inductor that was the other part of the line filter, so I had no qualms about getting rid of the capacitor. Luckily, the capacitor was its own easily removable module:
The other plus is now the inverter can be put in a much smaller box, and will have considerably less need for interior ventilation, making weather sealing a possibility.

Of course I tested the capacitorless inverter/motor setup the way my pappy taught me -- by revvin' er up real good a few times.