It has been another rollercoaster of a week on this project. At the end of last week I posted my inverter control board off to Jamie on the other side of the Pennines for him to test it in his setup. He found the same problems I did and set about trying to fix them. After much experimenting he came to the conclusion there was a slight short on the pin of the 50-pin connector (bane of this project) that carries the signal for the DC supply voltage. So, he wicked away some of the excess solder around the connector and…success! He got a stable reading on the DC bus.

Jamie kindly got the board straight in the post to me and I received it on Saturday. Excited and confident it was now working, I slotted it back into the Prius inverter, reconnected everything and bolted it all up. Where it promptly worked for all of ten minutes before failing again. Clearly the short was still there, now just intermittent. I tried cleaning around the connector some more but even though I got it working for another ten minutes, it clearly wasn’t going to be reliable.

So, on Monday I took the board back to my local repair shop where Nav desoldered the 50-pin connector, removed one from the stock board, and put this in its place. I got the board back yesterday and finally, it works!

I was too tired last night to do anything really exciting with it, so I set it aside for today. Work out of the way I tried the basics of getting the motor spinning. WARNING: we are entering territory here where I know very little right now.

The first thing I did was try to get the motor spinning with the default firmware. This was relatively straightforward – with some help from the forum. If you’ve been following this project you will know that I installed a heating element from a washing machine as a current limiting resistor. This was chewing up too much current, starving the motor. So I swapped this out for a 20 amp fuse, stuck the inverter in manual mode and hit the motor with some hertz and some amps. And sure enough, it turned.

The nature of my motor (synchronous) means that you need a variation on the firmware to control it properly. This is called ‘field oriented control‘ and if I’m honest, I don’t really understand it yet. But I do understand how to update firmware – especially as the OpenInverter software makes it so easy. So I downloaded the latest FOC firmware, stuck it on the board and started tweaking parameters.

One I had checked the parameters matched my board, I started going through the setup process for my motor documented here. Almost immediately the motor started spinning freely with very few amps applied.

I’ve done some basic tuning now so that the throttle controls motor speed. But I have a few issues: it takes a lot of throttle to start the motor and then it slows at half throttle. This might be an issue with the inverter complaining about a lack of cooling, so I’ll add that tomorrow.